Research On Two-stage Pv Grid-connected Inverter And Power Decoupling

The two-stage PV inverter is researched in this paper. The control principle of the two-stage PV inverter is present in detailed. The advantage and disadvantage of various MPPT methods are compared. The P&O-based MPPT method is chosen as it is the most widely used. Then the disadvantage of the method based on current optimal MPPT control is discussed. An adaptive MPPT method with variable step-size is adopted, the conflict between tracking rate and precision of steady state is resolved with this method.It is well known that there exists second-order harmonic current and corresponding ripple voltage on DC bus for two-stage inverter. The low frequency harmonic current is normally filtered using a bulk capacitor in the bus which is used to implement power decoupling. But, the cost of the system will be increased with volumes of capacitors, and the life of the PV system will decrease synchronously. The reason of the voltage ripple on DC bus for two-stage inverter is described, and the relationship among the value of capacitor and the voltage ripple of DC bus and the power rate and the average voltage of DC bus are analyzed quantificationally. Then a decoupling converter idea is derived. The DC-link capacitor can be reduced massively with this converter synchronously, the life of the system can be increased. The topology and the control strategy of the converter are researched deeply. Then the mechanism of the voltage ripple on DC bus for two-stage inverter is analyzed in the viewpoint of"current", the same points of the decoupling converter and the active power filter(APF) are revealed, a concept of"DC APF"is given out. The simulation model of this decoupling converter is built up. The academic analyses are proved with the simulation results.A 1kW prototype based on TMS320F2808 is built up. The experimental results are received based on this prototype. The feasibility and validity of the analysis are proved.