JPH0787716B2 - Induction motor controller - Google Patents

Description

The present invention relates to a control device for an induction motor using a pulse width modulation (hereinafter referred to as PWM) inverter, and is particularly suitable for driving the motor up to a high speed range. The present invention relates to a speed control device for an induction motor.

[Conventional technology]

For a device that uses a PWM inverter to control the speed of an induction motor in a closed loop, the 60th Annual Meeting of the Institute of Electrical Engineers of Japan
As described in No.678, the output signal of the current control system, which is configured as a minor loop of the speed control system, is used as a modulation wave (voltage command), and this is supplied to the motor by comparison with this carrier wave having a constant frequency. The pulse width of the electric current is adjusted to control the electric motor current to a predetermined value.

[Problems to be solved by the invention]

In the above-mentioned prior art, when performing constant torque control, control is performed such that the voltage-frequency ratio of the electric motor is constant, and as a result, the output signal (voltage command) of the current control system increases as the speed (frequency) increases. The amplitude becomes large. On the other hand, the amplitude of the carrier wave compared with this voltage command is constant, so if the voltage command becomes larger than this amplitude, that is, if the speed exceeds a certain level, the instantaneous value of the voltage command is extended over many cycles of the carrier wave. Takes a longer time, during which PW
The M inverter output does not turn on and off, and the PWM pulse number decreases over the entire period. This significantly reduces the response of the current control system.

An object of the present invention is to secure a control device for an induction motor capable of stably driving an electric motor by sufficiently securing current responsiveness even in a high speed range.

[Means for solving problems]

The above object is achieved by providing means for increasing the frequency of the carrier when the speed of the electric motor exceeds a speed at which the pulse number of the PWM signal sharply decreases.

[Action]

As mentioned above, PW in one cycle of the output voltage of the inverter
The pulse number of the M signal decreases when the speed of the motor increases when the carrier frequency is constant. The rate of decrease in the number of pulses sharply increases when the amplitude value of the voltage command signal obtained from the current control system is equal to or higher than the amplitude of the carrier wave. However, in the present invention, since the frequency of the carrier wave is increased at the above speed or more, it is possible to prevent the decrease in the number of pulses and keep the response of the current control system excellent.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The DC power source 10 is converted into a variable voltage and a variable frequency AC voltage by the PWM inverter 20 and applied to the induction motor 40, whereby the motor 40 is driven at a variable speed. Here, the PWM inverter is a 3-phase inverter composed of 6-arm power switching elements. A rotation detector 41 is directly connected to the rotor of the induction motor 40 and generates a number of pulses proportional to the rotation speed of the induction motor 40, which is input to the speed control circuit 50. The speed command ω _R is also input to the speed control circuit 50. The speed control circuit 50 obtains the inverter angular frequency command ω ₁₀ , the exciting current command I _M0 , the torque current command I _T0 , and the rotation speed ω _N of the electric motor 40 from these inputs, and _obtains the current command generation circuit 60 and the carrier frequency command. Send to generator 112. The current command generation circuit 60 calculates the current command signals i _U0 , i _V0 , i _W0 . Each of these signals is the current of each phase detected by the current detectors 31 to 33 connected to the output terminals of the PWM inverter.
i _U , i _V , i _W are compared with each subtractor 71-73, and the difference between them is multiplied by a constant (Kc) in current amplifiers 81-83 to obtain voltage command signal E.
_U0, E _V0, E _W0, to become. The comparator 91-93 compares these carriers from the voltage command signal and the carrier wave generator 113 generates a PWM signal U _P, V _P, W _P of three layers as described later, the gate drive circuit 100 is the gate signal U corresponding to these PWM signals
_PG , V _NG , to W _PG , W _NG are generated and applied to each of the six arm power switching elements (not shown) of the PWM inverter 20. Here, the carrier wave frequency from the carrier wave generator 113 is constant in the past, but in the present invention, the carrier wave frequency is changed by the command ω _C from the carrier frequency command generator 112 according to the rotation speed ω _M of the induction motor 40. The feature is that variable control is performed.

Next, the circuit operation of FIG. 1 will be described. The speed control circuit 50 determines the rotational speed ω _M of the induction motor from the number of pulses output from the rotation detector 41, which is a simple proportional calculation. Further, from the deviation between the speed command ω _R and the rotation speed ω _M , the inverter angular frequency command ω ₁₀ and the torque current command I _T0
Is calculated. The exciting current command I _M0 is obtained from the rotation speed ω _M. As a method for obtaining these commands, for example, eye triple e-transaction (IEEE Trans)
IE-3, No. 1 (1986), p52-58, may be used, and details thereof will be omitted here.

