JPH07106078B2 - AC motor controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling the speed of an AC motor, and particularly when the AC motor is in an unstable state such as electric vibration, the unstable state is suppressed. The present invention relates to a control device suitable for

[Background of the Invention]

Conventionally, when an AC motor is driven by the control device, it has a drawback that it electrically vibrates when the load is light and adversely affects the operation of the AC motor. In particular, when the pulse width control inverter has a large number of pulses, the output voltage of the inverter has a large rate of being in an indefinite state, so that electrical vibration becomes large.

[Object of the Invention] An object of the present invention is to suppress electric vibration by detecting an amount according to the reactive power in an AC motor causing electric vibration and controlling so as to reduce the fluctuation of the amount. It is to provide a control device.

[Outline of Invention]

The AC motor that causes electrical vibration has small friction loss,
It also tends to occur when the mechanical output is small. This means that it tends to occur when the reactive power is large. It is considered that electrical vibration is caused by amplification of fluctuations in reactive power. In order to suppress this electric vibration, an amount corresponding to the reactive power may be detected and control may be performed so as to suppress the fluctuation of the reactive power. That is, the present invention is a control device for an AC electric motor that changes the output frequency and the output voltage to control the speed of the AC electric motor, and a detecting means for detecting an amount of the output electric power of the control device according to the reactive power, and the detecting means. It is also characterized in that it comprises control means for controlling the output voltage so that the fluctuation becomes small when the detected amount due to the fluctuation.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS.

The present embodiment is applied to the case where the induction motor is driven by the unequal pulse width control voltage type inverter. When the number of pulses is increased by this inverter, the state where the potential is uncertain appears in the output voltage waveform. Therefore, the induction motor causes electric vibration. Especially when the slip is small, there is a marked tendency.

The structure of the present invention is shown in FIG. The DC power from the DC power supply 3 is converted into AC through the inverter 2 and drives the AC motor 1. This alternating current causes the frequency control circuit 5 and the voltage control circuit 6 to generate an output frequency command and an output voltage command of the arbitrary inverter 2. The pulse generation circuit 4 forms a pulse train which becomes a conduction command signal of a transistor forming the inverter 2 or a thyristor according to a command received from the frequency control circuit 5 and the voltage control circuit 6. This pulse train is formed so that the output current approaches a sine wave. In order to make the output current as close to a sine wave as possible, it is necessary to increase the number of pulses in one cycle. However, due to the circuit configuration of the inverter 2, an undefined potential state occurs. The larger the number of pulses, the larger the ratio of the potential indeterminate state during one cycle, which increases the fluctuation of the reactive power of the motor and makes the operation unstable. Also, when the DC power supply 3 is loaded with ripples, the fluctuation of the reactive power is increased, and the operation becomes unstable.

In order to suppress the unstable phenomenon, the output voltage is controlled according to the amount proportional to the reactive power. That is, if the reactive power increases, the voltage control circuit 5 gives a command to the pulse generating circuit 4 to decrease the output voltage, and if the reactive power decreases, it gives a command to increase the output voltage to the pulse generating circuit 4.

One method of detecting the amount proportional to the reactive power will be described with reference to FIGS. 2 and 3. The one-phase output current 21 of the inverter 2 is detected by using the current transformer 9, and the integrated amount of the current corresponding to the phase difference from the output voltage 20 (hatched portion in FIG. 2) is taken out to obtain the reactive power. A proportional amount can be detected. FIG. 3 shows a circuit for extracting the integrated amount of this current. This circuit corresponds to the reactive power detection circuit 8 in FIG. The switch 31 is closed only for the period of the signal 33 of the electrical angle of 0 ° (point a) and the signal 36 of the electrical current (point b) at which the output current is zero-crossed, and the capacitor 30 is charged with the amount of the output current of this period. To do. In this case, the electrical angle of 0 ° can be detected based on the output voltage of the inverter 2 or the signal of the pulse generating circuit 4. The charge collection amount of the capacitor 30 is equal to the integrated value of the output current from point a to point b in FIG. Therefore, the charging voltage of the capacitor 30 is proportional to the reactive power. The voltage control circuit 6 applies a correction amount to this voltage.
Give to.

In the figure, 7 is a soft start circuit, 10 is a speed setter,
34 is an OR circuit and 35 is a D-type flip-flop circuit.

