Research On Mppt And Double Closed-Loop Control Technology Of Photovoltaic Grid-Connected Inverter

Grid inverter is an important part of new energy power generation system. Based on three phase type single-stage isolated grid inverter as the research object, the two core problems of grid inverter, maximum power point tracking and double closed-loop control problems were In-depth studied.MPPT control technology is studied in the first place. Through the introduction of the working principle and the equivalent mode of photovoltaic battery, the output characteristic curve of photovoltaic battery is obtained. On this basis, some commonly used MPPT algorithm is analyzed, which Emphasis on the Implementation method of perturbation and observation method. For the oscillation and misjudgment phenomenon of perturbation and observation method, this paper put forward an improved perturbation and observation method, which principle is on the basis of traditional perturbation and observation method combined with constant voltage tracking method to improve the oscillation phenomenon. At the same time, by the change of current to judge whether the light intensity is changed or not, thus overcome misjudgment effectively. The simulation results indicate that the improved perturbation and observation method can rapidly track the maximum power point, as well as eliminate the phenomenon of the oscillation and miscalculation effectively.Secondly, the voltage and current double closed-loop control strategy is researched. On the basis of three-phase inverter dq model, Structure of control system are analyzed, and the parameters of PI controller is obtained by designing double loop control system. For PI controller cannot control the AC variable and its poor ability of grid interference resistance, a proportional resonant (PR) controller is introduced, comparing the performance of two kinds of controller obtain a result that PR controller has better ability to eliminating steady-state error and resisting the disturbance. Considering the superiority of PR controller, combining PR control and PI control constitute a kind of PI-PR control system, which is combined with voltage outer loop PI control and current inner loop control.Finally simulation and experimental research was carried out for the entire PV system, setting up the system simulation model of current inner loop monocyclic PI control, voltage and current double loop PI control and voltage outer loop PI control current inner loop PR control. The simulation results show that the control system can well follow the voltage and current waveforms. By comparing the simulation results in two kinds of control mode find that PI-PR inverter has a better effect of grid-connected. Experimental study in this paper is based on the experimental platform of100kw photovoltaic grid inverter. On this experimental platform, the software implementation of double loop control is explained in detail, and make the inverter grid-connected experiments, the experimental results show that the correctness of the voltage current double loop system.