The current command generation circuit 60 obtains a current command signal from the above-mentioned three commands ω ₁₀ , I _TO , I _{MO according} to the following equation.

_{i U0 = I 0 sinω 10 t} ... (1) i V0 = I 0 sin (ω 10 t-2π / 3) ... (2) i W0 = I 0 sin (ω 10 t-4π / 3) ... (3) However Is. The voltage command obtained from this three-phase current command signal and the deviation of the detected temporary current value of the induction motor 40 is given by the following equation.

E _U0 = Kc (I _U0 -I _U0 ) (4) E _V0 = Kc (i _V0 -i _u ) (5) E _W0 = Kc (i _W0 -i _W ) (6) This voltage command and carrier wave The operation of the comparators 91 to 93 that generate a PWM signal by comparing with the above will be described with reference to FIG. Considering this operation for the U phase, the temporary current i _U is weighted by its high-order harmonic components at the frequency of the PWM signal, and therefore the voltage command E _U0 is also weighted by the ripple caused by this high frequency. ing. By the way, the torque of the electric motor is controlled according to the fundamental wave component of the voltage command E _U0 , and in the case of constant torque control, the voltage applied to the motor is controlled so that the ratio of the frequency and the frequency is constant. The fundamental wave component of _U0 increases with velocity. Therefore, FIG. 2 shows the fundamental wave component V ₁ of the voltage command E _U0 when the speed is low and the fundamental wave component V ₂ of the voltage command E _U0 when the speed is high. Among them, in the case of a small fundamental wave component V ₁ , the number of pulses included in the half cycle T ₁ of the PWM signal a obtained as a result of comparison with the carrier is the number of carriers included therein. But,
In the PWM signal b when reaching the large fundamental wave component V ₂ , this pulse number decreases. Due to such a decrease in the number of pulses, the section in which the duty factor cannot be increased (T ₂ section of the PWM signal b) expands, and even if the voltage command signal changes, the duty factor cannot be controlled in this section, so Control response performance is reduced.
As can be seen from FIG. 2, such a decrease in the number of pulses is abrupt when the ratio of the amplitude of the fundamental wave component of the voltage command signal to the amplitude of the carrier wave (hereinafter referred to as the amplitude ratio) exceeds 1. Grows to.

FIG. 3 shows the characteristics of the fundamental wave component of the motor terminal voltage with respect to the speed ((a) figure), the characteristics of the amplitude ratio ((b) figure) and the number of pulses ((c) figure). If the speed at which the amplitude ratio becomes 1 is ω _M0 , the fundamental wave component V will have an amplitude ratio below this speed.
Almost proportional to K _H.

V = α · K _H (7) where α is a proportional constant. However, when the amplitude ratio K _H exceeds 1, it is no longer proportional to the voltage V. Moreover, in such a region, the ratio of the fundamental wave voltage V to the amplitude ratio K _H is smaller than that when the amplitude ratio is 1. For this reason, the current control system operates to compensate for this decrease in an attempt to keep the voltage / frequency ratio constant, so that the fundamental wave component of the voltage command increases at a greater rate than when the amplitude ratio is 1 or less. Will be done. Further, as the amplitude ratio becomes larger, the ratio of the fundamental wave voltage to the amplitude ratio further decreases, so that the amplitude ratio K _H rapidly increases with speed as shown in FIG. 3 (b). As a result, if the amplitude of the carrier wave is constant, the fundamental wave component of the voltage command will rapidly increase, and as shown in FIG. 3 (c), the number of pulses will rapidly decrease with speed.

FIG. 4 shows the acceleration characteristics of the electric motor when the speed command changes stepwise from zero to ω _R. Ideally, the motor accelerates in the shortest time with the acceleration time t _A determined by the equation (8).

t _A = t ₂ −t ₁ = (T _A / J) ω _R (8) where T _A is the average acceleration torque. However, as mentioned above, the pulse number decreases with speed in the high-speed region, so the current tracking (phase characteristic) deteriorates with increasing speed in such regions, and as shown by the breakdown, acceleration Time extends from t ₂ to t ₃ .

Therefore, in the present embodiment, in order to suppress the decrease in the number of pulses, a carrier frequency command generator 112 (FIG. 1) is provided so that the carrier frequency increases as the speed increases from near the speed ω _M0 where the amplitude ratio exceeds 1. Then, the carrier frequency command ω _C0 is output, and the carrier frequency of the carrier generator 113 is controlled by this.

