JPH0715997A - Controller for induction motor - Google Patents

Abstract

PURPOSE:To operate an induction motor with optimum admittance all the time for highly efficient operation by applying a control signal which makes a deviation of operating admittance from optimum reference admittance zero to a voltage regulating means. CONSTITUTION:A modulation means 35 in a control circuit 26 modulates the pulse duration modulation signal of a pulse duration modulation circuit 32 with modulation parameters corresponding to the output of a frequency commander 24 and the predetermined admittance of an induction motor 12, and changes supplied voltage according to a motor load on curve patterns for respective types of frequency. When the motor 12 is loaded, detected admittance 36a becomes higher than optimum admittance 52a, so that a voltage signal 28a is modulated by parameter output 42a supplied to a multiplication device 44 to obtain a high level signal 28'a. As a result, the pulse duration of a pulse duration modulation signal 32a becomes large to increase the supplied voltage of the motor 12. It is thus possible to adjust the detected admittance 36a until it matches the optimum reference admittance 52a.

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 AC induction motor, and more particularly to a control device for an induction motor capable of operating an induction motor with high efficiency.

[0002]

2. Description of the Related Art Conventionally, as a control device for an induction motor, there has been proposed a power factor control device which detects a load of the induction motor by using parameters such as electric power and power factor of the induction motor. These power factor control devices were effective when the load fluctuation of the electric motor was gentle. However, if a pulsating load such as a compressor is applied, or if an impact load is applied from the unloaded state to the maximum load within 0.1 seconds, such as in machine tools and injection molding machines, load detection becomes impossible. The controller could not respond to a sudden change in load. The reason is that when the electric motor is driven at a low voltage during idling and an impact load is applied to the electric motor, the slip of the electric motor suddenly rises at that moment. In other words, when the slip of the electric motor suddenly rises when the load suddenly increases, there is no increase in the electric power because the number of rotations of the electric motor decreases and the electric power decreases conversely, while the power factor that must be higher tends to decrease conversely. . At this time, the control device lowers the terminal voltage of the electric motor that must be increased in response to the decrease in the electric power or the decrease in the power factor, so that the control becomes impossible and the responsiveness to the sudden load increase of the electric motor is poor. .

[0003]

SUMMARY OF THE INVENTION The present invention provides an admittance (= I / which is the reciprocal of the impedance of an induction motor.
V: V = motor terminal voltage, I = motor current) in response to a sudden increase in torque, which enables extremely high responsiveness to realize excellent controllability. The relationship between torque, slip and motor admittance is as follows. (1) Torque increase → Slip increase → Motor admittance increase (2) Torque decrease → Slip decrease → Motor admittance decrease That is, by controlling the motor admittance to a constant level, the motor operates with a constant slip even if the load torque changes. And the admittance value is set to a value at the time of the most efficient slip of the induction motor, which enables highly efficient operation of the motor.

[0004]

In order to achieve the above object, the control device of the present invention calculates the operating admittance of an induction motor and compares the operating admittance with a predetermined reference admittance to determine both admittances. The voltage adjusting means is controlled so that the deviation of 0 becomes zero.

[0005]

