JP7783124B2 - Operation control method for inverter-driven compressor and inverter-driven compressor - Google Patents

Description

The present invention relates to an operation control method for an inverter-driven compressor and an inverter-driven compressor that executes said operation control method. More specifically, the present invention relates to an operation control method that enables reduction in power (power consumption) in an inverter-driven compressor that uses an inverter to control the rotational speed of the motor that drives the compressor body, and to an inverter-driven compressor that executes said operation control method.

An inverter-driven compressor has an inverter installed between the motor, which is the drive source for the compressor body, and the power supply. This inverter changes the frequency of the AC current input to the motor from the power supply between an upper limit frequency fmax and a lower limit frequency fmin, thereby changing the rotational speed of the motor, and therefore the rotational speed of the compressor body driven by the motor, between an upper limit rotational speed corresponding to the upper limit frequency fmax and a lower limit rotational speed corresponding to the lower limit frequency fmin.

Such inverter-driven compressors are configured to detect the pressure P of the compressed gas supplied to the consumer side (hereinafter referred to as "supply pressure") using a pressure detection means such as a pressure sensor, and when the supply pressure P exceeds the target pressure Ptarget, the frequency of the AC current output to the motor is reduced, and when the supply pressure P falls below the target pressure Ptarget, the frequency of the AC current output to the motor is increased, thereby changing the rotational speed of the compressor body.By performing rotational speed control, compressed gas at the target pressure Ptarget can be supplied to the consumer side regardless of changes in the amount of compressed gas consumed.

In addition to controlling the rotational speed in response to changes in the supply pressure P as described above, inverter-driven compressors have also been proposed that are designed to reduce power consumption by stopping the intake of air into the compressor body and/or transitioning to "unload operation" in which the discharge side of the compressor body is open to the atmosphere when the supply pressure P rises above a predetermined unload operation start pressure Punload due to, for example, the cessation of compressed gas consumption on the consumption side, thereby reducing power consumption.

However, when such an inverter-driven compressor is installed as production equipment in a factory, for example, and used as a common compressed gas source for multiple pneumatic devices located throughout the factory, the piping connecting the inverter-driven compressor to the pneumatic devices becomes long and complex, with many connections in the piping, making it inevitable that piping leaks will occur due to poor connections in various parts and deterioration of gas seals.

When such a pipe leak occurs, a relatively small amount of compressed gas due to the leak continues to be consumed. Therefore, even if all pneumatic equipment connected to the consumption side is stopped and the consumption of compressed gas by the pneumatic equipment is stopped, the supply pressure P does not rise to the unload operation start pressure P unload, or it takes a long time for the supply pressure P to rise to the unload operation start pressure P unload.

As a result, when only a small amount of compressed gas is consumed due to a pipe leak or the like, the inverter-driven compressor will continue to operate at a low speed (hereinafter referred to as "low-load operation") over a long period of time, using rotational speed control to operate the compressor at a frequency near the lower limit frequency fmin, thereby producing a relatively small amount of compressed gas.

Although this type of low-load operation consumes less power per unit time than full-load or high-load operation (hereinafter collectively referred to as "high-load operation"), which is performed at or near the upper limit of the rotational speed, it still consumes more power than no-load operation.

Furthermore, although power consumption per unit time is lower during low-load operation compared to high-load operation, when comparing the power consumption required to generate compressed gas per unit gas volume, efficiency is lower than during high-load operation.

As a result, if low-load operation is performed for a long period of time without transitioning to no-load operation, the efficiency of compressed gas generation relative to power consumption will decrease.

To address the decline in compressed gas production efficiency that occurs when a relatively small amount of compressed gas continues to be consumed due to pipe leaks, etc., resulting in the system not transitioning to no-load operation or taking a long time to transition to no-load operation, the applicant of the present invention has already proposed an operation control method for an inverter-driven compressor, as listed in Patent Document 1 below.

In the operation control method of Patent Document 1, as shown in the time chart of Figure 5, when the compressed gas load rate [load rate (%) = (air consumption rate / rated discharge air rate) x 100] begins to decrease below 100% (T1), and the compressor is determined to be in a predetermined low-load operating state by either maintaining an operating state below a reference frequency fref (22 Hz), which is a predetermined frequency higher than the lower limit frequency fmin (20 Hz), for a certain period of time (t; T2-T5), or by maintaining a state where the supply pressure P is above a reference pressure Pref (0.70 MPa), which is a predetermined pressure higher than the target pressure Ptarget (0.69 MPa), for a certain period of time (t'; T4-T5), the aforementioned rotational speed control, which changes the inverter output frequency in response to changes in supply pressure P, is stopped (T5).

Then, until the supply pressure P rises to the unload operation start pressure Punload, forced transition control is performed to temporarily (T5-T6) raise the inverter output frequency to a pressure rise frequency frise (40 Hz) that is a predetermined frequency higher than the frequency when the low-load operation state is determined (fmin: 20 Hz in the illustrated example) and that is capable of raising the supply pressure to the unload operation start pressure.

This forced transition control (T5-T6) raises the supply pressure P to the unload operation start pressure Punload (0.73 MPa), and forcibly transitions the operating state of the compressor body to unload operation (T6-T7) with the discharge side flow path open to the atmosphere. This eliminates a state in which low-load operation, which results in poor compressed gas generation efficiency relative to power consumption, continues for long periods of time, thereby reducing power consumption (see Figure 2 of Patent Document 1).

JP 2015-34535 A

In the operation control method described in Patent Document 1 above, if a specified low-load operation continues for a certain period of time (t or t'), the system forcibly switches to no-load operation. This prevents low-load operation from continuing for long periods of time, even if a small amount of compressed gas is constantly being consumed due to a pipe leak, etc., thereby reducing power consumption.

However, with the control method described in Patent Document 1, low-load operation is still performed frequently during periods when only a relatively small amount of compressed gas is consumed, leaving room for further reductions in power consumption.

To explain this point in more detail, the operation control method described in Patent Document 1 performs control such that, after the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa) and the system transitions to no-load operation, when the supply pressure P drops to the target pressure Ptarget (0.69 MPa), the no-load operation is terminated and the system returns to the aforementioned rotational speed control, which changes the inverter output frequency in accordance with the supply pressure P (Claim 1 of Patent Document 1).

For this reason, even if the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa) (T6), even if all pneumatic equipment connected to the consumption side remains stopped due to a constant small amount of compressed gas being consumed due to a pipe leak or other reason, the supply pressure P will decrease over time to the target pressure Ptarget (0.69 MPa) (T7), thereby ending unload operation (T7) and returning to rotational speed control (T7-T5').

When rotation speed control is restored (T7), the supply pressure P is close to the target pressure Ptarget (0.69 MPa). Therefore, when no-load operation ends and the compressor resumes generating compressed gas, the supply pressure P immediately rises above the target pressure Ptarget, and the compressor will perform the low-load operation described above during rotation speed control (T7-T5').

If this low-load operation state continues for a predetermined time (t or t'), the aforementioned forced transition control is performed again (T5'-T6'), which causes a transition to no-load operation again (T6'-T7'). This operation is repeated during the time (T3-T8) during which only a relatively small amount of compressed gas leaking from the piping is consumed on the consumption side.

In this way, with the operation control method described in Patent Document 1, when the consumption of compressed gas on the consumption side is only a relatively small amount due to a pipe leak, rotational speed control (T7-T5') always intervenes between the no-load operation (T6-T7) and the no-load operation (T6'-T7') that are performed during that time, and this rotational speed control (T7-T5') operates the compressor body at a low load for a predetermined period of time.

