The Design Of MPPT Controller On Stand-alone Photovoltaic Street-lamp System

With the increasing problems of energy exhaustion and environmental pollution, the application of photovoltaic technology has become a new field of the whole world. So the grid-connected photovoltaic system and the stand-alone photovoltaic system develop quickly. Especially, the stand-alone photovoltaic system has become the national emphasis of investment. It can supply residents who live in remote area with power.This paper focuses on the stand-alone photovoltaic street lamp system. In order to reduce cost of the system and improve the performance, we pay our emphases on the implementation about the characteristic of photovoltaic battery and characteristic of the valve regulated lead-acid battery (VRLA), and the basic principle of MPPT of photovoltaic system. The main contents are listed as follows:1. An overview of the research and development in the stand-alone photovoltaic system at home and abroad.2. The principle of photovoltaic system, the factors of influencing the photovoltaic array and charging and discharging electrochemistry mechanism of the storage battery are analyzed. The proper charging strategy is developed.3. A charging (discharging) circuit for storage battery and a DC-DC circuit for MPPT of array are designed. Simultaneously, the charging control technology (including the MPPT technology for photovoltaic array) in photovoltaic system is studied.4. The advantages and disadvantages of traditional Perturb and Observe algorithm and Incremental Conductance algorithm are analyzed, and then an improved algorithm of Varied-step Searching-best is proposed. The experiment results show that this algorithm can track the maximum power point fast and exactly.5. A control system based on an LPC2194 in stand-alone photovoltaic street lamp system is designed. It achieves array's MPPT control, the storage batteries' capacity prediction, charging and discharging control.6. A software program which is based on the real-time operating systemμC/OS-II is designed.Finally, the experimental results illustrate that the proposed control methods and the hardware and software designs are feasible and satisfactory.