Research On The Technology Of Photovoltaic MPPT And Islanding Detection

With the improvement of the overall living standard of the society,the degree of humans'dependence on resources has been gradually strengthened,especially the demand for electricity has been different from the past,but excessive exploitation has exacerbated the consumption rate of traditional resources.In recent years,countries in order to better develop,be responsible for the next generation and for the purpose of environment protection,so they accelerate the pace of new energy research,of course,the photovoltaic power generation system is an indispensable part of it.In this paper,the mathematical model of photovoltaic cell engineering is designed to analyze its output characteristics under different external environmental conditions,which is the basis for the follow-up research.Then,the paper studies the maximum power tracking(MPPT)of photovoltaic cells.Firstly,the principle of the algorithm is analyzed.Then,several traditional kinds of maximum power tracking algorithms are introduced.Then,a self-adaptive disturbance and observation method is introduced,but its performance still has some gap from the ideal effect.Based on the perturbation observation method,this paper proposes an improved MPPT based on the combination of variable step size and dead zone,which can better take into account both the tracking accuracy and tracking time.Finally,the correctness and validity of the proposed algorithm are verified by the simulation model.In the content of single-phase photovoltaic grid-connected control technology,this chapter shows there is a slight deviation in the single-phase phase-locked loop based on SOGI by detailed analysis,which can generate the second harmonic in the system,thus affecting the accuracy of the phase-locked loop,especially when the voltage occurs mutation,it is easy to lose the phase-locked capacity.Therefore,this chapter adds a notch filter in the process of phase-locked to filter the second harmonic,so that the phase locking effect is more accurate.By contrasting,it is concluded that the power grid voltage feed-forward compensation strategy based on the PR regulator better be suited for the grid-connected system in the case of power grid as the source of disturbance.Finally,this chapter content is verified by the simulation model.In the last chapter,the mechanism of islanding effect is analyzed,and some common passive and active island detection methods are introduced.The active frequency offset method is analyzed.On the basis of it,the positive feedback frequency offset method is studied.In order to further to improve the detection effect,this paper imitate the self-adaptive thinking,study the active frequency drift with variable feedback coefficient by combining variable step size and limit value,which can better balance the detection time and output current of the total harmonic distortion.Then,the undetectable region is analyzed.Through the comparison and analysis,this paper concluded that the blind region analysis based on the Qfo×Cnorm coordinate system can better reflect the real situation of the load and the validity of the active islanding detection method.Finally,this chapter content and the correctness and validity of the studied scheme are verified by the simulation model.