JP7573152B2 - Motor drive device and refrigerator using the same - Google Patents

Description

The present disclosure relates to a motor drive device that drives a brushless DC motor of a compressor and a refrigerator using the same.

Patent Document 1 discloses a motor drive device for a refrigerator that drives a brushless DC motor of a conventional compressor. A refrigeration device such as a refrigerator equipped with a compressor driven by this motor drive device aims to save energy by separating the refrigeration cycle into a high-pressure side and a low-pressure side when the cooling operation is stopped, and preventing the flow of refrigerant. However, when configured in this way, a large difference remains between the suction pressure and the discharge pressure inside the compressor, that is, a large pressure difference occurs between the suction section and the discharge section. Therefore, when the compressor is started, a large amount of energy is required to overcome the compression process, that is, to complete the compression process.

Therefore, in a conventional motor drive device for driving a compressor, the position of the piston of the compressor before starting is moved to a position close to the top dead center between the top dead center and the bottom dead center. After the piston is moved to a position close to the top dead center, the compressor is started, which causes a large acceleration and stores energy. This overcomes the compression stroke, i.e., the compression stroke is achieved, and the compressor starts.

Figure 6 shows a conventional motor drive device described in Patent Document 1. This motor drive device is composed of a brushless DC motor 201, a compressor 203 having a piston 202 connected to the rotor of the brushless DC motor 201, a control unit 204 including an initial alignment stage that moves the motor to the bottom dead center, a forced alignment stage that moves the starting position to adjacent to the top dead center in the intake stroke, and an acceleration stage that accelerates the rotor of the brushless DC motor 201, and an inverter 205 that supplies power to the motor from a drive signal from the control unit 204.

In the motor drive device configured as described above, when the compressor 203 stops, the piston 202 is likely to stop before the compression stroke, and the piston 202 is likely to stop near the bottom dead center. Therefore, in the initial alignment stage, the control unit 204 sends a signal to the inverter 205 that puts the piston 202 in the bottom dead center phase. After that, the inverter 205 passes a current through the stator of the brushless DC motor 201, causing the rotor of the brushless DC motor 201 to rotate, and the piston 202 to move to the bottom dead center.

Next, the control unit 204 sends a signal to the inverter 205 to sequentially switch the piston 202 from the bottom dead center phase to the reverse direction in the forced alignment stage. This moves the position of the piston 202 to next to the top dead center in the intake stroke.

Then, in the acceleration stage, the control unit 204 sends a signal to the inverter 205 to start and accelerate the brushless DC motor 201. This causes the brushless DC motor 201 to rotate. Because the piston 202 has been accelerating since the vicinity of the top dead center, the speed in the compression stroke increases, and the compression stroke is overcome, i.e., the compression stroke is achieved, and starting is possible.

JP 2007-107523 A

The present disclosure provides a motor drive device that is inexpensive, suppresses vibration, and can start stably, even under conditions of large load torque fluctuations such as a difference between the suction pressure and discharge pressure of the compressor.

The motor drive device of the present disclosure includes a brushless DC motor that drives a piston of a reciprocating compressor, and a piston position change unit that rotates the brushless DC motor to shift the piston from top dead center while the compressor is stopped.

The motor drive device of the present disclosure displaces the piston from the top dead center while the compressor is stopped, eliminating torque shortages. This improves drive performance during high torque drive and high load drive. This allows stable start-up even when the load torque fluctuates greatly.

