Nonlinear Behavior And Stability Analysis Of Photovoltaic Battery Hybrid Power System

There is still a large amount of population in the world suffers from lacking of electrical power,most of them locate in remote rural area and have a great demand of rural electrification.One of the ways to meet the energy demands in this regions is grid extinction,which has the disadvantage of high constructing costs,poor power quality at the end of grid and low efficiency due to long transmission lines.These drawbacks can be overcome by some kinds of distributed generation system.As a kind of flexible and renewable energy distributed power system,Photovoltaic-battery hybrid power system(PBHPS)is widely concerned and applied.Due to the application of power electronic converters,Photovoltaic-battery hybrid power system has a very strong nonlinearity.With the variation of light intensity,state of charge of the battery,and the load condition,the system needs to switch among different operating modes.This system has rich nonlinear dynamic such as Hopf bifurcation and catastrophic bifurcation under the specific operating modes.In this paper,we first introduce the operating modes of photovoltaic-battery hybrid power system under different conditions,and give the definition to some special operating conditions.Then,this paper gives the selections of key components and the designs of key circuits from the hardware perspective,and gives the solution of the structure of programs,autonomous control and closed loop control from the software perspective.Then,we identify the unstable phenomenon of Hopf bifurcation in a specific operating mode.Lyapunov linearization method is applied to establish the small signal mode of system,the small signal stability of system can be judged by solving the eigenvalues of Jacobian matrix and the stability boundaries for key parameters can be obtained,then we analyze the influence of key parameters to the small signal stability of system.Finally,the validity of stability boundaries have been verified by the simulations and experiments.Furthermore,because the current loop of system has the upper limitation,the bus voltage will collapses when the load steps up,this phenomenon is identified as a catastrophic bifurcation.This paper analyzes the physical mechanism of this phenomenon and gives the stability boundary of key parameters to keep the system stable.Then we discuss how to select the key parameters to avoid this kinds of catastrophic bifurcation.Finally,the validity of stability boundary has been verified by the simulations and experiments.Finally,based a simplified model,mixed potential function theory is applied to analyze the large signal stability of the system.At first,we establish the mixture potential function of the system.Then we apply the stability theorem of mixed potential function to get the large signal stability criterion,and analyze the influence of key parameters to the large signal stability of system.Finally,the validity of large signal stability criterion of system is verified by the simulations and experiments.