FIG. 5 shows the case where the carrier frequency is increased when the fundamental wave component V ₂ of the voltage command is large. The number of pulses included in the PWM signal c during the half cycle T ₃ of V ₂ is Second
It increases compared to the PWM signal b in the figure. As the number of pulses increases, the range in which the conduction ratio can be controlled expands, current followability is improved, response is improved, and the response of the current control system can be kept good from the low speed region to the high speed region. .

FIG. 6 shows another embodiment of the present invention. The difference from FIG. 1 is that a carrier amplitude command generator 111 for varying the amplitude A of the carrier is added. The carrier wave amplitude command generator 111 receives the speed ω _M as input, and controls so that the carrier wave amplitude command A decreases as the speed ω _M increases. This is because when the amplitude ratio exceeds 1, the rate of increase of the voltage with respect to the amplitude ratio decreases, and the gain of the current control system apparently decreases. Therefore, the amplitude of the carrier wave is reduced in such a region and the amplitude ratio is reduced. To increase the amplification gain Kc of the current control system. In this way, the gain characteristic of the current control system is improved in this embodiment. By adding the carrier frequency command generator 112 and compensating for the response delay (phase delay) accompanying the decrease in the number of pulses, both the gain and phase characteristics are improved, and stable and fast response is achieved. A good current control system can be realized.

In the embodiment of FIG. 6, the gain of the current control system is made variable by changing the amplitude ratio of the carrier wave, but the gain Kc of the current amplifiers 81 to 83 may be increased as the speed is increased. It goes without saying that the effect can be obtained.

〔The invention's effect〕

According to the present invention, it is possible to suppress the deterioration of the response due to the phase delay of the current due to the decrease in the number of pulses of the PWM signal in the high speed region and the deterioration of the gain of the current control system, so that the response is sufficiently secured and stable even in the high speed region. Moreover, there is an effect that the electric motor can be driven.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention, and FIG.
Fig. 3 is a diagram for explaining the PWM signal generation operation, Fig. 3 is a diagram showing the speed characteristics of the fundamental wave voltage, amplitude ratio, and the number of pulses of the PWM signal of the electric motor. FIG. 5 is a diagram showing a PWM signal obtained when the carrier frequency is increased in a region exceeding the amplitude ratio 1, and FIG. 6 is a block diagram showing a second embodiment of the present invention. 20 …… PWM inverter, 31, 32, 33 …… Current detector, 40…
… Induction motor, 41 …… Rotation detector, 50 …… Speed control circuit, 81,82,83 …… Current amplifier, 91,92,93 …… Comparator, 10
0 …… Gate drive circuit, 111 …… Carrier amplitude command generator,
112 ... Carrier frequency command generator, 113 ... Carrier wave generator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sadayuki Igarashi 7-1-1 Higashi Narashino, Narashino City, Chiba Prefecture Hitachi Keiyo Engineering Co., Ltd. Hitachi, Ltd. (72) Inventor Hiroyuki Tomita 7-1-1 Higashi Narashino, Narashino, Chiba Prefecture Hitachi, Ltd. Narashino Factory (56) References JP-A-60-187292 (JP, A) JP-A-59- 188377 (JP, A) JP 60-91898 (JP, A) JP 59-44976 (JP, A) JP 53-8888 (JP, B2)

Claims (3)

[Claims] 1. A current command calculating means for calculating a current command signal so as to obtain a predetermined torque and speed of the induction motor from the command speed and the detection speed of the induction motor, and the current command signal and the detected value of the motor current. It has a current control calculation means for calculating a voltage command signal according to the deviation and a pulse width modulation means for comparing the magnitudes of the voltage command signal and the carrier wave from the carrier wave generation means to generate a pulse width modulated signal. In the controller of the induction motor for controlling the inverter by the pulse width modulation signal to control the induction motor connected to the inverter at a variable speed, the carrier wave when the amplitude of the voltage command signal is equal to or larger than the amplitude of the carrier wave. Carrier wave generating means for generating a carrier wave so that the frequency of the carrier wave increases, and the amplitude of the carrier wave when the amplitude of the voltage command signal exceeds the amplitude of the carrier wave. There control for an induction motor, characterized by comprising one or both of a carrier generating means for generating a carrier wave as decrease. 2. The carrier wave generating means generates a carrier wave so that the frequency of the carrier wave increases monotonously when the amplitude of the voltage command signal becomes equal to or larger than the amplitude of the carrier wave. The control device for an induction motor according to claim 1. 3. The carrier wave generating means is for generating a carrier wave so that the amplitude of the carrier wave monotonously decreases when the amplitude of the voltage command signal exceeds the amplitude of the carrier wave. An induction motor control device according to claim 1.