Research On Control Technology Of The Photovoltaic Grid-Tied Inverters And Parallel System

In recent years,photovoltaic power generation technology is in a rapid development stage,three-phase photovoltaic grid-connected inverter plays a key role in photovoltaic power generation system,and has become an important research direction in distributed generation system,wind-solar complementary generation system and other fields.The parallel control operation of photovoltaic grid-connected inverter breaks the output power limitation of photovoltaic power generation system,and improves the flexibility of the system.At the same time,redundant structure design can improve the reliability of photovoltaic power generation system.Therefore,photovoltaic grid-connected inverter system and its parallel operation control become an important field of photovoltaic power generation.The research direction is of great significance.In view of the research background,this paper studies three-phase photovoltaic grid-connected inverter and its parallel system,the main contents are as follows:Firstly,the topology of a single photovoltaic inverter is introduced,and the three-phase full-bridge inverter is selected to analyze its working principle.The control strategy and parameters of the three-phase photovoltaic grid-connected inverter are designed,and the double closed-loop control strategy is used to simulate and analyze the three grid-connected inverter.Secondly,the structure of PV grid-connected inverter parallel system is analyzed,and the average model of parallel system is analyzed by choosing the parallel structure of common DC bus.The synchronization control strategy is designed based on the three-phase phase-locked loop.The three-phase phase-locked loop model and the simulation model of parallel system are built respectively.At the same time,the circulating current path of parallel system is analyzed.The circulating current generation principle of two inverter modules is analyzed when the carrier is not synchronous.The circulating current suppression strategy based on carrier phase modulation is proposed,and the circulating current suppression simulation model of parallel system is built for simulation analysis.Finally,an exploratory experimental study on the parallel system of photovoltaic grid-connected inverter is carried out.The hardware experimental circuit of the parallel system of photovoltaic grid-connected inverter is built by using the ARM chip made by ST company as the digital controller of the control system.The driving circuit and some sampling and controlling circuits of the inverter are designed,and the inverter is parallel.The connection characteristics and circulating current suppression characteristics of the system are verified.