Research On Grid Harmonic Suppression Technology For Large Scale Photovoltaic Power Station Inverters

With the shortage of traditional fossil energy and its increasing environmental pollution,it is extremely urgent to increase the proportion of clean renewable energy in the national production.As a major form of new energy,solar energy is being developed in scale and large-scale.Large scale photovoltaic power plants are an important form of large-scale,centralized use of solar energy,and also an effective way to achieve optimal energy allocation.However,large scale photovoltaic power plants are usually selected in areas where there are abundant illumination resources and far away from the load center.Long-distance transmission lines lead to a series of problems such as the limit of grid voltage fluctuation and low grid-connected power quality,which limits its development and application.Therefore,the research on the key technology issues of grid-connected large scale photovoltaic power plants has become extremely important and a hot topic of research.In this paper,a large-scale photovoltaic grid-connected system is taken as the research object to study the harmonic generation mechanism of grid-connected inverters for large-scale photovoltaic power plants.Based on the establishment of grid-connected closed-loop model of large-scale photovoltaic power station,the control strategies of grid voltage feedforward control and traditional parallel resonance harmonic compensation control are used respectively to improve the grid-connected current quality.The validity of these two methods is verified by establishing the simulation model with MATLAB/simulink.Secondly,for grid voltage feedforward control,the influence of harmonic components in the command signal on the grid-connected current cannot be effectively suppressed,and the traditional parallel resonant harmonic compensation control strategy cannot achieve good tracking of the command signal at the fundamental frequency and suppress specific 3rd?5rd and 7rd harmonics.Due to the shortcomings described above,a hybrid proportional-resonance control strategy based on QPR is proposed,and the detailed design process of its controller parameters is given in this paper.The open-loop and closed-loop transfer function Bode plots are also analyzed.The theoretical analysis show that the proposed method can effectively suppress the influence of harmonics of the grid background and the command signal on the grid-connected current of multiple inverters,effectively improve the quality of the grid-connected current,and realize grid connecton.Finally,the theoretical simulation is completed by MATLAB/simulink and compared with the traditional harmonic compensation control strategy.The results of the research show that the method proposed in this paper can achieve the purpose of no-difference tracking reference signal,and it has the dual suppression function of the background harmonic of the power grid voltage and the harmonic components of the command signal.