SUMMARYElectrical type tests are a key step to verify the design of voltage source converter valves for a specific modular multilevel converter (MMC) high-voltage direct current (HVDC) project. For a high-power handling capability of modern insulated gate bipolar transistor (IGBT), it is very difficult to balance between type test quality and test rig investment. In compliance with IEC 62501 and CIGRE 447 requirement, this paper presents a kind of synthetic test circuits (STCs), consisting of a steady-state test circuit, an IGBT overcurrent turn-off test circuit, and a short-circuit current test circuit, used for operational tests on MMC-based IGBT valve sections. Using the STCs, the current stress, the voltage stress, the junction temperature, di/dt, the performance of the valve's electronic circuits, and the protection capability of the parallel thyristor can be validated. Further, the parameters of the test circuits can be adjusted with the number of submodules of the MMC test valve. Thus, the STCs are an economical alternative for testing a representative part of an MMC valve. The paper describes and discusses the type tests, completely performed with the three test circuits, on MMC valves for a Xiamen MMC HVDC scheme, which is rated at 1000 MW/±320 kV. Copyright
The rapid progress of large-scale clean energy accessing to the grid promotes the development of DC grid technologies. HVDC (high voltage direct current) circuit breaker as one of the key equipment of the DC grid has gradually attracted more and more attentions. Direct current is more difficult to be interrupted comparing to alternative current because of without natural zero-crossing, especially in the high voltage and large capacity system. This paper briefly reviews the research status of DC circuit breaker firstly. Then a novel topology of DC circuit breaker with coupling transformer is proposed. Its topology is presented and operating principle is analyzed. The equivalent model for different stages is established, and the key component parameters are designed. Operating characteristic of the HVDC circuit breaker is simulated relying ZhouShan 5-terminal flexible HVDC project. Simulation results have verified the correctness of theoretical analysis and the effectiveness of the novel HVDC circuit breaker interrupting the fault current in the flexible HVDC transmission grid. This provides a basis for HVDC circuit breaker design.
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