JPH0337399B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a motor control device equipped with an inverter that can be commonly used in regions with different power supply frequencies and that can control output torque to a substantially constant level.

[Prior Art] Induction motors (hereinafter referred to as IM) have the features of a simple structure, low cost, long life, and easy maintenance. For this reason, IM is widely used from small capacity to large capacity.

However, until now there was no way to efficiently control the rotational speed of the IM, so its applications were limited.

However, in recent years, various semiconductor devices have been provided, and a static inverter device that can easily obtain an output at any frequency has been developed. By connecting this inverter device between a commercial power source and the IM, and changing the output frequency of the inverter device, it has become possible to efficiently control the speed of the IM over a wide range.

By the way, many of these inverter devices can not only change the output frequency arbitrarily, but also easily change the magnitude of the output voltage at the same time. On the other hand, in IM, it is often required to gradually increase the rotational speed toward a planned speed while keeping the torque constant. Therefore,
In a system in which the rotational speed of the IM is controlled by the inverter device described above, the output voltage of the inverter device is changed approximately in proportion to its output frequency, so that the rotational speed can be controlled while the torque is approximately constant. It is widely used.

An example of such an inverter device is shown in FIG. In the figure, 1 is a forward conversion unit for obtaining DC from commercial AC, 2 is an inverse conversion unit for obtaining 3-phase AC from DC, 3 is IM, 10 to 20 are diodes, 22
30 to 40 are transistors, switching elements such as gate turn-off thyristors, and 42 to 52 are freewheel diodes.

The diodes 10 to 20 rectify the input three-phase alternating current and supply it to the capacitor 22. Therefore, a substantially smoothed DC voltage is obtained between the terminals of the capacitor 22.

The switching elements 30 to 40 are turned on and off by gate signals supplied from a switching control circuit (not shown), and convert the DC voltage appearing between the terminals of the capacitor 22 into a three-phase AC voltage, which is then applied to the IM3. supply By controlling the gate signal described above, the frequency and voltage of the three-phase AC supplied to IM3 can be arbitrarily controlled, and thereby the rotation speed of IM3 can be arbitrarily controlled while keeping the torque of IM3 constant. can do.

FIG. 1 is an example of a pulse width modulation (hereinafter simply referred to as PWM) inverter device.

This is because the forward converter 1 does not have a voltage adjustment function, so the inverse converter 2 steps the output voltage to obtain the required voltage. FIG. 2 also shows a conventionally used inverter device, in which a forward conversion section 1 is composed of switching elements 10' to 20' such as thyristors or transistors, and has a voltage regulating function. Therefore, the value of the voltage applied to the motor 3 is controlled by the forward converter 1. In the case of this inverter device, the voltage applied to the electric motor 3 can also be controlled by also using chopping of the inverter 2.

Now, the output frequency fo and output voltage of the inverter device
The relationship with Vo (hereinafter referred to as V/F characteristics) is Vo=a・fo+b...(1) However, a and b are constants, and if the control is performed to satisfy equation (1), the torque will be as shown above. The rotation speed of the IM can be controlled arbitrarily under a constant condition. Therefore, if the constants a and b in equation (1) are set to predetermined values according to the maximum output frequency fomax, which is the upper limit of the variable range of the output frequency fo, the rotational speed of the IM to be controlled can be adjusted to a constant torque. The rotational speed can be controlled over a range from a sufficiently low speed to the rated rotational speed.

However, in the conventional inverter device described above, if the maximum value of the output frequency is different from the specified voltage and frequency of the IM, there is a problem that the capacity cannot be fully demonstrated or overload occurs. It was hot.

By the way, the frequency of the supplied power may differ due to reasons such as differences in power supply conditions depending on the region. For example, it is well known that in Japan, there are areas where electricity is supplied at 50 [Hz] and areas where electricity is supplied at 60 [Hz].