Block diagram of a motor drive device according to a first embodiment. FIG. 1 is a schematic diagram of components constituting a compressor according to a first embodiment; FIG. 1 is a waveform diagram showing the relationship between the pressure applied to the piston of the compressor and the rotation angle of the rotor in the first embodiment. FIG. 1 is a waveform diagram showing the relationship between the torque required when the brushless DC motor in the first embodiment is operating in the forward direction and the rotation angle of the rotor. FIG. 1 is a waveform diagram showing the relationship between the torque required when the brushless DC motor in the first embodiment is operating in the reverse direction and the rotation angle of the rotor. Waveform diagram showing the torque required to start from top dead center in a conventional configuration A waveform diagram showing the torque output to move the piston from the top dead center in a conventional configuration. Waveform diagram showing rotor speed when starting from top dead center in a conventional configuration FIG. 11 is a waveform diagram showing the torque required for starting from the top dead center in the first embodiment. FIG. 11 is a waveform diagram showing the torque output for moving the piston from the top dead center in the first embodiment. FIG. 11 is a waveform diagram showing the rotor speed when starting from the top dead center in the first embodiment. Block diagram of a conventional motor drive device

(The knowledge and other information that formed the basis of this disclosure)
At the time when the inventors came up with the idea of the present disclosure, a motor drive device was provided as described in Patent Document 1. In the conventional motor drive device, there was a difference between the suction pressure and the discharge pressure of the compressor, so that the load torque fluctuation was large, and it was difficult to stably start the motor drive device while suppressing vibration.

In the configuration of Patent Document 1, it is assumed that the piston is stopped near bottom dead center. Therefore, at the connecting part of the crankshaft and between the piston and the cylinder, etc., the oil contained in the refrigerant is pushed aside to the surroundings, resulting in metal contact. For this reason, when the piston stops near top dead center where frictional force is large, the torque required to move the piston from top dead center is greater than when the piston is in operation. As a result, there is insufficient torque and the piston cannot be moved to the correct position. This poses the problem of startup failure of the motor drive device.

In addition, when the piston stops at top dead center and the torque required to move the piston is applied, the oil circulates as the piston starts to move, reducing friction. This causes a sudden acceleration, which manifests itself as vibration. In other words, when the piston stops near top dead center during differential pressure startup, the motor drive unit will fail to start or will vibrate. The inventors discovered this problem and came to create the subject matter of the present disclosure in order to solve it.

The present disclosure provides a motor drive device that can inexpensively suppress vibrations and start stably, even under conditions of large load torque fluctuations such as a difference between the suction pressure and discharge pressure of the compressor.

Below, an embodiment, i.e., a motor drive device for a compressor mounted in a refrigerator, will be described as an example with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of matters that are already well known or duplicate explanations of substantially identical configurations may be omitted. This is to avoid making the following explanation unnecessarily redundant and to make it easier for those skilled in the art to understand.

It should be noted that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

(Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 5C.

[1-1. Configuration]
Fig. 1 is a block diagram of a motor drive device according to a first embodiment of the present disclosure. Fig. 2 is a schematic diagram of components constituting a compressor 17 according to the first embodiment.

As shown in Fig. 1, the motor drive device 30 is connected to an AC power source 1 and drives a brushless DC motor 5. As shown in Fig. 2, the rotor 5a, crankshaft 17a, piston 17b and cylinder 17c of the brushless DC motor 5 form a reciprocating compressor 17. The compressor 17 is mounted in a refrigerator 22 and forms part of a refrigeration cycle.

The AC power source 1 is a general commercial power source. For example, the AC power source 1 is a 50 Hz or 60 Hz power source with an effective value of 100 V.

The configuration of the motor drive device 30 is described below.

The rectifier circuit 2 receives the AC power from the AC power source 1 and rectifies the AC power into DC power. The rectifier circuit 2 is composed of four rectifier diodes 2a to 2d connected in a bridge configuration.

The smoothing unit 3 is connected to the output side of the rectifier circuit 2 and smoothes the output of the rectifier circuit 2. The smoothing unit 3 has a smoothing capacitor 3e and a reactor 3f. The output from the smoothing unit 3 is input to the inverter 4.

The reactor 3f is inserted between the AC power source 1 and the smoothing capacitor 3e. The reactor 3f may be provided either before or after the rectifier diodes 2a to 2d. When a common mode filter constituting the high frequency rejection section is provided in the circuit, the reactor 3f is configured taking into consideration the combined component with the reactance component of the high frequency rejection section.

