JPH0834665B2 - AC / DC converter - Google Patents

Description

The present invention relates to an improvement of an AC / DC converter using a voltage type self-excited AC / DC converter.

[Conventional technology]

The conventional AC / DC converter using the voltage type self-excited AC / DC converter has various problems in terms of reliability.

For example, Fig. 3 (a) of Hitachi Review VOL.68, NO8, p-610
In the AC / DC converter shown in (1), the power source is only on the AC side and does not exist on the DC side. In such a device, it is necessary to charge the capacitor on the DC side from the AC side through the AC / DC converter, and only the AC reactor limits the charging current at the time of charging, so the DC voltage is the peak value of the AC line voltage. There is a risk of jumping up to twice, and the AC-DC converter may be damaged by this overvoltage. Further, when the capacity of the AC / DC converter is large, the charging current of the capacitor also becomes large, so that there is a problem that the disturbance given to the AC system cannot be ignored.

Further, in the AC / DC converter shown in FIG. 1 of Toshiba Rev. 43, No. 4, P-352, only the mechanical switch (72M) is provided as a device for disconnecting the DC side line of the inverter (AC / DC). There is. In such a device, when a short circuit or a ground fault occurs on the DC side, even if the mechanical switch is released by detecting an overcurrent with DCCT or CT, there is a delay of several tens of milliseconds in the mechanical switch operation. During this time, a large short circuit (ground fault) current may flow from the AC system. Therefore, the inverter may be destroyed by a short circuit (ground fault) current. Further, since the smoothing capacitor is discharged, it needs to be recharged, and there is a problem that the inverter cannot be operated during that time.

[Problems to be Solved by the Invention]

As described above, the conventional AC / DC converter using the voltage type self-excited AC / DC converter has various problems and is insufficient in reliability.

It is an object of the present invention to provide an improved AC / DC converter which eliminates various problems of the conventional device and improves reliability.

[Means for solving the problem]

In order to achieve the above object, a DC switch is provided on the DC side of the voltage type self-exciting converter. In particular,
The DC switch is placed between (1) the voltage type self-exciting converter and the smoothing capacitor. (2) Three types of configurations, that is, the smoothing capacitor is arranged between the voltage type self-exciting converter and the DC switch, and (3) the combination of (1) and (2) is used. It is provided. The DC switch is composed of a self-extinguishing type semiconductor switching element, and in the forms of (1) and (3) above, it is possible to operate the chip at a frequency higher than the time constant determined by the impedance on the AC side and the smoothing capacitor. There is. In the configurations of (2) and (3), the current limiting DC reactor is provided in series with the DC switch.

[Action]

In the first mode in which the DC switch is arranged between the voltage type self-excited AC / DC converter and the smoothing capacitor, the charging current is limited and smoothed by operating the DC switch when the smoothing capacitor is charged from the AC system side. The capacitor is gradually charged. As a result, the magnitude of the charging current is smaller than that in the case of charging the smoothing capacitor when there is no DC switch, the disturbance given to the AC system can be reduced, and the smoothing capacitor can be prevented from being overcharged.

In addition, the DC switch is arranged such that the smoothing capacitor is located between the DC switch and the voltage type self-exciting AC / DC converter.
In the above form, the DC switch installed on the DC line side of the smoothing capacitor quickly cuts off or disconnects the overcurrent caused by a short circuit or ground fault on the DC side, which may damage the converter. Disappears. Furthermore, since the overcurrent is cut off at high speed, it is possible to prevent discharge of the smoothing capacitor, that is, it is possible to cut off the overcurrent in the event of an accident while maintaining the DC voltage of the converter. No charging is required, and high-speed restart is possible.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, reference numeral 1 is a voltage type self-excited AC / DC circuit formed by connecting a plurality of semiconductor switching elements such as thyristors and transistors and an anti-parallel connection unit of a diode in an inverter. Converter 3 is a smoothing capacitor connected in parallel between the DC side lines connected to the DC side terminals of the AC / DC converter 1, 2 is a DC reactor for current limiting connected in series to one side of the DC side line, and 4 is DC The DC switches, 6, 7 and 8 are arranged on one side of the side line so that the smoothing capacitor is located between the DC reactor 2 and the AC / DC converter 1, and the DC switches 6, 7 and 8 are sequentially connected to the AC side of the AC / DC converter 1. A transformer, a breaker, and an AC power supply, 10 is a ground fault detector that detects a ground fault from a signal from a sensor (CT) 9 arranged between the AC / DC converter 1 and the ground, and 12 is one of the DC side lines. Sensor (CT) placed on the side 11 A short-circuit detector for detecting a short-circuit accident from the signal No. 3, and a gate control circuit 13 for giving an ON / OFF signal to the DC switch 4 based on the signal from the ground fault detector 10 or the short-circuit detector 12. Reference numeral 14 is a load connected to the DC side line, and specifically, an induction motor or an AC power supply is often connected via an AC / DC converter.

In the AC / DC converter having such a configuration, when a short circuit or a ground fault occurs on the DC side of the AC / DC converter 1, the short circuit detector 12 or the ground fault detector 10 detects the fault from the overcurrent flowing in the line, and the gate control circuit. An OFF signal is applied to the DC switch 4 from 13 to turn off the DC switch 4 to cut off or cut off an overcurrent flowing through the AC / DC converter 1. As a result, the overcurrent does not flow through the AC / DC converter 1 for a long time, and the destruction of the AC / DC converter 1 due to the overcurrent can be prevented in advance. Further, since the smoothing capacitor 3 can be prevented from being discharged, the device can be restarted without recharging the smoothing capacitor, and a high speed restart is possible.

