Power Balancing with Zero Sequence Voltage Injection Method for Cascaded H-Bridge Inverter Fed Grid-Connected PV System

Abstract

Cascaded H- Bridge multilevel inverters are suitable for large-scale photovoltaic plants because of their modularity, scalability, and multiple low dc-link voltages. Based on the dc-link voltage, cascaded H-bridge multilevel inverters can be classified as symmetrical and asymmetrical configurations. Uneven irradiance, damage, and dusting of panels cause unequal power generation in the photovoltaic system causing unbalanced currents flowing into the grid. The zero-sequence voltage injection method is a popular technique to attain balanced grid currents with uneven power generation. However, severe imbalance may require the generation of higher pole voltages with the injection of zero-sequence voltage. This may force the H-bridge module into the overmodulation region, increasing the harmonics in grid current. Hence, to choose the appropriate configuration of cascaded H-bridge inverter for photovoltaic applications, a comparison of power balancing capability with zero sequence injection method between the symmetrical and asymmetrical configurations is proposed in this paper. Matlab-Simulink results are included to support the proposed method.