The inverter 4 converts the DC power, which contains a large ripple component with twice the power supply period of the AC power supply 1 in the voltage from the smoothing section 3, into AC power. The inverter 4 is composed of six switching elements 4a to 4f connected in a three-phase bridge. In addition, six freewheeling current diodes 4g to 4l are connected in the reverse direction to each of the switching elements 4a to 4f.

The brushless DC motor 5 has a rotor 5a with a permanent magnet and a stator 5b with a three-phase winding. The rotor 5a rotates when a three-phase AC current generated by the inverter 4 flows through the three-phase winding of the stator 5b.

The position detection unit 6 detects the magnetic pole position of the stator 5b based on the induced voltage generated in the three-phase winding of the stator 5b, as well as the current flowing through the three-phase winding of the stator 5b and the applied voltage.

In this embodiment, the position detection unit 6 acquires the terminal voltage of the brushless DC motor 5 and detects the relative magnetic pole position of the rotor 5a of the brushless DC motor 5. Specifically, the position detection unit 6 detects the relative rotational position of the rotor 5a based on the induced voltage generated in the three-phase winding of the stator 5b. The position detection unit 6 also compares the induced voltage with a reference voltage to detect zero crossing. The reference voltage for the zero crossing of the induced voltage may be the voltage when a virtual midpoint is created from the terminal voltages of the three phases, or may be the voltage when the DC bus voltage is acquired. In this embodiment, the reference voltage for the zero crossing of the induced voltage is the voltage of the virtual midpoint.

In this embodiment, the position detection unit 6 is a type that detects an induced voltage. However, the position detection unit 6 may also detect the position from the current flowing through the brushless DC motor 5. The position detection unit 6 may also be a type that detects the current flowing through the DC bus of the inverter 4 using a shunt voltage, and detects the current flowing through each phase from the energization state and current value. The position detection unit 6 may also be a type that monitors the current flowing through each of the three phases using a sensor and a shunt resistor, etc.

When compared as a means of detecting current, the method of detection from the current value of the DC bus is inexpensive, but there is a possibility that distortion of the waveform will occur due to the need to separate the current of each phase. When estimating position from current and in the case of induced voltage, the method based on induced voltage requires relatively less calculations than estimating position from current, and can be implemented with a simple configuration and low cost.

The speed detection unit 7 calculates the current drive speed of the brushless DC motor 5 from the position information detected by the position detection unit 6. In this embodiment, the speed detection unit 7 measures the time from the zero cross detection of the induced voltage, and calculates the current speed from the measured time.

The voltage detection unit 8 detects the voltage between the DC busbars of the inverter 4. In general, the voltage is divided by resistors and reduced to a range that can be handled by a microcomputer, i.e., from about 140 V to 5 V or less, and then the original voltage is calculated by back calculation using a microcomputer. In this embodiment, the value obtained by dividing the voltage by 1/100 is used.

The piston position change unit 11 drives the brushless DC motor 5 to move the position of the piston 17b of the compressor 17 when the target speed input from the outside changes from 0 to a value other than 0.

Generally, the stopping position of piston 17b when compressor 17 stops is not managed. Therefore, piston 17b stops at a random location. In this case, when piston 17b of compressor 17 stops near the top dead center, a large frictional force acts on piston 17b. Therefore, a larger torque is required than when piston 17b normally operates, making it difficult to move piston 17b. Therefore, to start compressor 17, a special operation is required to move piston 17b from near the top dead center.

The piston position change unit 11 changes the output phase around a phase where the rotor 5a is reversed 15 degrees from the top dead center as a special operation to move the piston 17b from near the top dead center. In the cycle in which the output changes, the rotor 5a does not completely follow the output phase. The change in output phase by the piston position change unit 11 ends when a predetermined specified time has elapsed. The predetermined specified time may be set to be longer than the period during which the rotor 5a can actually be operated and moved under maximum load. The predetermined specified time may also be calculated from the pressure, the friction coefficient and inertia of each part, etc.

