JPH04295228A - Protective unit for ac/dc converter - Google Patents

Abstract

PURPOSE:To suppress overvoltage at the time of overload interruption by transferring energy stored in a filter and a capacitor, installed in two AC systems linked through a converter and an inverter, to DC side and then opening a circuit breaker while dissipating thus transferred energy. CONSTITUTION:Two AC systems 100, 200 are connected through HPFs 12, 22, reactive power compensating capacitors 13, 23 and linking transformers 11, 21 with a converter 10 and an inverter 20, respectively, which are linked through a DC system 300 comprising coils 28, 28' and a resistor 29. When an inverter side controller 31 receives a load interruption command 201 from an overvoltage detector 25 or an emergency interruption command 202 from an operation command board 27, converter control angle is shifted from 120-160 deg. to within the operating region of the converter, i.e., 90 deg., thus making transfer to bypass pair operation. Energy stored in the HPF 22 and the capacitor 23 is converted and dissipated through the resistor 29 in the DC system 300. Consequently, overvoltage is suppressed upon opening of a load circuit breaker 24.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection device for a thyristor converter for AC/DC conversion used in DC power transmission, frequency conversion, etc.

0002

[Prior Art] It is well known that overvoltage occurs in the inverter AC system when load shedding is performed when overvoltage is detected due to fault detection in the AC system on the inverter side of a power AC/DC converter. It is a fact. However, data on the actual scale of this overvoltage had not been quantitatively determined, considering the damage it would cause to equipment in the unlikely event that it occurred.

[0003]Recently, analysis of the opening and closing of such circuit breakers is being carried out using power simulators that are free from overvoltage problems, but the magnitude of overvoltage generation during transient phenomena is several times greater than during normal operation. It became clear that the shock to equipment such as converters was greater than expected. The conventional load shedding procedure was to immediately switch to a bypass pair after detecting an overvoltage, and then open and close the circuit breaker.

[0004] However, even if the circuit breaker is switched to a bypass pair, the power flow remains in the direction from direct current to alternating current, and depending on the phase when the circuit breaker is off, there is a possibility that an overvoltage higher than that at the time of detection may occur. It was huge.

[0005]

[Problems to be Solved by the Invention] This invention has been made to solve the above-mentioned problems.In order to suppress the occurrence of overvoltage due to load shedding, a filter installed on the AC side and an accumulation of capacitors are used. The energy is returned to the DC side of the AC/DC converter, and the circuit breaker is opened and closed while extinguishing the energy. [Structure of the invention]

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention converts two different AC systems by a pair of conversion devices each having a filter and a reactive power compensation capacitor installed on the AC side. In a device that is interconnected with an AC/DC converter configured to transfer power between both AC systems,
When the overvoltage detection means for detecting overvoltage on the alternating current side of each of the conversion devices and the overvoltage detection means on the side of the conversion device that is operating the inverse converter of the conversion device or the circuit breaker on the side of the conversion device are operated. The present invention is characterized in that it includes means for shifting the converter to forward converter operation when an emergency shutdown command is issued, and then shifting to bypass pair operation.

[0007]

[Operation] According to the control device of the present invention configured as described above, during emergency load shedding and during normal operation, 120 degrees -
The inverse converter operation control angle of around 160 degrees is shifted to the forward converter operation within 90 degrees.

As a result, the energy that was being transmitted from the DC circuit to the AC system is returned to the DC side, the energy stored in the interconnection transformer reactor and filter is consumed, and the overvoltage when the circuit breaker opens and closes is reduced. It can be suppressed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an AC/DC converter having measures to prevent overvoltage during load cutoff according to the present invention.

The device shown in FIG. 1 includes a forward converter 10, a interconnection transformer 11, a harmonic removal filter 12, a reactive power compensation capacitor 13, an inverse converter 20, an interconnection transformer 21, a harmonic removal filter 22, and a reactive power Compensation capacitor 23
, circuit breaker 24, overvoltage detection device 25, operation command panel 26,
27, a DC circuit reactor 28, a resistor 29, converter control devices 30, 31, a forward converter side AC bus 100, an inverse converter side AC bus 200, and a DC circuit 300. Next, the operation of the apparatus having the above configuration will be explained.

FIG. 1 shows a normal AC/DC converter, which uses a forward converter 10 and an inverse converter 20 to convert an AC bus 100
power is transmitted to the AC bus 200 via the DC circuit 300. In this case, since the AC/DC converter generally converts power by switching, many harmonics are generated on the AC bus side. Therefore, filters 12, 22 are installed to remove this harmonic.

