JPH0763235B2 - AC motor controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a control device for an AC electric motor, in which an output of the chip is converted into an AC by an inverse converter to energize the AC electric motor.

[Conventional technology]

As shown in FIG. 1, the AC power supply 1 is rectified by the rectifier 2,
The direct-current voltage smoothed by the capacitor 3 is made into a variable voltage by the chip 4, and the variable voltage alternating current is made by the inverse converter 8 through the smoothing circuit constituted by the reactor 6 and the capacitor 7. The AC motor 10 is energized by the output of the inverse converter 8. Reference numeral 5 is a diode that constitutes a flywheel circuit.

In such a control device, it is disclosed in Japanese Patent Publication No. 60-42719 that an unstable phenomenon occurs when a load having a vibration characteristic such as an induction motor is operated as a load, and measures for this are also disclosed. Is disclosed in. The technique disclosed herein is characterized by detecting and rectifying an AC output current, and adding a deviation amount between a voltage reference value and a feed back signal value of the AC output voltage through a low-pass filter and a voltage limiter.

In addition to this, the inverter device described in JP-A-60-170467 is also known. In this inverter device, the effective load current of the motor is detected, and the change amount thereof is feedback-controlled as a control signal.

[Problems to be solved by the invention]

The size of the control device largely depends on the inductance value of the reactor 6.

FIG. 3 shows the relationship between the capacity of the reactor 6 and the capacitor 7 and the range in which the unstable phenomenon occurs.

It can be seen from this figure that the range where instability occurs is affected not only by the capacitance of the capacitor but also by the size of the inductance. If the magnitude of the inductance is reduced, the power source impedance is reduced, an unstable phenomenon is less likely to occur, and stable operation can be obtained.

On the other hand, on the other hand, the magnitude of the DC ripple current i is expressed by the equation (1). Therefore, when the inductance is reduced, the ripple current increases and the magnetic flux change in the reactor 6 increases, resulting in a large loss.

Therefore, if the inductance is increased, the volume of the entire control device becomes considerably large.

As described above, the unstable phenomenon can be suppressed by implementing the invention shown in Japanese Patent Publication No. 60-42719, but since the current on the AC side is detected in this invention, when the load is three-phase. Requires three detectors, which is expensive.

Further, in the inverter device described in JP-A-60-170467, the effective current of the electric motor is detected and the feedback control is performed, so that the unstable current cannot be detected unless it becomes large to some extent. Therefore, the unstable phenomenon cannot be suppressed or eliminated until the unstable current is detected, and even if the above control can be performed, some instability remains as a result, and the stable operation is stable. It was hard to say that I could secure driving.

The present invention has been made in view of such points,
An object of the invention is to provide a control device for an AC electric motor, which can surely suppress even a slight unstable phenomenon and can perform stable operation.

[Means for solving problems]

The purpose of the above is to obtain the differential value output means for obtaining the differential value of the direct current waveform of the portion located on the inverse converter side of the flywheel circuit, and the output of this differential value output means to the output command value of the chip plus. It is achieved by providing an arithmetic means for controlling the temperature.

[Action]

When a load having a vibration characteristic such as an induction motor is driven by the AC power supply device, a vibration phenomenon occurs due to fluctuations in load torque, disturbances such as power fluctuations, and the like. This vibration phenomenon is an unstable phenomenon, and when it is unstable, the direct current also vibrates. The differential compensation signal of the DC current vibration signal is added to the voltage command value to obtain the command value. In this way, when the DC current increases, the DC voltage is lowered to decrease the DC current, and conversely, when the DC current decreases, the negative feedback operation is performed to increase.

〔Example〕

The embodiment of the present invention shown in FIG. 1 will be described below. The output of the speed command circuit 50 is applied to the ramp circuit 11. The ramp circuit 11 acts so as to gradually bring its output closer to the output of the speed command circuit 50. The output of the lamp circuit 11 is the frequency command
It becomes cof and voltage command cov. The frequency command cof enters the base signal generation circuit 14. Base signal generation circuit 14 frequency command
It is configured to receive cof and output base signals having a phase difference with each other in a cycle according to this command. The inverse converter 8 receives the base signal, outputs an AC voltage having a frequency according to the frequency command cof, and applies the AC voltage to the AC motor 10.

