Research On Control Of LCL Grid-connected Inverter Based On Splitting-capacitor

With the vigorous development of new energy,the consumption of fossil energy has been greatly reduced and the dependence of daily life and industrial production on traditional energy has been further reduced.In addition,thanks to the progress of new energy technology,on one hand,serious environmental pollution problems will be effectively alleviated;on the other hand,the development of natural resources which is increasingly scarce is further reduced.As a link between the power grid and the power generation system,the grid-connected inverter plays an indispensable role.The efficiency of its work and the quality of the output current directly affect the quality of the grid-connected current.As the core of the grid-connected inverter,the control strategy plays a decisive role in final the performance of grid-connected inverter.In recent years,the research of control strategy has been a hot topic in grid-connected inverter research.By analyzing the resonance of the control system in LCL grid-connected inverter,this paper proposed the splitting-capacitor method,and discussed the working scheme of the LCL grid-connected inverter based on splitting-capacitor in detail.First,several traditional control strategies for restraining LCL grid-connected inverters are briefly introduced,and then the splitting-capacitor control scheme is emphatically analyzed,Which is based on remolding the control structure of LCL output filter and uses the active damping double feedback equivalent principle to simplify the system.This control scheme successfully simplify the control system of LCL grid-connected inverter.Owing to the simplification of LCL filter,the grade of control system is reduced from three to the one order,which can successfully eliminate the system resonance problem.However,through the analyze of system reduction process,it is found that the reduced order results of the control system are not absolutely established at f_r,because there is a neglected resonance point in the elimination process of the control system,and the existence of that will seriously affect the output of grid-connected inverter.To solve this problem,an active damping strategy for splitting-capacitor is proposed.The method can dramatically restrain the resonant peak that neglected during the order reduction process.The quality of grid-connected current is improved obviously.THD of grid-connected decreased from 3.82%to 1.92%,resonance content in the current decrease from 2.32%to 0.46%.Simulation experiments prove the correctness and effectiveness of the proposed strategy.In addition,the effect of the grid side inductor on the transfer function of control system and the output admittance is preliminarily studied.It is found that the transfer function of the inverter control system will be changed by the fluctuation of grid side inductor on one hand,this will lead to the failure of system degradation and the failure of the splitting-capacitor method,which can cause the resonance problem.On the other hand,the proposed active damping control strategy is unable to restrain the corresponding resonance peak effectively owing to the inductor fluctuation.Therefore,a voltage feed-forward decoupling control scheme based on splitting-capacitor for LCL grid-connected inverter is proposed.By using which,the disturbance no longer appears in the transfer function of control system.The proposed voltage control can eliminate the influence of the power grid fluctuation on the splitting-capacitor method and active damping control strategy.The correctness of the proposed method and the feasibility of its application are proved by simulations and experimental results.