State of charge balancing during fault tolerant operation of battery storage systems based on cascaded H-bridge multilevel inverter

The modular structure of the cascaded H-bridge inverter offers multiple benefits to the B6-bridge inverters used in many systems. State Of Charge Balancing algorithms are required to achieve maximum utilization of the energy stored in the batteries. With additional algorithms fault tolerant operation is possible. Both algorithms are based on the concept of Neutral Point Shift, which utilizes the existence of an ungrounded star point. The possible superposition of both neutral point shifts has to be considered to avoid over modulation of the inverter. This paper presents an algorithm that limits the amplitude of the neutral point shift for balancing purposes if a fault occurs.