JP2544321B2 - Induction motor controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an induction motor that controls the primary current of the induction motor by dividing it into an excitation component that creates a magnetic flux and a torque component that is orthogonal thereto.

[Background of the Invention]

A vector control method is known as a high response variable speed drive method for an induction current machine. According to the vector control method, 1
Since the magnetic flux component of the next current and the torque component orthogonal thereto are independently controlled, the generated torque of the electric motor can be quickly controlled. When the vector control method is applied to the one in which an induction motor is driven by using a voltage type PWM inverter, the harmonics contained in the output voltage of the inverter are large, so that the noise generated from the motor becomes large.

In order to solve this drawback, a method has been proposed in which the magnetic flux of the electric motor is controlled in proportion to the output signal by the torque or speed control means related thereto. Since this method reduces the magnetic flux as the load becomes lighter, the noise can be reduced in the light load state. However, there are the following problems.
That is, when the rated torque is suddenly requested during operation with no load, the magnetic flux does not suddenly increase.Therefore, it takes time until the predetermined torque is generated. Creates the problem of not being. Further, when no-load operation is performed, there is also a problem that it is difficult to remove the velocity vibration generated by the disturbance of the minute vibration because the torque does not immediately come out. Although these things try to make the response high by the vector control method, they cannot fully exhibit their characteristics.

[Object of the Invention]

The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to reduce noise without deteriorating torque response even when a rated load command is issued at no load when changing magnetic flux according to torque. An object of the present invention is to provide a control device for an induction motor that can reduce the noise.

[Outline of Invention]

The present invention relates to an induction motor control device for independently controlling an exciting current component of a primary current of an induction motor and a torque current component orthogonal thereto in accordance with each command signal. A magnetic flux command circuit that changes the magnetic flux command signal of the electric motor from a predetermined value that is greater than zero and equal to or less than the rated value to a rated value according to the size up to the rated value, and the magnetic flux command signal and the magnetic flux from the magnetic flux command circuit. An exciting current command means for generating a command signal of the exciting current component from a deviation from the magnetic flux signal from the arithmetic circuit, wherein the magnetic flux calculating circuit uses the exciting current component command signal from the exciting current command means as a delay element. It is characterized in that the magnetic flux signal is inputted to calculate the magnetic flux signal.

Although the outline of the present invention is as described above, the basic idea of the present invention will be briefly described. The magnetic flux should be as large as possible for high response control. On the other hand, when the magnetic flux is large, the noise is large. As described above, improving the responsiveness and reducing the noise are in a contradictory relationship. By the way, the noise is composed of an electromagnetic noise generated in proportion to the magnetic flux, a mechanical noise generated by the rotation of the electric motor, a wind noise caused by a cooling fan, and the like.
Therefore, even if the magnetic flux is zero when there is no load, noise is generated as long as the electric motor is operating. This means that there is no point in reducing the magnetic flux to zero when there is no load, and it is sufficient to reduce the magnetic flux to such an extent that the electromagnetic noise is at a noise level equal to or lower than the noise generated by the rotation of the electric motor.

Example of Invention

 FIG. 1 shows an embodiment of the present invention.

In FIG. 1, a frequency converter 2 is a PWM inverter composed of a rectifier, a smoothing capacitor, and an inverter, which receives electric power from an AC power source 1 and outputs an AC current having a frequency and a voltage necessary for driving the induction motor 3. To do. The induction motor 3 is connected to the frequency converter 2 and driven by being supplied with an alternating current from the frequency converter 2. The speed detector 4 is mechanically directly connected to the shaft end of the induction motor 3 and detects its rotation speed. A deviation signal between the speed command signal N ^* of the speed command circuit 5 and the speed detection signal N of the speed detector 4 is input to the speed control circuit 6. Speed control circuit 6 torque component of the primary current of the induction motor 3 in accordance with the speed deviation (hereinafter referred to as torque current) and outputs a torque current command signal I _t ^* for commanding. Torque current command signal I _t ^* is the magnetic flux command circuit 7, the motion vector computing circuit 12 and is inputted to the divider 9. Magnetic flux command circuit 7
Outputs a magnetic flux command signal Φ ^* according to the input signal.
The magnetic flux command signal Φ ^* is input to the magnetic flux control circuit 8. The magnetic flux control circuit 8 calculates the command signal I _m ^* of the excitation component of the primary current (hereinafter, abbreviated as excitation current) for creating the magnetic flux according to the magnetic flux command signal Φ ^* and the actual magnetic flux signal Φ in the induction motor 3. To do. The exciting current command signal I _m ^* is input to the vector calculation circuit 12. The torque current command signal I _t ^* is divided by the magnetic flux signal Φ in the divider 9. The output signal of the divider 9 becomes the slip angular frequency signal ω _s of the induction motor 3 and the adder 10
Is input to The adder 10 adds the slip angular frequency signal ω _s and the speed detection signal N to form a primary angular frequency signal ω ₁ . The primary angular frequency signal ω ₁ is input to the oscillator 11, and the oscillator 11 outputs a sine signal and a cosine signal with a constant amplitude and an angular frequency ω ₁ . Both signals are input to the vector operation circuit 12. The vector calculation circuit 12 performs vector addition of the torque current command signal I _t ^* and the exciting current command signal I _m ^{* on} the basis of the sine and cosine signals to obtain the AC primary current command signal i ^* flowing through the induction motor 3. Calculate A signal corresponding to the deviation between the primary current command signal i ^* and the current detection signal i of the current detector 13 is input to the current control circuit 14. The current control circuit 14 outputs a signal according to the current deviation. The signal is input to the PWM control circuit 15. The PWM control circuit 15 is the current control circuit 14
And the triangular wave signal (carrier wave) are compared, and a PWM pulse for controlling the switching element of the frequency converter 2 is created. The PWM pulse of the PWM control circuit 15 controls the firing of the frequency converter 2.

