Research On MPPT And Input Voltage Ripple Suppression Strategies For Single-Phase Photovoltaic Grid Connected Systems

In recent years,the total installed capacity of distributed photovoltaic power generation in China has continued to soar.As an important component of distributed photovoltaic power generation,single-phase photovoltaic grid-connected power generation systems have two main reasons for their reduced output power and power generation efficiency: First,the existing maximum power point tracking(MPPT)method does not provide a good balance between tracking speed and accuracy;Second,the system usually adopts a two-stage structure.Due to the mismatch of instantaneous power on the input and output sides,the input voltage of the front-end converter contains a large ripple twice the grid frequency,which affects the tracking effect of the MPPT.Therefore,this article conducts research on the MPPT method and input voltage ripple suppression strategy for single-phase photovoltaic grid connected systems.On the premise of fully studying the pre-structure of single-phase photovoltaic grid-connected power generation system,the traditional algorithm,intelligent optimization algorithm,and the recently proposed two-step composite algorithm(intelligent optimization algorithm combined with traditional algorithm)in MPPT algorithm are exemplified and studied,and the analysis and simulation prove that these three methods cannot well balance tracking speed and accuracy.In this paper,a three step composite MPPT algorithm based on IP&O-IBSO is proposed by combining the improved perturbation and observation(IP&O)with the improved beetle swarm optimization algorithm(IBSO)algorithm.The algorithm divides power tracking into three stages.In the early and late stages,it utilizes the advantage of IP&O algorithm’s fast optimization speed to improve tracking speed and reduce power oscillations;In the middle stage,IBSO algorithm was introduced,and the function of online adjustment of voltage search range was added to the feature of strong global searching ability of conventional Tenniu optimization algorithm,which greatly accelerated tracking speed while ensuring tracking accuracy.A single-phase photovoltaic grid-connected power generation system model was built in Simulink,and simulation comparisons were made between this algorithm and the above three algorithms under different operating conditions.The results showed that compared to traditional algorithms,the algorithm in this paper is not easy to fall into local optimization,and the tracking accuracy is greatly improved;Compared to the same type of intelligent optimization algorithm and two-step composite algorithm,the tracking time is shortened by more than 86% and 71% respectively,the tracking speed is greatly improved,and the power oscillation is small.Based on a detailed analysis of the mechanism of input voltage double frequency ripple generation in single-phase photovoltaic grid connected systems,a quasi proportional complex integral(QPCI)based input voltage ripple suppressor was designed.The QPCI controller extracts input and output voltage double frequency ripple,and performs compound feedforward control to suppress input voltage ripple and improve system power output efficiency.The simulation results show that this ripple suppressor can significantly reduce the input voltage double frequency ripple of a single-phase photovoltaic grid-connected power generation system,and has a good compatibility with the three-step composite MPPT algorithm based on IP&O-IBSO in this paper.They work together to suppress input voltage ripple by over 90%,effectively improving the photoelectric conversion efficiency of the system.