Hybrid cascaded H- bridge multilevel inverter for fuel cell power conditioning systems

This paper investigates the potentials of a hybrid cascaded multilevel inverter in the development of high-power AC power supplies with specific emphasis on power conditioning systems (PCS) for alternate sources of energy. Fuel cell generation systems in particular are expected to see increasing practical usage due to several advantages they offer over conventional generation systems. This article proposes a suitable modulation strategy that complies with the low switching frequency requirement of the hybrid seven-level cascaded inverter power devices while fulfilling the required performance specifications of a fuel cell PCS. A particular advantage of this topology is that the modulation, control and protection requirements of each bridge are modular and it requires only a single dc source in each phase leg. For the cascaded multilevel inverter a variety of modulation strategies have been reported, with the most popular being carrier - based and space vector modulation (SVM). This paper focuses on the FPGA based carrier PWM method for the cascade multilevel inverter in PCS. Both the hybrid circuit topology and its control scheme are described in detail and their performance is verified based on simulation and experimental results.