Polynomial Approximation Based Power System Parametric Transient And Mid-long Term Stability Analysis And Control

The stablity of power systems is a prerequisite for the continuous and reliable power supply to users.With the interconnection of power grids and the development of long-distanc transmission systems,ultra-high voltage AC/DC transmission systems and renewable energy sources,and the implementation of the power market,the stability of the power system will face a more severe challenge.In this paper,we focus on the parametric analysis and control of transient and midlong term stability problems,i.e.,the physical factors affecting the operating state and stability performance of the power system are regarded as variable parameters in the mathematical models,which are constructed for transient and mid-long term stability analysis and control problems.Based on the idea of polynomial approximation method,the quantitative relationship between the variable parameters and the system variables in the dynamic process,the optimal control scheme is explicitly portrayed,so as to improve the transient and mid-long term stability of the power system under complex,variable and uncertain operating environment.The main work includes:(1)A parametric transient trajectory approximation method based on polynomial approximation method is proposed for the parameterization problem in transient stability analysis.The proposed method uses a series of polynomial and coefficient combinations of parameters to approximate the system variables,so as to establish the relationship between parameters and dynamic behavior through polynomial expressions.The proposed method substantially improves the accuracy compared with the existing trajectory sensitivity methods in the case of large parameter variation and strong system nonlinearity,and has a global controllable accuracy property in the range of variable parameter variation.(2)To address the parameteric problem in transient stability control,a novel parameteric transient stability constrained optimal power flow(TSCOPF)model is proposed,which describes the relationship between the variable parameters and solution of the parametric TSCOPF.In order to solve the this problem,a polynomial approximation method based on the collocation method is proposed,which approximates the solution of the parametric TSCOPF by the polynomial expression of the variable parameters,through which the optimal preventive control scheme considering both transient stability and economy can be easily obtained by substituting the values of the variable parameters into the polynomial expression.(3)A polynomial approximation method for the approximarion of mid-long term voltage stability trajectory based on the quasi-steady-state model is proposed,which can accurately analyze the influence of the changes in system parameters using the polynomial approximation function.The continuous and discrete dynamics of the midlong term process of the power system are considered separately by the Galerkin method.Compared with the traditional linearized trajectory sensitivity method,the proposed method can describe the nonlinear characteristics of the mid-long term processes,and the approximation accuracy is greatly improved.Moreover,the polynomial approximation of the approximate relationship between the system variables and parameters can provide valuable information for the mid-long term voltage stability assessment and control.(4)In order to improve the mid-long term voltage stability related to the slow dynamic components and protection devices in power systems,a model preventive control(MPC)scheme based on the polynomial approximation method is proposed for the parameteric problem in the mid-long term stability control of power systems.By applying the optimal solution to the power system,the mid-long term voltage stability can be improved.The polynomial approximation function obtained based on the Galliakin method is used as a prediction model to predict the future dynamics of the power system.Since the polynomial function of higher order can reflect the nonlinear characteristics of the mid-long term processes of power systems,the proposed method has the advantage of higher prediction accuracy,which improves the control efficiency of MPC.