Hybrid DC converter valve group online deblocking circuit, method and device

Abstract

The invention discloses a hybrid DC converter valve group online deblocking circuit which is used for the online deblocking of a voltage source converter. The circuit at least comprises a valve groupconnection line connection switch or knife switch of a voltage source type valve group unit, a DC link connection switch or knife switch of the voltage source type valve group unit and a bypass switchor knife switch of a current source type valve unit, or at least comprises a valve group connection line connection switch or knife switch of the voltage source type valve group unit, a neutral busbar connection switch or knife switch of the voltage source type valve group unit, a bypass switch or knife switch of the voltage source type valve unit and a bypass switch or knife switch of the current source type valve unit. The invention also discloses a hybrid DC converter valve group online deblocking method and device, firstly the voltage source converter is unlocked, the voltage source converter is connected to two ends of a grid commutating converter in parallel, the grid commutating converter is locked, the grid commutating converter is connected to the voltage source converter in series, and the online deblocking of the grid commutating converter is carried out.

Description

technical field [0001] The invention belongs to the fields of hybrid direct current transmission and high-voltage direct current transmission, and in particular relates to an online input circuit, input method and device of a hybrid direct current converter valve group. Background technique [0002] The advantage of current source HVDC transmission based on thyristors is that the loss of the converter is small, and the DC system can be restarted by shifting the phase when a DC line fault occurs; the disadvantage is that the converter on the inverter side works in active inverter and cannot be connected to wireless Source system; the inverter side is connected to the weak AC system, and commutation failure is prone to occur after disturbance; the reactive power consumption is large, and the voltage and current harmonic content is high, so it is necessary to install a filtering device to provide reactive power and filtering. The advantages of DC transmission based on voltage s...

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Problems solved by technology

[0002] The advantage of current source HVDC transmission based on thyristors is that the loss of the converter is small, and the DC system can be restarted by shifting the phase when a DC line fault occurs; the disadvantage is that the converter on the inverter side works in active inverter and cannot be connected to wireless source system; the inverter side is connected to the weak AC system, and commutation failure is prone to occur after disturbance; the reactive power consumption is large, and the harmonic content of voltage and current is high, so it is necessary to install a filter device to provide reactive power and filter

The advantages of DC transmission based on voltage source converters are high controllability, can be connected to passive systems, and do not require reactive power compensation devices; the disadvantage is that the switching losses of the converters are large, and modular multi-level converters with a half-bridge structure are adopted. The current breaker cannot control the fault current when the DC side is faulty, and the fault can only be removed by disconnecting the AC side circuit breaker after the fault occurs

[0003] For DC side faults, ABB uses a DC circuit breaker with a DC line to solve the DC side fault, but the cost of the DC circuit breaker is high and the reliability has yet to be verified; Siemens uses a modular multilevel converter with a full bridge circuit structure However, the converter of the full-bridge circuit structure has a large loss; Alstom uses a full-bridge circuit and bridge arm series power electronic switching devices to solve the problem, but the reliability has yet to be verified; Zhejiang University adopts a series connection in the main circuit Diodes can be used to solve the problem, but the diodes do not participate in power conversion and will generate losses by themselves; NARI Relay uses a hybrid DC converter in series with a grid commutation converter with a bypass branch and a voltage source converter, and the voltage source The converter only needs to use a modular multilevel converter with a half-bridge circuit structure. The grid commutation converter can naturally block the DC side fault current, and the bypass branch can reliably protect the voltage source converter. The voltage adjustment range of the voltage source converter of the hybrid DC converter is limited. Unlike the grid commutation converter, the voltage cannot be adjusted to zero to realize online input. If the voltage source converter exits due to failure or maintenance, it needs to stop poles or Control the DC current to zero before it can be put into operation again, which affects the stable operation of the DC transmission system power

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