Research On Maximum Power Tracking And Grid-connected Inverter Control Of Photovoltaic Power Generation System

With the decrease of fossil energy and environmental pollution increasing,people are falling into an unprecedented crisis.As an emerging green energy,solar energy meets people’s requirements for production and life applications,and has great development prospects.Among them,photovoltaic power generation is the most widely used.However,due to the dispersion and instability of solar radiation,the photovoltaic power generation system has low photoelectric conversion efficiency.When the traditional double loop PI control mode is adopted for the grid connected inverter,the harmonic content of the incoming current is relatively large and the anti disturbance ability of the system is poor,which affects the power quality of the incoming power.Therefore,the MPPT and grid connected inverter control strategy of single-phase photovoltaic power generation system are studied in this paper.Firstly,this paper introduces the basic principle of photovoltaic cells in detail,and builds the internal simulation model of photovoltaic cells on the simulation software.The influence of external environment on the output characteristics of the battery was studied through simulation analysis,and the multi-peak characteristics of the P-V output curve under local shading conditions were elaborated in detail.Secondly,this paper deeply analyzes the MPPT control principle of photovoltaic cells.Then,the conventional MPPT technology is studied theoretically,and the advantages and disadvantages of the basic algorithm are compared through simulation.And pointed out their applicable place.In order to optimize the multi-peak MPPT control of photovoltaic array under partial shading,guarantee that the photovoltaic power generation system has been working at the maximum output power point,and avoid the problems of slow convergence speed,low tracking accuracy and easy to fall into local optimal value in local shading environment.Therefore,this paper proposes a maximum power tracking control method based on improved PSO algorithm in local shading environment,that is,the traditional PSO algorithm is optimized,the adaptive inertia weight and learning factor are introduced,and the algorithm flow is improved.The MPPT control effect of this algorithm and the basic PSO algorithm in different environments is compared by simulation test,It is verified that the control strategy proposed in this paper improves the tracking speed and accuracy to a certain extent in the case of multi peaks.Thirdly,by comparing different types of filters,this paper selects the appropriate filter,and studies the control status of grid connected inverter.Then in order to solve the harm of LCL filter resonance peak to the system,this paper adopts the active damping control method of double closed loop control structure to suppress;Aiming at the problems of low precision,slow dynamic response,high harmonic distortion rate and poor anti disturbance ability of the traditional double loop PI control of DC-AC photovoltaic inverter unit,a new control method is proposed.Since ADRC does not depend on the model of the controlled object and has the characteristics of high control accuracy,fast response and strong anti-interference ability,it is decided to adopt linear auto disturbance rejection control（LADRC）algorithm in the outer loop.The tuning method of control parameters of high-order linear ADRC is studied.In addition,aiming at the problem that the stability and observation accuracy of the extended state observer restrict each other,LADRC is improved,and an adaptive function is proposed to automatically adjust the parameters of ESO online.Finally,combining the linear ADRC technology with the grid voltage feed-forward control strategy,a grid voltage feed-forward control method based on improved linear ADRC is proposed.It not only improves the ability of the system to suppress grid voltage disturbance and makes the grid current conform to the national grid standard,but also solves the problem of mutual restriction between the stability and observation accuracy of the extended state observer.This control strategy is simulated on Simulink and compared with double loop PI,LADRC-pi and LADRC-pi+ feedforward under the same conditions.It proves the superiority of this method and achieves the expected effect.