According to the present invention, the operating admittance of the induction motor is detected, and the control signal for making the deviation between the operating admittance and the terminal voltage of the induction motor from the optimum reference admittance zero is given to the voltage adjusting means, so that the induction motor is always operated. It can be driven with optimum admittance to enable high-efficiency operation.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a first preferred embodiment of a control device 14 connected between an AC power supply 10 and an induction motor 12 is shown. The control device 14 includes a rectifier 16 that rectifies alternating current into direct current, an inverter unit 18 that converts the direct current output from the rectifier 16 into a supply voltage having a variable voltage and a variable frequency by pulse width modulation, and drives the electric motor 12, and a meter. A voltage detector 20 that detects the supply voltage of the induction motor 12 via the transformer 19, a current detector 22 that is a CT, a frequency commander 24 that commands an arbitrary frequency, and a control circuit 26 that is a microcomputer. Prepare The control circuit 26 outputs the reference voltage signal 28a corresponding to the frequency according to the output of the frequency commander 24, the V / F converter 28, the carrier generator 30 that generates the triangular wave carrier signal 30a, the reference voltage signal 28a, and the carrier signal 30a. And a pulse width modulation circuit 32 for generating a pulse width modulation signal 32a according to and drive the inverter unit 18 in response to the pulse width modulation signal 32a to convert DC power into AC power of variable voltage / variable frequency. The induction motor 12 is operated at a variable speed. The control circuit 26 controls the output of the frequency commander 24 and the induction motor 12
The pulse width modulation signal of the pulse width modulation circuit is modulated with the modulation parameter corresponding to the predetermined admittance of, and the lower limit value to the upper limit value along the motor load on a plurality of curve patterns for each frequency as described later. Up to the modulation means 35 for varying the supply voltage. The modulation means 35 includes an operation admittance detector 36 that detects the operation admittance of the electric motor 12, an optimum reference admittance commander 38, and
A deviation detecting comparator 40, an integrator 42, and a multiplier 44 are provided. The optimum reference admittance commander 38 responds to the reference admittance commander 46, a function generation base 48 that generates a large number of compensation functions that change on different curve patterns for each frequency in response to the supply voltage of the motor, and the frequency command signal 24a. Then, the function selector 50 that selects an arbitrary function from a large number of compensation functions of the function generator 48 is multiplied by the output of the reference admittance commander 46 and the output of the function generator 48 to operate the motor 12 with high efficiency. A multiplier 52 that outputs an optimum admittance signal 52a corresponding to a predetermined optimum reference admittance pattern (see FIG. 2) for each frequency is provided. Each of the optimum reference admittance patterns is set to a value for operating the induction motor at a predetermined slip for highly efficient operation of the induction motor at an arbitrary frequency.
FIG. 2 is a graph showing the relationship between the supply voltage of the induction motor and the optimum reference admittance. The admittance gradually increases as the supply voltage increases, the admittance increases as the operating frequency decreases, and the load increases at each frequency. Accordingly, the optimum supply voltage is supplied (see FIG. 3). In FIG. 1, the supply voltage of the induction motor 12 may be either the output voltage of the voltage detector 20 or the reference voltage signal 28a of the V / F converter 28. Here, if the supply voltage of the electric motor 12 is a parameter related to the supply voltage, the voltage detector 20
Or the voltage signal 28a of the V / F converter 28. The optimum reference admittance signal 52a output from the multiplier 52 is compared with the driving admittance signal 36a detected by the comparator 40, and its deviation is signal E.
The modulation parameter 42 is integrated by the integrator 42 as rr.
It is supplied to the multiplier 44 as a. The multiplier 44 multiplies the modulation parameter 42a and the reference voltage signal 28a and outputs the calculation result as the modulation reference voltage signal 28'a. The pulse width modulation signal of the pulse width modulation circuit 32 is modulated by the modulated reference voltage signal 28'a, and the supply voltage of the inverter unit 18 has a plurality of curve patterns according to the motor load for each frequency as shown in FIG. By changing from the lower limit value to the upper limit value above, it becomes possible to operate the induction motor 12 with high efficiency for each frequency.

In the configuration shown in FIG. 1, the induction motor 12 has the optimum reference admittance 5 as shown in FIG.
When operated at 2a, the parameter output 42a of the integrator 42 is at a low level as shown in FIG. 4 (b), so that the pulse width modulation circuit 32 has the carrier signal 30 as shown in FIG. 4 (d).
a and the pulse signal 28a in response to the voltage signal 28a.
a is output (see FIG. 4E). When the motor 12 is loaded at time T, the driving admittance 36a detected as shown in FIG. 4A becomes higher than the optimum reference admittance, and the parameter output 42'a as shown in FIG. 4B.
Rises. At this time, as shown in FIG.
8a is a parameter output 42'a supplied to the multiplier 44.
Is modulated into a high level voltage signal 28'a. The pulse voltage of the pulse width modulation signal 32'a is modulated by the modulated voltage signal 28'a so as to be large, and the supply voltage of the electric motor 12 is increased. The increase in the supply voltage is adjusted until the detected driving admittance 36a matches the optimum reference admittance 52a. At time T,
When the load of the electric motor 12 becomes lighter, the detected driving admittance falls below the optimum reference admittance, and the voltage signal 28a is modulated to a low level. Therefore, the pulse width modulation signal 32'a
Pulse width is modulated to be small, and the supply voltage of the electric motor 12 is lowered until the detected driving admittance 36a matches the optimum reference admittance 52a. In this way, the pulse width modulation signal 32a of the pulse width modulation circuit 32 is modulated by the parameter corresponding to the optimum reference admittance according to the load of the electric motor 12 and the arbitrary frequency, and the electric motor 12 is always operated with high efficiency.