Therefore, considering the rated input voltage and frequency specifications of IM, for example, 50 [Hz] for each region.
220V/50 [Hz] or 110V/50 in the area
[Hz], while in 60 [Hz] areas, for example, 220V/60
[Hz] or 110V/60 [Hz] IM is used in most cases. Therefore, if you use an inverter device that is set to a maximum output frequency of 60 [Hz] in a 50 [Hz] region, the frequency specifications will not match the 50 [Hz] specification IM used in that region. . Also, in the 60 [Hz] area, the same 50
If you use an inverter device that is set to a maximum output frequency of [Hz], the frequency specifications will not match the 60 [Hz] specification IM used in that area.

In other words, in areas with different power supply frequencies,
The input power supply specifications (input frequency specifications) of IM are often the input frequency specifications suitable for the region.
Therefore, if an inverter device used in a different frequency region is moved to an area with a different power supply frequency, the frequency specifications of this inverter device will be
The input frequency specifications of the IM may not necessarily match. Therefore, if the IM was used in combination with an inverter device with different specifications, the above-mentioned problems would occur, causing problems in operation. As described above, the conventional IM control device using an inverter device has the disadvantage that there is no compatibility in operating characteristics between different frequency regions.

This will be explained with reference to FIG.

First, consider the problem when using a 60 [Hz] inverter in a 50 [Hz] area.

If you use an IM with a specified frequency of 60 [Hz] in a 60 [Hz] region, the V/F characteristics of the inverter device will be set to the characteristic represented by B, but if you use this inverter device in a 50 [Hz] region V/F when used in
IM even though the characteristics have become those of B.
A 50 [Hz] specification is connected (because 50 [Hz] IM is used in this area).

For this reason, let us assume that an attempt is made to set the output frequency of the inverter device to 50 [Hz] in accordance with the IM specification frequency. In this case, the operating point of the inverter device is P ₁
Therefore, the voltage for IM of 50 [Hz] specification) is 100% x 50/60 = 83%, and the applied voltage is 83%.

In this case, the output torque cannot be obtained up to the rated value.
Also, depending on the load, the required torque may not be produced, and the IM rotational speed may not reach the specified value.

On the contrary, it is also conceivable to use an inverter for 50 [Hz] in a 60 [Hz] region.

If an IM with a specified frequency of 50 [Hz] is used in an area with a frequency of 50 [Hz], the V/F characteristics of the inverter will be set to the characteristic expressed by A, but if this inverter is used in an area with a frequency of 60 [Hz], V/F when used in
Even though the characteristics are like A, an IM with a specified frequency of 60 [Hz] is connected (because 60 [Hz] IMs are used in this area).

For this reason, let us assume that an attempt is made to set the output frequency of the inverter device to 60 [Hz] in accordance with the IM specification frequency. In this case, the output frequency of the inverter device is
If the frequency increases to 60 [Hz], the operating point becomes P ₂ , and 60 [Hz]
The voltage for the specified IM is 100% x 60/50 = 120%, so the applied voltage is 120%.

In this case, the voltage of IM exceeds the rated value, resulting in overexcitation, and the inverter device also becomes overloaded due to the increase in current due to overexcitation. Furthermore, if the setting specifications of the inverter device are such that the characteristic A in Figure 3 operates only at 50 [Hz] or lower, as shown by the dotted and solid lines (in the case of 50 [Hz] specifications, this may occur). (Possible) The maximum speed may not reach the rated speed.

In this way, the V/F characteristics of conventional motor control devices are fixed, and therefore sufficient compatibility of inverter devices between regions with different power supply frequencies cannot be achieved with conventional motor control devices. It was empty.

[Object of the Invention] An object of the present invention is to eliminate the drawbacks of the prior art described above, and to make it possible to transfer an inverter device used in a region with a predetermined power frequency to another region where the power power frequency is different. To provide a highly versatile electric motor control device that allows the use of electric motors whose specifications are set to be used in the region as they are, even if the user owns one. In other words,
It is an object of the present invention to provide a highly versatile electric motor control device that can be commonly supplied to regions with various power supply frequencies.

[Summary of the Invention] That is, the present invention provides means for detecting the input frequency to the inverter device, and automatically adjusts the output of the inverter device to the motor setting specifications (frequency setting specifications) according to the output of the detection means. A control signal generating means is provided.

