Battery Energy Support to Cascaded H-Bridge Converter-Fed Large-Scale PV System During Unbalanced Power Generation

The cascaded H-bridge (CHB) multilevel converter is an attractive solution for integrating photovoltaic (PV) generators with the ac grid. However, the power generated in the PV panels may be unequal due to partial shading, temperature change, and dust layer accumulation leading to unequal and unbalanced power between the phases and possible violation of power quality constraints. Fundamental frequency zero-sequence voltage (FFZSV) injection can be applied, but this method can produce overmodulation in conditions with high PV power mismatch. A new FFZSV is proposed in this article assuming a CHB with a battery energy support (BES) to compensate for the effects of unbalanced PV power generation. A barycentric coordinate representation helps to determine the capacity of the BES required. A coordinated control between the PV system and BES is also proposed in the article. Additionally, a novel approach to deliberate FFZSV injection is discussed in this article by which the maximum charge and discharge rate for the BES can be obtained along with balanced current injection into the grid. The effectiveness of the proposed technique is verified in numerical simulations and with experimental results.