When the target speed input from the outside changes from 0 to a value different from 0, the torque determination unit 12 outputs the torque required for the piston position change unit 11 to move the position of the piston 17b from near the top dead center. The torque determination unit 12 gradually increases the torque during a period when there is an output from the piston position change unit 11. When the piston position change unit 11 is not operating, the torque determination unit 12 determines and outputs the required torque based on the difference between the current speed of the brushless DC motor 5 input from the speed detection unit 7 and the target speed. If the current speed is insufficient compared to the target speed, the torque determination unit 12 increases the torque. If the current speed is higher than the target speed, the torque determination unit 12 reduces the torque to make the speed of the rotor 5a reach the target speed.

The output determination unit 10 determines the applied voltage from the torque constant, induced voltage constant, resistance value, etc. of the brushless DC motor 5 based on the torque determined by the torque determination unit 12. The output determination unit 10 calculates the PWM duty width based on the determined applied voltage and the voltage between the DC buses detected by the voltage detection unit 8.

In addition, the output determination unit 10 determines the output, i.e., which phase to apply current to, based on the information received from the position detection unit 6 and the speed detection unit 7, or the output of the piston position change unit 11. When there is an input signal from the piston position change unit 11, the output determination unit 10 determines the signal to be output based on the input signal from the piston position change unit 11. When there is no input signal from the piston position change unit 11, the output determination unit 10 determines the signal to be output based on the position information from the position detection unit 6 and the speed information from the speed detection unit 7.

Typically, drive waveforms include square waves and sine waves. However, in this embodiment, the drive waveform is not particularly limited. For example, in the case of a square wave, since the square wave has a simple configuration and is easy to calculate, it can be handled by an inexpensive microcomputer and can be realized at low cost. In addition, although complex calculations and current detection are required, it is possible to detect the motor position more precisely. In this embodiment, a square wave drive is adopted, which can be realized at a lower cost.

In this embodiment, the motor drive device 30 is driven by a 120-degree rectangular wave. Therefore, the switching elements 4a, 4c, and 4e of the upper arm are energized with a 120-degree offset between them. Similarly, the switching elements 4b, 4d, and 4f of the lower arm are energized with a 120-degree offset between them. There is an off period of 60 degrees between the energization periods of the switching elements 4a and 4b, 4c and 4d, and 4e and 4f.

The drive unit 9 outputs a drive signal based on the on ratio determined by the output determination unit 10, the power supply timing of the brushless DC motor 5, and a predetermined PWM period.

Specifically, the drive signal switches the switching elements 4a to 4f of the inverter 4 on or off. This causes the optimal AC power to be applied to the stator 5b. This causes the rotor 5a to rotate, driving the brushless DC motor 5.

Next, we will explain a refrigerator using the motor drive device 30 in this embodiment. In the following explanation, we will use a refrigerator as an example, but the same applies to a refrigeration device.

The refrigerator 22 is equipped with a compressor 17. The compressor 17 is, for example, a reciprocating type. The compressor 17 is composed of a compression mechanism having a brushless DC motor 5, a crankshaft 17a, a piston 17b, and a cylinder 17c.

The rotational motion of the rotor 5a of the brushless DC motor 5 is converted to reciprocating motion by the crankshaft 17a. The piston 17b connected to the crankshaft 17a reciprocates within the cylinder 17c, sucking the refrigerant into the cylinder 17c and compressing the refrigerant. The reciprocating type compressor 17 has large torque fluctuations during the suction and compression processes, and the speed and current value fluctuate greatly.

The refrigerant compressed by the compressor 17 flows through the refrigeration cycle, passing through the condenser 19, the two-way valve 18, the pressure reducer 20, and the evaporator 21 in that order, before returning to the compressor 17. During this process, heat is released in the condenser 19, and heat is absorbed in the evaporator 21. Thus, cooling and heating occur in the refrigeration cycle. The refrigerator 22 is equipped with such a refrigeration cycle.