[Embodiments of the Invention] Hereinafter, embodiments of an inverter device for controlling a motor according to the present invention will be described with reference to the drawings.

FIG. 4 is a block diagram schematically showing the basic configuration of an embodiment of the present invention. IM3 is connected to the inverter main circuit section, and an inverter control circuit section consisting of a frequency detection circuit 4, a control signal generation circuit 5, a rotation speed setting device 6, a switching control circuit 7, etc., and rotation control is performed. The device is shown. Here, the control device detects the frequency of the AC power source, automatically selects the V/F characteristic from the control signal generation circuit 5 according to this output, and controls the output voltage and output frequency of the inverter device. It is.

More specifically, the frequency detection circuit 4 detects the frequency of the supplied AC power, that is, the input frequency, and generates the input frequency signal fi.

The control signal generation circuit 5 receives the rotational speed command signal N set by the speed setting device and the input frequency signal fi from the frequency detection circuit 4, and generates a frequency control signal Sf corresponding to the signal N, and also generates the signal fi. Select either one of the V/F characteristics A or B shown in FIG. 3 in response to It functions to generate.

To be more specific, the inverter device is controlled so that the relationship between the output frequency fo and the output voltage Vo is determined by determining the values of the constants a and b, and substituting these values into equation (1). This is what I did.

The constant a can be found as follows: a=Vc-b/fi (2) where the rated voltage of the motor is Vc and the input frequency of the inverter device is fi.

Therefore, if the rated voltage Vc of the motor and the constant b are set, the value of the constant a can be easily determined by determining the input frequency fi using the detection means. Further, the constant b is a value necessary for causing the excitation current component to flow, and may be constant regardless of the input frequency of the inverter device. For example, if the input frequency value is
If it can be specified as either 50 [Hz] or 60 [Hz], use constants a and b according to each frequency.
can be stored in a memory, and this constant can be selected and used according to the output of the detection means. The switching control circuit 7 generates a gate signal G having a predetermined timing and pulse width according to the frequency control signal Sf and the voltage control signal Sv, and controls the switching elements 30 to 40 (the first
(Fig.) and performs switching to determine the output frequency fo and output voltage Vo corresponding to these signals Sf and Sv.
It works to generate three-phase alternating current and supply it to IM3.

Therefore, according to this embodiment, the rotation speed of the IM 3 can be arbitrarily controlled by the speed command signal N from the speed setting device 6 while the torque is constant, and in this case, the input frequency of the AC power source can be controlled as desired. is 50 [Hz]
60 [Hz], the relationship between the output voltage Vo and the output frequency fo is automatically changed to either V/F characteristics A or B in Figure 3, corresponding to each, and the operation is performed. Therefore, no matter which AC power source of 50 [Hz] or 60 [Hz] is used in a system, it will automatically match the frequency of the IM being used (the frequency of the power supply in the area and the frequency of the IM) will match the frequency of the IM being used. are the same).

Therefore, optimal operation can always be performed,
The rotation speed of IM can be controlled correctly.

Next, one embodiment of the control signal generation circuit 5 is shown in FIG. In FIG. 5, 55 is a frequency discriminator, 56 is a selection circuit, 57 is a memory, 58 is a limiter, and 59 is an arithmetic circuit.

The frequency discriminator 55 functions to generate a maximum frequency control signal m and a selection signal n according to the input frequency fi.

The selection circuit 56 selects the memory 57 according to the selection signal n.
It functions to read out either the constants (a, b) ₅₀ for 50 [Hz] or the constants (a, b) ₆₀ for 60 [Hz] and set it in the arithmetic circuit 59.

The limiter 58 sets the maximum value of the speed command signal N to 50 [Hz] or 60 [Hz] in response to the maximum frequency control signal m.
It functions to limit either of the following.

