Research On Photovoltaic Grid Connected Power Generation System Based On LCL Filter

The two major problems of energy crisis and environmental pollution restrict the economic development of all countries in the world,and clean renewable energy has become a hot spot of research in all countries.With its unique advantages,solar energy has been first to the development in the field of new energy ratio increased year by year,and it is urgent to develop the grid connected technology of photovoltaic power generation.Therefore,the photovoltaic power generation grid connected system is taken as the research object in this paper,focusing on the maximum power point tracking algorithm for photovoltaic cells,LCL filter parameters and inverter grid control strategy.The specific content and results are as follows:1.The working principle of photovoltaic cell is studied,and the equivalent mathematical model is established.The output characteristic curve under different conditions is simulated,and the principle and method of maximum power point tracking(MPPT)of photovoltaic cell is analyzed.The pv array output power voltage(P-U)characteristic curve under partial shading becomes more peak situation.In this condition,the traditional tracking method of maximum power point is failure.To overcome this difficulty,a composite MPPT method is proposed,which is mainly divided into two parts.Firstly,particle swarm optimization algorithm is applied to solve several pole problems,and it can locate near the maximum power point quickly and use the secondary search based on the incremental conductance method and accurately find the global optimal solution.Finally,the simulation experiments are carried out in the Boost circuit.The results show that no matter the pv arrays is partially shaded or not,the result of the compound control method is more accurate than the particle swarm optimization algorithm and incremental conductance and proves that the algorithm is correct and effective.2.The topology and output filter structure of three-phase grid connected inverter are introduced.Compared with the same inductance value of LCL filter and L filter,the former is more ideal for high-frequency harmonic suppression,and it is widely used in the grid connected system.However,there is a resonant spike in the LCL filter,and the parameters of the components interact with each other.It is also difficult to design and get the results quickly and accurately.Based on it,a mathematical model of LCL grid connected inverter system is established,and two ways to suppress the resonant peak are analyzed.Meanwhile,the parameter design of LCL filter is mainly studied.Considering the constraints of each parameter,the particle swarm optimization(PSO)algorithm is proposed to optimize the parameters of the LCL filter,and the algorithm flow is introduced in detail.Finally,theparameter groups of the LCL filter are quickly obtained by simulation.The fitness values are all in line with the conditions,and the parameter group with the minimum fitness value is selected for simulation verification in the grid-connected inverter system.3.Aiming at the LCL-type inverter grid-connected system,the closed-loop control of the network side current and the closed-loop control of the inverter side current are compared and analyzed.According to the obtained root locus map,the latter closed-loop control system is more stable.At the same time,to improve the power factor of the system,the capacitive current loop is introduced and the double loop control is established on the basis of the single current loop.After the simulation experiment,the parameter values of the particle swarm optimization and the traditional design method are compared respectively.The filter parameters designed by the particle swarm optimization algorithm have better filtering performance,and the harmonic distortion rate is obviously reduced by FFT analysis,which proves the correctness and superiority of the method.Finally,a three-phase photovoltaic power generation grid-connected system model is built,and the voltage outer loop is added to the current double loop.The simulation results verify the effectiveness of the three-loop control strategy and the stability of the system.