The two-way valve 18 is, for example, a solenoid valve that can be opened and closed by energizing it. The two-way valve 18 is in an open state while the compressor 17 is operating, connecting the condenser 19 and the pressure reducer 20 and allowing the refrigerant to flow. On the other hand, while the compressor 17 is stopped, the two-way valve 18 is in a closed state, blocking the space between the condenser 19 and the pressure reducer 20 and suppressing the flow of the refrigerant.

[1-2. Operation]
The motor drive device 30 mounted on the refrigerator 22 configured as above will be described with reference to Figs. 3A to 5C.

Figure 3A shows the relationship between the pressure applied to the piston 17b and the rotation angle of the rotor 5a. The vertical axis shows the pressure, and the horizontal axis shows the rotation angle of the rotor 5a with the top dead center at 0 degrees.

Figure 3B shows the relationship between the torque required when the brushless DC motor 5 is operating in the forward direction and the rotation angle of the rotor 5a. The vertical axis shows the torque, and the horizontal axis shows the rotation angle of the rotor 5a with the top dead center set to 0 degrees.

Figure 3C shows the relationship between the torque required when the brushless DC motor 5 is operating in the reverse direction and the rotation angle of the rotor 5a. The vertical axis shows the torque, and the horizontal axis shows the rotation angle of the rotor 5a with the top dead center at 0 degrees.

Figures 4A to 4C show waveforms for moving piston 17b from top dead center in a conventional configuration.

Figures 5A to 5C show waveforms for moving piston 17b from top dead center in this embodiment.

Figures 4A and 5A each show the torque required to start from top dead center, with the vertical axis showing forward torque upward and reverse torque downward, and the horizontal axis showing time.

Figures 4B and 5B show the torque output to move piston 17b, with the vertical axis indicating forward torque in the upward direction and reverse torque in the downward direction, and the horizontal axis indicating time.

Figures 4C and 5C show the speed of rotor 5a, with the vertical axis representing speed with the forward rotation direction being positive, and the horizontal axis representing time.

When the compressor 17 is stopped, the contact areas between the piston 17b and cylinder 17c, the crankshaft 17a and cylinder 17c, and the crankshaft 17a and rotor 5a are in metal contact, unlike the state in which the oil contained in the refrigerant during operation covers the surfaces as a lubricant. The coefficient of friction of metal contact is about 10 times larger than that of oil. The frictional force of the contact areas when the compressor 17 is stopped is proportional to the pressure of the piston 17b.

As shown in FIG. 3A, the pressure of piston 17b increases between the bottom dead center indicated by angle (A) and the top dead center indicated by angle (C). In the region where the angle is smaller than angle (A), the piston 17b is in a state where almost no pressure is applied. In particular, the pressure of piston 17b is maximum between angle (B) and angle (C) where the discharge from piston 17b begins. The pressure of piston 17b is almost the same between angle (A) which is the bottom dead center of piston 17b and angle (C) which is the top dead center. However, the angle at which the discharge from piston 17b begins is not constant, and varies depending on conditions such as the suction and discharge pressures of compressor 17 and the temperature of the refrigerant. Here, under the operating conditions of a general refrigerator, the angle at which the discharge of piston 17b begins is around 300 degrees. For this reason, the frictional force during a stop becomes very large before the top dead center.

Furthermore, the torque that the brushless DC motor 5 needs to output during normal rotation in the forward direction is as shown in Figure 3B. Near top dead center, the amount of movement of the piston 17b is small per degree of rotation of the rotor 5a. This reduces the torque applied to the rotor 5a. Therefore, when attempting to rotate the rotor 5a in the forward direction from a stopped state of the piston 17b near angle (B), a very large torque is required to move the piston 17b as a result of combining the static friction force and the torque required for rotation.

On the other hand, the torque that the brushless DC motor 5 needs to output when rotating in the reverse direction is as shown in Figure 3C. When moved in the reverse direction from near top dead center, the piston 17b performs an intake action rather than a compression action. Therefore, even near angle (B), it is possible to rotate it in the reverse direction to bottom dead center with a very small torque. As a result, when attempting to rotate the rotor 5a in the reverse direction while the piston 17b is stopped, it is possible to move the piston 17b by outputting a torque that is slightly greater than the frictional force.

