Introduce Of Max Power Point Tracking System

Solar arrays are generally used to generate power for the space power system, the output of which is affected much by the circumstance situation. Since the output of solar arrays is non-linear, it will present different I-V curves according to different irradiation and different temperature, in another sense, the output of solar arrays can be seen as a non-linear function of temperature, solar irradiation and space particle irradiation. Of each curve, the maximum rectangular area, also the product of IPV and VOC is named as the maximum power point, and defined as Pmax, it will generate the most power.The constant voltage technique (CVT) is widely used in domestic space power system, which means the solar can not work at the best power point bringing in an energy loss of 20%. While the maximum power point tracking technique (MPPT) can track the max power output of the solar cell on time, which can fully use the power generated by the solar array. Normally, the MPPT is more complicated and less stable compared to CVT. However, all these defects can be overcome through the development of electronic technology and the MPPT has already been used on the satellite of NASA and Russian rather than in China. This dissertation introduced the characteristic of illumination-voltage curve, DC-converter's principle, the general scheme and maximum power point tracking algorithm. The disturbance observation method and the fuzzy self-optimization method were combined to track the maximum power point of the solar cell, which is suitable for the space aircraft in orbit. If the best working point was found, the classic PI control method is taken into function, and the best voltage output of the solar cell is locked, meanwhile the Buck circuit will charge the Ge-Ni battery arrays. Such system can function with best stability and enhanced reliability. When satellite moves into next orbit cycle the MPPT program will be restart, tracking the best working point of solar array, taking PI control then repeating the process cycle after cycle.The hardware of the MPPT system is composed of DC-DC main loop and the computer control module. Buck low voltage converter was used in DC/DC circuit, the load was connected to the storage cell, while the main bus took in the scheme without modulation which means the voltage of storage was that of the main bus. All the components were selected according to the special requirement of military and space standard. Monochip AT89C55 was chosen as the main control chip, which has the characteristic of low power consumption and high performance with a reprogrammable Flash of 20k. The AT89CC55 can be seen as a powerful control chip of high agility and cost-quality ratio, especially for embedded system.The program was written in C, the parameters were set according to the stability and transient response requirement and the experimental results showed that parameters were chosen satisfyingly.After the final test and measurement, this system was proven to satisfy the requirement of space power system in function, electricity performance, response rate, system stability and reliability. It is also the first MPPT system that can be transferred into actual space power application. The conclusion and expectation were presented at last; further improvement needed was also discussed.