JPS6233838B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a control device for a squirrel cage induction machine.

Recently, a control method for induction machines called vector control has been studied. Since this control method independently controls each of the excitation current component and secondary current component of the induction machine, it is possible to make the speed response performance equivalent to that of a DC machine.

FIG. 1 shows a conventional example in which this control method is applied to a current source inverter. In FIG. 1, 1 is an AC power supply, 2 is a forward converter that converts AC to DC, 3 is a DC reactor that suppresses the pulsation of the DC current flowing through the main circuit, 4 is an inverse converter that converts DC to AC,
5 is a squirrel cage induction machine, and 6 is a speed generator for detecting the rotational speed of the induction machine 5. 7 is a speed command which commands the rotational speed of the induction machine 5; 8 is a speed control circuit that operates according to the deviation between the output signals of the speed command 7 and the speed generator 6;
This becomes a signal that commands the magnitude of the next current. Reference numeral 9 indicates an excitation current command which commands the secondary flux linkage of the induction machine 5, that is, the magnitude of the excitation current; A primary current calculation circuit 11 calculates and commands the current, and 11 is a current detector that detects the direct current flowing in the main circuit, and its output signal is proportional to the primary current of the induction machine 5. 12 is a current control circuit that operates according to the deviation between the output signal of the primary current calculation circuit 10 and the output signal of the current detector 11; 13 is a current control circuit 1;
This is an automatic pulse phase shifter that sends a firing signal with a phase corresponding to the output signal of forward converter 2 to the thyristor of forward converter 2.
14 is a slip frequency calculation circuit that calculates and commands the slip frequency of the induction machine 5; 15 is an adder that adds the output signals of the slip frequency calculation circuit 14 and the speed generator 6; This becomes a signal that commands the next frequency. 16 is a V/F converter that generates a sine wave signal with a frequency proportional to the input voltage; 17 is a primary current phase of the induction machine 5 based on the output signal of the speed control circuit 8 and the output signal of the excitation current command unit 9; 18 is a phase shifter that shifts the phase of the sine wave signal that is the output of the V/F converter 16 in accordance with the output signal of the phase calculation circuit 17; 19;
is a gate circuit that sequentially sends firing signals to the thyristors of the inverter 4 in accordance with the output signal of the phase shifter 18.

Next, the operation of this circuit will be explained. The output signal of the speed control circuit 8 is a signal I ₂ ^* that commands the secondary current of the induction machine 5. On the other hand, the excitation current command device 9 outputs a signal I ^* _n that commands the excitation current of the induction machine 5. The primary current calculation circuit 10 calculates the equation (1) and outputs a signal I ₁ ^* that commands the primary current of the induction machine 5.

I ₁ ^* = √ ( ₂ ^* ) ² + ( ^* _n ) ² ...... (1) When the primary current command I ₁ ^* is issued in this way, the forward converter 2
The output voltage of the induction machine 5 is controlled, and the direct current, that is, the primary current of the induction machine 5, is controlled so as to be proportional to the primary current command I ₁ ^* .

On the other hand, the primary frequency of the induction machine 5 is given as follows. The slip frequency calculation circuit 14 performs the following calculation and commands the slip frequency ω ^* _s .

ω ^* _s = KI ₂ ^* (2) where K = constant (∝R ₂ ), and R ₂ = secondary resistance of the induction machine. Frequency of primary current of induction machine 5 ω ₁ ^*
is expressed as the sum of the electrical rotation frequency ω _r and the slip frequency ω ^* _s .

ω ₁ ^* = ω _r + ω ^* _s ………(3) The adder 15 calculates the formula (3) and calculates the primary frequency ω
₁ ^* Command. The output signal of the V/F converter 16 is a sine wave signal having a frequency of ω ₁ ^* . Part 1
If the phase signal is a, then a = Asin (ω ₁ ^* t) (4). Here, A is a constant and t is time. The phase calculation circuit 17 calculates the equation (5) to obtain the phase θ ^* of the secondary current and the exciting current.

