A flexible five-level cascaded H-bridge inverter for photovoltaic gird-connected systems

With the rapid penetration of photovoltaic (PV) grid-connected system in industrial and commercial application, it is critical to improve the efficiency and enhance the utilization of PV power generation system. This paper proposes a flexible five-level topology based on cascaded multi-level inverter for PV grid-connected system. By adding a bidirectional switch to conventional multi-level inverter, the proposed topology transforms operating mode between two-level H-bridge inverter (HBI) and cascaded multilevel inverter (CMI) according to the variation of DC link voltage. When output voltages of PV arrays are lower, the proposed inverter works in CMI mode to widen the generation range. When output voltages of PV panels are higher, inverter works in HBI mode to increase the efficiency. Hence the system incorporate the low losses feature of HBI and low grid-connected current THD advantages of CMI. This way, a wide range output voltage operation with high efficiency can be achieved without extra DC-DC converter. Experimental results of the proposed five-level CMI are presented to validate the feasibility of the proposed topology.