JPH06153585A - Control apparatus for induction motor - Google Patents

Abstract

PURPOSE:To make a control apparatus small-sized and to lower its cost by suppressing a rotation irregularity and a vibration which are caused by the pulsating torque of a load machine. CONSTITUTION:The control apparatus of an induction motor IM connected to a load machine generating a pulsating torque synchronized with a rotational velocity is provided with an electric-power converter INV driving the induction motor IM and with its control circuit 100. The control circuit 100 is constituted in such a way that it generates a primary-voltage instruction value on the basis of the frequency instruction value of a primary voltage for the induction motor and that it gives the primary-voltage instruction value to the electric- power converter INV. The control circuit 100 is provided with an operation device 60 which operates the input electric power of the induction motor IM on the basis of the primary-current detection value and of the primary-voltage detection value or of the instruction value of the induction motor IM, with a bypass filter 70 which removes a DC component from an input electric-power operation value, and with a coefficient device 80 and an adder 90 whereby a value which has multiplied input electric power, whose DC component has been removed, by a factor Kf is added to a frequency instruction value f*.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an induction motor for driving a load machine such as a compressor of an air conditioner which produces a pulsating torque in synchronization with the number of revolutions.

[0002]

2. Description of the Related Art As is well known, a compressor has a function of repeating intake and exhaust by rotating a rotating portion, and mainly transmitting energy for circulating gas from a prime mover to the gas. As a prime mover used for this compressor, an inexpensive and easy-to-control induction motor is generally used. For this induction motor, the compressor load becomes a pulsating load in which the load torque largely changes due to intake air and exhaust gas even at the same rotation speed. Since the timing of such pulsating torque pulsation is determined by the structure of the compressor, it has the characteristic of being synchronized with the rotational speed.

On the other hand, a so-called V / f control is widely used as a control method for an induction motor, which is a prime mover, in which the ratio of applied primary voltage to primary frequency is controlled to be constant. FIG. 6 is an example showing a control block and a main circuit configuration of V / f control of the induction motor. The induction motor IM having a load of a compressor CP that produces pulsating torque is driven by a power converter INV capable of outputting a variable voltage and a variable frequency, such as a PWM inverter. The control circuit 100 ′ of the power converter INV outputs the amplitude command value | v ^* | of the primary voltage of the induction motor IM from the frequency setter 10 that commands the primary voltage frequency f ^* of the induction motor IM and the frequency command value f ^*. From the V / f pattern generator 20, the coordinate converter 40 that calculates the AC primary voltage command value based on the phase obtained by integrating the frequency command value f ^* by the integrator 30 and the primary voltage amplitude command value | v ^* | It is configured.

According to this method, it is possible to drive the induction motor IM at a variable speed without a speed detector. However, since it is an open loop control with respect to the rotation speed, the load machine having the pulsating torque is rotated. It causes unevenness. In the V / f control, the frequency and the voltage based on the constant command value are applied to the induction motor IM regardless of the load state, so that the rotation unevenness causes the induction motor IM to change the slip. As a result, the generated torque of the induction motor IM fluctuates and the current ripple is generated, and this current ripple further causes the generated torque fluctuation. However, since the phase of the fluctuation of the generated torque does not necessarily match the phase of the pulsating torque of the compressor, the rotation unevenness increases, and an extremely large rotation unevenness is constantly generated with respect to the rotation unevenness caused only by the pulsating torque of the load. Will occur.

FIG. 7 is a diagram showing a simulation result of a steady state in the drive system shown in FIG. In FIG. 7, (1) is the pulsating torque (load torque) generated by the compressor CP, (2) is the rotation unevenness of the induction motor IM, and (3) is the amplitude | i ₁ of the U-phase current i _u and the primary current vector. | (For convenience, “i ₁ ” is a primary current vector), and (4) indicates the torque generated by the induction motor IM.