When a separately excited converter is used, the power factor generally becomes poor, so reactive power compensation capacitors 13 and 23 are installed to improve the power factor. The compensation reactive power is approximately 1/2 of the transmitted active power, and the capacitor capacity is quite large.

The control devices 30 and 31 control the firing angle of the converter, and are generally installed separately. As shown in FIG. 2, the control method is such that constant current control is performed on the forward converter side, and constant voltage control (or constant margin angle control) is performed on the inverse converter side.

The firing angle control of the converter is performed using the AC bus 100,
The voltage, current, and power amount are taken in from 200 and set with the phase amount determined by constant current control and constant voltage control. The phase setting is
The voltage phase synchronized with the AC bus voltage is used as the reference.

[0015] If load shedding is performed with the above-mentioned filters and capacitors installed, overvoltage will be generated due to the energy stored in the above-mentioned equipment. Overvoltage may damage the equipment of the AC/DC converter and, depending on the situation, may result in loss of operating function.

[0016] Therefore, in order to suppress the occurrence of such overvoltage, the present invention transfers the energy stored in the filter or capacitor to the DC side and eliminates it while opening and closing the cutoff.

Now, when the control device 31 on the reverse converter side receives a load cutoff command 201 from the overvoltage detection device 25 or an emergency cutoff command 202 from the operation command panel 27, the converter control angle is changed to the normal control angle (120 -160 degrees) to operation within 90 degrees, which is the operating range of the converter.

As a result, the power on the AC bus 200 side, particularly the energy stored in the filter or capacitor, is transferred to the DC side. However, due to the operating principle of the AC/DC converter, the direction of the current in the DC circuit does not change. Therefore, if the bypass pair operation is performed after the transition to the forward converter operating region, the energy transferred to the DC circuit will be consumed by the resistance 29 in the DC circuit.

Normally, the circuit breaker 24 operates 2 to 3 times after the shutdown command.
Because it takes a cycle. During this time, a considerable amount of energy can be dissipated. Therefore, generation of overvoltage due to opening and closing of the circuit breaker 24 is suppressed. However, the above firing angle phase is set within a range where no overvoltage or harmonics occur from the inverter side, and as fast as possible.

For the series of operations in this case, it is convenient to use a microprocessor that can change control functions or control constants online. This is because if a microprocessor is used, the converter firing angle can be set more freely in terms of both phase shift width and phase shift time, compared to analog systems. Furthermore, if the AC system on the forward converter side is strong, the transition to the forward converter can be performed using the same principle as power flow reversal by changing the current margin.

[0021] However, since this is a process to be performed in the event of an accident, the speed of the current reversal is performed at a speed higher than the normal speed. In this case, the control speed can also be switched freely if a microprocessor is used.

[0022]

[Effects of the Invention] As explained above, according to the present invention, the energy stored in the filter and capacitor installed in the AC system on the inverter side of the AC/DC converter is transferred to the DC side and is eliminated. However, since the circuit breaker is opened and closed, overvoltage during load shedding can be suppressed. The present invention aims to apply a microprocessor to control the converter during load shedding. The microprocessor has the advantage of being able to freely control the firing angle phase from the inverse converter to the forward converter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an AC/DC converter according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of the AC/DC converter shown in FIG. 1 during normal operation.

[Explanation of symbols]

10... Forward conversion device
11... Grid connection transformer 12... Harmonic removal filter 1
3... Capacitor for reactive power compensation 20... Inverse conversion device
21... Grid connection transformer 22... Harmonic removal filter 2
3... Capacitor for reactive power compensation 24... Circuit breaker
25...Overvoltage detector 26...Operation command panel
27...Operation command panel 28...DC circuit coil
29...DC circuit resistance 30...Converter control device
31...Converter control device 100...AC bus bar
200...AC bus 201...Overvoltage detection signal
202...Emergency shutdown command 300...DC circuit

Claims (1)

[Claims] [Claim 1] Two different AC systems are interconnected by an AC/DC converter consisting of a pair of converters each having a filter and a reactive power compensation capacitor installed on the AC side, and a In a device configured to transfer and receive electric power, an overvoltage detection means for detecting overvoltage on the alternating current side of each of the conversion devices, and an overvoltage detection means on the side of the conversion device in which the inverter of the conversion device is operating. During operation,
Alternatively, a protection device for an AC/DC converter comprising means for shifting the converter to forward converter operation and then to bypass pair operation when an emergency shutdown command is issued to the circuit breaker on the converter side.