According to the present embodiment, by stabilizing the induction motor by detecting the amount of the instability phenomenon that occurs when the induction motor is operated by the unequal pulse width control voltage type inverter, in proportion to the reactive power and controlling the output voltage. There is an effect that you can drive to.

Next, another specific example for avoiding an unstable operating state of the AC motor will be described for reference.

In other words, in this specific example, when driving a V / f constant control type inverter, there is often a tune-up in a certain frequency range when the load is light.Therefore, when the carrier frequency is set to about 500 Hz, it becomes relatively stable. At the time, the carrier frequency is raised to the upper limit to improve the waveform ratio to improve the motor efficiency, and at the time of irregularity, the carrier frequency is lowered to stabilize.

A specific example will be described below with reference to FIG.

The induction motor 1 is driven by a voltage source transistor inverter including a diode bridge 30, a smoothing capacitor 40, and a transistor inverter bridge 50. In the inverter control, the PUM waveform synthesis circuit 4 outputs the base signal 51 from the speed command 10.

Here, 71 is a switching frequency command. In the asynchronous type, it becomes a carrier frequency command, and in the synchronous type, it becomes a pulse number command for the inverter output frequency.

When the induction motor 1 causes a disturbance phenomenon when the load is light, the current waveform is distorted as shown in FIG. Therefore, a current detector 9 is provided to monitor the waveform. Reference numeral 60 denotes a circuit that receives the phase signal 11 from the waveform synthesizing circuit 4 and samples a current value of a phase synchronized with the phase signal 11 to detect irregularities. Normally, according to the switching frequency command of 71, operation is performed at the switching frequency up to the allowable limit of the heat loss of the transistor of the transistor inverter bridge 50, and the approximation to the sine wave by the PUM waveform is improved.

However, if a disturbance is detected, a command is issued to lower the switching frequency to the stable switching frequency obtained by the test.

According to such a concrete example, as shown in FIG. 6, the vibration in the rotation direction of the induction motor is 100 μm when it is 1200 μpp before the countermeasure.
It has the effect of reducing to μpp. Further, the current pulsation is no longer seen as shown in FIG.

〔The invention's effect〕

According to the present invention, the amount corresponding to the reactive power is detected, the output voltage is controlled so that the fluctuation is reduced, and the fluctuation of the reactive power is controlled so as to suppress the fluctuation of the AC motor. Therefore, there is an effect that it is possible to take measures against vibration and pulsation of the AC motor when the AC motor is under a light load or the friction loss is small. Moreover, it is also effective against an unstable phenomenon caused by the control device.

[Brief description of drawings]

FIG. 1 is a configuration diagram when an AC motor is driven by an inverter equipped with an electrical vibration suppression circuit according to one embodiment of the present invention, and FIG. 2 is a circuit configuration diagram for detecting an amount proportional to reactive power. FIG. 3 is a circuit configuration diagram for detecting an amount proportional to reactive power, FIG. 4 is a specific example showing a voltage-type transistor inverter, FIG. 5 is a diagram showing a current waveform during disturbance, and FIG. 6 is a switching frequency and vibration. It is a diagram for explaining the relationship with. 1 ... AC motor, 6 ... Voltage control circuit, 8 ... Reactive power detection circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motonobu Hattori 7-1-1 Higashi Narashino, Narashino City, Chiba Prefecture Hitachi Narashino Factory (72) Inventor Nobuyoshi Muto 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Co., Ltd. Hitachi Research Laboratory, Hiritsu Manufacturing Co., Ltd. (56) Reference JP-A-56-141798 (JP, A) JP-A-54-150625 (JP, A)

Claims (3)

[Claims] 1. A control device for an AC electric motor for controlling the speed of an AC electric motor by changing an output frequency and an output voltage, and detecting means for detecting an amount of output power of the control device according to reactive power, and the detecting means. A control device for an AC electric motor, comprising: a control means for controlling an output voltage so that the fluctuation is reduced when the detected amount by the fluctuation. 2. The control means lowers the voltage applied to the AC electric motor when the amount detected by the detecting means increases, and supplies the AC electric motor when the amount detected by the detecting means decreases. The control device for an AC electric motor according to claim 1, wherein the control device is configured to increase the voltage. 3. The control device for an AC electric motor according to claim 1, wherein the detection means detects a value corresponding to the unscented power based on a reactive current component of an output current of the control device.