Research On The Maximum Power Point Tracking Controller For Photovoltaic Power Generation System

With the scarcity of fossil energy and the environmental pollution caused by utilization of fossil energy increasingly serious, it has become the main theme of the global energy development to seek for new clean, renewable energy. As one of the most rapid developing industry, photovoltaic industry maintains the rapid growth and the great development potential. Although photovoltaic power generation technology has been mature, still there are many issues to solve such as low power generation efficiency, high cost etc.A maximum power tracking controller for small household photovoltaic power generation system is presented, in which the improved combined method--the short circuit method combined with variable step perturbation and observation method is used a detailed description of the design of hardware and software and the experimental results. The experimental results show that the improved method can quickly and efficiently track the maximum power point of photovoltaic array, thus improving the energy efficiency of the photovoltaic system.First of all, According to the nonlinear characteristics of photovoltaic cells, A simulation model of the photovoltaic cells is established with the use of simulink platform in Matlab on the bases of the analysis of the equivalent circuit of the photovoltaic cells. In this thesis also further analyze the output characteristics of photovoltaic cells under several different environments by simulation. After researching the characteristics of the independent small-scale photovoltaic power generation system, comparison of the advantages and disadvantages of several common DC/DC converter circuit topologies are performed.Further more, the comparison of the several commonly used MPPT is made in principle by the simulation model of the photovoltaic cells. Then, an effective improved MPPT method is presented. This method is based on the short-current combined with variable step P&O. The result of simulation indicates that the method is better than commonly individual method, which can regulate the PV array operating point near the maximum-power point quickly and correctly and reduce the oscillation of the operation point of the photovoltaic cell when it operates the maximum power point steadily.After all, according to the requirements for sampling and calculation of the short-current combined with variable step P&O method, the TMS320F2812,a DSP from TI company is chosen to be the master chip. and the hardware circuit of the Maximum power point tracking control system is designed which based on TMS320F2812.This control circuit includes the main control circuit, power circuit, the AD sampling circuit, the AD calibration reference voltage circuit and isolated drive circuit, etc. The design is based on the consideration, that is, under the condition of the satisfying requirement of algorithm, the cost should be as low as possible. On the other hand, the software program of the maximum power point tracking control system is completed in the integrated development environment of CCS3.3, which includes the main program, ADC sampling interrupt program and PWM interrupt program.Finally a lot of simulation and experiments are done, the results prove that the short-current combined with variable step P&O method can trace the maximum-power point more quickly, efficiently and accurately, and can reduce the energy loss caused by the oscillation of the operating point about the maximum-power point, thus enhancing the PV system efficiency. From the above description, the conclusion can be drawn:the method is much better than ordinary MPPT method.