θ ^* =tan ⁻¹ (I ₂ ^* /I〓) (5) The phase shifter 18 shifts the phase of the signal a by θ ^* and outputs a signal b that commands the primary frequency.

b=Asin(ω ₁ ^* t+θ ^* ) (6) In this way, the output frequency of the inverter 4, that is, the primary frequency of the induction machine 5, is controlled to be given by equation (6).

By controlling the magnitude and frequency of the primary current of the induction machine in the manner described above, the secondary current component and the excitation current component can be independently vector-controlled. Therefore,
Torque and secondary flux linkage are controlled according to set values, and the rotational speed of the induction machine is controlled.

However, the above control method has the following problems. That is, the value of the secondary resistance R ₂ changes significantly depending on the load condition, ambient temperature, etc. The range of change is 40
% to 50%. The slip frequency ω ^* _s is given by a function of the secondary resistance R ₂ as shown in equation (2). Therefore
It is necessary to change the value of K in equation (2) according to the change in R ₂ . However, conventionally this value has been given as a constant value. As a result, voltage fluctuations and torque fluctuations occur, and not only the specified voltage and torque are not produced, but also
To take this into account, the converter and motor capacity had to be increased, which was a drawback.

An object of the present invention is to provide an induction motor control device that is not affected by secondary resistance changes and is capable of stable operation from low speeds.

The present invention focuses on the fact that the primary voltage of an induction machine changes when the secondary resistance changes. Detects the change in resistance,
The actual secondary resistance value is calculated by calculating the sum with the previously set secondary resistance value, and the voltage, current,
In addition to controlling the frequency, the input signal to the amplifier is turned off in an extremely low speed range.

First, the principle of the present invention will be explained with reference to FIGS. 2 and 3. For the sake of simplicity, the equivalent circuit of an induction machine can be expressed as shown in Figure 2, ignoring the primary resistance and primary and secondary leakage inductances. Here, L _n is the excitation inductance, R ₂ is the secondary resistance,
s is slip, and I〓 ₁ , I〓 ₂ , and I〓 _n are the primary current, secondary current, and exciting current, respectively. At this time, I
₁ , I〓 ₂ , and I〓 _n are expressed in a vector diagram as shown in Fig. 3. According to the control circuit shown in FIG. 1, the magnitude of the primary current I ₁ is determined by the output signal of the primary current calculation circuit 11, and the phase is determined by the output signal of the phase shifter 18. Now, assume that the vector of the primary current I ₁ is 0A when the actual secondary resistance value and the initially planned secondary resistance value are equal. In the control circuit shown in Fig. 1, assuming that the output signal of the speed control circuit 8 does not change, the magnitude of the primary current I ₁ and the command of the slip frequency remain constant regardless of changes in the secondary resistance R ₂ . be. Now, when the secondary resistance _R2 increases, the secondary current _I2 decreases, as seen from the equivalent circuit in Figure 2.
The excitation current _I〓n increases and the vector of the primary current _I〓1 becomes 0B. As a result, the voltage increases because I _n increases. This is because magnetic flux Φ and exciting current Im
This is because there is a relationship of Φ∝Im, and a relationship of E∝Φ× _ω1 exists between the voltage E, the magnetic flux Φ, and the primary frequency _ω1 . On the other hand, when the secondary resistance R ₂ decreases, the secondary current I〓 ₂ increases, the exciting current I〓 _n decreases, and the vector of the primary current I〓 ₁ becomes 0C. The voltage decreases because I _n decreases. Like this R ₂
If the voltage changes, the voltage will fluctuate. In other words, if the voltage change is known, the change in the secondary resistance _R2 can be found.

