JPH06153588A - Electric-power control device for ac induction motor - Google Patents

Abstract

PURPOSE:To achieve the high-speed responsiveness of the device by a method wherein the terminal voltage and the terminal current of an induction motor are operated at an optimum impedance to become a high-efficiency operation and the terminal voltage is changed instantaneously when an impact load is applied while the motor is operated in an idling manner. CONSTITUTION:The operating impedance of an induction motor 14 is operated by an impedance operation device 22, it is compared with an optimum impedance 24a, and an output signal 29a is generated in such a way that a deviation is made zero by an output-signal generation means 29 so as to respond to a deviation value Err.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power control device for an AC induction motor, and more specifically, it detects the impedance of the motor and automatically adjusts it to the most efficient operating voltage for the operating state of the motor. Moreover, the present invention relates to a power saving control device for an induction motor, which follows the load state of the motor at an extremely high speed.

[0002]

2. Description of the Related Art Conventionally, as a power saving 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 at idle, if an impact load is applied to the electric motor,
This is because the slip of the electric motor suddenly rises at that moment.
That is, if the slip of the electric motor suddenly rises when the load increases suddenly, the number of rotations of the electric motor decreases, so there is no increase in the electric power.
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 increase in the load of the electric motor is poor. .

[0003]

SUMMARY OF THE INVENTION The present invention realizes excellent controllability by making it possible to extremely speed up the response at the time of sudden torque increase by setting the control target for power saving control to the motor impedance. Made for. The relationship between torque, slip, and motor impedance is as follows. (1) Torque increase → Slip increase → Motor impedance decrease (2) Torque decrease → Slip decrease → Motor impedance increase In other words, by making the motor impedance constant, operate the motor with a constant slip even if the load torque changes. And the impedance value is set to a value at the time of the most efficient slip of the induction motor, it is possible to operate the motor with high efficiency.

[0004]

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

[0005]

According to the present invention, the operating impedance of the induction motor is detected by detecting the operating impedance of the induction motor and applying a control signal to the voltage adjusting means to make the deviation between the operating impedance and the terminal voltage of the induction motor zero the optimum reference impedance. High efficiency operation can be achieved by driving with the optimum impedance.

[0006]

FIG. 1 shows an equivalent circuit of an actual induction motor,
FIG. 2 shows a simple equivalent circuit of the induction motor. In FIG. 1, the following signals are respectively V1: primary voltage I1: primary current I0: exciting current I2: primary conversion secondary current R1: primary winding resistance [Ω] l1: primary winding inductance [H] Ri: Excitation resistance [Ω] L1: Excitation inductance [H] 12 ': Primary conversion secondary inductance [H] R2': Primary conversion secondary resistance [Ω] ω1: Primary input angular frequency [rad /
sec] s: represents slip. Where:

[0007]

[Formula 1] Is an electrical representation of the mechanical output of the induction motor. The operating impedance of the induction motor is V1 / I1
Therefore, if the operating impedance is controlled to be constant, among these variables, {R1, l1, R
Since i, L1, 12 ', R2', ω1} should be invariant, the slip s should be constant. Next, in FIG. 2, the following symbols are X: primary conversion motor leakage reactance [Ω] g0: exciting conductance [Ω ⁻¹ ] b0: exciting susceptance [Ω ⁻¹ ] J: constant x1: primary winding inductance ( ω1l1) x2 ′: Represents a primary conversion secondary inductance (ω1l2 ′). When the fixed loss and the load loss of the induction motor become equal, the efficiency of the induction motor becomes maximum. The fixed loss is the loss at g0, and the load loss is R1 and R
It is a loss at 2 '. The power consumption Pa at g0 is the following formula

[0008]

[Equation 2] Pa = Vl ² · g0 [W] and the power consumption Pc at R1 and R2 ′ is expressed by the following equation.

[0009]

[Formula 3] It is represented by. Pa = Pc at the highest efficiency of the induction motor
Becomes That is, the fixed loss g0 is

[0010]

[Formula 4] And the slip s is

[0011]

[Formula 5] Becomes Briefly, there are positive and negative solutions for the slip s, which is a positive solution for motors, and the variable X is only proportional to the frequency. It can be seen that the slip s for can be specified.

