A Transformerless Railway Power Quality Compensator Based on Cascaded H-Bridge Featuring Reduced Branch Capacity Requirement

Featuring high modularity, scalability and transformerless structure, cascaded H-bridge (CHB) based power quality compensator (PQC) is a promising power quality solution for railway power system (RPS). Firstly, branch rating requirements of the conventional CHB based PQCs for co-phase RPS are analyzed under two typical traction transformer schemes, i.e., the V-v scheme and the Scott scheme. Then, a novel CHB based PQC with a special wiring connection style of the Scott transformer is proposed, which achieves reduced total submodule quantity and total branch capacity compared with the conventional solution in V-v and Scott schemes. In addition, a branch current reference generation method is introduced for both branch energy balancing and power quality regulation, which avoids the complicated zero-sequence circulating current injection issue and thus facilitates controller implementation in practice. The effectiveness of the proposed CHB based PQC and the corresponding control strategy is verified by both simulations and experiments.