Research On Fractional Modeling And Controller Design Of Photovoltaic Grid-connected System

With the rapid development of photovoltaic power generation technology,the number of distributed photovoltaic power generation systems connected to the grid has increased rapidly,and the problems of harmonic pollution have become more serious.Therefore,improving the performance of photovoltaic grid-connected systems and grid-connected power quality has become a research hotspot.The inverter is the core component of the photovoltaic grid-connected system,and its performance improvement is an important means to improve the performance of the photovoltaic grid-connected system.Capacitive and inductive components are the key components of the inverter system.They play the role of storing electrical energy and filtering in the system.Their electrical characteristics will directly affect the dynamic and static characteristics of the photovoltaic inverter system.Existing research shows that capacitive and inductive components should be fractional-order in nature.In the past,the modeling,analysis and control of the inverter system were carried out on the theoretical basis of integer order calculus,which will inevitably cause certain errors.Therefore,this paper introduces fractional calculus into the photovoltaic inverter grid-connected system,and conducts fractional-order modeling,analysis and control for it,in order to improve the photovoltaic grid-connected power quality.In this paper,the fractional calculus is introduced into the photovoltaic inverter grid-connected system,and the following researches are mainly done:Firstly,this paper introduces the theory of fractional calculus and fractional order controller,and analyzes and discusses the classification of fractional PI~λD~μdevice,the influence of parameter changes on the system and the parameter design method of PI~λD~μdevice.And two kinds of parameter tuning schemes based on intelligent algorithm are given.Secondly,the paper establishes the time-domain and frequency-domain models of fractional-order capacitors and fractional-order inductors.The electrical characteristics of fractional-order components are analyzed and summarized in detail by comparing with integer-order components;The common approximation algorithms for fractional-order component approximation circuits are simulated and compared.The Oustaloup approximation algorithm with better approximation effect is used to theoretically deduce the topology and component values of the fractional-order component approximation circuit.The topology structure and component value formula of fractional-order component approximation circuit are obtained.Thirdly,none of the mainstream power electronic simulation platforms have a fractional-order component simulation module,which greatly hinders the simulation analysis of fractional-order power electronic systems.Based on the Matlab/Simscape platform,this paper uses the S language to build the simulation library files of arbitrary-order fractional-order capacitors and fractional-order inductance components,and realizes the device-level computer simulation.The simulation results show that the established model has the advantages of high efficiency,intuition and easy circuit topology modification.Finally,this paper introduces fractional-order components into the single-stage three-phase photovoltaic inverter system,and conducts fractional-order modeling.The fractional high and low frequency models of the system in three-phase stationary coordinate system(abc coordinate system),two-phase stationary coordinate system(DQ coordinate system)and two-phase rotating coordinate system(dq coordinate system)are established respectively.The fractional-order double closed-loop control structure in the dq coordinate system is deduced,the fractional-order PI~λcontroller is introduced,and its parameters are designed by the method of time domain optimization.The simulation analysis shows that the fractional-order model can provide a more general mathematical description,the fractional-order controller achieves better control effects,the fractional-order photovoltaic system has better dynamic and static characteristics,and the grid-connected power quality is also improved.