Research On Control Strategy Of Three-Level Photovoltaic Grid-Connected Inverter

Photovoltaic(PV) grid-connected generation is one of the effective ways of using solar energy, and the key of PV grid-connected technology is grid-connected inverter and grid-connected control scheme. This paper takes a three-level grid-connected inverter as the research object. On the basic of space vector pluse-width modulation (SVPWM), this paper adopt the current close-loop control strategy based on the grid voltage oriented, and it is simulated in MATLAB. To verify the control strategy's feasibility, this paper design the software and program it in a three-level inverter based on DSP, and then do the experiment of open-loop and clsoe-loop.Firstly, this paper introduce the topological structure and principle of three-level grid-connected inverter, and then reserch the SVPWM. On the analysis of the mechanism of inverter midpoint voltage fluctuation, This paper present a method for restaining the midpoint voltage fluctuation combining SVPWM. Experiments show that this method is simple and easy realization, more over it has good suppression effect to the midpoint voltage fluctuation.Secondly, this paper design the overall grid-connected crontrol strategy of the system. And it puts fordward to use of synchronous vector current PI control technology, adopt the current close-loop control strategy based on the grid voltage oriented to control the three-level inverter, and do the simulation in MATLAB. The simulation results show that the control strategy has good steady performance and dynamic performance and open on the unit power factor.And then, this paper analyses and compare several commonly used control method of maxium power point tracking(MPPT). For MPPT control requirements of the single stage system, this paper adopt perturbation and observation(P&O) as the system's MPPT control method. The simulation results show that this method is suitable and effective for the three-level grid-connected system.Finaly, this paper design the software and program it in a three-level inverter, and then do the experiment of open-loop and clsoe-loop. The experiment results show that the proposed control strategy is feasible and effective.