FIG. 4 shows an embodiment of the present invention. In FIG. 4, the same members as in FIG. 1 are given the same reference numerals. 20 is a multiplier whose output signal becomes a signal for commanding the primary voltage of the induction machine 5. 21
22 is a transformer for insulating the main circuit and control circuit and extracting the primary voltage (AC voltage) of the induction machine 5; 22 is a voltage for rectifying the output voltage of the transformer 21 and detecting the magnitude of the primary voltage; Detector 23 is a subtracter that calculates the deviation between the output signal of the voltage detector 22 and the output signal of the multiplier 20. 24 is a speed discrimination circuit that discriminates whether the rotation speed is high or low. is turned on and off. Reference numeral 25 denotes an analog gate that is turned on and off by the output signal of the speed discrimination circuit 24, and is turned off at extremely low speeds and turned on at higher speeds. 26 is the subtractor 23
This is a voltage control circuit that outputs a signal corresponding to the output signal of the induction machine 5.
The value corresponds to the change in resistance. 27 is a secondary resistance setter that sets the secondary resistance value in the steady state of the induction machine 5, and 28 is the sum of the output signals of the voltage control circuit 26 and the secondary resistance setter 27 to determine the actual secondary resistance value. Adder 29 outputs a proportional signal (2)
This is a multiplier that calculates the formula and outputs the slip frequency ω ^* _s .

The operation of the circuit of FIG. 4 will be explained below. The voltage setting value is the product of secondary magnetic flux Φ and rotational speed ω × Φ
is given by Since the rotational speed ω and the primary frequency ω ₁ are almost equal, Φ×ω ₁ may be used as the voltage setting value. Since Φ is proportional to the output I ^* _n of the excitation current command device 9, when configured as shown in FIG. 4, the voltage setting value is output from the multiplier 20. A subtracter 23 calculates the deviation between the output signal of the multiplier 20 and the output signal of the voltage detector 22. The analog gate 25 is on in a higher speed range than a preset rotation speed.
If the secondary resistance R ₂ increases above the set value, the actual voltage will increase above the set value. As a result, the voltage control circuit 26 outputs a positive signal corresponding to the output signal of the subtracter 23. This signal means the amount of change from the reference value due to the secondary resistance value set in advance by the secondary resistance setting device 27. Thus adder 2
From 8, the sum of the secondary resistance value and its change is calculated, and a signal proportional to the actual secondary resistance value is output. On the other hand, if the secondary resistance R ₂ decreases below the set value, the detected voltage value will be lower than the set value, so in this case as well, a signal proportional to the actual secondary resistance value is output from the adder 28. . As a result of calculating the secondary resistance R ₂ in this manner, the multiplier 29 that calculates equation (2) outputs a slip frequency ω ^* _s corresponding to the actual secondary resistance R ₂ .

By the way, in the very low speed range, the primary frequency of the induction machine 5 becomes very low, so the transformer 21 becomes saturated, making it difficult to detect the correct voltage value. In such an extremely low speed range, the analog gate 25 is turned off by the output of the speed discrimination circuit 24, and the input signal of the voltage control circuit 26 becomes zero. In this way, the influence of voltage detection errors in the extremely low speed range can be eliminated. If the voltage control circuit 26 is configured with an amplifier having an integral element, even if the input signal becomes zero, the signal corresponding to the change in secondary resistance is held, so the adder 28
A signal corresponding to the actual secondary resistance is output from. Therefore, even in the extremely low speed range, the multiplier 29
outputs a slip frequency ω ^* _s corresponding to the secondary resistance R ₂ .

If the slip frequency ω ^* _s is calculated as described above, it will not be affected by changes in the actual secondary resistance value, and the motor can always be operated at a predetermined voltage and torque from an extremely low speed range to a high speed range.

FIG. 5 is a block diagram showing another embodiment of the invention. This is an example of application to a device that performs control equivalent to field weakening control in a DC machine, and a feedback system is added to field control. In FIG. 5, the same members as in FIGS. 4 and 5 are given the same reference numerals. Descriptions of these will be omitted here. 30 is a magnetic flux command circuit that commands the secondary flux linkage according to the rotational speed of the induction machine 5, and gradually lowers the magnetic flux command in a high speed range according to the speed. 31 is a magnetic flux control circuit that operates according to the signal deviation between the output of the magnetic flux command circuit 30 and the output of the magnetic flux calculation circuit 32, and its output signal becomes a signal for commanding the excitation current component I ^* _n of the induction machine 5. . 3
2 is an induction machine 5 by the output signal of the magnetic flux control circuit 31.
This is a magnetic flux calculation circuit that calculates the secondary magnetic flux linkage Φ, and calculates equation (7).