Therefore, if the low-load operation time between no-load operation (T6-T7) and no-load operation (T6'-T7') can be shortened, or if low-load operation can be eliminated, the frequency of transitions to no-load operation can be increased, lengthening the total no-load operation time and further reducing power consumption.

The above explanation has been given as an example of the problems that occur when a relatively small amount of compressed gas is continuously consumed due to a pipe leak, etc.

However, this type of problem can occur not only when there is a pipe leak, but also when a relatively small amount of compressed gas is being consumed continuously, such as when only a small portion of multiple pneumatic devices connected to the consumer side are used for long periods of time, or when pneumatic devices that constantly consume a relatively small amount of compressed gas are connected to the consumer side.

The present invention therefore aims to provide an operation control method for an inverter-driven compressor that can further reduce power consumption during times when only a relatively small amount of compressed gas is consumed, and an inverter-driven compressor that executes this operation control method.

Below, the means for solving the problems are described along with the reference numerals used in the description of the embodiment of the invention. These reference numerals are intended to clarify the correspondence between the claims and the description of the embodiment of the invention, and needless to say, are not used to restrict the interpretation of the technical scope of the present invention.

In order to achieve the above object, the operation control method of the inverter-driven compressor 1 of the present invention comprises the steps of:
An inverter-driven compressor (1) is provided with a compressor main body (2), a motor (3) that drives the compressor main body (2), an inverter (4) that changes the AC current input to the motor (3), and an operation switching device (20) that switches the operating state of the compressor main body (2) between a load operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and is capable of frequency control that controls the output frequency of the inverter (4) and operation switching control that switches between the load operation and the no-load operation,
a check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52;
As the pressures used as the control reference, a predetermined target pressure Ptarget (for example, 0.69 MPa), an unload operation start pressure Punload (for example, 0.73 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) which is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa) are set,
The load operation is set to a steady operating state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the no-load operation start pressure P unload (0.73 MPa), the operation is switched to the no-load operation (T3-T4, T3'-T4'), and when the supply pressure P becomes equal to or lower than the target pressure P target (0.69 MPa), the operation switching control is performed to switch to the load operation.
The frequency control
The control system includes a variable frequency control that changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa), and a constant frequency control that maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 40 Hz), which is a predetermined frequency higher than the lower limit frequency fmin (20 Hz),
The variable frequency control is steady-state control, and when the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), the variable frequency control is switched to the constant frequency control, and when the supply pressure P falls to the automatic return pressure Preturn (0.50 MPa) or less, the variable frequency control is switched to the constant frequency control (see claim 1, Figures 1 and 2).

Another operation control method for an inverter-driven compressor according to the present invention comprises:
An inverter-driven compressor (1) is provided with a compressor main body (2), a motor (3) that drives the compressor main body (2), an inverter (4) that changes the AC current input to the motor (3), and an operation switching device (20) that switches the operating state of the compressor main body (2) between a load operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and is capable of frequency control that controls the output frequency of the inverter (4) and operation switching control that switches between the load operation and the no-load operation,
a check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52;
As the pressures used as the control reference, a predetermined target pressure Ptarget (for example, 0.69 MPa), an unload operation start pressure Punload (for example, 0.73 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) which is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa) are set,
The load operation is maintained in a steady operating state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the unload operation start pressure Punload (0.73 MPa), the operation is switched to the unload operation (T6-T7, T6'-T7' in FIG. 3; T7-T8, T7'-T8' in FIG. 4), and when the supply pressure P becomes equal to or lower than the target pressure Ptarget (0.69 MPa), the operation is switched to the load operation.
The frequency control
a variable frequency control that changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa); and a constant frequency control that maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 40 Hz) that is a frequency that is a predetermined frequency higher than the lower limit frequency fmin (20 Hz) and that can raise the supply pressure P to the no-load operation start pressure Punload (0.73 MPa) or higher,
The variable frequency control is a steady-state control, and after it is determined that the compressor body 2 is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure P becomes equal to or lower than the automatic return pressure Preturn (0.50 MPa), the control is switched back to the variable frequency control (see claim 2, FIGS. 1, 3, and 4).

In a configuration in which the constant frequency control is performed when it is determined that the compressor main body 2 is in a predetermined low-load operating state, when the inverter 4 continuously outputs a frequency equal to or lower than a reference frequency fref (for example, 22 Hz), which is a predetermined frequency higher than the lower limit frequency fmin (20 Hz), for a predetermined time t, and/or
When the supply pressure P continues for a predetermined time t' and becomes equal to or higher than a predetermined reference pressure Pref (for example, 0.70 MPa), which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa),
The compressor body 2 may be configured to determine that it is in the predetermined low load operating state (see claim 3, FIGS. 1, 3 and 4).

Similarly, in a configuration in which the constant frequency control is performed when it is determined that the compressor main body 2 is in a predetermined low-load operating state, after the variable frequency control is stopped (T5), the output frequency of the inverter 4 may be increased stepwise at predetermined time intervals t'', and the output frequency when the supply pressure P reaches the no-load operation start pressure Punload (0.73 MPa) (T7) may be set to the pressure rise frequency frise (30 Hz) to perform the constant frequency control (see claim 4, Figures 1 and 4).

Furthermore, in any of the above operation control methods, the air flow path 50 on the primary side of the check valve 54 is configured as a discharge flow path 51, and the no-load operation is performed as follows:
Either one of closing the intake port 2a of the compressor body 2, opening the discharge flow path 51 to the atmosphere, or connecting the discharge flow path 51 and the intake port 2a of the compressor body 2, or
This may be achieved by a combination of blocking the intake port 2a of the compressor main body 2 and opening the discharge flow path 51 to the atmosphere, or connecting the discharge flow path 51 to the intake port 2a of the compressor main body 2 (see claim 5 and Figure 1).

Furthermore, the inverter-driven compressor 1 of the present invention has the following features:
An inverter-driven compressor (1) includes a compressor body (2), a motor (3) that drives the compressor body (2), an inverter (4) that changes the AC current input to the motor (3), an operation switching device (20) that switches the operating state of the compressor body (2) between a loaded operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and a frequency control device (30) that controls the output frequency of the inverter (4),
a check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52;
A memory area 42c is provided which stores a predetermined target pressure Ptarget (for example, 0.69 MPa) which is set in advance as a reference pressure for control, an unload operation start pressure Punload (for example, 0.73 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) which is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa),
The operation switching device 20,
The load operation is maintained in a steady operating state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the no-load operation start pressure Punload (0.73 MPa), the operation is switched to the no-load operation (T3-T4, T3'-T4'), and when the supply pressure P becomes equal to or lower than the target pressure Ptarget (0.69 MPa), the operation is switched to the load operation.
The frequency control device 30
It is possible to execute variable frequency control, which changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa), and constant frequency control, which maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 40 Hz), which is a predetermined frequency higher than the lower limit frequency fmin (20 Hz),
The variable frequency control is steady-state control, and when the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), the variable frequency control is switched to the constant frequency control, and when the supply pressure P falls to the automatic return pressure Preturn (0.50 MPa) or less, the variable frequency control is switched to the constant frequency control (claim 6, see Figs. 1 and 2).

