Optimization of the pulse-width-modulation strategy for redundant and non-redundant multi-level cascaded-cell converters

Future energy supply will be mainly ensured by renewable energy sources. Measures have to be taken to buffer imbalances in the grid caused by these volatile power sources. Battery energy storage systems (BESS) present a good solution for many applications. Besides efficiency and cost, reliability of these systems becomes increasingly important. Redundancy reduces the hazard of system failures. Highly efficient and redundant BESS can be built with multi-level cascaded-cell converters (MLCCC). Phase-disposition pulse-width modulation (PDPWM) can be applied for generating the sinusoidal output voltage. The optimized PDPWM presented in this paper distributes the losses equally among the switches. This increases the system's ampacity and balances the load of each converter cell. Finally, the application with redundant MLCCC is presented. Hereby, bypass thyristors are additionally used to increase the efficiency of the converter.