Research On Current Sharing And Resonance Of Photovoltaic Microgrid

In recent years,with the development and comprehensive utilization of solar energy,photovoltaic microgrid has been widely used as one of the effective ways to absorb renewable energy.In order to give full play to the flexible and efficient performance of the photovoltaic microgrid system,multiple inverters are usually paralleled connection in the microgrid to realize the expansion of system capacity,which will lead to power quality problems such as circulations,uneven currents and resonances among inverters in the photovoltaic microgrid.Therefore,it is one of great significances to study effective control methods to reduce circulation,suppress resonance and ensure the reliable and stable operation of photovoltaic microgrid.In this thesis,the problem of current-sharing and resonance in photovoltaic microgrid is studied.The main contents are as follows:At present,many inverters in the photovoltaic microgrid are paralleled connection with traditional droop control methods,which is limited to the same equivalent output impedance as the parallel inverter,but can not achieve the uniform flow of the load side under the parallel mode of the differential capacity inverter.In order to achieve a good effect of parallel flow of differential capacity inverters,an improved method of reactive power droop control under the parallel mode of differential capacity inverters is presented.In order to realize the decoupling relationship between reactive power and output impedance,the power distribution of parallel inverter with different capacity is unbalanced and uneven.The design of the controller parameters makes the equivalent output impedance of the inverter sensitive.Under conventional droop control,the parallel inverter has better dynamic and static characteristics and improves the accuracy of power distribution.In the photovoltaic microgrid inverter output filter,produces resonance is one of the main factors that lead to the resonance,to solve the problem of harmonic filter itself,through to the passive damping method and active damping method of comparative analysis,active damping control strategy is presented in this thesis,the lateral detection capacitance current and virtual impedance multiplication of damping current component,the superposition to the voltage on the output current signal of outer ring,achieve resonance without extra power consumption.Through Matlab/Simulink simulation software simulation analysis,based on the two three-phase parallel photovoltaic inverters,when the capacity is not equal,the improved droop control strategy proposed in this thesis is verified,and the parallel inverter with different capacity can achieve a better uniform flow;When resonance occurs at the output of the system,the virtual impedance method is proved to be effective in suppressing resonance.