The calculation circuit 59 uses either the constants (a, b) ₅₀ or (a, b) ₆₀ set by the selection circuit 59, receives the frequency control signal sf as input, performs the calculation shown in equation (1), and outputs the result. Output voltage corresponding to frequency fo
It functions to generate a voltage control signal Sv for generating Vo from the inverse converter 2.

Therefore, according to the control signal generation circuit 5 shown in FIG. 5, the input frequency of the AC power source is 50 [Hz].
60 [Hz], it is possible to obtain the frequency control signal Sf and the voltage control signal Sv necessary to limit the rotational speed of IM3 under constant torque. According to IM3, the maximum frequency control signal m is input to the limiter 58, which controls the maximum value of the frequency control signal Sf to a predetermined value and operates so that the output frequency fo does not increase beyond the input frequency. The maximum frequency of the supplied power is always automatically limited to a value equal to the input frequency, and it is possible to prevent the rotation speed of the IM3 from being controlled to exceed the rated value. By the way, in a system using IM,
There are systems in which the speed command signal also serves as the IM activation signal, and in such systems, when the speed command signal N is given, the output frequency fo rises from a low value, and eventually the signal It may be desirable to perform control to converge to a frequency corresponding to the maximum speed set by N.

FIG. 6 shows an embodiment of the present invention suitable for such a case. In this figure, 60 is a comparison circuit, 61 is a clock oscillator, 62 is a counter, and 63 is a digital-to-analog converter (D/A
), and the rest is the same as in Figure 4.

Clock oscillator 61 oscillates only when the output of comparator circuit 60 is at "H" level, and supplies a clock signal to counter 62.

The D/A 63 functions to analogize the output of the counter 62 and convert it into a frequency control signal Sf. Therefore, let us now assume that a speed command signal N of a certain magnitude is supplied. Then, the output of the comparison circuit 60 becomes "H" and the clock oscillator 6
1 starts oscillation. Therefore, the output data of the counter 62 increases with the passage of time, and the output data of the D/A 6
The output voltage of No. 3 increases linearly with time. As a result, the frequency control signal Sf also increases linearly, and the output frequency fo supplied to IM3 (Fig. 4)
increases sequentially from approximately 0 [Hz] at a predetermined rate (this can be arbitrarily determined by the frequency of the clock signal), and at the same time, the output voltage Vo also increases, so IM3 There is almost no inrush current, and stable acceleration is achieved with a constant torque, allowing for smooth startup.

Eventually, when the frequency control signal Sf reaches the same value as the speed command signal N, the output of the comparison circuit 60 is reversed from "H" to "L". Therefore, at this point, the clock oscillator 61 stops oscillating, and the increase in the output data of the counter 62 also stops, so the output frequency fo becomes the frequency set by the speed command signal N, and the rotation speed of IM3 becomes the set value. keep.

Therefore, according to this embodiment, in addition to obtaining the same effect as the embodiment shown in FIG. The effect is that the activation can be performed.

Re is a reset terminal of the counter 62. A reset signal is input to this reset terminal Re before starting.

FIG. 7 shows yet another embodiment of the invention. This embodiment has two comparators 60a and 60b. Of these, the comparator 60a is similar to the one shown in FIG. 6, in which the speed command signal N is the frequency control signal Sf.
Outputs H when the value is smaller than .

Further, the comparator 60b outputs an output H when the speed command signal N is larger than the frequency control signal Sf. As the counter 62, an up-down counter is used.

Then, the output of the clock oscillator 61 and the comparator 6
A logical operation is performed on the output of 0a by the AND circuit Aa, and the result is input to the up-count input terminal 62a of the up-down counter. In addition, the output of the clock oscillator 61 and the output of the comparator 6 are connected to an AND circuit.
A logical operation is performed on Ab, and the result is input to the down count input terminal 62b.

In this way, the setting of the speed command signal N can be changed from a higher value to a lower value while the motor is in operation. FIG. 8 shows a further different embodiment of the present invention. In this embodiment, a forward converter 1 having switching means as shown in FIG. 2 is used.

Therefore, the switching control circuit 7
A switching signal necessary to change the output frequency to fo is given to the forward converter 1, and a switching signal to change the output voltage Vo according to the output frequency fo is also given to the forward converter 1.

