A Modular Resonant DC-DC Converter With High Step-Down Ratio for Tapping Power From HVDC Systems

In this article, a new circuit topology of DC-DC converter for high step-down ratio is proposed. The proposed DC-DC converter can be used to tap power from high-voltage direct current (HVDC) system to feed the local loads that are located in the vicinity of HVDC transmission corridor. The proposed DC-DC converter consists of a large number of identical submodules each having one controllable switch, two diodes, and one capacitor. The operation of DC-DC converter is based on repeated charging and discharging of capacitors through a resonant circuit. Zero-current switching is achieved for all the switches used in the converter. In case of failure of one submodule, the failed submodule could be bypassed without affecting the normal operation of the HVDC tap. Equations governing the behavior of the proposed converter and the design of the components have been included in this article. The operational performance of the line commutated converter based HVDC system along with the HVDC tapping scheme with the proposed converter is investigated using a simulation model developed in PSCAD/EMTDC. The proposed circuit topology has also been verified with a down scaled experimental prototype.