Another inverter-driven compressor 1 of the present invention is
An inverter-driven compressor (1) includes a compressor body (2), a motor (3) that drives the compressor body (2), an inverter (4) that changes the AC current input to the motor (3), an operation switching device (20) that switches the operating state of the compressor body (2) between a loaded operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and a frequency control device (30) that controls the output frequency of the inverter (4),
a check valve 54 is provided in an air flow path 50 extending from the discharge port 2b of the compressor body 2 to the consumption side, and the air flow path 50 on the secondary side of the check valve 54 serves as a supply flow path 52;
A memory area 42c is provided which stores a predetermined target pressure Ptarget (for example, 0.69 MPa) which is set in advance as a reference pressure for control, an unload operation start pressure Punload (for example, 0.73 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa), and an automatic return pressure Preturn (for example, 0.50 MPa) which is a predetermined lower pressure than the target pressure Ptarget (0.69 MPa),
The operation switching device 20,
The loaded operation is maintained in a steady operating state, and when the supply pressure P, which is the pressure in the supply flow path 52, rises to the unload operation start pressure Punload (0.73 MPa), the operation is switched to the unload operation (T6-T7, T6'-T7' in FIG. 3; T7-T8, T7'-T8' in FIG. 4), and when the supply pressure P becomes equal to or lower than the target pressure Ptarget (0.69 MPa), the operation is switched to the loaded operation.
The frequency control device 30
It is possible to execute variable frequency control, which changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (for example, 20 Hz) and an upper limit frequency fmax (for example, 60 Hz) so that the supply pressure P coincides with the target pressure Ptarget (0.69 MPa), and constant frequency control, which maintains the output frequency of the inverter 4 constant at a pressure rise frequency frise (for example, 30 Hz or 40 Hz) that is a frequency that is a predetermined frequency higher than the lower limit frequency fmin (20 Hz) and can raise the supply pressure P to the no-load operation start pressure Punload (0.73 MPa) or higher,
The variable frequency control is a steady-state control, and after it is determined that the compressor body is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure P becomes equal to or lower than the automatic return pressure Preturn (0.50 MPa), the control is switched to the variable frequency control (see claim 7, FIGS. 1, 3, and 4).

In a configuration in which the constant frequency control is performed when it is determined that the compressor main body 2 is in a predetermined low-load operating state, the storage area 42c further stores a judgment reference frequency fref (for example, 22 Hz) which is a predetermined higher frequency than the lower limit frequency fmin (20 Hz) and/or a judgment reference pressure Pref (for example, 0.70 MPa) which is a predetermined higher pressure than the target pressure Ptarget (0.69 MPa),
The frequency control device 30
The compressor main body 2 may be configured to be determined to be in the predetermined low-load operating state when the inverter outputs a frequency equal to or lower than the reference frequency fref (22 Hz) for a predetermined time t, and/or when the supply pressure P becomes equal to or higher than the reference pressure Pref (0.70 MPa) for a predetermined time t' (see claim 8, Figures 1, 3 and 4).

Similarly, in a configuration in which the constant frequency control is performed when it is determined that the compressor main body 2 is in a predetermined low load operating state,
The frequency control device 30
After the variable frequency control is stopped (T5), the output frequency of the inverter 4 may be increased stepwise at predetermined time intervals t'', and the output frequency when the supply pressure P reaches the no-load operation start pressure Punload (0.73 MPa) (T7) may be set to the pressure increase frequency frise (30 Hz), so as to perform the constant frequency control (see claim 9 and FIGS. 1 and 4).

In any of the above configurations of the inverter-driven compressor 1,
The air flow path 50 on the primary side of the check valve 54 serves as a discharge flow path 51,
The operation switching device 20,
The compressor includes one of an intake control valve 21 that opens and closes the intake port 2 a of the compressor body 2, an air release valve (solenoid valve 23 or 23′) that opens the discharge flow path 51 to the atmosphere, or a return flow path opening/closing valve (solenoid valve 23″) that opens and closes the return flow path 25 that communicates between the discharge flow path 51 and the intake port 2 a of the compressor body 2, or a combination of the intake control valve 21 and one of the air release valve (solenoid valve 23 or 23′) or the return flow path opening/closing valve (solenoid valve 23″),
The no-load operation may be achieved by closing the intake control valve 21, opening the air release valve (solenoid valve 23 or 23'), or opening the return flow path opening/closing valve (solenoid valve 23''), or by a combination of closing the intake control valve 21 and opening either the air release valve (solenoid valve 23 or 23') or the return flow path opening/closing valve (solenoid valve 23'') (see claim 10 and Figure 1).

In the configuration of the present invention described above, once the system switches to constant frequency control, the output frequency of the inverter 4 is maintained at the pressure rise frequency frise (30 Hz or 40 Hz) until the supply pressure drops below the specified automatic return pressure Preturn (0.50 MPa). During this time, only switching between load operation and no-load operation is performed by the operation switching device 20.

As a result, with the control method of the present invention, low-load operation does not occur between no-load operations during times when only a relatively small amount of compressed gas is consumed on the consumption side due to pipe leaks, etc. Therefore, compared to the control method of Patent Document 1, which always required a certain period of low-load operation between no-load operations, the frequency of transitions to no-load operation, and therefore the total no-load operation time, can be increased, making it possible to further reduce the power consumption of the inverter-driven compressor 1.

Furthermore, with the operation control method of the present invention, when switching from unloaded operation to loaded operation, the rotational speed of the compressor main body 2 has already been increased to a rotational speed corresponding to the pressure rise frequency frise (for example, 30 Hz or 40 Hz). Therefore, compared to the control method of Patent Document 1, in which the output frequency of the inverter 4 is increased from the lower limit frequency fmin (20 Hz) to the pressure rise frequency frise (for example, 40 Hz) to increase the rotational speed of the compressor main body 2 each time forced transition control is performed, the time required to increase the supply pressure P to the unload operation start pressure Punload (0.73 MPa) (see Δ' in Figures 2 to 4) can be made shorter than in the case of Patent Document 1 (see Δ in Figure 5).

As a result, the control method of the present invention can increase the frequency of transitioning to no-load operation during times when only a relatively small amount of compressed gas is consumed due to pipe leaks, etc., and therefore the total no-load operation time, thereby enabling further reductions in the power consumption of inverter-driven compressors.

When the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), the variable frequency control is stopped, the output frequency of the inverter 4 is increased to a pressure rise frequency frise (30 Hz or 40 Hz) that is a predetermined frequency higher than the lower limit frequency fmin (20 Hz), and the constant frequency control is switched to, maintaining the pressure rise frequency frise (30 Hz or 40 Hz). This configuration makes it easy to determine the transition conditions when switching from variable frequency control to constant frequency control without using a timer or other means to count.

On the other hand, in a configuration in which variable frequency control is stopped and control is switched to constant frequency control when it is determined that the compressor main body 2 is in a predetermined low-load operating state, it is possible to switch to constant frequency control before the supply pressure P rises to the unload operation start pressure P unload (0.73 MPa). Therefore, by setting the pressure rise frequency f rise applied during constant frequency control to a frequency that can raise the supply pressure P above the unload operation start pressure P unload (0.73 MPa), it is possible to force a transition to unload operation early by switching to constant frequency control.

Furthermore, in a configuration that transitions to constant frequency control when it is determined that the compressor main body 2 is in a predetermined low-load operating state, a configuration can be adopted in which, after variable frequency control ends, the output frequency of the inverter 4 is increased stepwise at predetermined time intervals, and the output frequency when the supply pressure P reaches the no-load operation start pressure is set to the pressure rise frequency frise.This makes it possible to keep the pressure rise frequency frise during constant frequency control as low as possible (for example, 30 Hz), resulting in even further reductions in power consumption.

1 is a schematic explanatory diagram of an inverter-driven compressor according to the present invention; 4 is a time chart showing the correspondence relationship between the supply pressure, the load factor, the operating state (load operation/unload operation), and the output frequency of the inverter in the control method (embodiment 1) of the present invention. 10 is a time chart showing the correspondence relationship between the supply pressure, the load factor, the operating state (load operation/unload operation), and the output frequency of the inverter in another control method (embodiment 2) of the present invention. 10 is a time chart showing the correspondence relationship between the supply pressure, the load factor, the operating state (load operation/unload operation), and the output frequency of the inverter in yet another control method (embodiment 3) of the present invention. 1 is a time chart showing the correspondence relationship between the supply pressure, the load factor, the blocking/opening of the discharge flow path, and the inverter output frequency in a conventional control method (Patent Document 1).

