Research On Photovoltaic Micro-grid System Controller

In order to study the PV micro-grid systems and network operation, run onoff-grid and automatic switching, and modulating control PV inverter output powerquality. Based on the photovoltaic power generation, this paper builds the simulationmodel of micro-grid PV system and designs micro-grid controller is responsible forcontrolling the entire operation of the system micro-grid PV which can achieve thetracking control of the photovoltaic array’s maximum power and make micro-gridphotovoltaic system runs on off-grid or grid mode according to the exist of the islandeffects or not. During the operation of photovoltaic grid inverter, the grid voltage andfrequency of the inverter output is clamped down. That is to say, micro grid controllerjust need to make the phase and the frequency of grid current be same with gridvoltage. At the running time of grid photovoltaic, micro-grid system is equivalent to avoltage source, and micro-network controller requires to adjust the output voltageamplitude and frequency of inverter without the reference of the grid voltage, in orderto ensure the normal operation of critical loads.Firstly, this paper built a Simulink model of photovoltaic cells and achieved thetracking control of the maximum power, based on working principle and theequivalent model of photovoltaic cells which deduced the expression of its outputcharacteristic curve. The result of the simulation simulation results shows theeffectiveness and stability of the model. Secondly, the basic structure and operatingprinciple of micro-grid controller in the photovoltaic micro-grid system areintroduced mostly. This paper deduced mathematical model expression in the dqcoordinate system according to the evolution of the mathematical model expression’sstructure diagram and analyzed the power PQ control strategy, current decouplingprinciple, V/f control strategies voltage and current decoupling principle. It alsointroduced the basic principle of SVPWM algorithm and islanding detection methods,and analyzed elaborated/off-grid switching control strategy. Then it designed the PVmicro-grid controller and the micro-network controller hardware circuits, such as theselection of the master chip DSP, analog signal sampling and conditioning circuitry, IPM drive and protection circuit design of the hardware and determined the values ofthe inductance and capacitance parameters based on designing principles of maincircuits. The control system software has been designed. Based on the hierarchicalthinking, software program can be divided into three basic levels, master control layer,algorithm layer and the interface layer according to the functions and tasks.Finally, in Simulink the simulation model of the PV inverter and networkoperation, off-grid simulation model and run/off switch network simulation has beenbuilt and been tested. The simulation results obtained various operating states of thephotovoltaic inverter operating under different conditions. Through the analysis of itsoperating characteristic curve, we verified the validity of the simulation model, andprovides a reliable theoretical platform for photovoltaic micro-grid hardware design.