The Research Of Stand-alone Photovoltaic System And Its Maximum Power Tracking Algorithm

Promoting the use of stand-alone photovoltaic system would not only solve thepower supply problems in some areas, meet the needs of the national economy and thepeople’s livelihood, but also relieve the dependence on non-renewable fossil fuels andbe friendly to the environment. Therefore, the research on stand-alone photovoltaicsystem had become one of the most important study for new energy generation andapplication areas.The principle of stand-alone photovoltaic system as well as the equivalent circuitof the solar cell and it’s engineering mathematical model were introduced firstly, anda simulation model of the solar cell had been established. The I-V, P-V characteristiccurves of the solar cell in standard test condition and changing environmentalcondition had been simulated by means of the simulation model.The above studieshad laid a good foundation for the reseach of photovoltaic power generation system.The photovoltaic MPPT system based on buck circuit was analyzed.On this basis,the realizing conditions of MPPT were came forward and a lot of conclusions hadbeen acquired.Then, the principles, merits and drawbacks of several MPPT algorithmscommonly used were described and compared.To overcomethe lacks of the commonlyused perturbation and observation methods in tracking speed and accuracy, a variablestep disturbance MPPT algorithm based on power threshold was proposed,and it’seffectiveness was validated by means of the MPPT simulation model established inMatlab.In this paper, the sinusoidal pulse width modulation (SPWM) technology waselaborated. And what’s more, the mathematical model and open loop control blockdiagrams of a single-phase inverter were established wich laid the foundation for thedesign and simulation of the control system. Moreover, the mathematical model andclose loop control block diagrams of a inverter, which adopted a PID closed loopcontrol based on voltage instantaneous value, were established and the parameters ofPID controller were designed by using the method of closed loop pole assignment.Finally, through establishing the closedloopsimulation model, the single-phase SPWMinverter was simulated and analysed.In order to verify the correctness of the method and theory developed in thisthesis, the softwares and hardwares of a stand-alone photovoltaic system weredesigned and introduced in detail. The properties of the MPPT algorithm corresponding to system startup, dramatic environmental changes and load changeswere tested in the experimental platform, and it was compared with the traditionalperturbation and observation method. Besides, the output voltage and currentwaveforms of a single-phase inverter based on voltage closed-loop control were alsoexperienced.The experiment results showed that the improved MPPT algorithm have fasterresponse speed and better stability behavior about the maximum power point than thetraditional algorithm, and the overall efficiency of photovoltaic system was alsoimproved. In addition to this, the inverter using PID control based on voltageinstantaneous value could output good sine wave to fit various loads of stand-alonephotovoltaic system.