FIG. 5 is a block diagram of a second preferred embodiment of the present invention, in which the same parts as those in FIG. 1 are designated by the same reference numerals. In the second embodiment, the control device 60 is composed of a magnetic flux control type inverter. The main circuit of the magnetic flux control type inverter is a rectifier 16 and an inverter unit 18.
It consists of and. In order to control this inverter, the control circuit 61 inputs the voltage set value from the voltage setter 23 and the frequency command value from the frequency commander 24 to calculate the magnetic flux command value Φ0, and the induction setter 62. Electric motor 1
The instrument transformer 19 for detecting the terminal voltage of 2 and the magnetic flux calculator 66 for calculating the actual magnetic flux value Φ by integrating the terminal voltage are provided, and the magnetic flux commander Φ 0 output by the magnetic flux setter 62. And a deviation between the actual magnetic flux value Φ output by the magnetic flux calculator 66 is input to the magnetic flux adjuster 68. The magnetic flux adjuster 68 sends a control signal for making the input deviation zero to the pulse width modulation circuit 7
0, and the inverter unit 18 converts the DC power into AC power having a desired supply voltage and frequency according to the pulse width modulation signal from the pulse width modulation circuit 70, and the induction motor 12
Variable speed operation. In order to operate the induction motor 12 with high efficiency at a predetermined slip, the multiplier 74 of the modulation means 72
The magnetic flux command value Φ0 output by the magnetic flux setter 62 is multiplied by the modulation parameter 42a of the integrator 42, and the calculation result is output as the magnetic flux command value ΦA. Magnetic flux controller 6
8 is a magnetic flux calculator 66 based on the integral calculation of the magnetic flux command value ΦA output from the multiplier 74 and the output voltage of the inverter unit 18.
The deviation from the actual value Φ of the magnetic flux of the induction motor is output, and the pulse width modulation circuit 70 gives the pulse width modulation signal to the inverter unit 18 in response to the control signal for controlling the input deviation to zero. As is clear from the description of the first embodiment,
If the load rapidly increases and the detected driving admittance increases while the induction motor 12 is operating at the optimal driving admittance, the output of the modulation parameter 42a increases.
The magnetic flux command value ΦA increases, and the magnetic flux adjuster 68 outputs a control signal for widening the pulse width of the pulse width modulation signal of the pulse width modulation circuit 70. At this time, the supply voltage of the induction motor 12 rises and the detected driving admittance 36a is adjusted to a level that matches the optimum reference admittance 52a. When the load suddenly decreases during the optimum admittance operation of the induction motor 12, the detection operation admittance 36a decreases, so that the output of the modulation parameter 42a decreases and the magnetic flux command value ΦA decreases. At this time, the magnetic flux adjuster 68 operates the pulse width modulation circuit 7
A control signal for narrowing the pulse width of the pulse width modulated signal of 0 is output. As a result, the supply voltage of the induction motor decreases, the operation admittance of the induction motor 12 increases, and the detected operation admittance is adjusted to a level that matches the optimum reference admittance. As described above, in the control device including the magnetic flux control type inverter, the output of the pulse width modulation circuit 70 is modulated by the modulation parameter 42a that is compensated by the arbitrary frequency and the supply voltage of the induction motor, and the induction motor is driven with a predetermined slip. Operated efficiently.

[0009]

As is apparent from the above, according to the present invention, in the control device including the inverter device, the pulse width modulation signal is modulated by the modulation parameter corresponding to the predetermined optimum reference admittance of the induction motor. The output voltage of the inverter section is adjusted along the load from the lower limit value to the upper limit value on different curve patterns to enable the induction motor to operate at high efficiency with optimum admittance. Is large.