The inverter-driven compressor of the present invention will be described below with reference to the accompanying drawings.

[Overall configuration of inverter-driven compressor]
In FIG. 1, reference numeral 1 denotes an inverter-driven compressor for carrying out the operation control method of the present invention.

This inverter-driven compressor 1 comprises a compressor main body 2, a motor 3 which serves as the drive source for the compressor main body 2, an inverter 4 which converts the frequency of AC current from a power source and outputs it to the motor 3, an operation switching device 20 which switches the operating state of the compressor main body 2 between loaded operation and unloaded operation, and a frequency control device 30 which controls the rotational speed of the motor 3 by changing the frequency of the current output by the inverter 4. By driving the compressor main body 2 with the motor 3, the compressor main body 2 is configured to draw in compressed gas (air in the illustrated example) through the intake port 2a and discharge the compressed gas from the discharge port 2b.

In this embodiment, the compressor main body 2 is an oil-cooled screw compressor that injects lubricating oil into the cylinder and compresses and discharges the compressed gas. A receiver tank 51b is provided to receive the compressed gas discharged from the compressor main body 2 along with the lubricating oil. The compressed gas and lubricating oil are separated in this receiver tank 51b, and the separated compressed gas can be supplied to pneumatic equipment (not shown) installed on the consuming side. The lubricating oil recovered in the receiver tank 51b can be supplied to the oil supply port 2c of the compressor main body 2 via an oil supply circuit.

A check valve 54 is provided in the compressed gas flow path (air flow path 50) that runs from the discharge port 2b of the compressor main body 2 to the pneumatic equipment (not shown) on the consumption side to prevent backflow of compressed air from the consumption side toward the compressor main body 2.

In the description of the present invention, the air flow path 50 from the discharge port 2b of the compressor main body 2 to the aforementioned check valve 54 (the air flow path 50 on the primary side of the check valve 54) will be referred to as the "discharge flow path (51)," and the air flow path 50 from the check valve 54 to the consumption side (the air flow path 50 on the secondary side of the check valve 54) will be referred to as the "supply flow path (52)."

Therefore, in the embodiment shown in Figure 1, the receiver tank 51b provided on the primary side of the check valve 54 constitutes part of the discharge flow path 51 defined above, and the aforementioned discharge flow path 51 is formed by this receiver tank 51b and the pipes 51a and 51c connected to the receiver tank 51b.

[Operation switching device]
As described above, the inverter-driven compressor 1 of the present invention is provided with an operation switching device 20 that switches the operating state of the compressor main body 2 between load operation, in which compressed gas is generated, and no-load operation, in which the generation of compressed gas is stopped.

In the illustrated embodiment, the operation switching device 20 is composed of an intake control valve 21 that opens and closes the intake port 2a of the compressor main body 2, a control flow path 22 that has one end connected to the discharge flow path 51 (receiver tank 51b), a solenoid valve 23 that opens and closes the control flow path 22, an air release flow path 24 that branches off from the control flow path 22 on the secondary side of the solenoid valve 23, a pressure detection means 41 that detects the pressure (supply pressure P) within the supply flow path 52, and an operation switching unit 42a of a control device 42 that controls the opening and closing of the solenoid valve 23 based on the detection signal from the pressure detection means 41.

The other end of the control flow path 22 is connected to the closed valve pressure chamber (not shown) of the intake control valve 21, and the release flow path 24 is connected to the primary side of the intake control valve 21 via an orifice. As a result, when the solenoid valve 23 opens, the compressed gas in the receiver tank 51b is released into the atmosphere via the release flow path 24 and an air filter installed on the primary side of the intake control valve 21, and operating pressure is introduced into the closed valve pressure chamber of the intake control valve 21, causing the intake control valve 21 to close.

Therefore, in the configuration of the inverter-driven compressor 1 shown in Figure 1, the aforementioned solenoid valve 23 functions as an "air release valve" that opens the discharge flow path 51 to the atmosphere.

With the configuration of the operation switching device 20, when the operation switching unit 42a of the control device 42 opens the solenoid valve 23, the intake control valve 21 closes, stopping the intake of air into the compressor main body 2, and the compressor main body 2 enters unloaded operation, driven with the discharge flow path 51 (receiver tank 51b) open to the atmosphere and reduced back pressure. When the operation switching unit 42a of the control device 42 closes the solenoid valve 23, the intake control valve 21 opens, starting the intake of air into the compressor main body 2, and the compressor main body 2 switches to a loaded operation state, driven with the discharge flow path 51 (receiver tank 51b) no longer open to the atmosphere.

In the embodiment shown in Figure 1, it has been explained that during no-load operation, both the intake control valve 21 is closed to stop the intake and the discharge flow path 51 (receiver tank 51b) is opened to the atmosphere to reduce back pressure. However, instead of this configuration, for example, the air release flow path 24 in Figure 1 may be omitted, and the system may be configured so that load operation and no-load operation are switched by opening and closing the intake control valve 21 alone.

Alternatively, as shown in Figure 1 as variant 1, the intake control valve 21 may not be provided, and the discharge flow path 51 (receiver tank 51b) may be connected to the intake port 2a of the compressor body 2 via the air release flow path 24', and the discharge flow path 51 may be opened to the atmosphere by opening the air release valve (solenoid valve 23') provided in the air release flow path 24', thereby transitioning to no-load operation.

Furthermore, as shown in Figure 1 as variant 2, a return flow path 25 is provided on the secondary side of the solenoid valve 23'', branching off from the control flow path 22. This return flow path 25 is connected to the secondary side of the intake control valve 21, so that when the solenoid valve 23'' is open for no-load operation, the intake control valve 21 is closed and the compressed gas in the discharge flow path 51 (receiver tank 51b) is returned to the intake port 2a of the compressor main body 2, thereby achieving no-load operation. In the configuration of variant 2, the solenoid valve 23'' also functions as a "return flow path opening/closing valve".

The aforementioned control device 42, which is a component of the operation switching device 20 described above, stores in memory area 42c the target pressure Ptarget (0.69 MPa, for example) and the unload operation start pressure Punload (0.73 MPa, for example), which is set as a predetermined pressure higher than the target pressure Ptarget (0.69 MPa), as the control reference pressure during operation switching control.

The operation switching unit 42a of the control device 42 executes operation switching control based on the detection signal received from the pressure detection means 41, which detects the supply pressure P, which is the pressure inside the supply flow path 52. When the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa) during loaded operation, the operation switching unit 42a opens the solenoid valves 23, 23', and 23" to transition to unload operation, and when the supply pressure P drops to the target pressure Ptarget (0.69 MPa) during unload operation, the operation switching unit 42a closes the solenoid valves 23, 23', and 23" to return to loaded operation.

[Frequency control device]
The inverter-driven compressor 1 of the present invention is provided with a frequency control device 30 that controls the rotation speed of the compressor body 2 by changing the output frequency of the inverter 4 .

This frequency control device 30 is configured to selectively perform variable frequency control, which changes the output frequency of the inverter 4 between a predetermined lower limit frequency fmin (20 Hz) and upper limit frequency fmax (60 Hz) so that the pressure in the supply flow path 52, and therefore the supply pressure P, which is the pressure of the compressed gas supplied to the consumption side, matches the target pressure Ptarget (0.69 MPa), or constant frequency control, which maintains the output frequency of the inverter 4 constant at a predetermined pressure rise frequency frise (for example, 30 Hz or 40 Hz) without changing it.

