Beserch On Control Strategy Of Three-level Grid-conneced Photovaltaic Inverter

The development and utilization of new energy sources is extremely important as global energy crisis and environmental pollution. Solar power which is efficient, clean, abundant, widely distributed, etc. is becoming the focus of governments and research institutions. In order to efficiently and extensively using of solar energy and high-quality, friendly photovoltaic (PV) grid connection, PV grid-connected inverter control strategy is the key issues to be addressed.Traditional photovoltaic grid connected inverters mainly adopt the voltage and current double closed-loop PI control method, yet path coupling, windup, inadequate harmonic suppressing capacity and other issues will seriously lead to a poor power quality of the inverter.This paper focuses on control method of three-phase photovoltaic grid connected inverter, and the research mainly includes the following contents. Firstly, this study introduces the PV grid system and the voltage and current double closed-loop PI control method. A new multi-vector proportional integral control strategy is proposed in order to achieve the high-quality of the power. Secondly, the DC side midpoint imbalance problem of the three-level NPC inverter is described, and a new midpoint potential balance control method that based on extended state observer and non-linear PI controller is presented. Lastly, experimental prototype of20kW three-phase grid-connected PV system was established which is used to testify the effectiveness of the proposed methods.