JPS6333391B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an induction motor control device that performs vector control of a squirrel cage induction motor. Recently, a control method for induction machines called vector control has been studied. This control method is one of the induction motors.
Since the secondary current is separated into an excitation current component that creates magnetic flux and a secondary current component orthogonal to it and each is controlled independently, it is possible to make the speed response performance equivalent to that of a DC machine. FIG. 1 shows a conventional example to which this control method is applied. In FIG. 1, 1 is an alternating current, and 2 is a frequency converter that converts the alternating current supplied from the alternating current power source 1 into alternating current of arbitrary frequency and voltage, such as a cycloconverter or a PWM inverter. 3 is a squirrel cage induction motor, 4 is a speed generator that detects the rotation speed of the induction machine 3, 5 is a speed command circuit that commands the rotation speed of the induction machine 3, and 6 is the output of the speed command circuit 5 and the speed generator 4. This is a speed control circuit that operates according to the signal deviation, and its output signal becomes a signal that commands the secondary current component of the induction machine 3. 7 is an excitation current command circuit that commands the excitation current component of the induction machine 3; 8 is a slip frequency calculation circuit that calculates the slip frequency of the induction machine 3 in proportion to the output signal of the speed control circuit 6; 9 is a slip frequency calculation circuit 8 and an adder that takes the sum of the output signal of the speed generator 4 and commands the primary frequency of the induction machine 3. 10 is a sine wave signal with a frequency proportional to the output signal of the adder 9 (primary frequency command signal). The output signal serves as a position reference signal for the secondary flux linkage of the induction machine 3. 11 is a current pattern circuit that commands the primary current of the induction machine 3 in accordance with the secondary current component command from the speed control circuit 6 and the excitation current component command from the excitation current command circuit 7, using the signal from the oscillator 10 as a reference; The output signal is an alternating current sinusoidal signal that commands the instantaneous value of the primary current. 12 is a current detector that detects the primary current of the induction machine 3; 13 is a current control circuit that operates according to the output signal deviation between the current pattern circuit 11 and the current detector 12; and 14 is a current control circuit that operates according to the output signal of the current control circuit 13. This is a gate control circuit that controls the gate of the thyristor of the frequency converter 2. Note that 12 to 14 show only one phase, but similar circuits exist for other phases as well. This circuit is characterized in that it controls the secondary current component and excitation current component of the induction machine in correspondence with the armature current and field current in the DC machine, respectively. Calculate the instantaneous value command signal of the primary current of the induction machine based on the sine wave magnetic flux reference signal from the secondary current component command signal and the excitation current component command signal, and control the instantaneous value of the primary current according to this signal. do. Controlling in this manner enables highly responsive and accurate torque control. However, this control circuit has the following problems. That is, the current control circuit 13
It works so that the instantaneous value of the primary current detected in step 2 matches the alternating current command signal. However, since such current control necessarily involves a control delay, when an AC signal is used, the actual current is no longer proportional to the current command signal, and the phase also lags. In particular, this tendency becomes more pronounced as the frequency becomes higher. Therefore, the actual secondary current component and excitation current component do not have values proportional to their respective command signals, which causes a problem that the torque and voltage do not reach predetermined values. As a result, high-response control of torque becomes impossible. The present invention has been made to address the above-mentioned drawbacks.
The purpose is to always match the command values and actual values of the secondary current component and excitation current component, and to
An object of the present invention is to provide a control device for an induction motor that can maintain voltage at a predetermined value. A feature of the present invention is that the current command means has a current component control function that detects the secondary current component and the excitation current component from the detected value of the primary current and controls them so that they match the respective command signals. The primary current is controlled by the current control means based on an alternating current signal that commands the primary current generated by the current command means. FIG. 2 shows an embodiment of the invention. Part number 1
Items 1 to 14 are the same as those shown in FIG. 10'
is an oscillator that outputs a sine wave signal of a frequency corresponding to the output signal of the adder 9 that commands the primary frequency, and outputs six signals to be described later. 11' is oscillator 1
0' as a reference, a first current component control circuit 16 and a second current component control circuit 17, which will be described later.
This is a current pattern circuit that outputs an alternating current signal that commands the instantaneous value of the primary current according to the output signal of the primary current. 1
5 is a current component detection circuit that detects the secondary current component I _2f and the exciting current component I _nf of the primary current of the induction machine 3;
Reference numeral 6 denotes a first current component control circuit that operates according to the deviation between I _2p , which commands the secondary current component with the output signal of the speed control circuit 6, and the secondary current component I _2f detected by the current component detection circuit 15. , 17 is a second current component control circuit that operates according to the deviation between the output signal I _np of the excitation current command circuit 7 and the excitation current component I _nf detected by the current component detection circuit 15. The detailed configuration and operation of this circuit will be explained below. FIG. 3 is a vector diagram showing the relationship between the primary current I ₁ , the secondary current component I ₂ and the exciting current component I _n . I ₁
is given by the vector sum of I ₂ and I _n , and I ₂ and I _n are orthogonal. A secondary current component I ₂ and an excitation current component I _n are determined based on the output signal of the oscillator 10'. First, the speed control circuit 6 outputs a secondary current component command signal I _2P according to the speed deviation. on the other hand,
The excitation current command circuit 7 outputs an excitation current component command signal.
