Research On Stand-alone Photovoltaic Power System

As one of the main substitute of petrifaction resource, solar energy is a kind of huge, reproducible and clean resource. Therefore, the exploitation of the solar energy has a great strategic meaning. Nowadays photovoltaic power system has become one of the most important ways of utilizing solar, but it costs too much, and consequently develops very slowly in developing countries. The stand-alone photovoltaic power system designed in thesis has low cost, high efficiency, high reliability and is easy to control and implement.First of all, this essay introduces the principles of solar battery and Lead-acid battery, then designed a reasonable Lead-acid battery charge circuit, which helps to prolong the service life of storage battery. The push-pull DC-DC converter adopts voltage closed-loop control converting low-voltage direct current into stable high-voltage direct current, which simplifies the inverter. At the same time high-frequency technology makes high-frequency transformers replace the frequency transformers, which not only reduces costs but also reduces the volume. In order to improve the efficiency of inverter and not affect the quality of pure Sinusoidal wave, MCU ATmega16L is used as the control of the core, and modified SPWM control technology is adopted, reducing the number of IGBT switch, through which the switching losses decreases, and efficiency naturally increases. Besides, it has the over-voltage, under-voltage, over-current and over-temperature protection to ensure that the system is safe and reliable to run.The orientation of sunshine changes continually because of the rotation of the earth, therefore this paper designs automatic tracking system. Photodiode is used to track the orientation of sunshine, and MCU ATmega8L is used to control rotation and stop of the stepper motor through the driver made up of L297 and L298 chip. They can make the solar panel always orient towards the sun. As a result, solar radiation received by the solar panel increases, and generating capacity comparatively increases.Finally, the result of the system testing showed that harmonic content of Sinusoidal wave is less, whose output power can reach 1 kW and efficiency can reach over 85 percent. The tracking error of solar tracking system is within the range of±8°.In conclusion, this design of the stand-alone photovoltaic power system is feasible.