Research On Reactive Power And Voltage Control Of Photovoltaic Microgrid

To alleviate the energy crisis and eliminate environmental pollution,the pace of comprehensive development and utilization of renewable energy has been accelerated,and the application of microgrids to consume renewable energy has attracted much attention.However,there are phenomena such as uneven power distribution and reactive power circulation in the operation of microgrids,which seriously affect voltage quality and system stability.Research on practical control methods is the key.Therefore,this thesis focuses on the research of reactive power and voltage control of photovoltaic microgrid,which has certain practical significance and application value.Firstly,analyze the three operation modes of microgrid and the control strategy of micro-source interface,construct the mathematical model of the inverter,and design reasonable filter parameters.Further analysis of the droop characteristics shows that due to environmental differences,the equivalent output impedance of the photovoltaic microgrid has a large difference,and the load cannot be distributed in proportion to the pre-designed capacity when the load is shared,which affects the entire system.stability.Here,two inverters of the same capacity are used in parallel to simulate the entire microgrid system for analysis,the reactive power is equally divided into the required conditions,and the phenomenon of reactive power circulation is analyzed.Secondly,it is difficult to pass the droop control coefficient regulate for the problem that the reactive power is reasonably allocated,this thesis presents a droop control strategy that introduces virtual complex impedance.After deducing the impedance characteristics after introducing the virtual complex impedance and comparing with the bode diagram,it is verified that the introduction strategy of the system improves the reliability of the reactive power sharing.When the reactive power can be distributed in proportion,the simulation shows that the reactive power circulation has also been greatly improved,eliminating the loss of the system equipment due to the circulation.However,the output voltage of the inverter fluctuates greatly,which affects the voltage quality of the microgrid.In response to this phenomenon,an improved droop control based on virtual complex impedance is proposed.The principle is to adjust the reactive power of the droop control coefficient by adjusting the difference between the rated output voltage and the actual output voltage in the droop control.Continuously circulate to meet the error requirements and reach the parameters required to meet the sag coefficient.In the droop control,this method can increase the voltage by a large margin,keep the frequency stable at 50 Hz,and reduce fluctuations so that the system can operate safely and stably.Finally,a simulation model was built in the Matlab/Simulink environment.Set up three inverters and equivalent lines with large differences in impedance parameters to simulate the actual application scenario conditions of the photovoltaic microgrid.Through the establishment of simulation and comparison experimental data,it is verified that the strategy of improving droop control after the introduction of virtual complex impedance can be used.Realize the reasonable distribution of power between the microgrid inverters,effectively suppress the reactive circulating current between the parallel inverters and maintain the stable output of the bus voltage and frequency.