A Hybrid Modular DC/DC Converter for HVDC Applications

Recently, remarkable progress has been made in the voltage-source-converter-based high-voltage direct current (HVdc) transmissions. For the upcoming need to interconnect multiple dc transmission lines with different voltage levels, high-voltage and large power dc/dc converters are necessary. This article investigates a nonisolated bidirectional dc/dc converter that is composed by cascaded half-bridge submodules, series-connected diodes, and mechanical disconnectors. This hybrid topology presents very attractive features, such as low cost, high efficiency, and light weight. Operation principle, parameter design, and dedicated control strategies are developed. Simulation of a 150-MW, 200 kV/300 kV dc/dc converter has been performed to verify its performance and evaluate the efficiency. Moreover, a downscaled three-phase prototype rated at 500 V/300 V 4.5 kW has been built and tested. The experimental results further confirm the effectiveness of the proposed dc/dc converter.