In the embodiment shown in Figure 1, the frequency control device 30 is composed of a pressure detection means 41 that detects the pressure (supply pressure P) within the supply flow path 52, and a frequency control section 42b of a control device 42 that outputs a control signal to the inverter 4 based on the detection signal from the pressure detection means 41.In the embodiment shown in Figure 1, the pressure detection means 41 and control device 42 share the same components as the operation switching device 20 described above, reducing the number of parts.

To perform the frequency control described above, the control device 42 stores the target pressure Ptarget (for example, 0.69 MPa) and the unload operation start pressure Punload (for example, 0.73 MPa) as reference pressures for frequency control, as well as the automatic return pressure Preturn (for example, 0.50 MPa) in the control device 42's memory area 42c.

The frequency control unit 42b of the control device 42 calculates the pressure difference between the supply pressure P detected by the pressure detection means 41 and the target pressure Ptarget until the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa), and uses this pressure difference to determine the output frequency of the inverter 4 through PI or PID calculation processing. It then generates a corresponding rotation speed command (frequency command) and outputs this as a control signal to the inverter 4, thereby performing "variable frequency control" as steady-state control, which varies the frequency output by the inverter 4 between a predetermined lower limit value fmin and upper limit value fmax, thereby controlling the rotation speed of the compressor main body so that the supply pressure P approaches the target pressure Ptarget.

As an example, in this variable frequency control, the rated frequency frating (for example, 50 Hz) is set to a frequency that is lower than the upper limit frequency fmax (60 Hz) by a specified margin, and that can bring the supply pressure P to the target pressure Ptarget (0.69 MPa) when compressed gas is being consumed on the consumption side with the load factor [(consumed air volume/rated discharge air volume) x 100 (%)] at 100%.When the load factor decreases and the pressure P in the discharge flow path 51 exceeds the target pressure Ptarget, the control device 42 reduces the output frequency of the inverter 4 to a frequency lower than the rated frequency frating (50 Hz), and switches the motor 3 to low-speed operation.

This reduction in output frequency is set so that the supply pressure P reaches the lower limit fmin (20Hz) before reaching the unload operation start pressure Punload (0.73MPa).

On the other hand, if an increase in the load factor causes the compressor main body 2 to be driven at a rotational speed corresponding to the lower limit frequency fmin (20 Hz), and the supply pressure P falls below the specified target pressure Ptarget (0.69 MPa), the output frequency of the inverter 4 is increased to a frequency higher than the lower limit value fmin (20 Hz), for example the rated frequency frating (50 Hz). By repeating this operation, the supply pressure P is made to match the target pressure Ptarget.

Furthermore, when the frequency control unit 42b of the control device 42 determines that the supply pressure P has risen to the unload operation start pressure Punload (0.73 MPa) during variable frequency control, or when it determines that the operating state of the compressor main body 2 has reached a predetermined low-load operating state, it stops the aforementioned variable frequency control and switches to "constant frequency control," in which the inverter output frequency is kept constant at a pressure rise frequency frise (for example, 30 Hz or 40 Hz) set as a predetermined higher frequency than the lower limit frequency fmin (for example, 20 Hz), and the motor 3 is driven.

The frequency control device 30 continues this constant frequency control until the supply pressure P drops to the automatic return pressure Preturn (for example, 0.50 MPa). When the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa), the constant frequency control stops and the frequency control returns to the variable frequency control described above.

Example 1
Hereinafter, the operation of the inverter-driven compressor (embodiment 1) configured to transition from variable frequency control to constant frequency control when the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa) will be described with reference to the time chart of FIG. 2.

The preconditions for the embodiment shown in FIG. 2 are as follows.
The rated frequency frating (50 Hz) is the frequency at which the supply pressure P can be maintained at the target pressure Ptarget when compressed gas is consumed at a load factor of 100%.
The lower limit frequency fmin (20 Hz) is the frequency at which the supply pressure P can be maintained at the target pressure Ptarget when compressed gas is consumed at a load factor of 40%.
- Due to a pipe leak, etc., compressed gas is consumed (leaked) at a load factor of 10% when all pneumatic equipment connected to the consumption side is stopped.

In the inverter-driven compressor 1 configured as described above, when compressed gas is being consumed at a load factor of 100%, the supply pressure P does not exceed the target pressure Ptarget and rise to the unload operation start pressure Punload. The frequency control unit 42b of the control device 42 closes the solenoid valve 23, opens the intake control valve 21, and stops the release of compressed gas from the discharge flow path 51 (receiver tank 51b), placing the compressor main body 2 in a steady operating state, that is, under load.

Furthermore, because the supply pressure P has not reached the unload operation start pressure Punload (0.73 MPa), the frequency control device 30 (frequency control unit 42b of the control device 42) performs "variable frequency control," which changes the frequency output by the inverter 4 according to the supply pressure P detected by the pressure detection means 41, and outputs a control signal to the inverter to output the rated frequency frating (50 Hz).

With variable frequency control being performed in this manner, when the amount of compressed gas consumed by the pneumatic equipment connected to the consumption side decreases and the load rate begins to drop from 100% (T1), the control device 42, which serves as the frequency control device 30, reduces the output frequency of the inverter 4 so that the supply pressure P maintains the target pressure Ptarget (0.69 MPa), and when the load rate drops to 40%, it reduces the output frequency of the inverter 4 to the lower limit frequency fmin (20 Hz).

As mentioned above, in the inverter-driven compressor 1 of this embodiment, the frequency at which the supply pressure P can be maintained at the target pressure Ptarget (0.69 MPa) when the load factor is 40% and compressed gas is being consumed is set to the lower limit frequency fmin (20 Hz). Therefore, if the consumption of compressed gas decreases further and the load factor falls below 40%, the discharge air volume from the compressor main body 2 will exceed the consumption of compressed gas, causing the supply pressure P to exceed the target pressure Ptarget (0.69 MPa) and begin to rise gradually.

Then, when all pneumatic equipment connected to the consumption side stops completely and the load factor drops to 10%, which corresponds to the consumption amount due to a pipe leak, etc. (T2), the increase in supply pressure P accelerates and then rises to the unload operation start pressure Punload (0.73 MPa) (T3).

When the operation switching unit 42a of the control device 42 determines based on the detection signal from the pressure detection means 41 that the supply pressure P has reached the unload operation start pressure Punload (0.73 MPa), it opens the solenoid valve 23, introduces compressed gas into the closed valve pressure chamber of the intake control valve 21 via the control flow path 22, stops the intake of the compressor main body 2, and releases compressed gas from the receiver tank 51b (discharge flow path 51) via the air release flow path 24, transitioning to unload operation (T3).

Furthermore, when the supply pressure P reaches the unload operation start pressure Punload (0.73 MPa), the frequency control unit 42b of the control device 42 stops the variable frequency control described above and outputs a control signal to the inverter 4 to output a pressure rise frequency frise (40 Hz). This increases the rotational speed of the compressor main body 2 from the lower limit rotational speed corresponding to the lower limit frequency fmin (20 Hz) to the rotational speed corresponding to the pressure rise frequency frise (40 Hz), and transitions to "constant frequency control" in which the compressor main body is operated at a constant pressure rise frequency frise (40 Hz) (T3).

This transition to constant frequency control increases the rotational speed of the compressor main unit 2, but because the compressor main unit 2 is in a no-load operation state where it is not producing compressed gas, the supply pressure P gradually decreases (T3-T4) as compressed gas is consumed at a load factor of 10% due to pipe leaks, etc.

Then, when the supply pressure P drops to the target pressure P (0.69 MPa), the operation switching unit 42a of the control device 42 closes the solenoid valve 23, opens the intake control valve 21, and stops opening the receiver tank 51b (discharge flow path 51) to the atmosphere via the release flow path 24, returning the compressor main body to load operation (T4).

