Research On Control Algorithms For Maximum Power Point Tracking Of Photovoltaic System Based On SEPIC Circuit

Photovoltaic power generation is an effective way to use solar energy. Photovoltaic cell converts solar energy into electricity. Environment will affect the power output of photovoltaic cell. Under different working conditions, the output power of photovoltaic cell is different, but there is only the maximum power point. In order to improve the efficiency of PV power generation system, the maximum power point tracking (MPPT) is required to track this maximum power operating point. In this paper, the research object is the PV power generation system, and the research objective is the maximum power point scheme for PV systems operating under variation of solar irradiation and load. Research results can be summarized in the following aspects.(1)Analyze the the principle of PV cell, and discuss the mathematical model and the engineering calculation method of PV cell. Build simulation model of PV cell in Matlab. Analyze the output characteristics of PV cell operating under varying solar irradiation and temperature.(2)Introduce several common MPPT algorithms which constant CVT method, P&O method, INC method and the advantages and disadvantages of these algorithms. Then the direct adjustment for switch duty cycle of SEPIC circuit to achieve MPPT purpose is proposed after analyzing MPPT algorithms, which excludes the PI control loop of traditional MPPT algorithms. Simulation model of PV system based on SEPIC circuit has been established, simulation and analysis have been made for the tracking performance of P&O method and CVT method combined with P&O method.(3)The variation of solar irradiation and load will affect the operating point of PV cell, and the tracking performance of traditional MPPT algorithms are not satisfactory under fast-varying solar irradiation and load. Hence, this paper proposes an improved INC method based on traditional INC method. Analyze the principle of the improved INC method, and design the flowchart. The simulation model of PV system with MPPT controller has been built in Matlab, and MPPT controllers respectively adopt the improved INC method, the fixed-step INC method with direct control for duty cycle and the variable-step INC method with direct control for duty cycle. Changing solar irradiation and load, the simulation results obtained for different MPPT algorithms. Compare and analyze the simulation results from dynamic performance and steady performance. The results verify that the improved algorithm compared to the other two algorithms has a faster response speed under fast-varying solar irradiation and load, and shorten the track time, reduce the power oscillation. So the improved INC method can effectively improve dynamic and steady performance of PV system.