Research On Small Signal Stability Evaluation And Damping Modulation Using Ambient Data

With increasingly constructing and operating of large energy bases and high capacity transmission path,small signal stability of power system has surely been deteriorated.The underlying weak damping mode poses a threat to security and stability operation of power system.Therefore,timely warning it under the condition of normal operation and using a proper damping regulation to improve the damping characteristics of system is of significance for ensuring normal operation of modern power system.Based on the random response data,this paper studies a small signal stability evaluation method under ambient excitation and a generator active power modulation to improve the weak damping mode.The specific research contents are as follows:First of all,the power system state equations including random variables need to be established,and then a time domain response analytic expression of state variable is obtained under environmental excitation.According to the physical meaning of variables,there is a large number of dynamic information related to the electromechanical oscillation characteristics in the random response,which provides a theory evidence for extracting the characteristic parameters of electromechanical oscillation from the ambient data.Secondly,based on the analysis of random response characteristics of power system under environmental excitation,the on-line recursive stochastic subspace identification(ORSSI)is applied to evaluate electromechanical small signal stability.ORSSI uses Givens rotation transform to replace the LQ decomposition process of Hankel matrix after data updating in the traditional stochastic subspace identification,and realizes the extended observation matrix updating online.This technology effectively improves the real-time characteristic of electromechanical characteristic parameter identification,which is important for tracking the dynamic process of power system and alarming weak damping oscillation mode.The proposed method can be proved to be feasible and effective by the simulation analysis of IEEE 4-machine,2-area system,16-machine,5-area system and the actual measured data.Finally,an active power modulation of generators based on the sensitivity of damping ratio with respect of generator power redispatch has been studied to eliminate the weak damping electromechanical oscillation mode.The generators active power output responses under ambient excitation are considered as natural perturbations.Combined with the damping ratio identification results evaluated from the data source of active random response,these two variations can be obtained.Then the sensitivity of damping ratio with respect of generator power redispatch can be calculated by perturbation.The sensitivity result is a reasonable basis for selecting the generator modulation sequence.According to the operation condition of selected generators and their active power output constraints,the amount of active power modulation is determined and the corresponding mode damping is improved.The proposed method can be proved to be feasible and effective by the simulation analysis of IEEE 4-machine,2-area system,16-machine,5-area system and an actual power grid.