A low-cost and low-ripple DC chopper with thyristors-based switch modules and flexible switching control strategy for the offshore wind VSC-HVDC system

The DC chopper (DCC) is crucial for achieving the fault ride through of the offshore wind VSC-HVDC system. Traditional DCCs use expensive fully-controlled devices and water-cooling systems, and the huge cost and losses limit their further application. A low-cost and low-ripple DC Chopper with thyristors-based switch modules and flexible switching control strategy (SC-DCC) is proposed in this paper, which uses low-cost thyristors to replace fully-controlled devices, returning the DCC technical route to the use of thyristors, and reducing the DC-link voltage ripple through the strategy of cycle rotation action. Furthermore, a parameter design methodology is introduced, and a 3 kV/1.8 MW SC-DCC prototype is built. The prototype experimental results have verified the feasibility of the proposed scheme. On this basis, the simulation is conducted at the system level, and the results show the good FRT performance of SC-DCC. Compared to the existing half-concentrated DCC, the cost of SC-DCC is reduced by more than 50%, providing a low-cost and high-performance FRT solution.