Research On A Two-stage Coordinated Optimization Method Of WAPSS Parameters

With the increasing scale of interconnected power grid,power system stability is becoming more and more complicated.Low frequency oscillation is one of the common problems that affects the safe and stable operation of the system.The power system stabilizer can effectively improve the damping of the power system and suppress the local low frequency oscillation.But only using the local information and figure as the feedback input signal of the damping controller is difficult to effectively reflect the modal information of the interval oscillation in the interconnected power system,which is not ideal for the suppression of the interval oscillation.In recent years,the wide area measurement system with phasor measurement devices as the basic unit has developed rapidly in the power system,and the coordinated optimization design of the wide area power system stabilizer based on the wide area measurement system can avoid bad results.This could provide a new idea and way for the interval low frequency oscillation in the interconnected power grid.The main research of this paper is as follows.In the first stage,a two-stage coordinated optimization strategy for WAPSS parameters is proposed.Based on the linearization model of multi machine system under local control and linearized model of multi machine system with wide area control,this paper establishes a linear model of multimachine system adapted to the wide area power system stabilizer access.In this paper,the two-stage coordination optimization strategy of WAPSS parameters is proposed.Firstly,the phase compensation parameters of the wide area power system stabilizer are optimized based on the principle of the residue,and the multi time constant of the whole area power system stabilizer is replaced by the multi time constant of the wide area power system stabilizer.The number of small follow-up parameters is optimized,and then the key gain parameters of the multi wide area power system stabilizer are optimized and optimized in the framework of the multi machine system linearization model.The two-stage coordinated optimization strategy transforms the optimization problem of the key parameters of the wide area power system stabilizer into the gain coordination and setting problem,effectively reducing the number of decision variables from M*N to N,which can significantly save the time which is used to optimize and calculate.An optimization method for gain parameters of wide area power system stabilizer based on improved TLBO(Teaching and Learning Based Optimization)algorithm is proposed.This method not only can effectively optimize the design and set gain parameters,but also shows that the system has a faster convergence rate and less iteration times than the global optimization method represented by the bird swarm algorithm,which improves the timeliness of the optimization method.At the same time,this paper establishes a multi-objective optimization function,which not only avoids the problem of improving the damping of other non dominant oscillation modes at the same time of improving the damping of a single dominant oscillation mode,that is to say,this method takes both the local and the interval two modes of low frequency oscillation to be coordinated and optimized,and the damping of the non dominant oscillation mode near the virtual axis is considered simultaneously.The simulation example shows that the two-stage coordinated optimization method based on the improved TLBO algorithm can significantly increase the damping ratio of various oscillation modes and effectively suppress the system interval low frequency oscillation and improve the stability control level of the system obviously.Finally,based on the operation data of power grid,the potential system stability problems and the optimization methods of various power system stabilizer parameters are compared and analyzed.In the background of Chongqing Hubei back-to-back flexible and straight project,this paper focuses on the potential problems of local oscillation in Chongqing power grid and the potential problems of interval frequency oscillation in Sichuan and Chongqing interconnected power grid.Aiming at the hidden danger of system stability in Chongqing power grid,the effectiveness of the proposed method is verified through the optimization strategy of various wide area power system stabilizer parameters.The simulation shows that this method can effectively increase the damping ratio of local and interval oscillations,improve power system stability significantly,improve the stability and control level of Chongqing power grid.