Research Of PV Micro-Inverter Based On Electrolytic Capacitor-Less Power Converter

The micro-inverter of photovoltaic power generation system has the advantages of low cost,flexible installation,and high efficiency of photovoltaic model power generation.However,due to the bad working environment,the DC-bus capacitor life of traditional micro-inverter is much lower than other components of the system,and result in a higher inverter failure rate.Electroyltic-less capacitor technology can effectively improve the reliability and life of the micro-inverter,but its lower energy storage capacity leads to serious fluctuations in the DC bus voltage.These problems will cause fluctuations in the output power of the PV module.It has a serious impact on the output power of the grid-connected inverter.In order to solve these problems,the paper focus on a single phase H-bridge inverter with decoupling bridge arm to effectively suppress the DC bus voltage fluctuation.On this basis,the paper also studies the design of maximum power point tracking control and grid-connected inverter controller.The specific work is as follows:Firstly,the mathematical model of photovoltaic devices is established.Based on this,the power characteristics of photovoltaic devices are deeply studied.The reasons of he output power of photovoltaic model is susceptible to external working environment and the basic principle of maximum power point tracking control are analyzed.Based on the above work,the existing MPPT methods are compared and analyzed,and the MPPT control method suitable for the system is selected.Secondly,the reasons for the bus voltage fluctuation after decoupling capacitor reduction and the theoretical basis of the influence of bus voltage fluctuation on system performance are studied.The analysis indicates that the fluctuation of the DC bus voltage can be effectively reduced by reasonable control of the pulsating energy of the power grid.Taking this as a guiding principle,this paper studies a single-phasebridge inverter with decoupling bridge arm,analyzes the control circuit of pulsating energy and the corresponding working mode,and proposes the control method of the inverter.Thirdly,in order to realize the grid-connected operation of the inverter,the working principle and existing methods of the phase-locked loop are studied in depth,and the theoretical analysis of the application of the second-order resonant filter and synchronous rotating coordinate transformation in the phase-locked loop is carried out.In order to reduce system cost and increase power density,the existing filters are analyzed and compared.Finally,the LCL filter is selected to filter out the switching frequency components in the grid-connected current.Aiming at the shortcomings of existing grid-connected current PI controllers,a proportional-resonant controller with grid voltage feedforward is studied,which can solve the problems of weak suppression of external interference and tracking of AC signals.Finally,the paper also designs the key components and system software and hardware of the proposed electroless capacitor micro-inverter,constructs 200 W experimental research and conducts several experiments.The results verify the validity and correctness of the electroless capacitor micro-inverter studied in the paper.