A Novel Flexible Thyristor Switch Modules Based AC Chopper for the Renewable Energy VSC-HVDC Transmission System

The renewable energy voltage sourced converter based high-voltage direct current (VSC-HVDC) system has a broad application prospect, and the AC chopper (ACC) is the core equipment to realise the system fault ride-through. The traditional ACC consists of multiple three-phase energy-dissipation valves, which requires a large number of thyristors, covers a large area, and is difficult to accurately match dissipated power, which restricts its further promotion and application. In this paper, the flexible thyristor switch modules based AC chopper (FTSM-ACC) is proposed, which adopts diode bridges for rectification and combines with thyristor energy-dissipation switches to reduce the cost and volume while realising the flexible casting and cutting of the FTSM-ACC, which provides a new way of thinking for the improvement of the technological and economic performance of ACC. Further, the FTSM-ACC control strategy and key parameter coordination method are proposed. And the system simulation is carried out to analyse the system fault ride-through characteristics of FTSM-ACC. On this basis, a 4 kV/3.2 MW FTSM-ACC prototype is built, and the experimental results verify the effectiveness of FTSM-ACC and demonstrate its advantages over traditional ACC. Finally, the performance and economic efficiency of different ACCs are compared. Compared with the traditional ACC, the FTSM-ACC improves the performance by more than 50%, and the total cost and volume are reduced by 33% and 46%, which has a great performance and economic advantage.