| In this paper, a photovoltaic unit of distributed photovoltaic generation is studied. Each part of the system of photovoltaic unit is analyzed in theory, a photovoltaic-cell simulator, a MPPT (maximum power point tracing) charger, an ultracapacitor adaptor, and a grid-connectable inverter are implemented. The topology structure of grid-connected generation system and its control strategy are studied in detail.By analyzing the I-V output characteristics of photovoltaic cell, a photovoltaic-cell simulator is designed based on Buck DC/DC converter. As the base of indoor experiment of the photovoltaic system, the output characteristics of the photovoltaic-cell simulator are designed to be identical with that of the real photovoltaic cell.In order to obtain the maximum power of the photovoltaic cell, a MPPT charger is designed and implemented based on Boost DC/DC converter to trace the maximum power point.As a new energy-storage device with the characteristics of large-current charge and discharge, the ultracapacitor has been employed in the system of photovoltaic generation. The ultracapacitor can smooth the output voltage and optimize the management of the battery in large-current charge and discharge processes based on bidirectional DC/DC converter.The parallel model of VSTI and CSTI is analyzed and closed-loop control circuit is designed. Synchronous phase lock loop (PLL) and switching method is introduced and tested by simulation and experiment. A high-performance DSP-based system of photovoltaic generation is developed and a experimental device of the system is designed to achieve high-speed data acquisition, event management and complex control arithmetic and complete intelligent protection of the system.
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