The Research Of Voltage Stability Nonlinear Equivalent Principle Considering Load Static Characteristics

The static voltage stability is the prerequisite of power system voltage stability.The current static voltage stability analysis method is mainly a continuous power flow method,using the constant power load model.Due to the continuous power flow method may not converge in the vicinity of the critical point and appear morbid phenomenon,the step size contral strategy is too tricky to ensure the calculation and accuracy requirements.Aiming at the problem of continuous method,we currently improve it from two major areas: firstly,study improvements of the local parameterization strategy,avoiding the global parameters method does not converge in the vicinity of the critical point and the flow equations circumstances;secondly,study the decline in fixed voltage and impedance dynamic control step by step and other dynamic variable step size control algorithm to track the solutions of power flow equations,while eusuring the accuracy of calculations.Based on the theory of dynamic variable step size control algorithm,this paper presents a nonlinear equivalent method for calculating the voltage stability limit.Basing on analysis of the Taylor series parameter,select the load impedance modulus,current modulus and voltage modulus to establish the nonlinear equivalent model of node voltage and load current.Transmission power limit criterion shows that a necessary condition for the system to reach the limit state is dynamic equivalent impedance modulus and static load equivalent imepedance modulus exactly equal.Combining with nonlinear equivalent model and transmission power limit criterion,we can quickly and accurately calculate the limit of load power and critical voltage.Nonlinear equivalent mehod not only can accurately obtain the voltage stability limit,and may,according to an initial state,forcast the power flow limit of system.The closer distance between the initial state and the limit state,the higher forcast accuracy,and forecasting results is more reliable.Testing the effectiveness of the proposed method in IEEE14 and IEEE30 node system simulation.Static characteristica are important factors affecting the the voltage stability,and the constant power load model is too conservative.To consider the impact of load voltage static characteristics of the nonlinear equivalent method,this paper uses ZIP load model to study the power flow limit with load composed of differentproportions.Current modulus is selected as the reference variable to a certain load composition as an example,to predict the power limit and threshold voltage.Considering load voltage static characteristics,test the nonlinear equivalent method is still valid in IEEE30 node system simulation.