 Next, the operation will be described.

Speed control circuit 6 outputs a ^* torque current command signal I _t. The magnetic flux command signal Φ ^* is determined according to the torque current command signal I _t ^* . 2 (a), (b) and (c) show examples of the characteristics, respectively. α is the rated value of the input signal (I _t ^* ),
β is the value of the magnetic flux command that commands the rated magnetic flux. Even if the input signal α becomes zero, the magnetic flux command is not zero, and the value τ weakened from the rated value β is maintained. Flux control circuit 8, the magnetic flux command signal [Phi ^* in accordance connexion, to create the excitation current command signal I _m ^*. FIG. 3 shows an example of the magnetic flux command circuit 8. The magnetic flux deviation amplifier 101 moves according to the deviation between the magnetic flux command signal Φ ^* and the magnetic flux signal Φ by the magnetic flux calculation circuit 102, and its output signal becomes the exciting current command signal I _m ^* . The magnetic flux calculation circuit 102 obtains the magnetic flux signal Φ by the following calculation.

Here, M is the exciting inductance of the induction motor 3, T ₂
Is the time constant of the secondary circuit and S is the Laplace operator. When the torque current command signal I _t ^* and the magnetic flux signal Φ are calculated in this way, the slip angular frequency ω _s is obtained by the following equation.

The operation of the equation (2) is performed by the divider 9. Next adder
At 10, the primary angular frequency signal ω ₁ is calculated from the slip angular frequency signal ω _s and the speed detection signal N.

ω ₁ = ω _s + N (3) The oscillator 11 outputs the sine signal p and the cosine signal q shown in the following equations.

The vector calculation circuit 12 calculates the vector sum of the torque current command signal I _t ^* and the exciting current command signal I _m ^{* on} the basis of the signals p and q to calculate a three-phase AC primary current command i ^* . Of these, one phase is expressed by the following equation.

i ^* = I _m ^* · p + I _t ^* · q (5) = I ₁ ^* sin (ω ₁ t + θ) (6) where Is. FIG. 4 shows a configuration example for executing the equation (5). The multipliers 103 and 104 and the adder 105 perform the calculation of the equation (5). Although configuration of the oscillator 11 and the motion vector computing circuit 12 is useful for implementing an analog circuit, when implemented in digital circuits using microcomputer, a torque current command signal I _t ^*, the excitation current command signal
With I _m ^* and the primary angular frequency signal ω ₁ as input, (7)
The AC primary current command i ^* may be obtained by executing the formula and then the formula (6). In this way, the primary current command i ^*
Is output, the current control circuit 14 works to detect the current detection signal i, that is, the primary current of the induction motor 3 is the command i.
Controlled to be proportional to ^* .

When controlled by the above-mentioned configuration, the magnetic flux of the induction motor 3 is controlled so as to be proportional to the output of the speed control circuit 6 and to maintain the threshold value even when this output is zero.

FIG. 5 shows operation waveforms at this time. (A)-(c)
Shows the characteristics in the conventional case, and (d) to (f) show the characteristics in the case of the present invention. Stepless speed command N at time t ₁ during no-load operation
^* Is added. (A) and (d) are magnetic flux signals Φ,
(B), (e) are torques generated by the induction motor 3, (c),
(F) represents the rotation speed. As can be seen from the figure, in the conventional case, the time until the time t ₃ is required to complete the acceleration. On the other hand, in the case of the present invention, since a large amount of torque is generated at time t ₁ , the acceleration end time is shortened to t ₂ . in this way,
According to the present invention, acceleration characteristics are improved.

