Comparison of the topologies of high efficiency neutral point clamping photovoltaic inverters

Photovoltaic (PV) inverter is one of the key elements in photovoltaic generation system. In order to enhance the utilization efficiency of solar energy and lower the cost of PV generation, high efficiency PV inverters have obtained much more attention during recent years. Neutral point clamping (NPC) three-level topologies have some attractive advantages, such as low switching loss, low EMI, no PV array leakage current and smaller filter inductors. Hence, NPC topologies are suitable for single-phase PV generation. In this paper, three typical NPC topologies (Diode NPC, Active NPC and Conergy NPC) are compared in detail, including modulation strategy, power loss distribution, device cost and operation characteristics. In addition, the conversion efficiencies of these three topologies are tested through experiments. The results show that: (1)Conergy NPC has the highest efficiency and lowest device number among the three topologies; (2)Active NPC has adjustable power loss distribution and is easy for heat sink design in high power applications, but it has complex control and the highest device cost among the three topologies; (3)The power loss distribution of diode NPC can not be adjustable and has negative influence on the heat sink design in high power applications.