Research And Design Of Independent Photovoltaic System

With the development of economics and technology, energy crisis and environmentpollution problem is increasingly more serious. New energy led by solar energy have attractedgreat attention all over the world, such efficient and clean renewable energy will undoubtedly bethe hot-spot in the later years. This paper researches and designs a multi-independentphotovoltaic system which is composed by PV array, Buck converter, Push-pull converter andfull-bridge inverter circuit. A deep investigation has been taken into charging the battery bymaximum power tracing algorithm and inverter under random modulation technology,simulation and experiment results show that each module conforms to the requirement of theproject.Storage battery is an indispensable part of the independent photovoltaic system, this thesisadopts the three-stages strategy for the battery charge, which are fast charging by MPPT,constant voltage charge and floating charge, with the over charging protection and the overdischarging protection, the battery charge and discharge management is achieved. And on thefix-step P&O algorithm’s basis, a further research about variable step and modified variable stepP&O algorithm are studied, by comparing the simulation of these algorithms, we can concludthat the improved algorithm is much prior to the conventional one both in dynamic response andstable precision, battery charging experiment is accomplished by MC9S12XS128at last.As the conventional PWM will cause harmonic spikes at the switching frequency and itsdouble frequency, this high energy harmonic will lead EMI, in order to improve this problem,this paper studies a single inverter under randomized period modulation, turning the triangularwave of fix switching frequency into a varied one within a certain range. Simulation resultsindicate that randomized period modulation has better effect to suppress the harmonic spikes,which will reduce EMI. In addition, the influence caused by different random degree and randomdistribution functions is considered.