JPH0686563A - Power conversion apparatus - Google Patents

Abstract

PURPOSE:To suppress grounding current and to reduce insulation to the earth and stabilize the circuit operation of a power conversion apparatus by directly grounding a DC intermediate circuit. CONSTITUTION:A power conversion apparatus includes a converter 1, an inverter 2 and a DC intermediate circuit 3 that is provided between the converter 1 and the inverter 2. The DC intermediate circuit 3 consists of DC smoothing capacitors 31 and 32, and a connection point Q between those capacitors is grounded through a fuse 6 which is blown by grounding current or a parallel connection of a fuse and a low-resistance resistor which reduces an earth capacitance even after blowing of the fuse.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting direct current into alternating current.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional NPC (neutral point potential fixing system) three-phase bridge inverter system power conversion device. Conversion Study Group Material SPC-91-
37 (published June 21, 1991, The Institute of Electrical Engineers of Japan), page 113. In the figure, 1 is a converter for converting alternating current to direct current, 2 is an inverter composed of GTO (gate turn-off thyristor) for converting direct current to alternating current by a control device (not shown), and 3 is a series connection for absorbing ripple components. The DC intermediate circuit 4 including the DC smoothing capacitors 31 and 32 is a DC smoothing reactor for suppressing high frequency components, and 5 is a load such as an induction motor.

Next, the operation will be described. Converter 1
DC output of the DC smoothing reactor 4 and the DC intermediate circuit 3
Thus, the high frequency component and the ripple voltage contained in the DC output are suppressed, smoothed, and added to the inverter 2.
The inverter 2 converts the DC voltage supplied from the inverter 1 into an AC voltage based on the control by the control device,
This AC voltage is supplied to the load 5. In such a power converter, the connection point Q of the DC smoothing capacitors 31 and 32 of the DC intermediate circuit 3 is directly grounded. This is because by reducing the ground capacitance of the entire circuit, the zero-phase current (ground leakage current) is suppressed and stabilized, and the ground insulation strength is reduced.

[0004]

In the conventional power converter configured as described above, when the P or N potential point in FIG. 5 has a ground fault, the ground fault is detected by an earth leakage breaker or the like. Immediately stop the converter 1 and the inverter 2. On this occasion,
Since the residual energy of the DC smoothing capacitors 31 and 32 is released in the short circuit circuit connecting the ground fault point P or N and the connection point Q, the discharge current causes serious damage to the ground fault point or the DC smoothing capacitor. There is a problem that 31, 32 may be destroyed.

The present invention has been made in order to solve the above-mentioned problems, and enables direct grounding of a DC intermediate circuit, reduces damage to a ground fault point, and suppresses a DC smoothing capacitor. An object of the present invention is to provide a power conversion device that can prevent destruction.

[0006]

A power conversion device according to the present invention includes a converter for converting an alternating current into a direct current, an inverter for converting a direct current generated by the converter into an alternating current, and an inverter interposed between the inverter and the converter. The DC intermediate circuit has a DC smoothing capacitor, and the DC intermediate circuit is grounded via a fuse or a parallel connection body of a fuse and a resistor. The DC intermediate circuit comprises at least one series connection body composed of a DC smoothing capacitor connected in series, and the intermediate connection point of the DC connection smoothing capacitor connected in series is a fuse or a parallel connection body of a fuse and a resistor. It is grounded through. Further, the DC intermediate circuit comprises a DC smoothing capacitor, and either the positive terminal or the negative terminal of the DC smoothing capacitor is grounded via a fuse or a parallel connection body of a fuse and a resistor.

[0007]

In the power converter according to the present invention, the DC intermediate circuit is grounded via the fuse or the parallel connection body of the fuse and the low resistance body, so that the residual energy of the DC smoothing capacitor is released when the DC intermediate circuit is grounded. The ground fault current is promptly cut off by the current limit.

[0008]

EXAMPLES Example 1. Embodiment 1 of the present invention will be described below with reference to the drawings. 1, the same reference numerals as those in FIG. 5 indicate the same parts, and the description of these same parts will be omitted.
A fuse 6 is connected between the ground point Q of the DC intermediate circuit 3 and the ground.

Next, the operation will be described. When the P or N potential point of the DC intermediate circuit is ground-faulted, a ground fault current flows from the ground fault point to the ground, the fuse 6 and the connection point Q, and its magnitude and waveform are the voltage across the DC smoothing capacitor terminals. , Capacitance, and loop inductance of the short circuit. When the voltage and capacitance between the terminals of the DC smoothing capacitors 31 and 32 are 3 KV and 20 mF, respectively, and the loop inductance is 50 μH, the ground fault current is an oscillating current with a peak value of 60 KA and a period of 6.28 ms, but between the Q point and the ground. Since the fuse 6 connected to the fuse 6 performs the current-cutting arc by the ground-fault current to perform a current-limiting action, the ground-fault current is interrupted as shown in FIG. 2 long before the peak value of 60 KA is reached. It Therefore, the ground fault point is not significantly damaged by the residual energy of the DC smoothing capacitors 31 and 32. Further, since the discharge current of the DC smoothing capacitor is also cut off by the current limiting, the capacitor is prevented from being broken.

