JPH0834704B2 - Motor control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device provided with means for reducing the influence of a current at the time of starting an AC servo driver on a power supply.

2. Description of the Related Art In general, when an AC servo driver or the like is connected to a commercial power source having a high power source impedance, a large current at the time of starting the motor may cause lighting flicker in a power line connected to the same system.

On the other hand, conventionally, when flicker is significant, there is a method of reducing the flicker by providing a means for lowering the limit level of the starting current.

Hereinafter, a conventional motor control device will be described with reference to the drawings.

FIG. 3 shows the configuration of a conventional motor control device. In FIG. 3, 1 is an AC power source, 2 is a rectifying diode, 3 is a smoothing capacitor, 4 is a motor drive circuit, 5 is a motor, and 6 is a current limiting circuit. Limit to the set current value. The current may be detected by detecting the line current of the motor 5. A current limit value setting circuit 8 sets the limit value of the current limit circuit 6. This limit is usually fixed. Reference numeral 9 is a setting circuit for externally varying and reducing the current limit setting value. 10 is a lamp for lighting.

The operation of the motor control device configured as described above will be described below. First, the setting circuit 9 is set to have the minimum resistance value, and the setting circuit 8 is set to the allowable current value of the motor drive circuit. Since the starting current of the motor in this case is large, flicker may occur in the lighting lamp 10 connected to the AC power line. In such a case, if the resistance value of the external setting circuit 9 is increased, the setting value of the setting circuit 8 is decreased, the limiting current value is decreased, and the input current from the power supply is also decreased, so that the illumination flicker is reduced. To be done.

The problem to be solved by the invention is, however, that in the method of lowering the current limit value itself, the starting current is constantly reduced, the motor torque is reduced, the instantaneous torque and the starting torque are also reduced, and the transient torque during starting is reduced. However, there is a drawback in that the torque becomes insufficient when the operation is required or during repeated operation for a short time.

In view of the above problems, the present invention provides a motor control device having a function of effectively reducing flicker without reducing transient torque and starting torque.

Means for Solving the Problems In order to solve the above-mentioned problems, the motor control device of the present invention, when the voltage of the smoothing capacitor is lowered, detects the voltage fluctuation of the smoothing capacitor by a differentiating circuit that detects a variation of the voltage. It is provided with a voltage drop prevention circuit for lowering the current limit value so as to suppress the drop.

Action The present invention detects, when the voltage of the smoothing capacitor is lowered by the above means, that the voltage is about to be lowered by the differentiating circuit that detects the fluctuation, and detects the current depending on the value of the current flowing from the smoothing capacitor. By lowering the limit value, only the variation is detected regardless of the absolute value of the input power supply voltage, and the voltage drop of the smoothing capacitor is suppressed. Further, it is possible to effectively reduce the flicker by lowering the current limit value for the frequency component of about 1 Hz to 60 Hz in which the flicker is likely to be felt among the fluctuation frequency components.

Embodiment Hereinafter, a motor control device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a motor control device according to an embodiment of the present invention. In FIG. 1, 1 is an AC power supply,
Reference numeral 2 is a rectifying diode, 3 is a smoothing capacitor, 4 is a motor drive circuit, 5 is a motor, and 6 is a current limiting circuit, which are the same as in the conventional example of FIG. A voltage drop prevention circuit 7 is composed of a differentiating circuit 7a and an integrating circuit 7b, and acts as a bandpass filter.

The operation of the motor control device configured as described above will be described. A concrete example of the voltage drop prevention circuit 7 is shown in FIG. In FIG. 2, A1 is a circuit for detecting the voltage V _DC of the smoothing capacitor 3, and A2 is a differentiating circuit and an integrating circuit for the detected voltage. In this circuit, when the detection voltage V _DC fluctuates so as to decrease, the low-frequency fluctuation component and the high-frequency fluctuation component are cut by the differential integration characteristic, and the output decreases due to the fluctuation component of the passing frequency component. Operate. If V _DC increases, the output will not change. This output acts on the current limiting circuit 6 to lower the separately set current limit. Therefore, only when the voltage of the smoothing capacitor 3 is about to decrease, the current limit value decreases and the decrease in voltage is suppressed. When the motor is locked and the voltage drops, or when the input voltage drops gently, the current limit value does not drop and the starting torque does not fluctuate.

Further, the flicker can be effectively reduced by selecting the pass component of the filter as a frequency component in which flicker is likely to be felt, for example, about 1 Hz to 60 Hz.

As described above, the present invention detects fluctuations in the voltage of the smoothing capacitor, reduces the limit value of the current limiting circuit only when the voltage is about to decrease, and suppresses the decrease in the voltage of the smoothing capacitor. The flicker can be effectively reduced without effectively reducing the starting torque of the motor by effectively acting on the fluctuation of the frequency component where the flicker is likely to occur.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a motor control device according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a voltage drop prevention circuit in FIG. 1, and FIG. 3 is a configuration diagram of a conventional motor control device. 1 ... AC power supply, 2 ... Rectifying diode, 3 ... Smoothing capacitor, 4 ... Motor drive circuit, 5 ... Motor, 6 ...
… Current limit circuit, 7 …… Voltage drop prevention circuit, 7a …… Differentiation circuit, 7b …… Integration circuit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenichi Ohara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Takashi Doi, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 56) References JP-A-61-293198 (JP, A)

Claims (1)

[Claims] 1. A rectifying diode connected to an AC power supply,
A smoothing capacitor that smoothes the output of the rectifying diode, a drive circuit that drives the motor with the voltage of the smoothing capacitor as an input, a differentiation circuit that detects a variation in the voltage of the smoothing capacitor, and the output of the differentiation circuit is integrated. And a current limiting circuit that detects an output voltage from the integrating circuit and a line current to the motor and limits a current to the motor. The voltage dropping prevention circuit includes the smoothing capacitor. The motor control device is configured to reduce the current limit value of the current limiting circuit to suppress the voltage drop of the smoothing capacitor only when the voltage of the above voltage drops.