A New MMC-LCC DC Converter Topology with No Reactive Power Consumption

This paper presents a new MMC-LCC DC converter, including the topology structure, operating principle, basic control strategy and economic analysis. This new converter adopts multiple modular capacitors between the converter transformer and valves of the conventional LCC topology. The capacitors are switched on to provide auxiliary commutation voltage to help commutate before the natural commutation point in rectifier or after the commutation ending point in inverter, and switched off after the commutation procedure, achieving no reactive power consumption even reactive power generation. The comparison to other topologies is conducted and control strategy is designed to not increase the insultation requirement. The basic main circuit equation is deduced and real project parameters are evaluated for economic analysis. The performance of the converter is validated by EMTDC simulation and the result shows that the project benefit will be significant compared to LCC.

I. Introduction

The conventional LCC DC project consumes substantial reactive power when in operation, and the AC filters and shunt capacitors should be installed for compensation, which occupied almost half the area of LCC converter station. The filters and capacitors are switched on by breakers, which react comparatively slowly as an mechanical equipment, limiting the LCC power rising rate and power reverse. The lag of cutoff of the capacitors is the main cause of the overvoltage when the converter blocks or retards at a AC of DC fault. Compared with VSC, the reactive power compensation equipment is a main disadvantage of LCC.