FIG. 6 shows noise characteristics. The horizontal axis represents the rotation speed N and the vertical axis represents the noise S. Further, NL is a characteristic under no load, FL is a characteristic under rated load, a is a conventional noise characteristic, and b is a noise characteristic in the case of the present invention. From the figure, the noise at NL under no load is lower than that at FL at rated load, and there is no difference between conventional a and invention b in FL at rated load, and the minimum value in Fig. 2 is also for NL at no load. τ
It can be seen that the difference between a and b is reduced by adjusting the value of.

As can be seen from the above, according to the present invention, not only high response control can be performed, but also the induction motor can be operated with low noise.

FIG. 7 shows another embodiment of the present invention. In FIG. 7, the same symbols as in FIG. 1 indicate the equivalents. The embodiment of FIG. 7 is characterized in that the output of the speed control circuit 6 is the slip angular frequency signal ω _s . The multiplier 16 multiplies the output signal ω _s of the speed control circuit 6 and the magnetic flux signal Φ of the magnetic flux control circuit 8. The output signal becomes the torque current command signal I _t ^* . Since ω _s , Φ, I _t ^* has the relation of equation (2), the multiplier 16 Is calculated. Even with this configuration, the same effect as in the example of FIG. 1 can be obtained, and since no divider is used, it is suitable for implementation in a micro computer. That is, since the division that requires the calculation time is eliminated and only the multiplication is performed, the calculation time of the entire control system is shortened, and as a result, the high response control is easily implemented.

〔The invention's effect〕

As described above, according to the present invention, since the magnitude of the magnetic flux and the magnitude of the exciting current are controlled in proportion to the magnitude of the torque current of the electric motor, it is possible to reduce the electric motor primary current when there is no load. Therefore, there is an effect that noise can be reduced.

Further, even when the torque current is changed suddenly, the exciting current is not directly controlled, but is converted into the fluctuation of the magnetic flux by the magnetic flux calculation circuit and the exciting current command means, and then the exciting current is controlled. The exciting current rises steeply with respect to the torque current fluctuation, and the delay due to the rising of the magnetic flux is compensated for, so the torque generated by the motor obtained by the product of the torque current and the magnetic flux improves, and there is no load. However, there is also an effect that a torque characteristic with high response can be obtained with respect to a sudden change in load (torque current).

Although the frequency converter has been described as a PWM inverter, it is obvious that the same effect can be obtained even if the present invention is used in another converter, for example, one that drives an induction motor with a cycloconverter or a current source inverter. Is. Further, although the above-described embodiment has been described by using a hardware circuit such as an analog circuit, it is needless to say that the embodiment may be executed by software by a microcomputer or the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 (a).
(C) is a characteristic diagram of the magnetic flux control circuit, FIGS. 3 and 4 are detailed configuration diagrams showing an example of the parts shown in FIG. 1, FIG. 5 is an operation waveform diagram, and FIG. 6 is a rotation speed and noise. Characteristic diagram showing the relationship of
FIG. 7 is a block diagram showing another embodiment of the present invention. 2 ... Frequency converter, 3 ... Induction motor, 6 ... Speed control circuit, 7 ... Flux command circuit, 8 ... Flux control circuit, 12
... Vector operation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyoshi Muto 3-1-1 Sachimachi, Hitachi City Hitachi Research Laboratory, Hitachi, Ltd. (72) Keijiro Sakai 3-1-1 Sachimachi, Hitachi Stock Hitachi Institute of Hitachi, Ltd. (72) Inventor, Juichi Ninomiya 7-1-1, Higashi-Narashino, Narashino City, Ltd. Hitachi, Ltd., Narashino Factory, (72) Inventor, Sadayuki Igarashi, 7-1-1, Higashi Narashino, Hitachi Narashino Hitachi Keiyo Engineering Co., Ltd. In-house (56) References JP-A-57-88891 (JP, A)

Claims (1)

(57) [Claims] 1. An induction motor controller for independently controlling an exciting current component of a primary current of an induction motor and a torque current component orthogonal to the exciting current component in accordance with each command signal. To the rated value, a magnetic flux command circuit (7) for varying the magnetic flux command signal of the electric motor from a predetermined value greater than zero to the rated value to a rated value, and a magnetic flux from the magnetic flux command circuit. Command signal and magnetic flux calculation circuit (10
2) Excitation current command means (101) for generating the excitation current component command signal from the deviation from the magnetic flux signal from the magnetic flux calculation circuit, and the excitation current component command signal from the excitation current command means. An induction motor control device, wherein the magnetic flux signal is calculated by inputting it to a delay element.