Generally, as shown in Figure 4B, the output torque is gradually increased, and piston 17b begins to move at timing (D) when the output torque exceeds the required torque shown in Figure 4A.

However, once the piston 17b starts to move, the metal contact is eliminated. Therefore, the friction coefficient becomes one tenth of its original value. For this reason, as shown at timing (D) in FIG. 4A, the friction force decreases rapidly, and the output torque becomes very large relative to the required torque. As a result, as shown at timing (D) in FIG. 4C and after, the rotor 5a accelerates rapidly. Therefore, because the rotor 5a has a large speed when it reaches the initial positioning phase when current is applied, the speed change when it stops at the positioning position is large. This causes the compressor to shake significantly.

Therefore, in this embodiment, the rotor 5a is vibrated in a range of ±30 degrees from the top dead center in the forward direction of the energized phase, centered on an angle of 330 degrees, and the output is gradually increased. When viewed as the torque applied at 330 degrees, i.e., the torque output at 330 degrees, the forward direction and the reverse direction change periodically, as shown in FIG. 5B. As a result, the rotor 5a rotates in the reverse direction from the timing (E) when the output torque exceeds the torque in the reverse direction. At this point, the metal contact is eliminated and the required torque is reduced. However, unlike the general method, the torque in the reverse direction gradually decreases and approaches 0, and then the torque in the forward direction gradually increases and decreases toward 0.

As a result, while torque is being applied in the reverse direction, the speed increases in the reverse direction. As the torque increases in the forward direction and exceeds the required torque, the speed increases in the forward direction. As a result, even if piston 17b starts to move at timing (E) and the required torque suddenly decreases, the speed of piston 17b does not increase significantly.

When such a periodically varying torque is applied and the metal contact is released, the rotor 5a is rotated in the reverse direction to the initial starting position. This allows the rotor 5a to move to the initial position without applying a large torque. Therefore, vibration caused by the increase in speed when the piston 17b moves to the initial position is suppressed.

Even if the piston 17b stops at a position other than the top dead center, for example, near the bottom dead center, the torque shown in FIG. 5B is output, so that the piston 17b moves gently to the central phase. Therefore, the piston 17b does not accelerate to a speed that would cause large vibrations. Furthermore, when the piston 17b moves to the initial position thereafter, vibrations are not an issue, just like when the piston 17b is positioned from a normal stop near the bottom dead center.

If the initial starting position is not near 300 degrees ±30 degrees as shown by angle (B) in Figure 3B, where the required torque peak is likely to occur, it is possible to accelerate the rotor 5a, overcome top dead center, and start the compressor 17 even under differential pressure conditions where there is a pressure difference between the suction and discharge of the compressor 17.

The brushless DC motor 5 in this embodiment has four poles. The same pattern of current flows to the brushless DC motor 5 as it moves to the top dead center and bottom dead center. Therefore, a current pattern corresponding to 270 degrees, which is halfway between the top dead center and bottom dead center, is output, and then a current pattern corresponding to 210 degrees is output, thereby avoiding a phase of 300 degrees ±30 degrees.

In the same current pattern, when piston 17b is near bottom dead center, if current is applied equivalent to 270 degrees, piston 17b moves to 270 degrees or 90 degrees. After that, if current is applied equivalent to 210 degrees, piston 17b moves to 30 degrees or 210 degrees. In this way, under any circumstances, piston 17b will not start from 300 degrees ±30 degrees. Therefore, compressor 17 can be operated even under differential pressure conditions.