In the first embodiment, the fuse 6 is used to cut off the ground fault current, but when the fuse 6 is blown, the DC intermediate circuit 3 is disconnected from the ground. Normally, the operation of the power converter is stopped by the detection of the ground fault current, so there is no problem even if the fuse 6 is disconnected from the ground by being blown. However, the second embodiment shown in FIG. 3 is applied to the power conversion device that needs to be connected to the ground even after the fuse is blown.

Embodiment 2. Example 2 of the present invention FIG.
It will be described based on. The same reference numerals as those in FIG. 1 indicate the same parts, and the description of the same parts will be omitted. Reference numeral 7 denotes a low resistance body connected in parallel with the fuse 6. After the fuse 6 is blown by the ground fault current, the ground fault current moves to the low resistance body 7, and the voltage between the terminals of the DC smoothing capacitor 31 or 32 becomes low. The current is limited to a size determined by the resistance value of the resistor 7. The ground fault current is attenuated with a time constant determined by the capacitance of the DC smoothing capacitor 31 or 32 and the resistance value of the low resistance body 7, as shown in FIG. 4 as a resistor current. By setting the resistance value of the low resistance body 7 to be sufficiently low at about 0.1 to 1Ω, the power converter is grounded through the low resistance body 7 even after the fuse is blown, so that the DC intermediate circuit 3 is grounded. The capacitance can be made sufficiently low, and thereby the circuit can be stabilized.

Embodiment 3. In the first and second embodiments, the case where the midpoint Q of two sets of the DC smoothing capacitors 31 and 32 connected in series is grounded via the fuse 6 or the parallel connection body of the fuse 6 and the low resistance body 7 has been described. When the DC smoothing capacitors forming the DC intermediate circuit 3 are not connected in series, that is, when there is no connection intermediate point Q, a fuse or a fuse and a low resistance are provided between either one of the positive terminal or the negative terminal of the DC smoothing capacitor and the ground. It suffices to connect the parallel-connected bodies.
Further, when the DC intermediate circuit 3 is composed of more than two sets of DC smoothing capacitors connected in series and there are a plurality of connection intermediate points Q, a fuse or a fuse is connected between the intermediate points which need to be connected and the ground. A parallel connection body of low resistance bodies may be provided.

[0013]

As described above, according to the power converter of the present invention, the grounding of the DC intermediate circuit is performed via the fuse or the parallel connection body of the fuse and the low resistance body, so that the DC intermediate circuit is grounded. Even if a fault occurs, the ground fault current is cut off by the fuse to limit the damage to the ground fault point, and the DC smoothing capacitor is not destroyed. Even after the fuse is blown, the ground resistance of the power converter is kept sufficiently low by the parallel resistance, so the ground capacitance of the entire circuit of the power converter increases and the zero-phase current increases to increase the ground potential. Does not become unstable, and there is an effect that a safe and stable power conversion device can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power conversion device of the present invention.

FIG. 2 is a conceptual diagram of a ground fault current waveform in FIG.

FIG. 3 is a circuit diagram showing a second embodiment of the power conversion device of the present invention.

FIG. 4 is a conceptual diagram of a ground fault current waveform in FIG.

FIG. 5 is a circuit diagram showing an example of a conventional power conversion device.

[Explanation of symbols]

 1 Converter 2 Inverter 3 DC Intermediate Circuit 4 DC Smoothing Reactor 5 Load 6 Fuse 7 Low Resistor

Claims (3)

[Claims] 1. A converter for converting alternating current into direct current, an inverter for converting direct current generated by the converter into alternating current,
And a direct current intermediate circuit having a direct current smoothing capacitor interposed between the inverter and the converter, wherein the direct current intermediate circuit is grounded via a fuse or a parallel connection body of a fuse and a resistor. An electric power converter characterized by being provided. 2. The direct current intermediate circuit comprises at least one series connection body composed of direct current smoothing capacitors connected in series, and the intermediate connection point of the direct current smoothing capacitors connected in series is a fuse or a parallel connection of a fuse and a resistor. The power conversion device according to claim 1, wherein the power conversion device is grounded via a connection body. 3. The DC intermediate circuit comprises a DC smoothing capacitor, and either the positive terminal or the negative terminal of the DC smoothing capacitor is grounded via a fuse or a parallel connection body of a fuse and a resistor. Claim 1 characterized by
The power converter described.