The AC / DC converter having the configuration shown in FIG. 1 has the above-described effects and is particularly effective when the smoothing capacitor does not have another charging means.

FIG. 2 shows a specific configuration of the DC switch 4,
A self-extinguishing type switching element 41 connected in series to the DC side line, a flywheel diode 42 connected in anti-parallel to the switching element 41, and a switching element 41 are operated by a ON / OFF signal from the gate control circuit 13. A snubber circuit composed of a resistor 431, a diode 432, and a capacitor 433 connected in parallel with the switching element 41.
And a nonlinear resistor 44 connected in parallel with the switching element 41 to protect the switching element 41 from overvoltage. As the self-extinguishing type switching element 41, a well-known semiconductor element such as a transistor, a gate turn-off thyristor, or an electrostatic induction thyristor can be used.

FIG. 3 shows a second embodiment of the present invention. The first embodiment is different from the first embodiment in that the DC switch 4 is arranged between the AC / DC converter 1 and the smoothing capacitor 3, and the ground fault detection. The difference is that there is no switch and short-circuit detector, and that the gate control circuit 13 detects the closing operation of the AC side or the breaker 7 and turns it on and off.

In the AC / DC converter having such a configuration, when the circuit breaker 7 is turned on to start charging the smoothing capacitor 3 from the AC side, at the same time, the gate control circuit 13 transfers the DC switch 4 to the AC side impedance and the time constant determined by the smoothing capacitor 3. The application of ON and OFF signals is started at a faster cycle. As a result, the DC switch 4 starts the checker operation, the charging current of the smoothing capacitor 3 is limited, and the smoothing capacitor 3
Is gradually charged. As a result, the magnitude of the charging current is smaller than that of the charging of the smoothing capacitor when there is no DC switch, the disturbance given to the AC system can be reduced, and the AC / DC converter can be protected from damage due to overcurrent. The device having this configuration is effective in the case of direct-current power transmission using a cable.

In this case, the peak value of the voltage of the AC / DC converter 1 side of the transformer 6 may be lower than the rated DC voltage, but at that time, the transformer 6 is provided with a tap engineer so that the peak voltage of the secondary side of the transformer is reduced. The value should be higher than the DC rated voltage.

FIG. 4 shows a third embodiment of the present invention, which is different from the first embodiment in that the smoothing capacitor 3 is connected to the AC / DC converter 1 side (A side) and the DC reactor 2 side (B side) of the DC switch 4. ) Is provided with a switching switch 15 so that the gate control circuit 13 can generate ON and OFF signals even by detecting the closing operation of the switch 7 and the circuit breaker 7. ing.

In the AC / DC converter having such a configuration, when the smoothing capacitor 3 is charged, the same operation as in the case of the second embodiment is performed by turning on the switch 15 on the B side and turning on the disconnector 7. The effect of can be expected. next,
In the steady operation state, the switch 15 is closed on the A side to prepare for a short circuit or a ground fault. When an accident occurs, the same operation and effects as described in the first embodiment can be expected.

The device of this configuration is effective when the smoothing capacitor does not have another charging means and sends DC power through an overhead line.

〔The invention's effect〕

According to the present invention, it is possible to realize an AC / DC converter using a voltage type self-excited AC / DC converter capable of performing high-speed current supply / disconnection and high-speed restart with respect to a ground fault or a short circuit of a DC line. As described above, there is an effect of improving the reliability when the voltage type self-excited AC / DC converter is applied to a system in which the DC line is long and the frequency of occurrence of ground fault and short circuit of the DC line is high. Further, charging of the smoothing capacitor of the voltage type self-excited AC / DC converter when there is no power source on the DC side does not result in overcharging, and the charging current peak value can be made small. When configuring a DC power transmission system using more than one unit, it is possible to reduce the overvoltage withstanding capability and the overcurrent withstanding capability of the converter.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the AC / DC converter of the present invention, FIG. 2 is a concrete circuit diagram of the DC switch shown in FIG. 1, and FIG. 3 is a schematic diagram showing another embodiment of the present invention. FIG. 4 is a schematic diagram showing still another embodiment of the present invention. 1 ... Voltage type self-excited AC / DC converter, 3 ... Smoothing capacitor, 4
... DC switch, 13 ... Gate control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Miyazaki 2-4-1 Tsutsujigaoka, Chofu City, Tokyo Inside the Technical Research Institute, Tokyo Electric Power Co., Inc. (56) Reference JP-A-61-131318 (JP, A) JP Sho 62-213520 (JP, A) Actually opened Sho 60-55240 (JP, U)

Claims (1)

[Claims] 1. A voltage type self-excited AC / DC converter, which is arranged between an AC system, a DC system, and both systems, and is constituted by connecting a plurality of anti-parallel connection units of a semiconductor switching element and a diode by an inverter. A smoothing capacitor connected to the DC system side of the AC / DC converter, a DC switch is arranged on the DC system side, and a changeover switch for switching the smoothing capacitor to the AC / DC converter side of the DC switch or the opposite side thereof is provided. In addition to the above, the operation signal of the circuit breaker provided between the AC power supply and the AC / DC converter, the short-circuit detector in the DC system, the signal from the short-circuit detector for detecting the ground fault and the signal from the ground fault detector are input, and the DC An AC / DC converter comprising a gate control circuit for generating a signal for turning a switch on and off.