The simulation condition here is a rating of 5
0 [Hz], 1500 [rpm], 4-pole induction motor I
Set the frequency of 10 [Hz] to M and set the compressor CP
The load torque of the induction motor IM is 5 of the rated torque (1.0) of the induction motor IM as shown in the pulsating torque (1) of FIG.
It is assumed that there is a sinusoidal pulsating component having an amplitude of 25% with 0% as a central value and synchronized with the rotation speed. As is clear from this simulation, the ripple of the generated torque (4) occurs more than the pulsating torque of the compressor itself.

Further, FIG. 7 (5) shows an induction motor IM on two dq axis coordinates which are rotated and orthogonal to each other when a coordinate converter which performs the reverse conversion to the coordinate converter 40 is used.
The primary currents i _d and i _q are shown. As shown in the figure, since the primary current has a ripple component, the currents i _d and i _q also have ripples. (6) of FIG. 7 is the input power of the induction motor IM calculated from the primary current and the voltage command value of the induction motor IM, and the influence of pulsation also appears in this.

Next, FIG. 8 is a diagram in which a block for detecting or calculating the amplitude of the current vector, the current on the rotating coordinates, and the input power shown in the simulation result of FIG. 7 is added to FIG. That is, the primary current of the induction motor IM is detected by using the current detector CT, and the detected current is detected by the control circuit 10.
The coordinate converter 41 in 0 "decomposes into two orthogonal coordinate components i _d and i _q that rotate in synchronization with the primary voltage. The square root of the sum of squares of these two current components is calculated by the primary current amplitude calculation circuit 50.
When calculated by, the amplitude of the primary current vector | i ₁ |
Can be calculated. Further, the arithmetic circuit 60 calculates the input power of the induction motor IM using the primary current detected by the current detector CT and the command value or actual value of the primary voltage. Since the calculation method is a normal calculation of three-phase power, detailed description will be omitted.

[0009]

As described above, when a load such as a compressor CP that generates pulsating torque is connected to the induction motor IM driven by the conventional V / f control, ripples occur in the primary current, resulting in extreme fluctuations. In such a case, the current limit value of the power converter INV may be exceeded and operation may not be possible. In addition, considering this current ripple, the power converter INV
When designing a device, it is necessary to increase the current rating of the parts used, and there is also the problem that the device becomes expensive and large. Further, the compressor CP itself also vibrates due to large rotation unevenness, and if the frequency of this rotation unevenness approaches the resonance frequency of the load machine, the entire load machine may generate extremely large vibration.

The present invention has been made to solve the above problems, and an object thereof is to provide a variable speed drive without a speed detector, which is an advantage of the conventional V / f control. It is an object of the present invention to provide a control device for an induction motor that reduces the primary current ripple of the induction motor, prevents the power converter from being expensive and large, and suppresses the vibration of the load machine while making full use of it.

[0011]

In order to achieve the above object, the present invention relates to an electric physical quantity input from an electric power converter to an induction motor, in which an input power which is originally a direct current quantity in a steady state. It was made by paying attention to the primary current amplitude, etc., and detects the AC component of the electrical physical quantity that is generated by pulsating torque and is amplified by the induction motor, and operates the primary frequency applied to the induction motor from the AC component. By forming a closed loop, uneven rotation is suppressed and an increase in current ripple is prevented. Here, the gain that determines the amount of the primary frequency to be operated from the detected alternating current component of the electrical physical quantity is not only determined by the optimum number of pole pairs of the motor, inertia of the load machine, etc., but also by operating conditions such as the number of revolutions. Adjustable variable gain is used because it changes.

That is, the first aspect of the present invention provides a control circuit of the power converter with a means for calculating the input power of the induction motor from the primary current detection value and the primary voltage detection value or the command value of the induction motor, and this means. It is characterized by comprising means for removing a direct current component from the calculated input power, and means for adding a value obtained by multiplying the input power from which the direct current component has been removed by this means by a coefficient to the frequency command value.

