Research On Fly-back Micro-inverter For Photovoltaic System

With the substantial reduction of fossil energy and the increasing pollution of the environment,new energy technologies with photovoltaic power generation as the direction are booming at home and abroad.The inverter is the hub of the photovoltaic power generation grid connection system,and completes the DC to AC inverter.the micro-inverter has become one of the main development trends of small-power distributed photovoltaic power generation grid-connected systems due to its many advantages such as small size,flexible installation,high solar energy utilization rate,and convenient maintenance.Research on micro-inverters with high efficiency,high reliability and low cost has broad market prospects.The flyback converter has a simple structure and high safety while achieving boosting.This paper takes the flyback photovoltaic micro-inverter as the research object,and focuses on its conversion efficiency,reliability and service life from the aspects of maximum power tracking(MPPT)control and power decoupling.The specific research is as follows:(1)In view of the deficiencies of the traditional MPPT control method in terms of stability and transient response speed,and the problem of using the control voltage to search for the maximum power point does not apply to the flyback micro-inverter in discontinuous mode.This paper improves on the basis of the traditional disturbance observation method,and studies a variable step size MPPT control method based on current disturbance.Using the change of the output power of the photovoltaic cell for PI adjustment,it can output a flexibly adjustable current disturbance step according to the distance of the maximum power point and the sudden change of external factors.The simulation comparison between the traditional disturbance observation method and the improved MPPT control method in PSIM software verifies the advantages of this method in terms of transient response speed and stability,and improves the efficiency of the inverter.(2)For the problem of double frequency power disturbance at the input of the flyback micro-inverter in a single-phase photovoltaic grid-connected system,the traditional solution is to parallel electrolytic capacitors on the photovoltaic side,but its service life and reliability will be serious Affect the inverter performance.This paper proposes a flyback micro-inverter based on a new power decoupling circuit.This decoupling circuit can use long-life thin-film capacitors to replace low-reliability electrolytic capacitors,and can solve double-frequency power disturbances;the service life of the inverter is improved;and the circuit structure is simple,the use of fewer components,further reducing the cost of the inverter.In addition,the working process of the new inverter is analyzed in detail,and the control method of the circuit and the design of the main parameters are described.Finally,the feasibility of the decoupling circuit is verified in the PSIM simulation software.(3)Design the software and hardware of the flyback photovoltaic system on the basis of completing the above theoretical derivation and analysis.The selection of the main components in the system is expounded,and the sampling circuit,switch drive circuit and system software are designed.A 100 W experimental prototype was built to verify the grid connection quality and efficiency of the designed flyback photovoltaic micro-inverter through experiments.