In addition, if the brushless DC motor has six poles, the bottom dead center and 300 degrees have the same current conduction pattern. Therefore, by conducting current equivalent to 300 degrees and then conducting current equivalent to 260 degrees, the initial position can be avoided from 300 degrees ± 30 degrees, that is, it can be shifted from the range of 300 degrees ± 30 degrees. For example, if the piston 17b is stopped near the top dead center, it moves to 300 degrees and then to 260 degrees. On the other hand, if the piston 17b is stopped near the bottom dead center, it first moves to the bottom dead center, which is in the same phase as the current conduction of 300 degrees, and then moves to 140 degrees, which is rotated 40 degrees in the reverse direction from the bottom dead center. If the piston 17b is stopped near 60 degrees, it moves to 60 degrees, which is the same current conduction phase as 300 degrees, and then moves to 20 degrees, which is rotated 40 degrees in the reverse direction.

In this way, whether the compressor is a 4-pole or 6-pole type commonly used in refrigerators, by outputting a torque that varies periodically, including the top dead center, to the piston 17b near the top dead center, the compressor 17 can be started stably and vibrations during positioning when the piston 17b moves to the initial position can be suppressed.

Next, we will explain the case where the motor drive device 30 of this embodiment is used in a compressor 17 and installed in a refrigerator 22.

At the same time as the compressor 17 starts, the two-way valve 18 is opened to connect the pressure reducer 20 and the condenser 19. In this embodiment, the two-way valve 18 is opened at the same time as the compressor 17 starts, but this is not limited to the same time and may occur slightly earlier or later in time. When the compressor 17 continues to operate, the condenser 19 becomes high pressure, the pressure is reduced in the pressure reducer 20, and the evaporator 21 becomes low pressure.

At this time, the discharge side of compressor 17 connected to condenser 19 is at high pressure, and the suction side connected to evaporator 21 is at low pressure. Now, assume that the temperature inside refrigerator 22 drops and compressor 17 is stopped. In this case, if two-way valve 18 remains open, the pressures of condenser 19 and evaporator 21 gradually change to balance, that is, to close values. Although it depends on the system configuration of refrigerator 22, it usually takes about 10 minutes until the pressure difference between the suction side and discharge side of compressor 17 reaches a state of 0.05 MPa or less, that is, a state that can be said to be balanced.

When the two-way valve 18 is switched from an open state to a closed state at the same time as the compressor 17 is stopped, the pressure difference between the condenser 19 and the evaporator 21 is almost maintained. At this time, a pressure difference remains between the suction side and the discharge side of the compressor 17. When the compressor 17 is started after the temperature inside the refrigerator 22 has risen, comparing a state in which the two-way valve 18 is closed while the compressor 17 is stopped and the pressure difference is maintained with a state in which the pressures are balanced, the state in which the two-way valve 18 is closed and the pressure difference is maintained requires less power to re-establish a pressure difference between the condenser 19 and the evaporator 21, thereby realizing energy savings.

In addition, if the two-way valve 18 is left open even when the compressor 17 is stopped, or if the two-way valve 18 is not provided, if the temperature inside the cabinet rises before the approximately 10 minutes required for the pressure to balance after the compressor 17 is stopped, it is necessary to wait for the 10 minutes to pass. This is because, conventionally, the motor drive device 30 could only be started when the pressure difference between the suction side and discharge side of the compressor 17 was 0.05 MPa or less.

In contrast, in this embodiment, it is possible to start up even with a pressure difference greater than 0.05 MPa. Therefore, even if the temperature inside the cabinet rises, it is possible to start up the motor drive unit 30 at a timing when operation of the compressor 17 is required. Therefore, compared to starting up with the pressures on the suction side and discharge side of the compressor 17 balanced, the power required to create a pressure difference between the condenser 19 and the evaporator 21 is reduced. This makes it possible to save energy.

In addition, the two-way valve 18 allows the system of a refrigerator or the like to be configured more simply than a three-way or four-way valve. Therefore, the pressure difference between the suction side and the discharge side of the compressor 17 can be maintained with a simple configuration.