As shown in FIG. 9, the control signal generating circuit 5 has a writing means 70 for writing the rated voltage Vc of IM and the value of the constant b into the memory 57'.

The calculation means 59' receives the rated voltage Vc from the memory 57'.
and a constant b, and also receives an input frequency fi from the frequency detection circuit 4, and calculates a constant a matching the input frequency fi according to equation (2).

Further, the calculation means 59' substitutes the constants a, b and the frequency fo determined by the rotational speed setting N into equation (1) to obtain the command Sv for setting the output voltage to Vo.

The limiter 58 receives the speed command signal N and the input frequency signal fi, and when the signal N is smaller than the signal fi, it outputs the signal N as it is as the signal Sf, but when the signal N becomes larger than the signal fi, the magnitude of the signal N changes. The signal fi is output as the signal Sf regardless of the signal Sf.

With this configuration, an appropriate output frequency vs. output voltage characteristic can be obtained depending on the frequency of the input voltage.
When the output frequency becomes equal to the frequency of the power supply voltage, the voltage applied to IM3 becomes the rated voltage of IM.

[Effects of the Invention] According to the present invention, as is clear from the above explanation, it is possible to automatically select the voltage versus frequency characteristic (V/F characteristic) according to the input frequency even in areas where the power supply frequency is different. This has the effect of providing a highly versatile motor control device that can commonly apply an inverter device with the same specifications to regions with different power supply frequencies.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are circuit diagrams of a main circuit section showing a conventional example of a motor control device. FIG. 3 is a diagram showing the characteristics of output frequency versus output voltage required for an inverter device for controlling a motor. FIG. 4 is a block diagram showing an embodiment of the motor control device of the present invention. FIG. 5, FIG. 6, and FIG. 7 are block diagrams showing different embodiments of the control signal generation circuit shown in FIG. 4. FIG. 8 is a block diagram showing an embodiment of the motor control device of the present invention. FIG. 9 is a block diagram showing an embodiment of the control signal generation circuit shown in FIG. 7. 1 is a forward converter constituting the inverter device, 2 is an inverse converter constituting the inverter device, 3 is an induction motor, 4 is a frequency detection circuit, 5 is a control signal generation circuit, 6 is a rotation speed setting device, and 7 is a switching device. It is a control circuit.

Claims (1)

[Scope of Claims] 1. A motor control device having an AC power supply, an inverter connected to be supplied with power from the AC power supply, and an induction motor connected to an output part of the inverter and whose rotation is controlled, comprising: Inverter control means for detecting the frequency of an AC power source and controlling the output voltage versus output frequency characteristic (V/F characteristic) of the inverter supplied to the induction motor to be changed in accordance with the detected frequency. An electric motor control device characterized by: 2. The inverter control means includes: a frequency detection means that detects the frequency of the AC power supply; and a frequency detection means that is connected to the frequency detection means and adjusts the output frequency command according to the detected frequency and a given rotational speed command value. control signal generation means for calculating and outputting an output voltage command; and a control signal generation means connected to the control signal generation means, receiving the output frequency command and the output voltage command from the control signal generation means, and supplying the output voltage command to the induction motor. Claim 1, characterized in that it comprises switching control means for controlling the output frequency and output voltage of the inverter.
The electric motor control device described in . 3. The control signal generating means includes: a frequency determining means for generating a maximum frequency control signal and a selection signal according to the output of the frequency detecting means; and a constant memory storing a constant for determining the V/F characteristic. means for reading a constant from the constant storage means in response to the selection signal and outputting the constant; and an output frequency command value in response to the given rotational speed command value and the maximum frequency control signal. and a calculation means for calculating the V/F characteristic to be supplied to an inverter based on the output of the restriction means and the output of the selection means. 2. The electric motor control device according to item 2. 4. The electric motor according to claim 2, wherein the control signal generating means includes a frequency command means configured such that the output frequency command asymptotically approaches the rotational speed command signal over time. Control device.