JPS61251419A - Zero current detection of variable frequency inverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a variable frequency inverter with a ground fault detection device.

[Background of the invention]

Conventionally, VC, a method for detecting ground faults in variable frequency inverters, uses a current transformer or a zero-phase current transformer from the AC line to detect the current of each phase, as described in Japanese Patent Application Laid-open No. 79236/1983. A method is used to detect zero-sequence current caused by unbalance. Fig. 2 shows a basic block diagram of a conventional ground fault detection device using a zero-phase current transformer, and Fig. 3 shows the output current waveforms (υ, Iv, Iw) of a variable frequency inverter. During normal operation, the output currents Io, Iv, and Iw are balanced and the zero-sequence current is kept at zero, but in the event of a ground fault, ■. .

An imbalance occurs between Iv and Iw, and this is detected by the zero-phase current transformer 4. However, during normal operation, the output currents I+y, Iv, and Iw have a third
As shown in Figures (a), (b), and (C), ripples during commutation operation of the inverter 3 are superimposed, so the resulting zero-sequence current has a zero-sequence current as shown in Figure 3 (d). As such, the ripple portion does not cancel out and remains. This ripple current flows to the ground through the system cable and the ground-to-ground capacitance 7 of the induction motor 6, so the zero-phase current transformer 4
This means that ripple current is constantly flowing through. Conventionally, there has been a problem that this ripple current is applied to the ground fault detector and causes false detection.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a zero-sequence current detection method for a variable frequency inverter device that prevents erroneous detection due to the shadow of an inverter when detecting a zero-sequence current of a variable frequency inverter.

[Summary of the invention]

The present invention detects current unbalance using a current transformer provided in the DC line of a variable frequency inverter, thereby making it possible to reliably detect a load ground fault without being affected by the inverter's ripple current.

[Embodiments of the invention]

Fig. gi shows a basic block diagram of the ground fault detection method according to the present invention, and Fig. 4 shows the DC line current. The input side lines of the inverter 30, that is, the direct # and P N lines, pass through the same current transformer 9Vc so that the magnetic flux generated by each line current cancels each other, and this current transformer 9 detects the flow imbalance. and performs ground fault detection. During normal operation, the DC P line is connected to Fig. 4 (a).

A current as shown in (b) K flows through the N line.

Since the P line current and the N line current are balanced, when two lines pass through the same current transformer 9 so that their magnetic fluxes cancel each other out, the current detected by the current transformer 9vc is as shown in Fig. 4 (c ) VC becomes 0 as shown.

Furthermore, at the time of a ground fault 1C, a ground fault current flows, causing imbalance in the IE current of the DC PN line, and a current is induced in the current transformer 9. By detecting this current, ground faults can be detected. Since ripple current due to the commutation operation of the inverter does not flow through the DC PN line VC, the ground fault detection device 5 is not affected by the pull current, which is a problem in the conventional method. 1 is an AC power supply, 2 is a converter device, 8! l
'i reactor.

〔Effect of the invention〕

According to the present invention, it is possible to prevent erroneous detection by a ground fault detection device due to ripple current in an inverter device, and to perform ground fault detection reliably.

[Brief explanation of the drawing]

FIG. 1 is a basic block diagram of a ground fault detection method according to an embodiment of the present invention, FIG. 2 is a basic block diagram of a conventional ground fault detection method in which a zero-phase flow filter is connected to an AC line, and FIG. The figure is a diagram showing the output current waveform of the inverter device, and FIG. 4 is a diagram showing the waveform of the DC line current. 1... AC power supply, 2... converter device, 3...
Inverter device, 4...Zero-phase current transformer, 5...Ground fault detection device, 6...Load (induction motor), 7...Capacity between cable and load to ground, 8...Reactor, 9...
·Current transformer.

Claims (1)

[Claims] 1. In an inverter device that uses semiconductor elements to convert direct current to alternating current and supply it to a load,
A zero-sequence current detection method for a variable frequency inverter, characterized in that the zero-sequence current detection method of a variable frequency inverter is characterized in that it is used by passing through the same current transformer to detect current unbalance.