High-frequency Isolated Photovoltaic Grid-connected Inverter Based On LC-T Resonance

From the long-term development of energy point of view,the new energy will eventually replace the conventional energy.From the recent development point of view,the new energy is bound to become an important part of the electricity market.For the support of the policy,the photovoltaic power generation industry as an important part of the new energy field in the past decade the rapid development.Photovoltaic grid-connected inverter is also the core component of energy conversion and control,which has become the focus of domestic and foreign scholars.In this paper,an LC-T resonant high-frequency isolated photovoltaic grid-connected inverter is proposed,which is based on the development trend of miniaturization and high power density of power devices.The inverter has the advantages of light weight,high power density and electrical isolation.It is suitable for single-phase low-power distributed photovoltaic grid-connected power generation system.Firstly,the topology of the inverter circuit is introduced,and the working mode of the circuit is briefly described,and the function of each module is explained.The mathematical model is deduced in the resonant state,and the phase shift angle is less than the critical phase shift angle.The feasibility of the scheme is proved.Then,the steady state analysis of the circuit model is carried out,and the resonant equivalent model is established.The influence of the parameters of the resonant unit on the gain,the soft switch and the efficiency of the inverter is obtained,and the principle of designing the resonant parameters is given.Secondly,according to the working characteristics of the circuit topology,the closed-loop control strategy including voltage feedforward and dead-zone compensation is designed to realize the efficient and stable operation of the inverter unit power factor.The system is described systematically from the principle to the simulation of the maximum power point tracking,dead zone compensation,phase locked loop technology and island detection.Then the stability of the control system is analyzed theoretically,the feasibility of the closed-loop system is verified,and the whole inverter system model is verified.Finally,according to the proposed circuit topology and control strategy,the hardware system and software system of the prototype are designed,which realizes the stable and efficient operation of the inverter under the closed-loop control system.Through the analysis of the waveforms of each part of the prototype,the feasibility and the correctness of the hardware and software system are proved,which can provide reference for the follow-up study of the inverter.