Research On Control Strategy Of Multifunctional Inverter For Photovoltaic Power Generation System

China has rich light resourse.To replace the traditional fossil energy consumption,national policies encourage the development of solar energy.At present,China vigorously develops the construction of photovoltaic power plants,but the photovoltaic panels are difficult to breakthrough the limitations of power generation because of the light,temperature and other external conditions often change.There are many factors lead to the public grid harmonic pollution and reactive power consumption,such as the increasing of power devices in photovoltaic generation(PV)system,the nonlinear load ratio in grid user side.In the PV system,the two kinds of equipment,as inverter and active filter have similar characteristics in function,structure and control method.In order to improve the output power from the PV grid-connected system,reduce the harmonic pollution which come from the distributed power,and improve the stability of grid,the inverter can play a dual-purpose function due to the above characteristics.When the light is sufficient,the PV system is connected to the grid,and when the power generation condition is poor,the inverter will suppress the harmonic and compensate the reactive power.The function of changing the inverter needs to be achieved through the control strategy.Therefore,that is necessary to study the function expansion of inverter and its control strategy.Firstly,the inverter of the three-phase voltage source topology is selected as the research object by analyzing the similarities and differences between the multi-function inverter and the parallel active filter in the PV grid-connected power generation system.Then,in order to efficient control the PV generation system;the main circuit topology of the two-stage photovoltaic system is determined.The principle of setting the capacitor in the inverter and the output side of the inverter is described,so as to provide the basis for setting the simulation parameters for the photovoltaic power generation system model.The method of selecting the working mode of the multifunctional inverter is introduced.The signal switch is set in the system control circuit,and the setting of the inverter operating mode is realized by controlling the components in the synthetic command current.In order to improve the power transmission efficiency of PV system,the maximum power point tracking(MPPT)algorithm of PV array is improved.On thebasis of adaptive variable step-length conductance increment(INC)method,the power prediction is added to suppress the maximum power point tracking oscillation caused by light mutation.In the paper,the direct current control strategy is adopted in control of inverter.And harmonic and reactive current detection module,the command current synthesis module is analyzed.The main work has designed the command current tracking controller.In order to improve the control effect of the command current in the system,a fuzzy control and variable band hysteresis control are proposed to optimize the internal loop control of the inverter.Finally,the performance of multi-function inverter is simulated by MATLAB.The simulation results show that the proposed variable-loop hysteresis current control method can accurately track the command current of the PV system in the composite working mode,which not only improves the dynamic nature of the grid-connected current tracking control but also add harmonic and reactive power compensation function to improve the cost of inverter equipment.Meanwhile the results verify the correctness of the proposed control strategy.