Cascaded Single-Stage NPC Boost Multilevel Inverter for Distributed Generation Systems

This paper presents a new cascaded single-stage boost multilevel inverter topology for distributed generation (DG) systems, which integrates the advantages of the Z-Source network, the Neutral Point Clamped (NPC) and the cascaded H-Bridge (CHB). Most of DG systems, such as photovoltaic (PV), wind turbine and fuel cells, normally require a two-stage power converter with the buck-boost properties, which make it expensive, less efficient and difficult to control. However, the proposed inverter topology can implement voltage boost in a cost effective single-stage, solving the imbalance problem of the DC-link voltage. Also, it enables existing power systems to reach a much higher output voltage just by using the standard low-voltage switch devices and low voltage DC-sources in a reduced number of power cells. Moreover, it can enhance the reliability by allowing the shoot-through states without damaging the switch devices. The topology configuration and operating principle of this inverter are analyzed, and the inverter control schemes are proposed and simulated. Simulation and experimental results with a 1.2kW system are presented to validate the proposed topology and control method.