[Brief description of drawings]

FIG. 1 is a desirable first example of a control device for an induction motor according to the present invention.
It is a block diagram showing an example.

FIG. 2 is a graph showing a relationship between a motor supply voltage and optimum reference admittance for each frequency in the control device of the present invention.

FIG. 3 is a graph showing a relationship between a motor load and a supply voltage for each frequency in the control device of the present invention.

4 shows waveform diagrams of various output signals in the control device of FIG.

FIG. 5 is a block diagram showing a second embodiment of the control device of the present invention.

[Explanation of symbols]

10 AC power supply 46 Reference admittance commander 12 Induction motor 48 Compensation function generator 14 Control device 52 Multiplier 16 Rectifier 62 Flux setting device 18 Inverter section 66 Flux calculator 20 Voltage detector 68 Flux regulator 22 Current detector 70 Pulse width Modulation circuit 28 V / F converter 32 PWM control circuit 35 Modulation means 36 Operation admittance detector 38 Optimal operation admittance commander 40 Comparator 42 Integrator 44 Multiplier

Claims (4)

[Claims] 1. A rectifier for rectifying AC into DC, an inverter unit for driving an induction motor by converting a DC voltage output from the rectifier into a supply voltage of variable voltage / variable frequency by pulse width modulation control, and an arbitrary frequency. And a PWM signal generating means for generating a PWM signal for controlling the inverter section in response to an arbitrary frequency,
Means for instructing a reference admittance, means for detecting the driving admittance of the motor from the supply voltage and the current of the induction motor, means for generating a modulation signal according to the deviation between the reference admittance and the driving admittance, and modulation A control device for an induction motor, comprising: a modulation unit that modulates a PWM signal according to the signal. 2. A rectifier for rectifying AC into DC, an inverter unit for converting a DC voltage output from the rectifier into a supply voltage of variable voltage / variable frequency by pulse width modulation control, and driving an induction motor, and an arbitrary frequency. , A magnetic flux setting means for calculating a magnetic flux command value in response to an arbitrary frequency, a magnetic flux calculating means for detecting a supply voltage of the induction motor and calculating an actual magnetic flux value from the supplied voltage, a magnetic flux A magnetic flux adjusting means for inputting a deviation between the command value and the actual magnetic flux and giving a control signal for controlling the input deviation to zero, and a pulse width modulation for driving the inverter in response to the control signal. Circuit means for generating a signal, means for instructing reference admittance, means for detecting driving admittance from the supply voltage and current flowing in the induction motor, and reference admittance And a multiplication means for calculating the product of the modulation parameter and the magnetic flux command value and outputting the calculated value to the magnetic flux adjusting means. An induction motor control device characterized by: 3. A rectifier for rectifying alternating current to direct current, an inverter part for converting a direct current voltage output from this rectifier into a variable voltage / variable frequency supply voltage by pulse width modulation to drive an induction motor, and an arbitrary frequency Frequency command means for commanding, pulse width modulation signal generating circuit means for generating a pulse width modulation signal for controlling the inverter part in response to an arbitrary frequency, means for commanding an optimum reference admittance of the induction motor, and an induction motor And a modulation means for modulating the pulse width modulation signal so that the operating admittance of the pulse width modulation signal follows the optimum reference admittance. 4. A rectifier for rectifying alternating current to direct current, an inverter part for converting a direct current voltage output from this rectifier into a variable voltage / variable frequency supply voltage by pulse width modulation to drive an induction motor, and an arbitrary frequency Frequency command means for commanding, pulse width modulation signal generating circuit means for generating a pulse width modulation signal for controlling the inverter section in response to an arbitrary frequency, means for commanding the optimum admittance of the induction motor, and induction motor A modulation means for modulating the pulse width modulation signal so that the driving admittance follows the optimum admittance, and the optimum admittance command means multiplies the reference admittance command means, the compensation function generation means and these outputs to output the optimum admittance. An induction motor control device comprising: a multiplication means.