Research On Reactive Power Control Technology Of Photovoltaic Grid-Connected Inverter

Today,with the continuous improvement of the quality of life,faced with the drawbacks of less and less fossil energy,human beings began to seek new energy sources that are cleaner,more accessible and infinitely used to replace traditional fossil energy to alleviate the imminent energy crisis.The advantages of using solar power are obvious,and the capacity under construction in the world is also increasing rapidly every year.As the proportion of photovoltaic power generation into the power grid is gradually increasing,the unfavorable factors brought about by the operation of the distribution network have received more and more attention.The electric energy generated by the photovoltaic system studied in this paper is firstly transported to the local load with close distance.After meeting the local demand,the excess power is connected to the 0.4kV distribution network through a transmission line at the grid connection point,and the output of the photovoltaic system is analyzed.The influence of the power on the voltage at the grid connection point is studied.The remaining capacity of the inverter is used to output a certain reactive power according to the control demand,so as to stabilize the voltage at the grid connection point within a reasonable range.The main contents of this paper are as follows:Firstly,the two-stage photovoltaic system topology is used as the research basis of this paper.The equivalent circuit of photovoltaic cell is established.The mathematical formula of its output current is derived by simplifying the parameters.The PU and UI output characteristics of the photovoltaic cell are verified by Simulink simulation.The principle of using the Boost circuit to realize the MPPT of the DC side of the inverter is analyzed.The simulation method of Simulink is used to verify that the power tracking method used in this paper can achieve better tracking effect under both illumination and temperature changes.Secondly,by deducing the mathematical model of the inverter and transforming it into dq coordinates by using abc/dq,the coupling of the dq axis is released by introducing the equivalent current variable;the control mode of the inverter is based on the grid voltage vector.The double closed-loop is used to analyze and design the current inner loop,voltage outer loop and filter circuit.The inner loop error regulator adopts fuzzy PI.Finally,the simulation model is built by Simulink to verify that the control method adopted on the inverter side can achieve active power.Separate adjustment with reactive power,control the inverter to perform active output,and also perform reactive power control to meet the reactive demand of the nearby load.Finally,the inverter reactive power control method is studied.Firstly,the principle of reactive power output of the inverter and the reactive output limit are analyzed.The voltage characteristics of the PCC are studied.When the output of the photovoltaic system exceeds a certain value,the voltage value at the PCC will exceed the specified range.The reactive power output of the device outputs a certain amount of reactive power to stabilize the voltage at the PCC,and at the same time,the method for obtaining the reactive reference value Qref is studied.Inverter control is studied when the grid voltage is reduced to a large extent,that is,when the grid voltage is reduced to a large extent,the system should switch the DC side working mode to reduce the active output on the DC side while maintaining the bus capacitor voltage value.Stable,limiting the AC side output current can also deliver a certain amount of reactive power to the grid to support the voltage at the PCC.Finally,simulink is used to build the simulation model to verify the reactive power control under normal conditions of grid voltage and grid voltage.