Modular Photovoltaic Power Generation System Based On DC Bus

Photovoltaic module output performance has a non-linear output characteristics due to the impact of solar radiation and shadow conditions. Maximum power point tracking control can effectively improve the utilization efficiency of the photovoltaic modules. Under normal circumstances, the current tracking algorithm can make the photovoltaic power generation system operating at maximum power point. But the output power curve of the photovoltaic power generation system presents non-convex characteristics in partial shadow conditions. Current maximum power point tracking strategy does not distinguish between the local peak and the global peak of the photovoltaic power generation system, resulting in lower utilization of the photovoltaic power generation system.Aiming at increasing energy harvest from the PV power generation system during instances of partial shading and improving the utilization of PV system, a modular photovoltaic power generation system is proposed. Mismatched PV strings timely isolation from system, the impact on the system is presented by the detection of power matching. Modular PV system can work in several different system structure. Each PV string is connected with a separate boost converter and Distributed maximum power point tracking(DMPPT) architecture is adopted to reduce the effects of strings mismatch and partial shading on system as MPPT is implemented for each Photovoltaic string. The reliability and utilization efficiency of Photovoltaic power generation system can be improved.In order to reduce the power losses caused by power fluctuation for photovoltaic power generation system and improve the power quality and efficiency of the PV system, the interleaving techniques are adopted in modular photovoltaic power generation system. Interleaving techniques makes the system flexible due to its stronger ability of anti-partial shading and high fault tolerance. On the basis of analysis of PV power generation system with interleaved boost operating characteristics, the mathematical model of interleaved boost based on state-space equation was established to design reasonable compensation block and improve the system steady-state and dynamic performance.Simulation and experimental results indicate that an overall reduction of current ripple amplitude and inductor size as well as high frequency of current ripple can be achieved in this configuration with interleaved boost. Low current device can be used in the system. The oscillation of the system decreases and the speed of maximum power point tracking is faster. Distributed maximum power point tracking control can improve the independence of each PV string and achieve the maximum power point tracking control of the PV system and mismatched strings. The perfect performance and flexibility of the photovoltaic power generation system can be obtained.