JPS60139128A - Ground protecting device for power converter - 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 [Technical Field of the Invention] The present invention relates to a grounding protection device for a power converter that supplies power from a grounded AC power source to a load.

[Technical background of the invention and its problems]

Generally, the speed control of an AC motor is often performed by a power conversion device consisting of a rectifier and an inverter.
A grounding protection device is provided to protect this power converter from grounding accidents and short circuit accidents on the load side. An example of this type of earth protection device is the one shown in FIG.

In FIG. 1, 1 is a nine-three-phase AC power source with a grounded neutral point, 2 is a diode bridge rectifier consisting of diodes 21 to 26, 3 is a smoothing capacitor, and 4 is a transistor 41 to 46 as a semiconductor switch. diode 4
Inverters 7 to 52 are inverters, and 5 is a load terminal 5a, 5b, and 5c. 6 is a current detector, 7 is a zero-phase current transformer, 8.9 is a level detector, 10 is an OR circuit, and 11 is an inverter control circuit.

Next, an explanation will be given of an accident that occurs when the vehicle touches down in FIG. 1.

For example, if a ground fault occurs at the load terminal 5C, the path of the ground current will differ depending on which of the transistors 45 and 46 is turned on.

(a) When transistor 45 is on, power supply 1° rectifier 2, transistor 45. A ground current flows through the earth path, and the positive DC current 11 increases.

(b) ground when transistor 46 is on, transistor 46. A ground current flows through the path between the rectifier 2 and the power supply 1, and the negative side DC current 12 increases.

Therefore, as in the device shown in FIG.
In this case, an accident cannot be detected when the transistor 45 is on. Therefore, it was necessary to provide the zero-phase current transformer 7 in order to detect an accident when the transistor 45 is on.

Due to recent advances in electronics, power conversion devices using semiconductor elements of several KVA or less have become widely used. Because of this, it was not possible to reduce the price and make it more compact.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks, and includes:
The present invention aims to provide a grounding protection device for a power converter that is low in cost and compact and can detect accidents using a single current detector.

[Summary of the invention]

In order to achieve the above object in the present invention.

A current detector is provided in the direction in which the positive DC current and negative DC current of the power conversion device are subtracted, and when the value of the output signal of this current detector exceeds a set value, the inverter of the power conversion device is activated. All semiconductor switches that make up the system are turned off.

Examples of the invention] An embodiment of the present invention will be described with reference to FIG.

In FIG. 2, 1 is a three-phase AC power supply, and the neutral point is grounded. 2 is a rectifier, which converts the AC power of the three-phase AC power supply 1 into DC/power. 3 is a capacitor;
The DC power output from the rectifier 2 is smoothed. 4 is an inverter which inputs DC power, converts it into AC power, and outputs it to the load terminal 5. Reference numeral 60 denotes a Hall current detector as a detector for detecting direct current, and it is connected so that the positive side direct current 11 and the negative side direct current are subtracted, that is, in the direction in which the magnetic flux is subtracted. In this case, if the positive and negative windings are made equal, overcurrent detection in normal conditions becomes impossible, so the turns ratio is changed. Considering the case where the ground current flows through the side with a lower turns ratio,
The positive/negative side turns ratio is set to an appropriate value (n:1).

The output of this Hall current detector 60 is proportional to 1/n times the DC current i3 flowing between the rectifier 2 and the inverter 4, and is a value proportional to the difference between the positive DC current 11 and the negative DC current. becomes. A level detector 8 outputs an overcurrent detection signal when the output signal of the Hall current detector 60 exceeds a set value.

Reference numeral 11 denotes an inverter control circuit, which controls on/off of transistors 41 to 46 forming the inverter 4. The control circuit 11 of this inverter includes a frequency setter 61.
PWM (pulse width modulation) control circuit 62, AND circuit 63
, and a drive circuit 64. The frequency setter 61 outputs signals as setting values for the voltage and frequency of the inverter 4. The FW=M control circuit 62 inputs the output signal of the frequency setter 61 and outputs a signal for controlling the voltage and frequency of the inverter 4. The AND circuit 63 outputs a signal that turns off all transistors 41 to 46 of the inverter 4 when the overcurrent detection signal is input from the level detector 8, and when the overcurrent detection signal is not input, the PWM control circuit 62 Outputs the output signal. The drive circuit 64 inputs the output signal of the AND circuit 63 and outputs a signal for turning on/off the transistors 41 to 46 of the inverter 4.

Next, the operation of this embodiment configured as described above will be explained.

If a short circuit accident occurs between load terminals 5a and 5b,
At the moment when transistors 41 and 44 turn on, capacitor 3. A short circuit current flows in the closed circuit consisting of transistors 41,44. Therefore, the DC current i3 increases.

Next, consider a case where a grounding fault occurs at the load terminal 5C.

