A Grid-connected Inverter With Mppt Function

Grid-connected inverter with maximum power point tracking(MPPT) function is focused in this thesis. All aspects of photovoltaic(PV) grid-connected system are comprehensively studied, which includes the nonlinear output characteristic of PV cell, MPPT methods and phase-lock control strategy of grid-connected inverter.The nonlinear output curves of PV cell are obtained by editting MATLAB M files based on the equivalent model of PV cell, and the nonlinear output characteristic is validated by experimenting on the TH110 PV cell. The results of simulation and experiment are agreed with each other. Then, discussion about MPPT methods is educed by this nonlinear output characteristic. Because the classical perturbation and observation method will surge around the maximum power point, an improved method is introduced and simulated using MATLAB. The simulation results indicate that the improved perturbation and observation method can reduce the power loss caused by the surge.The topology of power circuits are chosen and three stage PV grid-connected system is designed, so control of MPPT, control of DC generatrix voltage stabilization and control of phase-lock can be decoupled. Parameters of key components are calculated based on analysis of power circuits'principles. Moreover, PCB boards are manufactured.Control circuit of which the core is dsPIC30F4011 digital signal controller is built, and it is studied how to realize phase-lock control using dsPIC30F4011. The correlatively measure circuits are built at the same time. Moreover, PCB boards of each circuits are manufactured. Control frame of the whole system is designed. That is to say, power is controlled by outer loop and current is controlled by inner loop, while DC generatrix voltage is controlled separately. Control program is written according to the control frame.At last, hardware and software of system are combined together and debugged. Experimentation results indicate that the output current can preferably track grid voltage, and better control effect is obtained.