A second invention is a control circuit for a power converter,
Means for calculating the amplitude of the primary current based on the detected primary current of the induction motor, means for removing the direct current component from the amplitude of the primary current calculated by this means, and primary current from which the direct current component has been removed by this means Means for adding to the frequency command value a value obtained by multiplying the amplitude of 1 by a coefficient.

A third invention is a control circuit for a power converter,
A means for coordinate-converting the primary current detection value of the induction motor into a current component on a rectangular coordinate axis that rotates in synchronization with the primary voltage; and means for removing a DC component from one of the current components coordinate-transformed by this means, Means for adding a value obtained by multiplying the current component from which the direct current component is removed by this means by a coefficient to the frequency command value.

[0015]

[Function] The primary current of the induction motor is distorted by the fluctuation of the slip caused by the uneven rotation due to the pulsating torque of the load machine,
Due to this current distortion, the rotation unevenness further increases, and as a result, the current ripple also increases. In the present invention, this phenomenon is detected by the input power or primary current of the induction motor, and the generated torque of the induction motor is changed by providing a closed loop for operating the frequency of the voltage applied to the induction motor so as to reduce the fluctuation of the slip, Reduces rotation irregularity. As a result, the generation of current ripple is suppressed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the first invention. In the figure, an induction motor IM having a load of a compressor CP that generates pulsating torque is driven by a power converter INV such as a PWM inverter as in the conventional case.
In the control circuit 100 of the power converter INV, the frequency setter 10 for setting the frequency (applied frequency) f ^* of the induction motor primary voltage, the induction motor IM from the frequency command value f ^*.
V / f pattern generator 20 that outputs the amplitude command value | v ^* | of the primary voltage, the phase obtained by integrating the frequency command value f ^* by the integrator 30, and the amplitude command value | v ^* | A coordinate converter 40 that calculates a voltage command value, and a power calculation circuit 60 that calculates the input power of the electric motor IM from the detected values of the voltage and current applied to the induction motor IM.
Has the same configuration as the conventional control circuit 100 ″ shown in FIG.

The difference from FIG. 8 is that in this embodiment,
A high-pass filter 70 that passes only the AC component of the input power calculated by the power calculation circuit 60, a coefficient unit 80 that multiplies the AC component of the input power by a preset gain K _f , and the multiplication result are added to the above configuration. A loop for adding to the frequency command value f ^* by the device 90 is newly added.

Next, the operation of this embodiment will be described. First, when pulsating torque is generated by the operation of the compressor CP, current ripple occurs, and the electric power input to the induction motor IM is not constant even in a steady state and has an AC component. This input power is detected by the power calculation circuit 60. Then, the high-pass filter 70 removes the direct current component to extract only the alternating current component of the input power. This alternating current component is amplified by the pulsating torque and the rotational unevenness caused thereby, so that the current detector CT which is relatively inexpensive
Using the power calculation circuit 60 and the high-pass filter 7
Even if 0 is not particularly high in accuracy, it can be sufficiently detected.

The AC component of the input power that has passed through the high-pass filter 70 is multiplied by the gain K _f by the coefficient unit 80, and the applied frequency (primary frequency command value f ^* ) is increased or decreased in a phase opposite to the AC component of the input power. For example, when the AC component of the input power is positive, the slip is large, which indicates that the speed of the induction motor IM is reduced due to the uneven rotation. Therefore, the output of the coefficient unit 80 is added to the original primary frequency command value f ^* by the adder 90, so to speak, so to speak, so as to reduce the opposite phase, that is, the applied frequency.

Here, the gain K _f of the coefficient unit 80 may be set so as to correct the frequency corresponding to the rated slip when the induction motor IM is at the rated speed and the AC component of the input power is at the rated value. . Also, even with the same torque ripple, the AC component that appears in the input power changes depending on the rotational speed,
It is possible to expect a stable effect regardless of speed by changing the gain K _f according to the number of revolutions, rather than by setting a constant value set in advance. In this case, the gain K _f is
It is desirable to make it inversely proportional to the frequency command value f ^* .