Once the frequency control unit 42b of the control device 42 stops variable frequency control and switches to constant frequency control, it will not resume variable frequency control until the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa), which is set as a predetermined pressure lower than the target pressure Ptarget (0.69 MPa).

As a result, the compressor main body 2 transitions to load operation while maintaining a relatively high rotational speed corresponding to the pressure rise frequency frise (40 Hz), and the supply pressure P rises to the unload operation start pressure Punload (0.73 MPa) in a relatively short time Δ' (T4-T3'). Therefore, the operation switching unit 42a of the control device 42 transitions the operating state of the compressor main body back to unload operation in a relatively short time (T3').

Then, the same process is repeated as long as the consumption of compressed gas at a load rate of less than 40%, such as when the consumption of compressed gas on the consumer side is limited to a load rate of 10%, which corresponds to the consumption of a small amount of compressed gas due to a pipe leak, etc.

Then, if use of pneumatic equipment connected to the consumption side is resumed, the load rate rises above 10%, which corresponds to consumption due to pipe leaks, etc., and the rate at which the supply pressure P decreases accelerates. When the supply pressure P decreases to the target pressure P (0.69 MPa), the operation switching device 20 returns the operating state of the compressor main body 2 to loaded operation. Furthermore, when the supply pressure P decreases to the automatic return pressure Preturn (0.50 MPa), the frequency control device 30 terminates the constant frequency control described above and returns to variable frequency control, which changes the frequency output by the inverter in accordance with the supply pressure P.

In this way, according to the operation control method of the present invention, during constant frequency control, the pressure rise frequency frise (40 Hz), which is a predetermined higher frequency than the lower limit frequency fmin (20 Hz), is maintained while transitioning to load operation.

As a result, there is no time lag (see TL in Figure 5) until the rotation speed increases, as occurs when the pressure rise frequency frise (40 Hz) is increased from the lower limit frequency fmin (20 Hz) to the pressure rise frequency frise (40 Hz) each time a forced transition to unload operation is made, as in the conventional configuration introduced in Patent Document 1. Therefore, compared to the time (Δ in Figure 5) required to increase the supply pressure P to the unload operation start pressure Punload (0.73 MPa) using the method of Patent Document 1, it is possible to increase the supply pressure P to the unload operation start pressure Punload (0.73 MPa) in a shorter time (Δ' in Figure 2), making it possible to shorten the load operation time during constant frequency control.

Furthermore, once the system has switched to constant frequency control, the operation state is simply switched between load operation and no-load operation by the operation switching device 20 (operation switching section 42a of the control device 42), and constant frequency control continues until the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa).

As a result, with the control method of the present invention, during the time period (T2-T5) when only a relatively small amount of compressed gas is consumed on the consumer side due to pipe leaks, etc., there is no low-load operation between no-load operations, and transitions to no-load operation occur frequently, resulting in a longer total time of no-load operation and enabling further reductions in power consumption compared to the conventional control method cited in Patent Document 1.

Example 2
In the configuration of the first embodiment described with reference to the time chart of FIG. 2, an example of a configuration has been described in which, when the supply pressure P rises to the unload operation start pressure P unload (0.73 MPa) during variable frequency control, the variable frequency control is stopped and the system switches to constant frequency control.

In contrast, the configuration of Example 2, which will be explained with reference to the time chart in Figure 3, is configured to transition from variable frequency control to constant frequency control when it is determined that the compressor main body 2 is in a predetermined low-load operating state, and other operations are the same as those of the inverter-driven compressor explained with reference to Figure 2.

Note that, among the operating conditions of the inverter-driven compressor assumed in Example 2 shown in Figure 3, the rated frequency frating (50 Hz) is the frequency that can maintain the pressure P in the supply flow path at the target pressure Ptarget (0.69 MPa) when compressed gas is consumed at a load factor of 100%, and the lower limit frequency fmin is the frequency that can maintain the supply pressure P at the target pressure Ptarget (0.69 MPa) when compressed gas is consumed at a load factor of 40%, which are the same as those of the inverter-driven compressor in Example 1.

However, the explanation of the operation of the inverter-driven compressor 1 in this embodiment (Embodiment 2) assumes a situation in which all pneumatic equipment connected to the consumption side is stopped and a compressed gas leak occurs at a load rate of 20% due to a piping leak on the consumption side, etc., which differs from Embodiment 1, which assumed a leak at a load rate of 10%.

In the inverter-driven compressor 1 of Example 2, when variable frequency control is being performed and the amount of compressed gas consumed by the pneumatic equipment connected to the consumption side decreases and the load factor begins to decrease from 100% (T1), the frequency control device 30 (frequency control unit 42b of the control device 42) reduces the output frequency of the inverter 4 so that the supply pressure P maintains the target pressure Ptarget (0.69 MPa), and when the load factor reaches 40%, the output frequency of the inverter 4 is reduced to the lower limit frequency fmin (20 Hz) (T1-T3).

Furthermore, when the consumption of compressed gas falls below a load factor of 40% (T3), the amount of air discharged from the compressor main body 2 exceeds the consumption of compressed gas, causing the supply pressure P to exceed the target pressure Ptarget (0.69 MPa) and begin to rise gradually.

If the use of the pneumatic equipment connected to the consumer side is completely stopped, the consumption of compressed gas on the consumer side will drop to a load factor of 20%, which is caused by a pipe leak, etc. (T4).

The frequency control device 30 (frequency control unit 42b of the control device 42) compares the output frequency of the inverter 4 with a reference frequency fref (22Hz), which is preset as a predetermined higher frequency than the lower limit frequency fmin (20Hz). When it counts that the output frequency of the inverter 4 has remained below the reference frequency fref (22Hz) for a predetermined time t (T2-T5), it determines that the compressor main body 2 is in a predetermined low-load operating state, stops variable frequency control, and switches to constant frequency control.

Alternatively, instead of or in addition to the above criteria, the supply pressure P detected by the pressure detection means 41 can be compared with a reference pressure Pref (0.70 MPa) that is preset as a predetermined higher pressure than the target pressure Ptarget (0.69 MPa). When it is counted that the supply pressure P remains above the reference pressure Pref (0.70 MPa) for a predetermined time t' (T4-T5), it can be determined that the compressor main body 2 is in a predetermined low-load operating state, and variable frequency control can be stopped and a transition to constant frequency control can be made.

When it is determined in this way that the compressor main body 2 is in a predetermined low-load operating state, the frequency control device 30 (frequency control unit 42b of the control device 42) stops variable frequency control and outputs a control signal to the inverter 4 to output the pressure rise frequency frise (40 Hz), increasing the rotational speed of the compressor main body from the lower limit rotational speed corresponding to the lower limit frequency fmin (20 Hz) to the rotational speed corresponding to the pressure rise frequency frise (40 Hz), and transitioning to "constant frequency control" in which the compressor main body 2 is operated at a constant pressure rise frequency frise (T5).

By setting this pressure rise frequency (frise) (40 Hz) to a frequency corresponding to the rotational speed that can raise the supply pressure P to the unload operation start pressure Punload (0.73 MPa), the supply pressure P can be raised to the unload operation start pressure Punload (0.73 MPa) in a short period of time by switching to constant frequency control (T5-T6).

The operation switching device 20 (operation switching section 42a of the control device 42) determines based on the detection signal from the pressure detection means 41 that the supply pressure P has risen to the unload operation start pressure Punload (0.73 MPa). The operation switching device 20 then opens the solenoid valve 23, introduces compressed gas into the closed valve pressure chamber of the intake control valve 21 via the control flow path 22, closes the intake port 2a of the compressor main body 2, and transitions to unload operation, releasing the compressed gas from the receiver tank 51b (discharge flow path 51) via the release flow path 24 (T6).

