An MMC With Integrated Energy Dissipation Function Using Thyristor-Based Chopper Modules for the Offshore Wind VSC-HVDC System

The dc chopper (DCC) is the key equipment to realize the ac fault ride through (FRT) of the offshore wind voltage source converter (VSC)-HVdc system. The existing DCC is arranged independently, and the full control device is used to control the absorbed surplus power, which is costly and limits its further application. In this article, an modular multilevel converter (MMC) with integrated energy dissipation function using thyristor-based chopper modules (TCM MMC) is proposed. It distributes the chopper module that dissipates the surplus power of the system into the submodules of MMC, shares the energy supply and water-cooling system with the MMC, and uses the semicontrol device, namely thyristor, to cooperate with the
LC
circuit to realize the control of the energy dissipation function, thus providing a low-cost solution to the FRT problem. Furthermore, the control strategy and parameter matching method are proposed. The 0.75 kV/0.37 MW TCM MMC prototype is built, and the experimental results verify the effectiveness of the proposed scheme. Finally, the performance of TCM MMC in the different FRT process of the ±150 kV/700 MW VSC-HVdc system is analyzed, and the proposed scheme is compared with existing schemes in various aspects.