Research On Control Strategies Of Dual Inverter Open-End Winding Photovoltaic Generation System

In the context of the global energy crisis and environmental pollution,the development of clean energy has received worldwide attention.As a technology to convert solar energy into electric energy,photovoltaic power generation technology has incomparable advantages in the field of clean energy utilization.The huge reserve of solar energy provides a solid guarantee for the rapid development of photovoltaic technology.Multilevel inverters have been widely used in high-voltage and high-power photovoltaic power generation due to the topological advantages.The dual inverter openend winding photovoltaic generation system topology is a multi-level topology formed by series connection of the AC output sides of the two inverters through the primary side of the open-winding transformer,which can effectively improve the level of the output voltage and utilization ratio of DC voltage.The two inverters are powered by two independent PV arrays,each of which can operate at different maximum power points,so that the efficiency of the photovoltaic generation system can be effectively improved.In addition,the dual inverter open-end winding topology also reduces the use of clamp diodes and flying capacitors,effectively reducing system cost.However,the dual inverter open-end winding photovoltaic generation system faces many problems and challenges in practical applications.Firstly,the output power of two sets of PV arrays will be different due to environmental factors.Therefore,it is necessary to study the unbalanced power control strategy of the dual inverter open-end winding photovoltaic generation system.Secondly,the inverter with larger output power will be over-modulated if the output power of the two sets of PV arrays varies greatly,so corresponding solutions need to be put forward.Finally,the differential common mode voltage in the dual inverter open-end winding photovoltaic system will generate zerosequence current through the zero-sequence current channel,reducing the quality of gridconnected current,so the differential common mode voltage suppression scheme is also required.Based on the mathematical model of the dual inverter open-end winding photovoltaic generation system,the 180° decoupling and 120° decoupling control scheme for the dual inverter open-end winding are introduced,and the control block diagram under unbalanced power operating conditions is given.Secondly,the mechanism of the overmodulation problem of the dual inverter open-end winding system under the condition of large unbalanced power is analyzed in detail.Meanwhile,two reactive power compensation control schemes are proposed based on the operation vector diagram of dual inverter open-end winding system.Finally,the differential common mode voltage suppression problem in dual inverter open-end winding photovoltaic generation system is studied,and a novel differential common mode voltage suppression strategy is put forward.The correctness of each control strategy proposed in this paper has been verified by simulations and experiments.