Improved cascaded multilevel battery inverters with phase-to-phase SOC balancing capability

This paper presents a circuit to enable phase-to-phase SOC balancing for cascaded multilevel battery inverters that have separate battery modules for each phase. The balancing circuit called six-switch energy-level balancing circuit can help achieve a uniform three-phase SOC operation of the battery units in the entire system among all the phases. The balancing operation by transferring energy among different phases can be carried out without interrupting the whole system and the uniform SOC can be continuously maintained. Moreover, the three-phase balancing circuit can be a part of the cascaded multilevel inverters to increase the system power/energy capacity if needed. Since the uniform SOC operation is achieved for the entire battery energy storage system (BESS), the utilization and reliability of the batteries are increased. Simulation results have been carried out to verify the performance of the proposed three-phase SOC balancing circuit.