JPH05316747A - Grounding protection system for motor - Google Patents

Abstract

PURPOSE:To improve system efficiency by splitting voltage by a capacitor and grounding the midpoint potential of the DC voltage circuit through a resistor, and by detecting the grounding of the system by the current change by the grounding resistor. CONSTITUTION:DC voltage is obtained by rectifying a 3-phase AC power source 7 by a converter 1. The DC voltage is smoothened by a smoothing capacitor 2, and the DC voltage is stabilized simultaneously. The DC voltage is PWM- modulated by an inverter 3, and the AC voltage is supplied to a load 8. The midpoint potential of the DC potential is produced by splitting-into-two capacitors 4 and 5 inserted in the DC voltage circuit, and a grounding resistor 9 is inserted between its midpoint potential and the ground. Moreover, grounding is detected by a grounding detector 6 arranged in series to the grounding resistor 9. Since no resistors are used in the DC voltage circuit, in this way, no resistor loss is produced. Accordingly, the system efficiency is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground protection method for an AC variable speed drive system for a mill using an inverter power supply.

[0002]

2. Description of the Related Art Conventionally, as described in Japanese Patent Laid-Open No. 55-141920, a DC voltage between a converter and an inverter is divided into two by a resistor, and the middle point is directly grounded to detect grounding. It was

[0003]

The above-mentioned conventional technique has a problem that resistance is generated in the DC circuit because resistance is inserted in the DC circuit, and system efficiency is reduced.

[0004]

In the present invention, the neutral point of the DC voltage is set to the middle point of the ground detection capacitor, and the influence of the third harmonic component flowing in the normal state is reduced. Further, by separating from the smoothing capacitor, the circuit constant can be freely set only for the ground detection circuit, so that the circuit can be optimized.

[0005]

The converter rectifies a three-phase AC power source to generate a DC voltage. The smoothing capacitor smoothes the pulsating flow component included in the DC voltage of the converter. Furthermore, the fluctuation of the DC voltage is reduced. The inverter generates a PWM-modulated output voltage according to a switching signal from the control device. The ground detection capacitor divides the DC voltage into two and outputs the neutral point of the DC voltage. The ground detection resistor is inserted between the neutral point of the ground detection capacitor and the ground, and flows the ground current. The ground detector detects the ground current and detects the ground of the system.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

The three-phase AC power supply 7 is rectified by the converter 1 to obtain a DC voltage. The DC voltage is smoothed by the smoothing capacitor 2, and at the same time, the DC voltage is stabilized.
The DC voltage is PWM-modulated by the inverter 3 and the AC voltage is supplied to the load 8. The midpoint potential of the DC voltage is generated by the two-divided capacitors 4 and 5 inserted in the DC voltage circuit, and the ground resistance 9 is inserted between the midpoint potential and the ground. Further, the grounding detector 6 inserted in series with the grounding resistor detects the grounding.

In a system in which a plurality of inverters are connected to one converter as shown in FIG. 3, the ground of the system can be detected by a single ground detection circuit provided at the converter output. The ripple effect is great. Further, since the capacitor of the ground detection circuit can have a smaller capacity than the smoothing capacitor, it is easy to replace parts and maintainability is excellent.

[0009]

According to the present invention, since no resistance is used in the DC voltage circuit, resistance loss does not occur and the efficiency of the system can be improved. Also, since the amount of heat generated is small, the ground detection circuit can be housed in the panel, and space can be saved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

FIG. 3 is a circuit diagram of an embodiment of a common converter system.

[Explanation of symbols]

1 ... Converter, 2 ... Smoothing capacitor, 3 ... Inverter, 4, 5 ... Divided capacitor, 6 ... Ground detector, 7 ...
Three-phase AC power supply, 8 ... Load, 9 ... Ground resistance.

Claims (2)

[Claims] 1. In an AC variable speed drive system for a mill using an inverter power supply, the midpoint potential of a DC voltage circuit is resistively grounded by voltage division by a capacitor, and the system is grounded by a change in current flowing through the grounding resistance. Motor ground protection method characterized by detection. 2. A common converter system in which a plurality of inverters are connected in parallel to one converter,
A motor ground protection method that divides the common converter output voltage into two with a capacitor, grounds the middle point, and detects the ground.