Power Balance Optimization of Cascaded H-Bridge Multilevel Converters for Large-Scale Photovoltaic Integration

Multilevel-cascaded H-bridge converters are promising candidates for next generation photovoltaic power converters. They feature reduced switching losses and higher conversion efficiency with modular structure; characteristics vital for large-scale photovoltaic power plants. However, the stochastically-variable nature of irradiance levels and ambient temperatures affects the normal operation of this topology, because power levels in the three phases can be unequal. The existing zero sequence injection-method can deal with the power imbalance problem, but it is limited in its application. The paper proposes a zero sequence injection method to optimize the converter power balance, extending the converter operation with severe power imbalance. Based on the proposed optimal method, a simplified optimal zero sequence injection method requiring less calculation effort is derived and compared with the optimal method. Simulation and experimental results validate the effectiveness and feasibility of the proposed methods.