By switching to constant frequency control, the rotational speed of the compressor main unit 2 increases, but the compressor main unit 2 transitions to a no-load operation state in which no compressed gas is produced, and the supply pressure P gradually decreases as compressed gas is consumed due to pipe leaks, etc. (T6-T7).

Then, when the pressure P in the supply flow path drops to the target pressure Ptarget (0.69 MPa), the operation switching device 20 (operation switching section 42a of the control device 42) closes the solenoid valve 23, opens the intake control valve 21, and stops opening the receiver tank 51b (discharge flow path 51) to the atmosphere via the release flow path 24, returning the compressor main body to load operation (T7).

Once the frequency control device 30 (frequency control unit 42b of the control device 42) stops variable frequency control and switches to constant frequency control, it will not return to variable frequency control until the supply pressure P drops to the automatic return pressure Preturn (0.50 MPa).

For this reason, during constant frequency control, the compressor transitions to load operation while maintaining a relatively high rotational speed corresponding to the pressure rise frequency frise (40 Hz). This allows load operation during constant frequency control (T7-T6') to be completed in a shorter time (Δ') than when the output frequency is increased from the lower limit frequency fmin (20 Hz) to the pressure rise frequency frise (40 Hz) to increase the rotational speed and the supply pressure P at the same time (Δ in the case of T5-T6), as occurs when transitioning to constant frequency control.

This load operation (T7-T6') causes the supply pressure P to rise to the unload operation start pressure Punload (0.73 MPa) (T7-T6'), and the operation switching device 20 (operation switching section 42a of the control device 42) re-transfers the operating state of the compressor body to unload operation in a relatively short time (T6'-T7').

After that, if the only compressed gas consumed on the consumer side is a small amount due to a pipe leak, etc., the same process will be repeated.

Then, when the use of pneumatic equipment connected to the consumption side is resumed, for example, and the load rate begins to rise above 20%, which corresponds to consumption due to a pipe leak, etc. (T9), the rate at which the supply pressure P decreases accelerates. When the supply pressure P decreases to the target pressure P (0.69 MPa), the operation switching device 20 (operation switching section 42a of the control device 42) returns the operating state of the compressor main body 2 to loaded operation. Furthermore, when the supply pressure P decreases to the automatic return pressure Preturn (0.50 MPa), the frequency control device 30 (frequency control section 42b of the control device 42) terminates constant frequency control, which rotates the compressor main body 2 at a constant rotational speed corresponding to the aforementioned pressure rise frequency frise (40 Hz), and returns to variable frequency control, which varies the frequency output to the inverter 4 according to the supply pressure P.

In the control method of Example 1 described with reference to Figure 2, variable frequency control was stopped and a transition to constant frequency control was made when the supply pressure P rose to the unload operation start pressure P unload (0.73 MPa). However, in this example (Example 2), the control is configured to transition to constant frequency control when the compressor main body 2 is in a specified low-load operating state. This makes it possible to transition from variable frequency control to constant frequency control before the supply pressure P rises to the unload operation start pressure P unload (0.73 MPa).

As a result, the configuration of this embodiment (embodiment 2) not only achieves the effects achieved by the configuration of embodiment 1, but also has the additional effect of shortening the low-load operation time before transitioning to constant frequency control.

In other words, if the load rate due to compressed gas consumption due to piping leaks, etc., is close to the discharge rate at the lower limit frequency fmin (20 Hz) (the discharge rate corresponding to a load rate of 40% in this embodiment), such as from 10% in Example 1 to 20% as assumed in this embodiment, it will take a longer time for the supply pressure P to rise to the unload operation start pressure Punload (0.73 MPa) even if use of the pneumatic equipment connected to the consumption side is stopped, and a longer time will be required to switch to constant frequency control.

In contrast, the method of this embodiment switches to constant frequency control and forcibly switches to no-load operation when a specified low-load operating state is reached, thereby shortening the low-load operating time before switching to constant frequency control even in such cases.

Example 3
FIG. 4 shows a time chart according to still another embodiment of the method for controlling an inverter-driven compressor of the present invention.

In the embodiment (embodiment 2) described with reference to Figure 3, when switching from variable frequency control to constant frequency control, a configuration is adopted in which the output frequency of the inverter 4 is directly increased from the output frequency during low load operation (20 Hz, the lower limit frequency fmin in the example of Figure 3) to the pressure rise frequency frise (40 Hz).

In contrast, in the embodiment (embodiment 3) shown in Figure 4, when transitioning from variable frequency control to constant frequency control, the output frequency of the inverter 4 is increased in stages from the output frequency during low-load operation (20 Hz, the lower limit frequency fmin in the example of Figure 4) to, for example, fmin + Δf (T5; for example, 25 Hz), fmin + 2Δf (T6; for example, 30 Hz), fmin + 3Δf (for example, 35 Hz), etc., every certain time t'' (for example, a time arbitrarily selected by the user between 5 and 60 seconds depending on the usage status of the inverter-driven compressor 1), and the frequency when the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa), frequency fmin + 2Δf (T7; for example, 30 Hz) in the example of Figure 4, is set as the pressure rise frequency frise, thereby performing the constant frequency control described above. In all other respects, the control method is the same as that described with reference to Figure 3.

In this way, in this embodiment (embodiment 3), the output frequency of the inverter 4 is gradually increased from the output frequency during low-load operation (for example, the lower limit frequency fmin: 20 Hz) and the frequency when the supply pressure P rises to the no-load operation start pressure Punload (0.73 MPa) is set to the aforementioned pressure rise frequency frise.By doing so, the pressure rise frequency frise applied during constant frequency control can be set as low as possible depending on the operating conditions, etc., and therefore the rotational speed of the motor 3 during constant frequency control can be kept as low as possible, thereby further reducing power consumption.

This gradual increase in output frequency may be performed each time there is a transition from variable frequency control to constant frequency control. However, for example, it is also possible to perform a gradual increase in output frequency only during the first transition to constant frequency control, and store the output frequency (fmin + 2Δf = 30Hz in the example in Figure 4) at which the no-load operation start pressure Punload (0.73MPa) is reached. Then, during subsequent transitions to constant frequency control, the output frequency may be directly increased from the output frequency during low-load operation (for example, the lower limit frequency fmin) to the pressure rise frequency frise (fmin + 2Δf = 30Hz) stored during the first transition to constant frequency control, and constant frequency control may be performed at this frequency.

1 inverter-driven compressor 2 compressor body 2a intake port (of compressor body)
2b Discharge port (of compressor body)
2c Fuel filler port 3 Motor 4 Inverter 20 Operation switching device 21 Intake control valve 22 Control flow path 23 Solenoid valve (air release valve)
23' Air release valve (solenoid valve)
23'' solenoid valve (circulation flow path opening/closing valve)
24, 24': Air release flow path 25: Circulation flow path 30: Frequency control device 41: Pressure detection means (pressure sensor)
42 Control device 42a Operation switching unit (of control device 42)
42b Frequency control section (of control device 42)
42c Storage area (of control device 42)
50 Air flow path 51 Discharge flow path 51a Pipe line (between the discharge port of the compressor body and the receiver tank)
51b Receiver tank 51c Pipeline (between receiver tank and check valve)
52 Supply flow path 54 Check valve Punload Unload operation start pressure Ptarget Target pressure Preturn Automatic return pressure Pref Judgment reference pressure fmax Upper limit frequency frating Rated frequency frise Pressure rise frequency fmin Lower limit frequency fref Judgment reference frequency

Claims (10)