In FIG. 3, the power saving control device 10 is connected between the AC power supply 12 and the induction motor 14. The power saving control device 10 is connected between the AC power supply 12 and the induction motor 14 and is a voltage regulator 16 for adjusting the terminal voltage of the induction motor 14 to an optimum level, and a current for detecting the terminal current of the induction motor 14. Detector 18 and induction motor 14
The voltage detector 20 for detecting the terminal voltage of the device, an impedance calculator 22, a reference impedance setting device 24, an error detector 26, and an integrator 28. The impedance calculator 22 includes a current detector 18 and a voltage detector 2.
The impedance of the induction motor 14 is calculated from the terminal current 18a and the terminal voltage 20a detected at 0, and the motor or operating impedance 22a is generated. On the other hand, the reference impedance setting device 24 generates an optimum impedance setting value 24a which should be an impedance for high efficiency operation of the induction motor 14. The error detector 26 is (optimal impedance setting value 24a-operating impedance 22
a) is calculated and sent to the integrator 28 as the error value Err. The integrator 28 integrates the error value for stability of the control system and outputs it as the output voltage adjustment signal 28a to the output signal generator 29. The output signal generator 29 outputs the output voltage adjustment signal 28a.
When the signal 28a rises, an output signal 29a with a large pulse width is generated, and when the signal 28a falls, an output signal 29a with a narrow pulse width is output. In this way, the output signal generator 2
9 produces an output signal 29a such that the error signal Err becomes zero. The voltage regulator 16 controls the voltage applied to the induction motor 14 by the output signal 29a so that the error value Err becomes zero. As a result, the induction motor 14 is always operated with the optimum impedance and a remarkable power saving effect is obtained. Further, in an electric motor with large torque pulsation or an electric motor for fluctuating loads, when the torque sharply increases, the voltage can respond at high speed, and the electric motor can be smoothly operated.

FIG. 4 shows a power saving control apparatus 10 'according to 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 FIG. 4, the power saving control device 10 ′ includes an impedance compensation unit 30. The impedance compensator 30 is a voltage compensator 3 for compensating the impedance value by the detected voltage signal 20a corresponding to the terminal voltage.
2 and a multiplier 34, the voltage compensator 32 generates an impedance compensation value 32a according to the detected voltage signal 20a. The voltage compensator 32 has a plurality of compensation curves 32b corresponding to the motor load so that any compensation curve 32a can be selected in response to the voltage signal 20a. The impedance compensation value 32a corresponding to the voltage signal 20a is supplied to the multiplier 34, where it is multiplied by the reference impedance value 24a and the optimum impedance 34a is output. The error detector 26 calculates (optimal impedance value 34a-operating impedance 22a) and integrates it as an error value 28
Send to. The integrator 28 integrates the error value to stabilize the control system, and outputs it as the output voltage adjustment signal 28a to the output signal generator 29. The voltage regulator 16 controls the terminal voltage of the induction motor 14 by the output signal 29a so that the error signal Err becomes zero. In this way, the reference impedance value 24a is compensated by the detection voltage 20a that is the voltage applied to the motor to become the optimum impedance 34a, so that the optimum voltage is always supplied to the electric motor 14 and the electric motor 14 is operated at a constant optimum impedance. .

FIG. 5 is a block diagram of a power saving control device 40 constructed by an inverter device according to a third preferred embodiment of the present invention. In FIG. 5, the power saving control device 40 is connected between the AC power supply 42 and the induction motor 44.
The power saving control device 40 includes a rectifier circuit 46 that rectifies a power supply voltage from an AC power supply 42 into a DC voltage, and an inverter unit 48 that converts the DC voltage into an AC voltage having a variable voltage and a variable frequency.
And a control circuit 50 for controlling the inverter unit 48. The power saving control device 40 further includes a current detector 52 that detects the terminal current of the electric motor 44, a voltage detector 54 that detects the terminal voltage of the electric motor 44, an impedance calculator 56 that calculates the operating impedance of the electric motor 44, and an optimum impedance. It comprises a generator or impedance compensator 58, an error detector 60 and an integrator 62.

The control circuit 50 includes a triangular wave generator 64 for generating a triangular wave signal 64a, an output voltage adjusting signal 62a of the integrator 62, and a voltage comparator 66 for the triangular wave signal 64a and the output voltage adjusting signal 62a. The comparator 66 compares the triangular wave signal 64a with the output voltage adjustment signal 62a and outputs P
The WM modulation signal PWMV is generated. The waveform dividing unit 68 is P
The WMV signal is divided into three-phase waveforms and the drive waveforms are sent to the drive circuit 70. The drive circuit 70 is the inverter unit 4
Drive eight. The microcomputer 72 is the control circuit 5
It generates various control signals within 0 and outputs a frequency signal 50a corresponding to the operating frequency of the terminal voltage.

The optimum impedance generator 58 includes a reference impedance setting unit 74 for outputting a reference impedance 74a and a frequency compensation signal 7 in response to the frequency signal 72a.
6a, a voltage compensator 78 that outputs a voltage compensation signal 78a according to the detected voltage value 54a corresponding to the terminal voltage of the motor 44, a reference impedance 74a, a frequency compensation signal 76a, and a voltage compensation signal. 7
8a and a multiplier 80 that calculates the optimum reference impedance 80a compensated by the frequency and terminal voltage of the electric motor 44. The frequency compensator 76 has a plurality of compensation curves 7 corresponding to the operating frequency of the electric motor 44 and the electric motor load.
6b so that any compensation curve 76b can be selected in response to the frequency signal 72a. Voltage compensator 7
Reference numeral 8 has a plurality of compensation curves 78b corresponding to the terminal voltage and the motor load, and an arbitrary compensation curve 78b can be selected in response to the voltage signal 54a.

