Reseach On Coordinated Compensation Strategy For Photovoltaic Inverter Of Microgrid

The contradiction between society Energy demand and environmental problems caused by the excessive use of fossil energy, so that new energy power generation is increasing attention. Due to Sufficient energy and less affected by region,the photovoltaic generation (PV) is most representative distributed power generation(DG).However, a large number of connecting the traditional grid by DG brought a lot of negative effects, and the microgrid accessing is an effective way to solve the new energy accessing the traditional grid. Therefore, the study of photovoltaic power generation system of microgrid control has very important significance.The PV array is the only power source of the PV system when there is not battery installed on the DC side. The PV array will lose the output capability when the isolation is weak or it is night, which forces the system to be removed from the microgrid and reduces the utilization factor of the system. The frequent parallel operation and break-up actions are unavoidable since the day and night is alternant everyday, which makes an impact on the PV system and shortens the service life of the system. In this dissertation, the technique of reactive power compensation(RPC) introducing to the PV system is presented. The proposed system delivers active power produced by the PV array to the grid and compensates reactive power for the system. When the light intensity is very weak, the function of RPC can still be used.The main work about this thesis as below:Firstly, a common solar cell engineering model is established. Perturbation and observation method is used to realize Maximum power point tracking (MPPT).4kW Photovoltaic Maximum Power Point Tracking model is built in Matlab/Simulink.Secondly, the technique of grid-connected power supplying and RPC for load is presented. Based on the theory of the instantaneous reactive power, the dq transformation is used to separate the inverter currents into the active currents and reactive currents. It is adjusted the active currents and reactive currents respectively in dq coordinate system, making the system output the active power and reactive power compensation at the same time.Thirdly, the model of V/f control strategy is given, V/f control is as the control strategy for master control DG in the island mode of microgrid. Based on the capacity of the PV inverter, a coordinated control strategy is designed. The PV inverter under different sunlight intensities can output reactive power according to the reactive load changes in the capacity range, which beyond the PV inverter RPC range is provided by the master control DG.A simulation model of microgrid is built based on the above control strategy, microgrid under different operation conditions is simulated and analyzed.Finally, the method of inverter partially compensate load reactive to detect the island, the effectiveness of the proposed method is verified by simulation.