An inverter-driven compressor comprising: a compressor body; a motor that drives the compressor body; an inverter that changes the AC current input to the motor; and an operation switching device that switches the operating state of the compressor body between a load operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and that enables frequency control that controls the output frequency of the inverter and operation switching control that switches between the load operation and no-load operation,
a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path;
As pressures to be used as control standards, a predetermined target pressure, a no-load operation start pressure which is a predetermined higher pressure than the target pressure, and an automatic return pressure which is a predetermined lower pressure than the target pressure are respectively set;
The load operation is maintained in a steady state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the supply pressure becomes equal to or lower than the target pressure, the operation is switched to the load operation.
the frequency control includes variable frequency control that changes the output frequency of the inverter between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure equal to the target pressure, and constant frequency control that maintains the output frequency of the inverter constant at a pressure rise frequency that is a predetermined frequency higher than the lower limit frequency,
an inverter-driven compressor operation control method comprising: setting the variable frequency control as steady-state control; shifting from the variable frequency control to the constant frequency control when the supply pressure rises to the no-load operation start pressure; and shifting back to the variable frequency control when the supply pressure falls to or below the automatic return pressure. An inverter-driven compressor comprising: a compressor body; a motor that drives the compressor body; an inverter that changes the AC current input to the motor; and an operation switching device that switches the operating state of the compressor body between a load operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and that enables frequency control that controls the output frequency of the inverter and operation switching control that switches between the load operation and no-load operation,
a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path;
As pressures to be used as control standards, a predetermined target pressure, a no-load operation start pressure which is a predetermined higher pressure than the target pressure, and an automatic return pressure which is a predetermined lower pressure than the target pressure are set,
The load operation is maintained as a steady operating state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the supply pressure becomes equal to or lower than the target pressure, the operation is switched to the load operation.
the frequency control includes variable frequency control for varying the output frequency of the inverter between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure coincide with the target pressure, and constant frequency control for maintaining the output frequency of the inverter constant at a frequency that is predetermined higher than the lower limit frequency and at a pressure increase frequency that can increase the supply pressure to or above the no-load operation start pressure,
an operation control method for an inverter-driven compressor, characterized in that the variable frequency control is a steady-state control, and after it is determined that the compressor main body is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure becomes equal to or lower than the automatic return pressure, the operation control method is switched to the variable frequency control. When the inverter outputs a frequency equal to or lower than a reference frequency, which is a predetermined frequency higher than the lower limit frequency, for a predetermined period of time, and/or
When the supply pressure continues to be equal to or higher than a reference pressure, which is a predetermined higher pressure than the target pressure, for a predetermined time,
3. The operation control method for an inverter-driven compressor according to claim 2, further comprising determining that the compressor body is in the predetermined low-load operating state. An operation control method for an inverter-driven compressor as described in claim 2, characterized in that after the variable frequency control is stopped, the inverter output frequency is increased stepwise at predetermined time intervals, and the output frequency when the supply pressure reaches the no-load operation start pressure is set as the pressure increase frequency, thereby performing the constant frequency control. The air flow path on the primary side of the check valve serves as a discharge flow path,
The no-load operation is
Either closing the intake port of the compressor body, opening the discharge flow path to the atmosphere, or connecting the discharge flow path to the intake port of the compressor body, or
5. The operation control method for an inverter-driven compressor according to claim 1, wherein the operation control is performed by a combination of closing the intake port of the compressor body and either opening the discharge flow path to the atmosphere or connecting the discharge flow path to the intake port of the compressor body. An inverter-driven compressor including a compressor body, a motor that drives the compressor body, an inverter that changes the AC current input to the motor, an operation switching device that switches the operating state of the compressor body between a loaded operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and a frequency control device that controls the output frequency of the inverter,
a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path;
a storage area for storing a predetermined target pressure, a no-load operation start pressure that is a predetermined higher pressure than the target pressure, and an automatic return pressure that is a predetermined lower pressure than the target pressure, which are preset as a reference pressure for control;
The operation switching device,
The load operation is maintained as a steady operating state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the pressure in the supply flow path falls to the target pressure or less, the operation is switched to the load operation.
The frequency control device
The inverter is capable of executing variable frequency control, which changes the output frequency of the inverter between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure equal to the target pressure, and constant frequency control, which maintains the output frequency of the inverter constant at a pressure rise frequency that is a predetermined frequency higher than the lower limit frequency,
an inverter-driven compressor, characterized in that the variable frequency control is a steady-state control, the variable frequency control is switched to the constant frequency control when the supply pressure rises to the no-load operation start pressure, and the variable frequency control is switched to when the supply pressure falls to or below the automatic return pressure. An inverter-driven compressor including a compressor body, a motor that drives the compressor body, an inverter that changes the AC current input to the motor, an operation switching device that switches the operating state of the compressor body between a loaded operation in which compressed gas is generated and a no-load operation in which the generation of compressed gas is stopped, and a frequency control device that controls the output frequency of the inverter,
a check valve is provided in an air flow path from the discharge port of the compressor body to the consumption side, and the air flow path on the secondary side of the check valve serves as a supply flow path;
a storage area for storing a predetermined target pressure, a no-load operation start pressure that is a predetermined higher pressure than the target pressure, and an automatic return pressure that is a predetermined lower pressure than the target pressure, which are preset as a reference pressure for control;
The operation switching device,
The load operation is maintained in a steady state, and when the supply pressure, which is the pressure in the supply flow path, rises to the no-load operation start pressure, the operation is switched to the no-load operation, and when the supply pressure becomes equal to or lower than the target pressure, the operation is switched to the load operation.
The frequency control device
variable frequency control is possible in which the output frequency of the inverter is changed between a predetermined lower limit frequency and an upper limit frequency so as to make the supply pressure coincide with the target pressure, and constant frequency control is possible in which the output frequency of the inverter is maintained constant at a frequency that is predetermined higher than the lower limit frequency and at a pressure increase frequency that is a frequency at which the supply pressure can be increased to or above the no-load operation start pressure,
an inverter-driven compressor characterized in that the variable frequency control is a steady-state control, and after it is determined that the compressor main body is in a predetermined low-load operating state, the variable frequency control is switched to the constant frequency control, and when the supply pressure becomes equal to or lower than the automatic return pressure, the compressor switches back to the variable frequency control. The storage area further stores a reference frequency that is a predetermined higher frequency than the lower limit frequency and/or a reference pressure that is a predetermined higher pressure than the target pressure,
The frequency control device
8. The inverter-driven compressor according to claim 7, wherein the compressor body is determined to be in the predetermined low-load operating state when the inverter outputs a frequency equal to or lower than the judgment reference frequency for a predetermined period of time, and/or when the supply pressure is equal to or higher than the judgment reference pressure for a predetermined period of time. The frequency control device
8. The inverter-driven compressor according to claim 7, wherein after the variable frequency control is stopped, the output frequency of the inverter is increased stepwise at predetermined time intervals, and the output frequency at which the supply pressure reaches the no-load operation start pressure is set as the pressure increase frequency, and the constant frequency control is performed. The air flow path on the primary side of the check valve serves as a discharge flow path,
The operation switching device,
The compressor includes one of an intake control valve that opens and closes the intake port of the compressor body, an air release valve that opens the discharge flow path to the atmosphere, or a return flow path opening/closing valve that opens and closes the return flow path that communicates between the discharge flow path and the intake port of the compressor body, or a combination of the intake control valve and either the air release valve or the return flow path opening/closing valve,
The inverter-driven compressor according to any one of claims 6 to 9, characterized in that the no-load operation is achieved by closing the intake control valve, opening the air release valve, or opening the return flow path on-off valve, or by a combination of closing the intake control valve and opening either the air release valve or the return flow path on-off valve.