Next, regarding the operation of the inverter device of FIG.
Description will be given based on the waveform diagrams of FIGS. Now, it is assumed that the load torque T2 of the electric motor 44 increases at point a. At this time, the motor slip increases and the motor speed N2 decreases slightly.
At the same time, the motor impedance Z1 decreases. When the motor impedance Z1 decreases, a difference from the optimum impedance value Z2 (80a) occurs, and a "+" output is produced at the output 60a of the error detector 60. For simplicity of explanation, the pattern of the voltage compensator 78 is a constant. Integrator 62
The output voltage adjustment signal 62a of the output starts to rise, the pulse width modulation (PWM) signal PWMV has a wider conduction width, and the output voltage rises. The load torque becomes constant from point b,
The motor impedance 56a is the optimum impedance value 8
When it matches 0a, the error signal Err becomes zero and the output voltage adjustment signal 62a maintains a constant value. It is assumed that the load torque T2 of the electric motor 44 decreases at point c. At this time, the motor slip is decreased and the motor rotation speed N2 is slightly increased.
At the same time, the motor impedance Z1 (56a) rises. When the motor impedance Z1 rises, a difference from the optimum impedance value Z2 (80a) occurs, and the output Err of the error detector 60 produces a "-" output. Integrator 6
The output voltage adjustment signal 62a of the output of 2 starts to fall, the pulse width modulation (PWM) signal PWMV has a narrow conduction width,
The output voltage drops. The load torque becomes constant from the point d, and when the motor impedance Z1 matches the optimum impedance value Z2, the error signal Err becomes zero and the output voltage adjustment signal 62a maintains a constant value.

FIG. 7 shows a waveform diagram comparing the operation when the present invention is adopted and the operation when the present invention is not used. When the load torque T of the electric motor is 0%, the electric motor 4
The rotation speed N1 of 4 is at a high level, and the motor impedance Z1 at that time is at a high level. This is an electric motor 4
Since the terminal voltage V1 of No. 4 is applied at a level of 100%, the input power P1 of the electric motor 44 at this time is at a high level. According to the present invention, when the load torque T is small, the terminal voltage VIX of the electric motor is maintained at a low level, and the input power PIX of the electric motor 44 is held low. When the load torque increases, the rotation speed of the electric motor 44 decreases and the electric motor impedance Z1 decreases, so that it can be seen that the terminal voltage VIX automatically increases correspondingly.
As described above, since the terminal voltage of the electric motor 44 changes in inverse proportion to the electric motor impedance, it can be seen that the slip is held constant and the rotation speed NIX is constant. Number of revolutions N
IX represents the result of impedance control according to the present invention, impedance ZIX represents the optimum impedance, motor voltage VIX represents the voltage change when impedance control is performed, and PIX represents the input power of the motor when impedance control is performed. That is, the dotted line portion in FIG. 7 shows the operation when the present invention is adopted.

FIG. 8 is a voltage / current waveform diagram showing the result of the response of the power saving control device 40 of FIG. In FIG. 8, waveform (a) represents voltage and waveform (b) represents current.
Time t1 indicates a state in which the electric motor 14 is operated with no load (idle). In this state, when a load is suddenly applied to the electric motor 44, the control device 50 raises the voltage to the level of 100% within the period t2 (81 msec) in response to the change in the electric motor impedance. At this time, the current flowing through the electric motor 44 is limited to around 150% of the rated value,
When the period t3 is entered, the voltage is also maintained at the 100% level and the current is maintained at the rated level. In this way, the electric motor 44
Even if a torque is suddenly applied to the electric motor when the motor is idle, the power saving control device 40 can respond to the sudden increase in the torque at high speed, the controllability is improved, and the stable operation of the electric motor can be obtained.

[0020]

According to the present invention, the AC induction motor can be operated with high efficiency so as to always have a constant optimum impedance, and a significant energy saving effect can be obtained. Further, even when an impact load is applied to the electric motor, the terminal voltage of the electric motor can be made to respond instantaneously, so that high-speed response becomes possible.
Further, since the slip of the electric motor can be suppressed within a desired range, stable constant speed operation can always be performed even when the load fluctuation of the electric motor is large. Although the power control device of the present invention has been described as being applied to an AC induction motor, it goes without saying that the power control device can be applied to a device such as a high frequency induction device whose impedance changes depending on the load.

[0021]

[Brief description of drawings]

FIG. 1 shows an equivalent circuit of an AC induction motor.

