JPS60197190A - AC motor control device - Google Patents

Abstract

PURPOSE:To suppress the electric vibration by providing a reactive power detector, detecting the amount proportional to the reactive power, and varying a voltage applied to an AC motor in response to the variation in the amount. CONSTITUTION:A reactive power is detected by a reactive power detector 8, and if the reactive power increases, a command for decreasing the output voltage by a voltage controller 6 is applied to a pulse generator 4, and if the reactive power decreases, a command for increasing the output voltage is applied to the generator 4. Thus, the amount proportional to the reactive power is detected to control the output voltage, thereby stabilizing the operation of an induction motor by suppressing the unstable phenomenon.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a control device for controlling the speed of an AC motor, and in particular, when the AC motor is in an unstable state such as electrical vibration, it is possible to control the speed of the AC motor. Concerning a control device # suitable for suppressing.

[Invention σ) Background]

Conventionally, when an AC motor is driven by the control device, electrical vibrations occur under light loads, which has a negative effect on the operation of the AC motor. Particularly when a pulse width controlled inverter has a large number of pulses, the inverter's output voltage is often unstable, resulting in large electrical oscillations.

[Purpose of the invention]

The purpose of the present invention is to use an AC electric motor that generates electrical imaging to pump out an amount proportional to its reactive power, and to generate a voltage that increases by using AC as a motive in response to changes in that amount. The object of the present invention is to provide a control device that suppresses lightning-induced perturbations.

[Summary of the invention] AC motors that generate electrical vibrations have low friction loss,
Also, mechanical loss is small. It also tends to occur when the mechanical skewering force is small. This means that this is likely to occur when the reactive power is large. Electrical imaging is thought to occur when reactive power fluctuations are amplified. Therefore, it is necessary to compare the reactive power or J4'v proportional to it and control the reactive power reduction to a small value, or to perform control according to fluctuations in the reactive power. In other words, when the non-current power becomes large, the output voltage is lowered and the reactive power is controlled in the direction of decreasing. Therefore, it is sufficient to add compensation in which the voltage control system acts in the direction of reducing the reactive power in the control device that controls the AC motor.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained from the first embodiment to the third embodiment.

This embodiment is applied to a case where an induction motor is driven by an unequal pulse width controlled voltage type inverter. In this inverter, an undefined state appears in the output voltage waveform of the moat, which increases the number of pulses. This causes the induction motor to oscillate electrically. In particular, it tends to be better to carry items with less slippage.

The configuration of the present invention is shown in the first south. The DC power from the DC power source 3 is converted to AC through the inverter 2, and the AC motor 1
v Drive. This alternating current generates an output frequency and output voltage of an arbitrary inverter 2 from a frequency control circuit 5 and a voltage control circuit 6. The pulse generation circuit 4 forms a pulse train that serves as a conduction command signal for the transistors or thyristors constituting the inverter 2 based on commands 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 per cycle. However, due to the circuit configuration of the inverter 2, a potential insufficient state occurs. As the number of pulses increases, the rate of potential instability during one cycle increases, which increases the reactive power of the motor and makes the operation unstable. Furthermore, if there is ripple on the DC power supply 3, the reactive power increases and the operation becomes unstable.

In order to suppress unstable phenomena, the output voltage is controlled according to an 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 lower the output voltage, and if the reactive power decreases, a command to increase the output voltage is given to the pulse generating circuit 4.

One method of detecting an amount proportional to reactive power will be explained using FIGS. 2 and 3. The output current 21 of one phase of the inverter 2 is detected using a current transformer 91, and the output voltage 20
By extracting the integral amount of current corresponding to the phase difference (hatched portion in FIG. 2), an amount proportional to the reactive power can be detected.FIG. 6 shows a circuit for extracting the integral amount of current.

This circuit corresponds to the reactive power detection circuit 8 in FIG.

The switch 31V is closed only during the period between the signal S3 at the electrical angle of 0° (point a) of the voltage and the signal 36 at the electrical angle at which the output current crosses zero (point b), and the capacitor 30 is charged with the output current during this period. . In this case, the detection of the 0 electrical angle of the voltage can be performed based on the output voltage of the inverter 2 or the signal V of the pulse generating circuit 4. capacitor 3
The amount of charge at zero is equal to the integral 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. This voltage is multiplied by the correction amount and provided to the voltage control circuit 6.

In the figure, 7 is a soft start circuit, 10 is a speed setting device, 34 is an OR circuit, and 35 is a D-type flip 70 tube circuit.

According to this embodiment, the unstable phenomenon that occurs when an induction motor is operated with an unequal pulse width control voltage type inverter is stabilized by detecting an amount proportional to reactive power and controlling the output voltage. This has the effect of allowing you to drive.

Other specific examples for avoiding busy and unstable AC motor operation will be described for reference.

That is, in this specific example, when driving a constant V/f control type inverter, there is often disturbance in a certain frequency range at light loads, so setting the transmission frequency to about 500H2 will make it relatively stable. During normal operation, the carrier wave frequency is raised to the upper limit, the waveform rate is improved, the motor efficiency is increased,
In the event of disturbance, the carrier wave frequency is lowered to stabilize the signal.

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

One induction motor is driven by a voltage type transistor inverter consisting of a diode bridge 30, a smoothing capacitor 40, and a transistor inverter bridge 50.

For inverter control, the PWM waveform synthesis circuit 4 outputs a base signal 51 based on the speed command 10.

Here, 71 is a switching frequency command.

In the case of an asynchronous type, it is a carrier wave frequency command, and in the case of a synchronous type, it is a pulse number command for the inverter output frequency.

When the induction motor 1 causes a disturbance phenomenon under light load, the current waveform is distorted as shown in the fifth factor. Therefore, a current detector 9 is provided to monitor the waveform. 60 is a circuit that receives the phase signal 1-1 from the waveform synthesis circuit 4, and detects disturbance from K when the current value of the phase synchronized with this signal is sampled. Normally, the transistor inverter bridge 5 is controlled by the switching frequency command of 71.
The operation is performed at a switching frequency up to the allowable limit of heat loss of the transistor of 0, and the approximation to the sine wave by the PWM waveform is improved.

However, if disturbance is detected, a command is given to lower the switching frequency to a stable switching frequency obtained through testing.

According to such a specific example, as shown in No. 65j)K, there is an effect of reducing the vibration of the induction motor in the direction of transmission by 100 μP'EJK, which was 1200 μpp before the countermeasure.

Further, the current pulsation as shown in FIG. 5 is no longer observed.

〔Effect of the invention〕

According to the present invention, by detecting an amount proportional to reactive power and controlling the voltage applied to the AC motor, the AC motor can be stabilized. It has the effect of being able to take measures against vibration and pulsation of the electric motor. It is also effective against unstable phenomena caused by controlled loading.

[Brief explanation 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. Figure 3 is a circuit configuration diagram for detecting an amount proportional to reactive power, Figure 4 is a specific example of a voltage source transistor inverter, Figure 5 is a current waveform during disturbance, and Figure 6 is a diagram showing the switching frequency. FIG. 3 is a diagram for explaining the relationship with vibration. 1... AC motor, 6... Voltage control circuit, 8...
Reactive power detection - Road agent Patent attorney Akio Gao ○ 524 +.

Claims (1)

[Claims] In a control device whose purpose is to control the speed of an AC motor and which can change the frequency and voltage to be applied to the AC motor, the control device 4 detects an amount proportional to the reactive power among the output power of the position, A control device for an AC motor, characterized in that it attenuates fluctuations in reactive power by changing the voltage applied to the AC motor in accordance with the amount of variation, thereby suppressing electrical vibrations of the AC motor.