Research On Control Strategy Of PV Microgrid-Connected Based On The Improvement Of Droop Method

Energy crisis and environment problems are becoming more and more significant, and it makes wind energy, solar energy and other clean renewable energy attract extensive attention. Distributed generation (DG) is an effective way of developing and using renewable energy. It will have an effect on the running of system when distributed power is connected to grid since the randomness and dispersiveness of DG, this kind of impact limits the development of DG technology. Microgrid combines DG and energy store device for a controllable system that provide electric power to local load. It will not only solve the problem above well enough, but also complement bulk grid, and enhance the reliability of power supply. The running of microgrid has grid-connecting model and island model. Ensuring microgrid system plays its strengths, choosing appropriate control strategy under different running model is premise. Therefore, it’ll be of great significance to control simulation model through setting up microgrid system of which distributed generation is PV cell.First of all, this thesis started from the topological structure of photovoltaic (PV) microgrid grid-connected system, we built simulation model of PV cell, realized maximum power point tracking of PV cell through perturbation and observation method. Considering mass harmonic wave content in current that DG interface inverter outputs under microgrid system, to reduce harmonic wave content, we analyzed and compared different kinds filter, then LC form filter was chose and its parameters were adjusted. Then we undertook research on droop control principle of microgrid; various elements were analyzed, which have effect on reactive power sharing when DG is under parallel operation in island model. Based on traditional droop control methods, this thesis proposed droop control method of compensated line pressure drop, reactive power sharing of DG under island model was improved apparently through adjusted method. This thesis designed presynchronizing controller for grid-connection to reduce the impact of the surge current to bulk grid at the moment that the system was connected to grid. Again, to meet requirement of that microgrid system and bulk grid were connected for running, it kept output power constant through bringing voltage pressure, frequency reference value setting ring into droop controller, realized constant PQ control of DG. At last, miniature microgrid model which contains PV cell was set up under Matlab/Simulink simulation environment, improved droop control strategy, grid-connected presynchronizing controller and improved constant PQ control strategy was applied into the example we designed, simulation results showed the validity of improved control strategy according running model switching and the characteristics of load changing.