Study On Control Algorithm Of Maximum Power Point Tracking For Photovoltaic Grid-connected Power System Based On Sliding Mode Theory

As a renewable energy, solar energy is clean and widely distributed. It’s gradually becoming one of the traditional fossil fuels alternative energy. The photovoltaic power generation is one of the main ways of using solar energy. The grid-connected PV power generation technology represents a great potential of the21st century energy technologies. Therefore, The PV power generation technology is becoming a hot research topic today. This paper mainly researches the grid-connected PV power generation technology. This paper studies the PV system’s structure, the mathematical model of PV arrays and the maximum power point tracking algorithm. It is need to solve two key issues of photovoltaic grid-connected power system:(1) How to make the maximum output power of PV arrays in the process of converting solar energy to electrical energy?(2) Since the electricity generated DC forms, how to convert DC to AC with the same frequency, the same phase and amplitude of the grid. In this paper, we mainly discuss the first issue.Considering the nonlinear characteristics and using environment changes of PV arrays, it is need a dedicated circuit to adjust the operating point of the PV arrays in order to achieve the maximum power point tracking (MPPT). As so far, the MPPT algorithm concludes Perturbation and Observation algorithm, Incremental Conductance algorithm, Ripple Correlation Control algorithm, and so on. These algorithms can achieve MPPT under slowly varying conditions of temperature and the amount of light. However, once the environmental factors (temperature and amount of light) mutate, the above algorithms would be a miscarriage of justice and are difficult to ensure the MPPT. To solve this problem, this paper analyzes the conventional MPPT algorithms in detail, and then proposes a new MPPT algorithm based on sliding mode variable structure theory combined with the nonlinear characteristics of the PV arrays.The sliding mode variable structure control is essentially a switch control. It constantly adjusts the structure of the system based on the change of system’s state to maintain the trajectory of the system at the desired sliding surface. The system controlled by the sliding mode is fast dynamic response and unaffected by the changes of object parameters or external disturbance factors. Therefore, combined with the characteristics of PV arrays, this paper designs a new MPPT algorithm based on this theory. This algorithm solves the problems of maximum power output under the conditions of temperature and light amount of mutation.In order to verity the rationality of the algorithm, design and achieve the simulation experiments in Matlab/Simulink, and a prototype of grid-connected inverter based on TMS320LF2407. Simulation and experimental results show that:compared with other MPPT algorithm, the new algorithm based on sliding mode theory is fast dynamic response and stability, and could tracing the maximum power point under the conditions of temperature and light amount of mutation.