FIG. 2 shows a configuration for that purpose. In FIG. 2, the coefficient unit 80 'has an applied frequency (frequency command value f ^* ).
It is composed of a circuit 81 for calculating the reciprocal of R, a multiplier 82 for multiplying a constant gain K _f ', and a multiplier 83 for multiplying the output by the AC component ΔP of the input power.

Although the high-pass filter 70 is used to obtain the AC component of the input power in FIG. 1, it is usually difficult to remove only the AC component without changing the phase of the AC component at all. . Therefore, the following method is conceivable as the simplest method for removing the DC component without changing the phase of the AC component at all. That is, the DC component of the input power, that is, the input power value in the steady state is prepared in advance, and this may be subtracted from the input power value calculated by the power calculation circuit 60. In particular, in the compressor, when the rotation speed of the induction motor IM is determined by the commanded frequency, the steady value of the load torque is a constant value that is hardly affected by other conditions.
By making this a function that is proportional to the applied frequency (that is, the set value increases as the frequency increases), a value substantially equal to the DC value of the input power can be set.

FIG. 3 shows a structure for that purpose. The high-pass filter 70 ′ shown in FIG. 3 has a function 71 showing the relationship between the applied frequency (frequency command value f ^* ) and the input power command value P ^* ,
And a subtracter 72 for subtracting the input power command value P ^* from the input power value P calculated by the power calculation circuit 60. Even with such a configuration, it is impossible to set the input power command value P ^* that completely matches the DC component of the input power. However, if the DC component that could not be removed is small, the applied voltage is not changed and the operating frequency and the V / f ratio are only slightly changed. Therefore, the rotation of the induction motor IM is not unstable.

FIG. 4 shows an example of a simulation result based on the above embodiment. Here, under the same conditions as the simulation shown in FIG. 7, a loop for correcting the applied frequency was added from 0.25 seconds after the simulation was started. As is clear from FIG. 4, it was confirmed that the addition of the correction loop of this embodiment eliminates the ripple of the generated torque and the input power, and the primary current also becomes a substantially sine wave.

Further, FIG. 5 shows an embodiment of the second and third inventions. In the embodiment of FIG. 1, the applied frequency is corrected by the AC component ΔP of the input power, whereas in FIG. 5, the amplitude | i ₁ | of the primary current vector is used, which is the second invention. It corresponds to the embodiment. That is, as its configuration, as in the case of FIG. 8, the coordinate converter 41 to which the output of the integrator 30 and the primary current detection value are input, and the primary to which the two components i _d and i _q of the orthogonal coordinates, which are the output thereof, are input. Current amplitude calculation circuit 50, and the amplitude of the primary current vector |
i ₁ | is input to the high-pass filter 70 to remove the DC component. The operation is similar to that of the embodiment shown in FIG.

As is clear from the simulation result of FIG. 4, the same correction can be performed by using the component of the primary current of the Cartesian coordinates on the coordinate axis rotating in synchronization with the primary voltage. 3 corresponds to the embodiment of the invention.
In the case of FIG. 4, i _q can be used. The operation of this embodiment is also similar to that of the embodiment of FIG.

[0027]

As described above, in the first to third inventions, there is a problem in that the torque generated by the induction motor, which is the drive machine, vibrates more than the pulsating torque due to the influence of the rotational unevenness caused by the pulsating torque of the load machine. , In the steady state, pay attention to the electrical physical quantities such as the input power and the primary current amplitude, which are direct current, and correct the applied frequency by multiplying these alternating current components with a predetermined gain to suppress the fluctuation of slip caused by uneven rotation. I tried to solve it.

As a result, conventionally, it was necessary to increase the current capacity due to the current distortion due to the pulsating torque, and it was difficult to reduce the size and cost of the component parts or apparatus. , These problems can be solved. Further, when the present invention is applied, the rotational unevenness is not amplified by the pulsating torque, so that large vibration in the load machine can be suppressed.