Φ=K'/1+TsI ^* m (7) Here, K'=constant, T=secondary circuit time constant of induction machine (∝1/R ₂ ), and s=differential operator. 36
is a divider which receives the output signal I ₂ ^* of the speed control circuit 8 and the output signal Φ of the magnetic flux calculation circuit 32 as inputs.
Since K in formula (2) is exactly K∝R ₂ /Φ,
When performing magnetic flux control, the slip frequency command ω ^* _s
When calculating , it is necessary to consider changes in the magnetic flux φ. A divider 36 is provided for this purpose.

FIG. 6 shows an example of a specific configuration of the magnetic flux calculation circuit 32. In Figure 6, 51, 52
is an operational amplifier, 53 and 54 are multipliers, and R and C are resistors and capacitors, respectively. The relationship between x, y, and z in this diagram is becomes. x is I ^* _n in formula (7), y is Φ in formula (7), Z is
Corresponding to R ₂ , the time constant CR/Z for calculation of equation (8) changes in inverse proportion to the change in Z, that is, the secondary resistance R ₂ . Therefore, according to the configuration shown in FIG. 4, the calculation of equation (7) can be performed using the time constant T that corresponds to the change in _R2 .
By doing the above, it is possible to operate at a predetermined voltage and torque from low speed to high speed, including the region where field weakening control is performed, regardless of secondary resistance changes.

In the examples described so far, a current source inverter is applied to the converter, but it goes without saying that the present invention can also be applied to a case where a converter such as a PWM inverter or a cycloconverter is used.

In addition, in FIG. 5, the voltage control circuit 26 is
When having the function of the secondary resistance setter 27, the secondary resistance setter 27 and the adder 28 can be omitted. Furthermore, if the transformer 21 is not saturated, the speed determination circuit 24 and analog gate 25 can be omitted. Furthermore, if voltage drops due to primary resistance, primary, and secondary leakage reactances are a problem when detecting voltage, if the voltage drops due to these impedances are compensated for, 1
The secondary voltage can be detected from the secondary voltage.

In the examples shown in FIGS. 4 and 5, the secondary resistance value is calculated by comparing the voltage command value and the detected value, but the secondary resistance value can also be calculated by comparing the magnetic flux command value and the detected value. Figure 7 shows an example of the control circuit in this case,
Only the portions of the previously described embodiments that are modified will be shown. In FIG. 7, the transformer 21, subtracter 23, speed discrimination circuit 24, and analog gate 25 are the same as in FIG. 4. 33 is an integrator that integrates voltage and calculates the instantaneous value of magnetic flux; 34 is a magnetic flux detector that rectifies the output signal of integrator 33 and detects the magnitude of magnetic flux;
Reference numeral 5 denotes a magnetic flux control circuit that operates according to the output signal of the subtracter 23, and its output signal becomes a signal proportional to the change in secondary resistance. The magnetic flux command signal is the excitation current command device 9
signal proportional to the output of or magnetic flux control circuit 3
Use an output signal of 0. With this configuration, it is possible to know the change in the secondary resistance R ₂ from the deviation between the magnetic flux command value and the detected value. Since the integrator 33 serves as a noise filter for the input signal, a detection signal containing no noise can be obtained, and the magnetic flux control circuit 35 outputs a signal proportional to the change in secondary resistance without being affected by noise. only can be taken out. Therefore, this is effective when the primary voltage of the induction machine 5 contains many harmonics due to commutation of the converter thyristor.

