On extending the energy balancing limit of multilevel cascaded H-bridge converters for large-scale photovoltaic farms

When multilevel cascaded H-bridge converters are used to interface large-scale photovoltaic farms to the electricity grid, the stochastic variation of irradiance and other factors lead to unequal power generation among the phases, affecting the three-phase balanced system. Injections of fundamental frequency zero sequence to modulation references can deal with this problem. This paper proposes the third harmonic injection to extend the balancing limit of three-phase unbalanced power generation. The concepts and definitions of converter energy balancing limit are presented to assess its energy balancing capability. Numerical comparison results reveal that the proposed third harmonic injection method has greater energy balancing capability. Selected simulation results are provided to verify the performance of the proposed method.