Further, in order to detect the AC component of the electrical physical quantity which is the DC amount in the steady state, if the value which changes according to the applied frequency is subtracted from the detected amount, the phase of the AC component is changed at all. The AC component can be easily detected without any need. In addition, when the applied frequency is corrected using the AC amount of the input power of the induction motor, if the gain that determines the correction frequency from the AC component is made variable according to the applied frequency or the amplitude of the applied voltage command value, It is possible to obtain a stable effect in the operation region.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a first invention.

FIG. 2 is a diagram showing another example of a coefficient unit.

FIG. 3 is a diagram showing another example of a high-pass filter.

FIG. 4 is a diagram showing simulation results according to the embodiment of FIG.

FIG. 5 is a block diagram showing an embodiment of second and third inventions.

FIG. 6 is a block diagram showing a conventional technique.

FIG. 7 is a diagram showing a simulation result for explaining a problem in the configuration of FIG.

FIG. 8 is a diagram in which an input power calculation circuit and a circuit for calculating the amplitude of a primary current vector are added to FIG.

[Explanation of symbols]

 10 frequency setting device 20 V / f pattern generator 30 integrator 40, 41 coordinate converter 50 primary current amplitude calculation circuit 60 power calculation circuit 70, 70 'high pass filter 80, 80' coefficient unit 90 adder 100, 100A control circuit INV Power converter CT Current detector IM Induction motor CP Compressor

Claims (6)

[Claims] 1. A control device for an induction motor connected to a load machine that generates a pulsating torque in synchronization with a rotation speed, the control device including a power converter for driving the induction motor and a control circuit therefor. In the controller of the induction motor configured to generate a primary voltage command value based on the frequency command value of the induction motor primary voltage and give the primary voltage command value to the power converter, the control circuit includes a primary current detection value of the induction motor and Means for calculating the input power of the induction motor from the detected primary voltage value or command value, means for removing the direct current component from the input power calculated by this means, and a coefficient for the input power from which the direct current component has been removed by this means A control device for an induction motor, comprising: a unit that adds a value obtained by multiplying the frequency command value to the frequency command value. 2. A control device for an induction motor connected to a load machine that generates a pulsating torque synchronized with a rotation speed, the control device including a power converter for driving the induction motor and a control circuit therefor. In the controller of the induction motor configured to generate a primary voltage command value based on the frequency command value of the induction motor primary voltage and give the primary voltage command value to the power converter, the control circuit sets the primary current detection value to the induction motor. Means for calculating the amplitude of the primary current based on the means, means for removing the direct current component from the amplitude of the primary current calculated by this means, and a value obtained by multiplying the amplitude of the primary current for which the direct current component has been removed by this means by a coefficient. Is added to the frequency command value, and a control device for an induction motor, comprising: 3. A control device for an induction motor connected to a load machine that generates a pulsating torque synchronized with a rotation speed, the control device including a power converter for driving the induction motor and a control circuit therefor. In the controller of the induction motor configured to generate a primary voltage command value based on the frequency command value of the induction motor primary voltage and give the primary voltage command value to the power converter, the control circuit controls the primary current detection value of the induction motor. Means for coordinate conversion to a current component on a rectangular coordinate axis that rotates in synchronization with the primary voltage, means for removing a DC component from one of the current components coordinate-converted by this means, and this component for removing a DC component. And a unit for adding a value obtained by multiplying the current component by a coefficient, to the frequency command value, and a controller for an induction motor. 4. The induction motor control device according to claim 1, wherein the means for removing the direct current component is constituted by means for subtracting a preset value. 5. The control device for an induction motor according to claim 4, wherein the preset value is a value that changes according to a frequency command value of the induction motor primary voltage. 6. A coefficient for multiplying a value obtained by removing a direct current component,
The control device for an induction motor according to claim 1, 2, 3, 4 or 5, wherein the control is variable according to a frequency command value of the induction motor primary voltage.