Research On MPPT Technology Of Photovoltaic Generation System

The main research object of this paper is the MPPT technology of photovoltaic generation system under partial shading. Based on the analysis and study of photovoltaic (PV) cell’s performance, the goal of a theoretical study and mechanism analysis of PV array’s output characteristics under partial shading is achieved by model building. In order to solve the sharp decline and multi-peak characteristic of PV array’s output power resulting from partial shading fundamentally, this paper made a comparison study involving topologies, MPPT control strategies and output power among the centralized, string and modular PV generation systems, and finally the conclusion of modular MPPT’s evidently superiority was drew. The study of MPPT technology in modular system is mainly carried out based on the topologies of Bi-directional Buck-Boost converter and Sepic converter, a current and voltage double-loop MPPT control strategy is proposed and the loop design is implemented on the basis of small signal model study, and an improved hysteresis comparison MPPT algorithm is applied to the system. Besides, a dual-carrier modulation scheme is put forward for the Bi-directional Buck-Boost converter. The simulation results of the system models based on Matlab and Psim turn out that the PV array can make a maximum power output under any conditions, which verifies the effectiveness of the double-loop MPPT control strategy and the improved hysteresis MPPT algorithm. A comparison between these two kinds of topologies has been made in different aspects including parameter selection, modulation scheme, the complexity of the control and efficiency, etc. Overall, the Bi-directional Buck-Boost converter tends to gain the advantage over the Sepic converter. The mainly innovations of this paper can be included as follows:①Considering the disadvantages of the mathematicaland simplified models, an accurate engineering model is proposed, which is obtained by fitting and correcting the compensation parameters of simplified model based on the mathematical model, and has a good compromise between simplicity and accuracy;②An improved hysteresis MPPT algorithm is presented, which can effectively solve the problem of shock and misjudgment, while taking into account of speed and precision, leading to a more effective and accurate MPPT;③An dual-carrier modulation scheme is put forward for the Bi-directionalBuck-Boost converter, which can realize the adaptive mode switching, thus ensuring a maximum power output of the PV cell under any external conditions;④A current and voltage double-loop MPPT control strategy is proposed, which can realize the decoupling control of state variables, and has higher robustness, faster response characteristics and higher reliability.