Research On MPPT Of Photovoltaic Power Generation System

As a pollution-free and green power, solar energy, instead of the traditional fossil energy, with great advantages, has become a current research focus home and abroad. Our country has a high development speed in the aspect of new energy power generation as well. The independent photovoltaic generation has a significant practical value for the remote areas without electricity. Estricted by its fancy price of photovoltaic cell and relatively low conversion efficiency, the Maximum Power Point Tracking (MPPT) is absolutely necessary in photovoltaic generation system.DC/DC converter which applied in photovoltaic generation system has been studied mainly in this paper. Except its electricity-transformation, DC/DC converter realizes the Maximum Power Point Tracking (MPPT) function to improve the photoelectric conversion efficiency of photovoltaic cell. The power fluctuation in the maximum power point caused by constant-step of incremental conductance method was improved in this paper, which based on the analysis of traditional constant voltage tracking (CVT) method, Perturbation & Observation method and incremental conductance method. It uses a variable-step incremental conductance method, combined with better startup characteristics of CVT to improve the tracking precision and startup characteristic simultaneously. That is in the starting stage it uses CVT method when the working voltage is more than 0.78 times of its open circuit voltage(which corresponding to maximum power approximately),and then uses a variable-step incremental conductance method.Boost circuit was adopted in DC/DC converter that analyzed in this paper. Its common topologies, application range as well as the necessity of soft-switching using were summarized; Simultaneously it made a comparison of ZVT-PWM Boost converter and ZVZCS Boost converter, and then gave a thoroughly research on Boost ZVT-PWM converter; The parameters such as boost inductor L, output filtering capacitor Cf etc in the circuit were designed, which can lower switching loss by using soft-switching, detection and protection circuit.Experimental circuit of the Maximum Power Point Tracking has been built in this paper. At the same environment, CVT method and a variable-step incremental conductance method taking MPPT experiment. The results of the experiment showed that both methods can achieve control of tracking. But the variable-step incremental conductance method has a better tracking effect than the CVT method tracking effect.