Research on operation test circuit and energy supplement scheme of valve section for VSC-HVDC transmission

The modular multi-level converter (MMC) is the core equipment of the voltage-sourced converter based high voltage direct current (VSC-HVDC) transmission system, and its reliability directly affects the system stability. The IEC standard points out that the operation test of the MMC is carried out with the valve section as the tested object. It evaluates the power unit's ability to withstand voltage and current stress. In this regard, first, the existing valve section operation test (VSOT) topology were summarized. And compare and analyze the advantages and disadvantages of the energy supplement methods in each VSOT system. Then, a new energy supplement scheme for VSOT is proposed. Based on an asymmetrical operation test topology, a multi-port low-voltage DC power supply scheme is proposed. The output ports of the energizing power are connected in parallel with some power units in the energy supplement valve section to provide active power loss for the VSOT system. Compared with the high-voltage energy supplementing method of the original system, the proposed scheme has the advantages of small equipment footprint and high power factor, etc. Multiple low-voltage DC ports can be connected in series or parallel, so the output voltage and current range are wider. The correctness of the proposed energy supplement topology and scheme is verified by simulation.