Furthermore, if the compressor 17 is provided at the top of the refrigerator 22, the dead space in the refrigerator 22 that is difficult for the user to reach is reduced, making it easier to use, i.e., more convenient. On the other hand, in the refrigerator 22, the compressor 17, which is the source of the seismic vibration, is located at the farthest position with the floor as the fulcrum. Therefore, due to the principle of leverage, the vibration of the compressor 17 is easily transmitted to the refrigerator 22. However, in this embodiment, the vibration of the compressor 17 caused by the movement of the compressor 17 to its initial position before startup is suppressed. Therefore, the vibration and noise generated by the refrigerator 22 are reduced.

[1-3. Effects, etc.]
As described above, the motor drive device 30 of this embodiment includes the brushless DC motor 5 that drives the piston 17b of the reciprocating compressor 17, and the piston position changing unit 11 that rotates the brushless DC motor 5 so as to shift the piston 17b from the top dead center while the compressor 17 is stopped.

With this configuration, when the piston 17b stops near the top dead center, the motor drive device 30 can move the piston 17b from the top dead center, where it is most difficult to start, even if the piston 17b comes into metal contact with the cylinder 17c that covers the piston 17b and the static friction force is greater than during operation. Therefore, the brushless DC motor is started up with a torque similar to that when no pressure difference is applied.

In addition, the motor drive device 30 according to the embodiment of the present invention energizes the brushless DC motor 5 when the piston position change unit 11 rotates the brushless DC motor 5. The phase in which the piston position change unit 11 energizes the brushless DC motor 5 includes the top dead center, and is set so as to periodically change the output.

With this configuration, even if the motor drive unit starts moving from the top dead center, the current is applied in the reverse phase. Therefore, the speed of the piston 17b does not increase significantly, and the oil flows around the pistons that make up the compressor, reducing friction. Therefore, it is possible to start up the compressor 17 from the top dead center while suppressing vibrations caused by the piston 17b.

In addition, the refrigerator of the embodiment of the present disclosure has a compressor 17 located at the top of the housing.

With this configuration, the refrigerator 22 suppresses vibrations in the housing even when the compressor 17 installed at the top starts operating, when the effect of vibrations becomes greater due to the principle of leverage. This makes it possible to provide a very quiet refrigerator. In addition, because the compressor 17 is installed in an area at the top that is likely to become dead space, the internal storage volume that can actually be used by the user is expanded, making it possible to provide a very convenient refrigerator 22.

The technology of the present disclosure has been explained above using the above-mentioned embodiments, but since the above-mentioned embodiments are intended to illustrate the technology in the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

The present disclosure can be used in a motor drive device for starting a compressor that has large load torque fluctuations, and can be suitably applied to refrigerators, freezers, showcases, and various other refrigeration devices that use compressors.

1 AC power supply (power supply)
2 Rectifier circuit 2a, 2b, 2c, 2d Rectifier diode 3 Smoothing section 3e Smoothing capacitor 3f Reactor 4 Inverter 4a, 4b, 4c, 4d, 4e, 4f Switching elements 4g, 4h, 4i, 4j, 4k, 4l Diode for return current 5 Brushless DC motor 5a Rotor 5b Stator 6 Position detection section 7 Speed detection section 8 Voltage detection section 9 Drive section 10 Output determination section 11 Piston position change section 12 Torque determination section 17 Compressor 17a Crankshaft 17b Piston 17c Cylinder 18 Two-way valve 19 Condenser 20 Pressure reducer 21 Evaporator 22 Refrigerator 30 Motor drive device 201 Brushless DC motor 202 Piston 203 Compressor 204 Control section 205 Inverter

Claims (2)

A brushless DC motor that drives a piston of a reciprocating compressor;
a piston position changing unit that rotates the brushless DC motor so as to shift the piston from a top dead center while the compressor is stopped ,
the piston position changing unit energizes the brushless DC motor when rotating the brushless DC motor,
The phase in which the piston position change unit energizes the brushless DC motor includes a top dead center, and is set so that the output is changed periodically.
Motor drive device. The compressor driven by the motor drive device according to claim 1 is provided in an upper part of a housing.
refrigerator.

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