The Investigation Of Maximum Power Point Tracking Control Technology In Stand-alone PV System And Its Control System Design

As a clean,inexhaustible and renewable energy,solar energy has been extensively harnessed nowadays.Photovoltaic(PV)power generation technology is one of the most effective ways to utilize solar energy.The output characteristics of PV modules,however,show a strong non-linear relationship with external environmental factors,such as solar radiation intensity and ambient temperature,which result in photovoltaic power generation system being unable to work at the maximum power point(MPPT),leading to a waste of resources.With the purpose of taking full use of solar energy,based on off-grid PV system,this paper investigated into the maximum power point tracking of the PV system.Firstly,based on the mathematical model of PV cells and actual parameters of PV modules,this paper has established a PV cell simulation model to simulate the photovoltaic cells placing in different intensity of solar radiation and ambient temperature,recording these output characteristics.According to the simulation results,the photovoltaic cell output power curves at each ambient condition show a single peak,e.g.,there is a unique maximum power point,and it changes with the external environment.At the same time,according to the output characteristics of the PV cells,this paper has described what is the maximum power point tracking and utilize the DC-DC converter to realize the maximum power point tracking.Several traditional MPPT methods had been presented in detail,such as the Perturbation and Observation(P&O)method and the Conductance Incremental(CI)method.By analyzing their working principles and compared their advantages and disadvantages,an innovative method which is named improved three-point tracking method has been proposed.A simulation model combining with those MPPT algorithms had been built to compare tracking performance of those MPPT algorithms.The results demonstrate that the improved three-point tracking method could track the maximum power point quickly,accurately and efficiently and it is more superior than the Perturbation and Observation(P&O)method and the Conductance Incremental(CI)method.As for hardware design,we selected the Boost circuit as the main control circuit.STC12C5A60S2 MCU was invoked as the master chip to design the hardware circuit.The hardware circuits of the maximum power point tracking control system include Microcomputer Minimum System,regulated power supply circuit module,data acquisition circuit module.MOS drive circuit,display circuit and display driving circuit module,etc.In software design,the software program of the maximum power point tracking control system is completed,including the main program,MPPT program,data acquisition procedure,display program,etc.Finally,a Photovoltaic power generation system which can supply 30W power is built to complete MPPT experiment to demonstrate the tracking performance of the improved three-point tracking method.Measuring solar radiation by solar radiometer,catching temperature by thermometer,reading voltage and current of the maximum power point through digital tube display circuit,we calculated the maximum output power in ambient circumstance and analyzed the data.Experiment results show that the improved three-point tracking method is not only able to track the maximum power point quickly,but also have a good tracking stability.It could ensure the tracking sensitivity in the case of rapidly changing external conditions.