FIG. 2 shows a simple equivalent circuit of an AC induction motor.

FIG. 3 is a block diagram of a power control device according to a preferred embodiment of the present invention.

FIG. 4 is a block diagram of a power controller according to another preferred embodiment of the present invention.

FIG. 5 is a block diagram of a power controller according to still another preferred embodiment of the present invention.

6 is a waveform diagram showing the operation of FIG.

FIG. 7 is a waveform diagram showing the operational difference between the case where the principle of the present invention is used and the case where it is not used.

8 is a waveform diagram showing a relationship between a terminal voltage and a terminal current by the power control device of FIG.

[Explanation of symbols]

 10 Power Control Device 12 AC Power Supply 14 AC Induction Motor 16 Voltage Regulator 18 Current Detector 20 Terminal Voltage Detector 22 Impedance Calculator 24 Impedance Setting Device 26 Error Detector 28 Integrator 29 Output Signal Generator 30 Impedance Compensator 40 Power Control device 42 AC power supply 44 AC induction motor 46 Rectifier circuit 48 Inverter unit 50 Control circuit 52 Current detector 54 Terminal voltage detector 56 Impedance calculation unit 58 Impedance compensation unit 60 Error detector 62 Integrator

Claims (12)

[Claims] 1. A power control device for highly efficiently controlling an AC induction motor with a constant impedance, comprising: (a) calculating means for calculating an operating impedance of the induction motor;
(B) means for setting a reference impedance; (c) output signal generating means for comparing the reference impedance with the operating impedance to generate an output signal for reducing the deviation thereof; and (d) the output signal. A voltage control unit that responds to adjust the terminal voltage of the induction motor. 2. The power control apparatus according to claim 1, further comprising means for compensating the reference impedance to generate an optimum reference impedance corresponding to a load of the induction motor. 3. The power control apparatus according to claim 1, further comprising means for compensating the reference impedance with the voltage to generate an optimum reference impedance. 4. A power control device for driving an AC induction motor with an optimum impedance, wherein (a) voltage means for detecting a terminal voltage of the induction motor and (b) current detection means for detecting a terminal current of the induction motor. And (c) impedance calculation means for calculating the operating impedance of the induction motor from the effective value of the terminal voltage and the effective value of the terminal current, and (d) generation of an optimum reference impedance corresponding to the load of the induction motor. And (e) means for generating an output signal for comparing the optimum reference impedance with the operating impedance to reduce the deviation thereof to zero, and (f) the terminal in response to the output signal. Voltage adjusting means for operating the induction motor at the optimum reference impedance by controlling the voltage. Power control device. 5. A means for outputting the predetermined reference impedance by said optimum reference impedance generating means,
The power control apparatus according to claim 4, further comprising impedance compensating means for compensating the reference impedance to generate the optimum reference impedance. 6. The power control apparatus according to claim 5, wherein the impedance compensating means comprises voltage compensating means for compensating the value of the reference impedance with a value corresponding to the terminal voltage. 7. The power control device according to claim 4, wherein the power control device is an inverter device. 8. An inverter device for operating an AC induction motor with a variable voltage and a variable frequency at a constant impedance, wherein (a) rectifying circuit means for rectifying an AC power supply voltage into a DC voltage, and (b) the DC voltage. An inverter unit that drives the induction motor by converting into an alternating voltage of a variable voltage and a variable frequency, (c) a control circuit that drives the inverter unit, and (d) a voltage detection unit that detects a terminal voltage of the induction motor. And (e) current detection means for detecting the terminal current of the induction motor, and (f) impedance calculation means for calculating the operating impedance of the induction motor from the effective value of the terminal voltage and the effective value of the terminal current. (G) optimum reference impedance generating means for generating an optimum reference impedance corresponding to the load of the induction motor, and (h)
Means for comparing the optimum reference impedance and the operating impedance and generating an output signal for reducing the deviation thereof to zero, wherein the control circuit drives the inverter section in response to the output signal. An inverter device, characterized in that the induction motor is operated along the optimum reference impedance. 9. The inverter device according to claim 8, wherein said optimum reference impedance generating means comprises means for generating said optimum reference impedance in response to a frequency signal from said control circuit. 10. The inverter device according to claim 8, wherein said optimum reference impedance generating means comprises means for generating said optimum reference impedance in response to said terminal voltage. 11. The inverter according to claim 10, wherein said optimum reference impedance generating means comprises means for generating said optimum reference impedance in response to a frequency signal from said control circuit and said terminal voltage. apparatus. 12. The optimum reference impedance generating means comprises reference impedance generating means and compensating means for generating the optimum reference impedance by compensating the reference impedance in response to the frequency signal and the terminal voltage. The inverter device according to claim 11, wherein the inverter device is provided.