Research On Probabilistic Stability Of Small Disturbance In Power System Based On Risk

With the development of interconnected power grids,the scale of power grids is expanding and the low frequency oscillations between the interconnected large power grids cannot be neglected.At the same time,with the development of new energy sources such as wind power and the formation of electricity market,the system uncertainty increases gradually,thus the effects of random parameters on low frequency oscillation of power grid cannot be ignored.It is of great theoretical and engineering application value to study the low frequency oscillations in interconnected power grid considering uncertainty factors and to ensure the safe and stable operation of the grid.In this paper,the uncertain factors such as wind power and load fluctuation in the power system are taken into account,and a probabilistic stability model of small disturbance stability is established.After modeling,power system small signal stability risk assessment and optimization control strategy of the power system low frequency oscillation are developed based on the risk assessment theory.The main research contents in this paper are summarized as follows:(1)Considering the randomness of the grid,a system model for small signal probabilistic stability analysis and risk analysis is established,which mainly includes wind power modeling taking into account the wind correlation and the load modeling taking into account the load correlation,and the small disturbance stability model of power system and its linearization are also introduced.Then the correlation modeling method based on Copula function is applied to generate random wind power and load data,which is used in the modeling of the classic two areas four machines grid and the East China Power Grid.(2)Based on risk assessment theory and evaluation method,a risk index based on the sensitivity of damping ratio is proposed and the risk assessment model of small disturbance stability is established,which can effectively integrate the probability of small disturbance instability and the loss of active power after failure,and can provide the decision basis for the safe and stable operation of the system.(3)Based on the risk model,the risk analysis of the small interference probability stability of the system is carried out.Firstly,the risk analysis process is introduced.Based on the Monte Carlo simulation,a large number of operational scenarios are generated based on the system model and Copula function simulation.Then,the deterministic small disturbance stability analysis is carried out in different scenarios to form the probability density function of the damping ratio of critical oscillation mode.The risk and stability of the system are analyzed,and the risk value is calculated and the risk assessment of the small signal stability is carried out.The feasibility and effectiveness of the risk assessment index and the evaluation method are verified by modeling,simulation and evaluation of the systems.(4)Risk-based low frequency oscillation control decision strategies are studied for control personnel to provide control decision basis.Based on the analysis of the probability small signal stability and the risk assessment of the system,the optimal control strategies,including the generator output adjustment and the reduction of the load and the determination of the control quantity and location,are put forward to improve the system’s probability small signal stability and reduce the system risk.Then this paper introduces the dynamic model reduction technique based on singular value decomposition which can be applied to time domain simulation.In this method,the non-characteristic generators are linearly represented by the characteristic generators,which can greatly improve the speed of time domain simulation,and provide a more efficient simulation algorithm.Finally,through the time domain simulation,when there is a risk of oscillation instability and the small disturbance occurs,the low frequency oscillation of the system will soon subside after the implementation of the control strategy,which verifies the effectiveness of the control strategy considering the risk in power system.