Maximum Power Point Tracking Scheme For Photovoltaic System Under Partially Shaded Condition

With the increasing demand of global energy,renewable energy power generation has attracted wide attention.As a new renewable energy with huge reservers,no pollution and no noise,photovoltaic energy has become one of the hottest research fields.The practical photovoltaic system is influenced by complex partially shade,thus the output power is unstable.The photovoltaic system often falls into the local maximum power point.Therefore,how to track the photovoltaic maximum power point effectively and accurately has become a hot research field in improving the efficiency of photovoltaic power generation system.In this paper,the photovoltaic model and its characteristics under local shadows are studied in depth,The advantages and disadvantages of the traditional maximum power point tracking algorithm are analyzed,A new algorithm with high tracking efficiency is proposed,that is,the improved differential evolution algorithm(DE)combined with the Incremental conductance(INC)algorithm with variable step size.The main research contents are as follows:Aiming at the shortcomings of slow convergence speed and low precision of the standard DE algorithm,a new method for searching global maximum power point of photovoltaic system is proposed by combining improved DE algorithm with variable step size INC algorithm.When the photovoltaic array starts and the illumination or temperature conditions change,the new algorithm uses the improved DE algorithm for global optimization,which makes the photovoltaic array track to the global maximum power point after a certain number of iterations.After determining the approximate maximum power point,the improved variable step size INC algorithm is used to search accurately.The proposed algorithm is simulated by a photovoltaic array simulation model consisting of three series photovoltaic panels.The power tracking under static and dynamic partial shading is studied.The results show that the average tracking accuracy of the proposed method is 99.97% under non-uniform illumination,and the average tracking speed is 16.7% higher than that of particle swarm optimization(PSO).In order to verify the performance of the algorithm in the actual system,a photovoltaic array MPPT experimental platform is designed.As the main control circuit,the output PWM waveform of the main control circuit is adjusted by driving Boost circuit.In the software part,CCS 3.3 is used to program the main program,sampling program and MPPT program,simulate non-uniform illumination conditions,and measure the output current,voltage and duty cycle of the three MPPT control algorithms.The maximum output power of the proposed algorithm is 3.1% higher than that of the PSO algorithm,which proves that the proposed algorithm has some advantages in maximum power point tracking of photovoltaic system under partial shading.The simulation results and experimental results show that the improved DE-INC algorithm proposed in this paper can track the global maximum power point of photovoltaic system rapidly under local shading,and its accuracy and stability are very outstanding.It has a certain role in promoting the maximum power point tracking technology of photovoltaic system under local shading.