Circular Power Balancing Topology and Power Flow Optimization Strategy for Solving PV Power Mismatch Problem of Modular MVDC Converters

Abstract

Power balancing topology is an effective solution to the photovoltaic power mismatch problem in a medium voltage dc system. However, the existing power balancing topologies are all based on a chain structure, in which the mismatched power needs to be transferred through multiple power balancing units (PBUs). In the case of severe power mismatch, the accumulated balancing power is very large, resulting in increased system power losses and current stress on the switches. To solve this problem, a circular power balancing topology is proposed in this article. By connecting another PBU between the first and last submodules of the modular converter, the power balancing path becomes circular. With this new structure adopted, there are two paths for power transfer between any two SMs. An optimization method is also proposed to reduce the current stress by half. Compared with an existing scheme, the proposed topology is able to improve the power efficiency. The theoretical analysis is verified by simulation and experiment.