Study On Off-grid Micro Photovoltaic Inverter Using Multilevel Boost

Off-grid photovoltaic(PV)inverter is the core module of independent PV photovoltaic power generation system,its work-efficiency is one of the important factors for affecting the performance of PV photovoltaic power generation system.In this thesis,a low-loss off-grid micro PV inverter has been developed after studying topologies of power main circuit,auxiliary circuits and control strategies etc.Basing on the study of off-grid PV inverter principles,the main circuit scheme using multilevel boost and bridge inverter has been determined,and an inverter composed of three-level boost DC-DC converter and full-bridge DC-AC converter has been designed.Wherein,the DC-DC converter consists of boost circuit,high frequency transformer and voltage doubling rectifier circuit,the DC-AC converter consists of full-bridge inverter circuit and LC filter circuit.Working principles of the DC-DC converter and the DC-AC converter have been analyzed in this thesis,and closed-loop control schemes of the DC-DC converter using PWM signal and the DC-AC converter using SPWM signal converter have been designed.Besides,the DC-DC/DC-AC converter and the entire PV inverter have been simulated by Matlab/Simulink software.Parameters of the PV inverter have been selected,hardware circuits have been built,and control programs have been compiled.In order to meet control requirements of the inverter,detecting circuits,driving circuits and auxiliary power supply circuits have been designed.Wherein,detecting circuits are used for collecting input/output voltage of the DC-DC converter and output voltage/current of the DC-AC converter,driving circuits are used for driving power switch of the DC-AC converter and the DC-DC converter by amplifying the signals of controller,and auxiliary power supply circuits are used for supplying power of the detecting and driving circuits.Micro controller has been used in this thesis.Control programs including AD sampling,control algorithm,PWM and SPWM driving etc.Closed loop control schemes have been realized by combination of the software and the hardware.Experiments about the off-grid micro PV inverter have been taken in laboratory,and the acquired data and waveforms have been analyzed.