JPS6057295B2 - Cycloconverter protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for a cycloconverter.

A cycloconverter is generally a power converter that converts constant frequency AC power into variable frequency AC power as a power source for an AC variable speed drive, and has a basic configuration as shown in FIG.

Then, as shown in FIG. 2, the firing phase is controlled by a phase control signal that amplifies the deviation between the driving command pattern and the output current, and the output current changes in accordance with the driving command pattern. Therefore,
The output voltage Vt is Vt 1×EXCoSα, where: constant E determined by the number of input power supply phases: power supply voltage α: ignition phase angle.

Conventionally, an overcurrent relay (OCR) is used to protect the output power supply system from accidents (for example, short circuit to ground). However, in the current control type, as described above, the ignition phase is narrowed so that the output current follows the command pattern, so there is a risk that overcurrent will not occur and it will not be detected by OCR, which poses a protection problem. For this reason, a method is sometimes used to detect short circuits, ground faults, etc. by comparing the voltages of each phase on the output side, but in this case, a 0Hz voltage detector is used.
A special voltage relay with a variable frequency of up to several tens of H2 is required, which has the drawback of making the device expensive. The present invention has been made in view of the above points, and focuses on the fact that the phase control signal of the ignition phase control circuit uniquely determines the output voltage in a current control type three-phase output cycloconverter. By comparing the average value of 1 cycle between each phase of the 3-phase cycloconverter, it is possible to detect faults in the output power supply system (e.g. ground faults, short circuits) without using an output voltage detector.
The present invention provides a cycloconverter protection device that detects and protects the cycloconverter.

The present invention will be explained below with reference to the drawings.

FIG. 3 is a block diagram showing the basic configuration of one phase of an embodiment of the present invention. In FIG. 3, numeral 1 denotes a rectifier circuit, which obtains a waveform obtained by rectifying the phase control signal ec-υ. 2
is an average value calculation circuit, which uses an output frequency signal (analog signal) and a synchronization pulse (calculation reset) signal, which will be described later.
Calculate the average value of rectified ec-u.

3 is a cycle hold circuit which samples the average value calculated using the synchronization pulse signal and holds the average value PD? of ec-u until the next synchronization pulse comes. Hold U.

Reference numeral 4 denotes the above-mentioned synchronous pulse signal generation circuit, which generates a pulse signal for each cycle in synchronization with the driving command pattern.

5 is an F-■ conversion circuit which converts the above-mentioned output frequency into an analog level using a pulse signal synchronized with the driving command pattern. The average value PD-U of the phase control signals of each phase obtained in this way. ．． PD1V. ．． The PD-W is input to the comparison circuit shown in FIG. 4 and compared for each phase. Next, the operation of the present invention will be explained in detail.

In the phase control circuit shown in FIG. 3, the phase control signal Ec
There is a relationship between and the firing phase α.

Therefore, the above-mentioned output voltage Vt becomes, and Vt can be obtained from Ec. FIG. 5 shows an example of the relationship between the waveforms of the phase control signal Ec and the output voltage Vt in a sinusoidal driving command pattern. For example, in the circuit shown in Fig. 1, when a U-phase short circuit accident occurs, the U-phase converter CC-u uses the output wire impedance as a load, and the firing phase α is throttled so that the output current follows the operation command pattern. Therefore, the output power -u decreases rapidly.

In a normal system, the impedance drop of the output wire is about 2% with respect to the load terminal voltage ■0, so ■-u becomes ■-V, ■-w, and therefore the phase control signal also becomes Ec-o. It becomes Ec-V, ec-t. For this reason, the fourth
In the figure, Ec-
v average value PD-V, ec-w average value PD-w, and therefore for margin value ε.

Therefore, the deviation level determiner Au. The logic output of l5Aw becomes ゜゜1゛, the logic output of Av becomes ゜゜0゛, the U-phase fault detection signal A becomes "1-V", and the W-phase fault detection signals B and C become "゜0゛" through the AND element. Therefore, an accident in the U phase can be detected.With this detection signal A, B, Cf)0R output,
Each phase converter CCVlCCV, . C.C. Gate block R, and then open the input cable disconnector to protect the power supply system. As explained above, according to the present invention, by using the phase control signals of each phase, the three-phase output voltages of the cycloconverter can be compared with each other without using an output voltage detector, and thereby the power supply system can be controlled. It is possible to obtain a protection device for a cycloconverter that can detect accidents (for example, ground faults and short circuits), has a simple configuration, is free from malfunctions due to output voltage ripple, and is highly reliable.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the general configuration of the main circuit and control circuit of a current-controlled cycloconverter, respectively;
3 and 4 are circuit diagrams showing the basic configuration of a cycloconverter protection device according to the present invention, and FIG. 5 is a diagram showing waveforms of various parts for explaining the present invention. CCu, CCv, CCvv...Each phase cycloconverter, PDu, PDv, PDw...Each phase phase control signal average value, Au, Av, Avv...Each phase deviation level determiner, 1...Phase control Signal detector, 2... Average value calculation circuit, 3... Sample hold circuit, 4... Synchronous pulse generation circuit, 5... F-V conversion circuit.

Claims (1)

[Claims] 1. In a current-controlled cycloconverter, a circuit that calculates the voltage average value of the phase control signal of each phase, and a phase deviation level that generates an output signal when the difference between the above average values for each phase exceeds a predetermined value. A cycloconverter comprising: a determiner; and a logic circuit that determines a short circuit or a ground fault in the output power supply system of the cycloconverter for each phase based on the AND of the respective output signals of the deviation level determiner. protection device.