I _np is output. Furthermore, the primary angular frequency ω ₁ is calculated by the following equation, as is well known. ωs=(R ₂ /M+L ₂・1/I _np )I _2p ...(1) ω ₁ =ωs+ωr ...(2) Here, ωs is the slip angular frequency, and ωr is the induction machine 3
, R ² is the secondary resistance, M is the excitation inductance, and L ₂ is the secondary leakage inductance. The calculation of equation (1) is executed by the slip frequency calculation circuit 8, and the calculation of equation (2) is executed by the adder 9. The primary angular frequency signal ω ₁ which is the output of the adder 9 is input to the oscillator 10'. Oscillator 10' outputs a sinusoidal signal of angular frequency ω ₁ . Then, the secondary current component I ₂ and the excitation current component I _n are determined using the following principle. The output signal of the oscillator 10' is a reference signal of the secondary flux linkage of the induction machine 3, and is expressed by the following formula a
Six signals of ~f are output. a=Asinω ₁ t...(3) b=Asin(ω ₁ t+120°)...(4) c=Asin(ω ₁ t+240°)...(5) d=Asin(ω ₁ t+90°)...( 6) e=Asin(ω ₁ t+210°) ……(7) f=Asin(ω ₁ t+330°) ……(8) It can be expressed as follows. Here A is the oscillator 10'
is the amplitude of the output signal. FIG. 4 shows an example of the oscillator 10'. In FIG. 4, 101 is a variable frequency oscillator that outputs a sine wave signal with a frequency proportional to the input signal, and outputs two signals a and d expressed by equations (3) and (6). Operational amplifiers 102 to 104 perform the following calculations and output signals b, c, e, and f. In addition, R,
2R, √3R, (3-√3)R, 1/2R,

[Formula] is the resistance, and the ratio of those resistances is 1:2:√
3:(3-√3):1/2:

Select as shown in [Formula]. With this configuration, six signals a to f having frequencies proportional to the input signal are output. From these signals, the secondary current component of the primary current I ₂
and excitation current component I _n are determined as follows. That is, if the primary currents (three phases) detected by the current detector 12 are i _1U , i _1V , _{i 1W} , then with reference to _FIG . ₁ t + θ) ... (13) i _1V = kI ₁ sin (ω ₁ t + θ + 120°) ... (14) i _1W = kI ₁ sin (ω ₁ t + θ + 240°) ... (15) Here, k is the detection gain of the current detector 12. The secondary current component I 2 and the exciting current component I _n are calculated from the magnetic flux position reference signal expressed by equations (3) to (8) and the primary current detection signal expressed by equations (13) to ( ₁₅ ).
is required. d・i _1U +e・i _1V +f・i _1W = 3/2kAI ₁ sinθ=
(3/2kA) I ₂ ... (16) a・i _1U + b・i _1V +c・i _1W = 3/2kAI ₁ cosθ=
(3/2 kA) I _n ... (17) By performing the calculations of equations (16) and (17), a signal proportional to the secondary current component I ₂ and exciting current component I _n of the primary current I 1 is obtained, _respectively . Can be detected. FIG. 5 shows a specific circuit of the current component detection circuit 15 for calculating equations (16) and (17). In FIG. 5, 106 to 111 are multipliers, 112, 11
3 is an operational amplifier, and R is a resistor. Operational amplifier 1
12 outputs a signal I _2f proportional to the secondary current component I ₂ , and an operational amplifier 113 outputs a signal I _nf proportional to the excitation current component I _n . The first current component control circuit 16 operates according to the deviation between the secondary current component command signal I _2P and the detection signal I _2f , and operates so that the two match, and is a signal that corrects the amplitude of the AC primary current command signal. Output x. The second current component control circuit 17 uses an excitation current component command signal I _np
It operates according to the deviation between the detection signal I nf and the detection signal I _nf , and outputs a signal y that corrects the amplitude of the alternating current primary current command signal by operating so that the two coincide. The current pattern calculation circuit 11' outputs AC signals i _1Up , i _1Vp , i _1Wp that command the instantaneous value of the primary current from the signals x and y by the following calculations. i _1Up = x・d+y・a=Bsin(ω ₁ t+α)
...(18) i _1Vp = x・e+y・b=Bsin(ω ₁ t+α+120°)
...(19) i _1Wp = x・f+y・c=Bsin(ω ₁ t+α+240°)
...(20) Here, B=√ ² + ² tanα=x/y. FIG. 6 shows the configuration of the current pattern circuit 11'.
