Research On Optimizing Power System Stabilizers Parameters

As modern power system are interconnected, the low frequency oscillation has become a problem comcerned in power system planning and operation. Power System Stabilizers(PSS) are effective in damping the low frequency oscillation.Even equipped with power system stabilizer, the power system may also experience nonlinear oscillation due to its nonlinear characteristics. For example, low frequency oscillation ever happened in east-north china power system, many experts ascribe it to the nonlinear characteristics of power system.Through analyzing the large disturbanceoscillation theory we find t hat both fundamental frequency electromechanical oscillation and high frequency electromechanical oscillation are exist in time domain simulation. Since small signal stability analysis neglects the high order terms of Taylor series of the system state equation, so this method can not reflect the nonlinear characteristics of system oscillation, so the PSS which is designed based on small signal stability analysis sometimes can not damp great oscillation brought out by a large disturbance effectively.Trajectory sensitivity simulation is carried out using a group of time varying linear equations accompanied with original system equations along a system trajectory. It offers us a useful tool to study variation behavior of an original trajectory due to small deviations both in system parameters and initial conditions for avoiding repetitive trajectory integrations. It is an advantage that the trajectory sensitivity analysis can be used to study large power system represented by complicated system models, and can provide rich information about multiple trajectory scenarios.Since trajectory sensitivity enables us to confidently extrapolate the system behaviors for a small change in PSS parameters, it is possible to extend the applications of the trajectory sensitivity approach to the area of PSS design, a significant topicin power eng ineering.This paper proposed a new method to design PSS parameters. The method is based on time domain simulation and formulates the problem of turning PSS parameters as an optimization problem. A trajectory sensitivity approach is adopted to provide valuable gradient information of objective function of the optimization problem. Using the gradient, a conjugate gradient method is employed to solve theoptimization problem. The method not only can improve small signal stability of systems, but also can significantly damp out great oscillations brought out by a severe disturbance because of the considerations of large system oscillations in the objective function.The method studies the formulations and the computation techniques of the trajectory sensitivity of power system with respect to the PSS parameters that will found a basis for developing new tools for optimal PSS design. Results on four typical system are given to show the effectiveness of the method.