As explained above, according to the embodiments of the present invention,
In the high speed range, the change in secondary resistance is detected from the output signal of the amplifier that inputs the deviation signal between the set value of the primary voltage of the induction machine and its detected value, and the change in the secondary resistance is detected from the previously set secondary resistance value. The actual secondary resistance value is calculated by calculating the sum, and the actual secondary resistance value is calculated by turning off the input signal of the amplifier in the resistance speed range, and the slip frequency or secondary linkage is calculated by turning off the input signal of the amplifier in the resistance speed range. Since the magnetic flux is calculated, it is possible to always operate at a predetermined voltage and torque from a low speed range to a high speed range, regardless of secondary resistance changes.

As is clear from the above, according to the present invention, stable operation can be performed in all speed ranges regardless of secondary resistance changes.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional induction motor control device, Fig. 2 is an equivalent circuit diagram showing the principle of the present invention, Fig. 3 is a vector diagram showing the principle of the present invention, and Fig. 4 is a diagram showing the principle of the present invention. 5 is a block diagram of the second embodiment of the present invention, and FIG. 6 is a block diagram of the second embodiment of the present invention.
FIG. 7 is a circuit diagram of the magnetic velocity calculation circuit 32 of the embodiment shown in the figure, and FIG. 7 is a main part block diagram of the third embodiment. 2... Forward converter, 4... Inverse converter, 5... Induction machine, 7... Speed command device, 8... Speed control circuit, 9
... Excitation current command device, 10 ... Primary current calculation circuit, 13 ... Automatic pulse phase shifter, 14 ... Slip frequency calculation circuit, 15, 28 ... Adder, 16 ...
...V/F converter, 17... Phase calculation circuit, 18...
... Phase shifter, 19 ... Gate circuit, 22 ... Voltage detector, 23 ... Subtractor, 24 ... Speed discrimination circuit,
25... Analog gate, 26... Voltage control circuit, 27... Secondary resistance setter, 29... Multiplier,
30... Magnetic flux command circuit, 31... Magnetic speed control circuit,
32...Magnetic flux calculation circuit.

Claims (1)

[Scope of Claims] 1. A control command is issued to a converter that controls the voltage and frequency to drive the squirrel cage induction machine, dividing it into an excitation current component and a current component orthogonal to the excitation current component. A control device for an induction machine that controls the primary current of the induction machine, comprising: a switch that receives as input the deviation between the detected primary voltage value and the set primary voltage value of the induction machine and turns on at a predetermined rotational speed or higher; and an output of the switch. an arithmetic unit that calculates a secondary resistance change based on the signal; and a calculation condition for the slip frequency that is one element of the orthogonal current component, which is the sum of the output signal of the arithmetic unit and a preset secondary resistance setting value. 1. A control device for an induction machine, comprising: means for controlling an induction motor; 2. The control device for an induction machine according to claim 1, wherein the arithmetic unit includes a circuit that maintains a signal corresponding to a change in secondary resistance even when an input signal becomes zero. 3. Control the primary current of the squirrel-cage induction machine by controlling the voltage and frequency and issuing control commands to a converter that drives the squirrel-cage induction machine, dividing it into an excitation current component and a current component orthogonal to the excitation current component. A control device for an induction machine, comprising: subtraction means for obtaining a deviation between a detected primary voltage value and a set primary voltage value of the induction machine; and an operation for calculating a change in secondary resistance based on an output signal of the subtraction means. A control device for an induction machine, comprising: a controller; and means for using the output signal of the calculator as a calculation condition for a time constant and a slip frequency of the magnetic flux calculation among the elements of the primary current command. . 4. The control device for an induction machine according to claim 3, further comprising switch means that is turned on at a predetermined rotational speed or higher and transmits the output of the subtraction means to the arithmetic unit. 5. Claim 3 or 4, characterized in that adding means for calculating the sum of the output signal of the arithmetic unit and a preset secondary resistance setting value is provided immediately after the arithmetic unit. Induction machine control device. 6. According to any one of claims 3 to 5, the arithmetic unit includes a circuit that maintains a signal corresponding to a change in secondary resistance even if the input signal becomes zero. A control device for an induction machine.