Design and Implementation of a High-Power DC/DC Converter for HVDC Interconnections With Wide DC Voltage Range and Fault-Blocking Capability

Highly efficient and lightweight high-voltage high-power dc/dc converter is one of the key equipments needed by future HVDC grid. In order to satisfy the technical requirements of interconnecting HVDC lines with different voltage levels, this article develops a thyristor-submodule hybrid dc/dc converter (TSDC) by combining the merits of low cost, low conduction loss, and high robustness of thyristors with the high controllability of the cascaded half-bridge submodules (SMs). The proposed converter presents the attractive features of efficient dc/dc conversion, reliable turn-on and turn-off of the thyristors, wide dc voltage operation range, and above all, the dc fault-blocking capability which avoids the installation of dc circuit breakers. The circuit structure, operating principle, and control schemes are discussed. The validity and effectiveness of the TSDC are verified by 150-MW, 100-kV/300-kV simulation case study as well as the experimental tests from a 4.5-kW, 300-V/450-V scaled-down prototype.