In FIG. 6, 114 to 119 are multipliers, 12
0 to 122 are operational amplifiers, and R is a resistor. With the illustrated configuration, the primary current command signal i _1Up ,
i _1Vp and i _1Wp are output. This primary current command signal
i _iUp , i _1Vp , i _1Wp and current detection signals i _1U , i _1V , i _1W from the current detector 12 are input to the current control circuit 13 . The current control circuit 13 operates according to the current deviation of each phase, and the frequency converter 2 is controlled by its output signal. In this way, one of the induction machines 3
The next current is controlled. Control is performed as described above, and the current component is controlled so that the command signal and detection signal of the secondary current component and the command signal and detection signal of the excitation current component always match, and furthermore, both current components are Current command signal (AC signal) obtained by controlling
Since the current control circuit that controls the alternating current is operated by, the alternating current is controlled to match the command waveform, so the current is always controlled with high precision. As a result, operation with a predetermined torque and voltage can be achieved regardless of the rotational speed or load condition. In addition, in the above embodiment, when detecting two current components [calculations of equations (16) to (17)] and when calculating the AC primary current command signal [formulas (18) to (20)] [(3)
For example, in the 1970s,
The well-known conversion method as shown in Publication No. 34725,
That is, it is also possible to obtain the current component and the primary current command signal using a two-phase sine wave signal and two-phase to three-phase conversion. Next, the vector diagram shown in Figure 3 is
Next, I drew a vector diagram based on the flux linkage, but
It is also possible to draw a vector diagram based on the main magnetic flux. FIG. 7 shows a vector diagram when considering the secondary leakage inductance when it is large to some extent. The secondary current component I ₂ is the magnetic flux and the in-phase component I _2r and 90
It consists of a degree phase difference component I _2a . I _2a is a component related to torque, and the relationship between I _2r and I _2a is expressed as I _2r = ω ₂ L ₂ /R ₂ I _2a (21). FIG. 8 shows the configuration of the current component detection circuit 15 when considering secondary leakage inductance. In FIG. 8, 123-129 are multipliers, 130-1
33 is an operational amplifier, and R, Ra, Rb, and Rc are resistors.
2R has twice the resistance value of R. The output signal of the operational amplifier 130 is a signal proportional to the component _{I 2a having} a phase of 90 degrees with the main magnetic flux of I 1 in FIG. 7, and the output signal of the operational amplifier 131 is the same as the main magnetic flux of I ₁ in FIG. This is a component proportional to the phase component (I _2r +I _n ).
Operational amplifier 132 and multiplier 129 are operational amplifier 1
30 and the signal from the slip frequency calculation circuit 8, calculate the equation (21) and obtain the same phase component as the magnetic flux of _I2 .
Calculate I _2r . If a signal proportional to I _2r is found, the excitation current component I _n can be found from this signal and the output signal of the operational amplifier 131. If the current component detection circuit 15 is configured as shown in FIG. 8, the influence of secondary leakage inductance is taken into consideration, so that the primary current component can be detected with higher accuracy. In this way, even a motor with a relatively large secondary leakage inductance can be operated at a predetermined torque and voltage. As described above, according to the present invention, the AC primary current is controlled so that the secondary current component and the excitation current component always reach the set value by the function of the current component control circuit that handles the DC signal, regardless of the operating state. The magnitude and phase of the command signal are determined. As a result, even if there is a delay in the current control circuit that handles AC signals, accurate current control can be performed, allowing operation with predetermined torque and voltage.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional example, Fig. 2 is a diagram showing an embodiment of the present invention, Fig. 3 is an explanatory diagram of the operation of Fig. 2,
4 to 6 are detailed views of the components shown in FIG. 2, FIG. 7 is another operational explanatory view of the parts shown in FIG. 2, and FIG. 8 is another detailed view of the parts shown in FIG. 2. 2... Frequency converter, 3... Induction machine, 6... Speed control circuit, 7... Excitation current command circuit, 8... Slip frequency calculation circuit, 9... Adder, 10... Oscillator, 11'... ...Current pattern circuit, 13...Current control circuit, 15...Current component detection circuit, 16,
17...Current component control circuit.

Claims (1)

[Claims] 1 A frequency converter that can control the output voltage and output frequency, an induction motor driven by the frequency converter, and a primary current of the induction motor that is controlled by an excitation current component command signal that is in phase with the magnetic flux and a quadrature component. current component command means for commanding a secondary current component command signal using a direct current signal; and signal generation means for outputting a magnetic flux position reference signal generated in response to the primary frequency command signal of the induction motor. , current component detection means for detecting a secondary current component and an exciting current component of the primary current of the induction motor as DC signals based on the magnetic flux position reference signal; and detection of the secondary current component command signal and the secondary current component. a first current component control means for outputting a signal according to the deviation of the signal; a second current component control means for outputting a signal according to the deviation between the excitation current component command signal and the excitation current component detection signal; and current command means for generating an alternating current signal for commanding the primary current in response to the output signal of the second current component control means, and a current for controlling the primary current of the induction motor based on the output signal of the current command means. A control device for an induction motor, comprising a control means.