If a ground fault occurs while the transistor 45 is on, a ground current flows from the current 1 through the transistor 45 to the ground. Therefore, the positive side DC current 11 increases.

On the other hand, if a ground fault occurs while the transistor 46 is on, a large current flows from the ground to the power supply 1 through the transistor 46. Therefore, the negative side DC current I2 increases.

Therefore, when a short circuit accident between the load terminals 5a and 5b or a grounding accident occurs at the load terminal 5C, the value of the output signal of the Hall current detector 60 increases. When the output signal of the Hall current detector 60 exceeds a set value, the level detector 8 outputs an overcurrent detection signal. AND circuit 63
When this overcurrent detection signal is input to the drive circuit 6
4 outputs a signal that turns off all transistors 41 to 46 of inverter 4.

Note that since the level detector 8 does not normally output an overcurrent detection signal, the drive circuit 64 uses PWM, Ii control circuit 6
2, the transistor 41 of the inverter 4
- Outputs a signal to turn on/off 46.

As described above, the short circuit accident between load terminals 5a and 5b and the load terminal 5
Although the grounding accident at C was explained, the load terminal 5b,
Short circuit accident between load terminals 5c and 5c.

5a short circuit accident, load terminal, grounding accident at child 5a,
The same applies to a grounding accident at the load terminal 5b.

Here, we will consider the overcurrent detection level when the Hall current detector 60 is wound in a ratio of 1:1 in the direction of adding the positive side current and the negative side current. If the rated current is Io and the overcurrent detection level is 1.5Io, the rated current is 2Io and the overcurrent is 1.5 (2IO = 3IO) is input to the level detector 8, and in the case of a short circuit between the load terminals, 1 .5 Io + 1.5
Io -3Io, and can be detected at 1.5 times the overcurrent. On the other hand, in the case of grounding, since only the positive and negative currents increase, the overcurrent detection current becomes twice the rated current at 2Io+l0=3IO.

In the case of the present invention, as an example, the winding ratio for the positive side current and the negative side current is 4:3 when winding is performed in the subtractive direction 4 I6-3
Io "'Io becomes the input value of the level detector 8 when the load is 10 (1). In the case of a short circuit between the load terminals, it becomes 4X (1, 5
Io) 3X(1,5IO)=1.5IO, that is, it can be detected at 1.5 times the rated overcurrent. Also, when the transistor on the positive side bus is on, the ground current increases only on the positive side, so it is 4X (1,125IO) - 3Io -1
, 5Io, that is, the ground current can be detected at an overcurrent of 112.5%, while the ground current when the negative side transistor is on is 4Io -3X (1,83Is) = -1,
It can be detected at a ground current of 51o or 183chi.

According to this embodiment, by providing one current detector (Hall current detector 60), a grounding protection device for a power conversion device is provided that detects a short-circuit accident between load terminals and a grounding accident at a load terminal. be able to.

In addition, in this embodiment, a three-phase AC power supply 1° rectifier 2
．． Although the capacitor 3 constitutes a DC power source, a DC power source such as a battery may be used instead. The inverter 4 may be a three-phase inverter or a single-phase inverter, and the load terminal 5 may be supplied with either AC power or DC power.

Furthermore, as semiconductor elements constituting the inverter 4tl, thyristors and GTs are used instead of the transistors 41 to 46.
It goes without saying that it functions similarly as an element such as O. Further, as a device for converting the AC power of the power source 1 into DC power, a thyristor bridge or a chopper circuit capable of forced commutation may be used instead of the rectifier 2 using a diode/brillage. In this case, it is advisable to stop these converters as soon as possible after detecting the accident.

〔Effect of the invention〕

According to the present invention, as explained above, a grounding fault can be detected with one current detector, so that it is possible to reduce the cost and make the power converter more compact, thereby providing a grounding protection device for the raw power converter. I can do what I want.

[Brief explanation of drawings]

FIG. 2 is a block diagram showing a conventional ground protection device for a power converter, and FIG. 2 is a block diagram showing an embodiment of the present invention. 1... AC power supply 2... Rectifier 4...
Inverter 5...Load terminal 8...Level detector 11...Inverter control device 41-46...Semiconductor switch (transistor) 6
0...Current detector (Hall current detector) (7317
) Agent: Patent Attorney Noriyuki Chika (and 1 other person) 1st
Figure L J

Claims (1)

[Claims] Current detection installed in the direction of subtracting the positive DC current and negative DC current of the power converter that converts the AC power from the AC power supply into DC power through a rectifier, converts it into AC power using an inverter, and supplies it to the load terminal. a level detector that outputs an overcurrent detection signal when the output signal of the current detector exceeds a set value; and a level detector that outputs a signal that normally turns on and off the semiconductor switches that constitute the inverter. 1. A ground protection device for a power converter, comprising: an inverter control circuit that outputs a signal that turns off all of the semiconductor switches when an overcurrent detection signal is input.