On the other hand, the voltage command cov is added to the output of the differential value output means 15 by the calculation means 16.

The differential value output means 15 is configured to receive the output of the DC current transformer 17 and output the differential value of this output.

FIG. 2 is a detailed diagram showing an example of the differential value output means and its periphery. In this figure, the output of the DC current transformer 17 is amplified by an amplifier 18, and then differentially compensated by a differential circuit composed of a resistor 20, a capacitor 21, an amplifier 19, etc., and a signal 24 is formed. An example in which it is added to cov and becomes negative feedback is shown.

Now, this DC current transformer 17 is provided in the portion where the DC load current flows in the portion located closer to the inverse converter 8 than the flywheel circuit 5. Therefore, this may be on the side of the inverse converter 8 rather than the capacitor 7.

The output of the calculation means 16 is subtracted by the subtraction circuit 12 from the output of the DC voltage detection circuit 13 that detects the voltage across the capacitor 7. The output of the subtraction circuit is the chip control signal generation circuit.
Entered in 31. The chip control signal generation circuit 31 outputs the base signal of the chip 4 so that the output of the chip 4 is proportional to the output of the subtraction circuit 12.

With such a configuration, the output of the calculating means 26 operates so as to decrease the output voltage of the chip 4 when the direct current increases, and operates so as to increase the output voltage of the chip 4 when the current decreases. Reference numeral 22 is an embodiment of a limiter for the differential signal, which prevents overcompensation if the differential signal, that is, the compensation signal, is too large.

6 and 7 are FIGS. 4 and 5 when the differential value output means 15 is not activated (that is, when the present invention is not carried out).
The figure shows the waveform of each part when the differential value output means 15 is activated (that is, the waveform of each part when the present invention is carried out, in which (a) is the voltage waveform across the capacitor 7, and (b) is one phase of the motor 10. Input current, (c) is the output waveform of the DC current transformer 17, (d)
Is the output waveform of the differential value output means 15. Compared to the waveforms (a) to (c) shown in FIGS. 6 and 7, the waveforms when the present invention is implemented, that is, the waveforms (a) to (c) in FIGS. 4 and 5.
It turns out that is much more stable.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, the calculation means may be provided on the output side of the subtractor 12. It is also possible to use a hall element or shunt resistor instead of a DC current transformer.

9 is a flywheel diode, and 23 is a resistor.

〔The invention's effect〕

As is clear from the above description, according to the present invention, since the DC load current is detected, it is possible to accurately detect even a slight change in current, and control is performed based on this detection result. Even a slight instability phenomenon can be surely suppressed, and stable operation becomes possible.

[Brief description of drawings]

1 and 2 show an embodiment of the control device of the present invention. FIG. 1 is an overall block diagram, and FIG. 2 is a circuit diagram of a main part. FIG. 3 is a graph showing the range in which the control device can be stably operated in relation to the output frequency vs. the capacitor capacity, with the inductance capacity as a parameter, FIG.
FIG. 5 is a diagram showing waveforms of respective portions when the present invention is carried out, and FIGS. 6 and 7 are diagrams when the present invention is not carried out. Reference numeral 4 is a chipper, 5 is a flywheel circuit, 6 is a reactor, 7 is a capacitor, 8 is an inverse converter, 15 is a differential value output means, and 16 is a calculation means.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Takano 7-1-1 Higashi Narashino, Narashino City, Chiba Prefecture Hitachi Keiyo Engineering Co., Ltd. (56) Reference JP-A-60-170467 (JP, A)

Claims (1)

[Claims] 1. An output of a chip is smoothed by a smoothing circuit having a capacitor and a reactor, which is given as an input of an inverse converter, and an AC motor is driven by the output of the inverse converter. In parallel, and in which a flywheel circuit is provided by connecting one end from the chip to the reactor, the differential value of the DC load current waveform of the portion located closer to the inverse converter than the flywheel circuit. A control device for an AC electric motor, comprising: a differential value output means for obtaining the differential value; and a computing means for causing the output of the differential value output means to act positively on the output command value of the chipper.