JPH0224102B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a suppression circuit that suppresses harmonic zero-sequence current flowing through a power conversion device that receives AC power as input.

[Conventional technology]

FIG. 1 is a block diagram showing a conventional example of a system for driving an induction machine at variable speed using a PWM inverter supplied with power from a three-phase power source.

In Figure 1, 1 is a one-phase or three-phase AC power supply whose neutral point is grounded, 2 is an earth leakage breaker that operates by detecting zero-phase current, 3 is a known PWM inverter, and 4 is a PWM inverter 3. For example, an AC motor such as an induction machine is driven by an AC motor. here,
The housing of the PWM inverter 3 and induction machine 4 is connected to ground wires 5 and 6 at points A and B to prevent electric shock.
It is connected to the ground terminal E of the inverter 3, and the ground terminal E is grounded to the earth by a ground wire 7 having a ground resistance 8 with a low impedance Z ₀ [Ω].

That is, recently, electric leakage circuit breakers (ELBs) are increasingly being installed in power supply equipment as required by law. On the other hand, power supply equipment constituted by a power conversion device 3 such as a transistor inverter or a PWM inverter device that performs high frequency switching has come into widespread use. Since such an inverter 3 generally performs power switching at a high frequency, its input/output current includes a large amount of harmonic current. However, in such a power converter 3, there are stray capacitances (not shown) of various sizes between it and the ground, and this stray capacitance flows into the PWM inverter 3 and the casing of the induction machine 4, which is the load. In the system shown in FIG. 1, a so-called zero-sequence current i ₀ flows from grounding wire 7 to earth through grounding wires 5 and 6.
becomes. Since the earth leakage breaker 2 detects earth leakage using zero-sequence current, the earth leakage breaker 2 may malfunction due to harmonic current from the power converter 3 even though no earth leakage accident has occurred. There are cases where this happens. For this reason, it is often experienced that the power conversion device stops operating even though it is normal. In such cases, conventionally, a zero-sequence reactor for suppressing the zero-sequence current is provided at the input or output of the power converter, or an earth leakage breaker 2 is installed.
Countermeasures were taken, such as lowering the operating sensitivity.

[Problem to be solved by the invention]

However, since the zero-phase reactor provided for this purpose is generally expensive, problems arise in that the cost increases and the installation space for it increases. Further, lowering the sensitivity of the earth leakage breaker is not preferable from a safety point of view.

Therefore, an object of the present invention is to simply and inexpensively suppress the harmonic zero-sequence current caused by the ground stray capacitance of the power converter and the high frequency switching operation of the power converter.

[Means to solve the problem]

A ground leakage breaker is connected between a power converter device that has stray capacitance, is switched at high frequency, and has a ground terminal that is grounded via a power supply terminal and ground impedance, and an AC power source that supplies power to the power converter device. At the same time, the power supply terminal and the ground terminal are connected via a capacitor.

[Effect]

By absorbing the harmonic zero-sequence current generated by the power converter with the capacitor, it is possible to prevent any adverse effects on the power supply, including malfunction of the earth leakage breaker.

〔Example〕

FIG. 2 is a block diagram showing an embodiment of the invention.

The one shown in the figure is characterized in that a capacitor 9 is provided between the input (power supply) terminals R, S, and T of the PWM inverter 3 and the ground terminal E. That is, by providing the capacitor 9, the harmonic zero-sequence current i ₀ that has been flowing to the ground through the grounding wire 7 until now
Most of them are low impedance capacitors 9
This allows the zero-phase current to be returned to the PWM inverter 3 and induction machine 4, which are the generation sources of the zero-phase current, through the PWM inverter 3 and the induction machine 4. In other words, by proactively providing the capacitor 9 on the input side of the power conversion device 3, the harmonic zero-sequence current _{i 0} that conventionally passed through the earth leakage breaker 2 via the grounding wire 7 → earth → power supply 1 Since the harmonic zero-sequence current i ₀ is significantly reduced, the adverse effect on the power supply due to the harmonic zero-sequence current i 0 is reduced, and it is possible to prevent the earth leakage breaker from malfunctioning.

FIG. 3 is a block diagram showing another embodiment of the invention. This is an example in which only the T phase of the power supply 1 is grounded (one phase grounded), and the capacitor 9 is connected to the T phase (ground phase) and the E terminal (ground terminal).
It differs from the one shown in FIG. 2 only in that it is provided between the two, but is basically based on the same idea as in FIG. 2, and the effect obtained is also the same.

〔Effect of the invention〕

According to this invention, by providing a capacitor on the input side of the power converter, harmonic zero-sequence current leaking from the power converter and its load is returned to its source without passing through the power supply and earth leakage breaker. This provides an advantage in that it is possible to easily and inexpensively solve the problems of the power supply being adversely affected by this zero-sequence current and the earth leakage circuit breaker malfunctioning.

Note that the present invention can be applied not only to a system in which an induction machine is driven by a PWM inverter, but also to the case of suppressing the zero-sequence current of a power conversion device that generally generates harmonic current.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional example of a system for driving an AC motor using a PWM inverter, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a block diagram showing a conventional example of a system for driving an AC motor using a PWM inverter.
The figure is a block diagram showing another embodiment of the invention. Symbol explanation, 1...AC power supply, 2...Earth leakage breaker, 3...PWM inverter (power converter),
4...AC motor (induction machine), 5-7...ground wire,
8...Grounding resistance, 9...Capacitor.

Claims (1)

[Scope of Claims] 1. A power converter having a stray capacitance, switched at high frequency, and having a power terminal and a ground terminal that is grounded via ground impedance, and an AC power supply that supplies power to the power converter. A zero-sequence current characterized in that an earth leakage breaker is connected between the power supply terminal and the ground terminal, and a capacitor is connected between the power supply terminal and the ground terminal, and the harmonic zero-sequence current is absorbed by the capacitor. Inhibitory circuit. 2. In the zero-phase current suppression circuit according to claim 1, the alternating current power source is multi-phase.
A zero-sequence current suppression circuit characterized in that when a phase is grounded, the power supply terminal corresponding to the ground phase and the ground terminal are connected via a capacitor.