Design and Experimental Research on MMC Valves with Energy Dissipation Capability

In order to solve the problem of surplus power during the fault ride-through process of the offshore wind power flexible DC system, a flexible DC converter valve with integrated controllable energy discharge has been researched and designed. When a receiving-end AC fault occurs in the flexible DC system based on this topology, it has the ability to discharge the excess power. There is no need to separately configure centralized energy-consuming devices, and it will not increase the floor area of the converter station, thus having relatively high economic efficiency. The working principle of the flexible DC converter valve with Energy Dissipation Capability has been studied. The working mode of sub-modules and the control logic for energy discharge switching have been clarified. The design method of sub-modules has been put forward. Taking the ±400kV/1100MW flexible high-voltage direct - current (HVDC) project as an example, a 2Ω/300kJ energy - dissipation resistor was selected for the sub - module. Simulations and tests verified the electrical performance of the sub - module with the added energy - dissipation branch. The measured maximum temperature on the surface of the carbon resistor was 69.8°C, and the maximum temperature of the secondary circuit board was 42.4°C, verifying the feasibility of the scheme.