Battery energy support to Cascaded H-Bridge converter fed large scale PV system during unbalanced power generation

In this paper, a large-scale grid-connected PV system along with a battery energy system is analyzed for unbalanced power generation in the PV system. The system is connected to the medium-voltage grid through a Cascaded H-Bridge converter where each cell of the converter has individual PV and an integrated battery system. With the integrated battery energy system, the intermittent and unequal power generation in the PV modules can be highly smoothed. However, the interphase power unbalance in the converter remains. To inject balanced current in presence of unbalanced power generation in the phase legs, a novel method of fundamental frequency zero-sequence voltage injection (FFZSI) method is proposed. The extent of unbalance that can be tolerated by the converter without going into overmodulation and without sending unbalance power into the grid is established. Simulation results are included to verify the effectiveness of the proposed approach.