| Micro-inverter used in distributed photovoltaic power generation system is the core device converting electricity.The outputing waveform quality and working efficiency of micro-inverter directly affect the performance of the generation system.The inverter struct,controlling stratege and auxiliary circuit are studied in this thesis,and the off-grid micro photovoltaic inverter outting pure sine wave is designed.On the basis of principle of micro-inverter studied,a two-stage inverter scheme composed by full-bridge DC-DC boost converter and full-bridge DC-AC converter has been designed.Working principle of the two stage inverter has been analyzed.DC-DC converter controlled by PWM signal and DC-AC converter controlled by SPWM signal have been designed.The DC-DC converter,the DC-AC converter and the whole inverter have been modeled and simulated by Matlab/Simulink software.The hardware circuit of inverter has been established and closed loop controlling program has been compiled.Parameters of the micro-inverter,DC-DC converter circuit,DC-AC converter circuit,isolating drive circuit,voltage/current detection circuit,auxiliary power supply circuits have been designed.Wherein,DC-DC converter circuit and DC-AC converter circuit are used to boost and invert respectively,isolating drive circuit is used to amplify controlling signal to drive power switches,voltage/current detection circuit is used to detect input/output voltage and output current,auxiliary power supply circuit is used to supply power of the control chip,isolating drive circuits and detection circuits.DSP control chip has been used,and the controlling program,include closed-loop controlling program of DC-DC converter and DC-AC converter,has been programmed.Inverter prototype has been made,experiments has been carried out in the laboratory environment,and the output waveforms/data of the inverter were measured and analyzed.Analyzed results show that the off-grid micro photovoltaic inverter fulfill the design requirement. |
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