Eigenvalue Calculation And Wide-area Damping Controller Design Of Power Systems Considering Time Delay

The inter-area low-frequency oscillation in the large-scale power system has been a bottleneck limiting system’s transfer capacity and a key factor influencing system’s safe and stable operation. The current power system stabilizer can not effectively suppress the inter-area low-frequency oscillation in the interconnected power systems. Based on the wide area measurement systems, the wide area damping control plays an important role in the suppression of inter-area low-frequency oscillation. The time delay in the transmission of the wide-area feedback signal has a significant negative effect on the stability of the power system, which can not be ignored. It is necessary to research on the inter-area damping control considering time delay.Eigen analysis method is the most effective method in the small disturbance stability analysis of the power system without time delay and is widely applied in the electric industry. However, exponential terms appear in the characteristic equation of a power system when time delays of wide area feedback signals are considered. This makes it very difficult to obtain critical eiganvalues of the system via direct solution of the equation.This dissertation investigates the eigenvalue calculation and the wide-area damping controller design of time-delayed power systems. A method for computation of part eigenvalues of time-delayed power systems is proposed based on Pade approximation; the analysis of time delay on the power system eigenvalues is presented; controllers are designed to suppress the inter-area low-frequency oscillation effectively..A method for computation of part eigenvalues of time-delayed power systems is proposed by using Pade rational polynomials to approximate the time delay terms. The polynomials are transformed into equivalent state space expression. Based on interconnections with the original power system without time delay and the wide area damping controllers, the linear model for the time-delayed power system is established. Lastly, sparse eigenvalue algorithms can be used to compute part eigenvalues of the system according to the sparse characteristic of system coefficient matrices. The method make it possible to analyze the small disturbance stability and design wide area damping controller of time-delayed power systems by inheriting the conventional method of eigenvalue.The eigenvalue sensitivity to time delay is derived. A simple and effective method to determine the delay stability margin is proposed using eigenvalue sensitivity to time delay. The eigenvalues of the time-delayed power system are divided into two categories:the eigenvalues related to system dynamic components and the eigenvalues introduced by the time delay. The track of eigenvalues changing with time delay is obtained to analyse the impact of time delay on the system stability. Two kinds of bifurcations are found, illustrated, and studied.A method is proposed for the design of wide area damping controller considering time delay. The parameters of the controller are optimized by particle swarm optimization algorithm. Eigenvalues of time-delayed power system is computed based on Pade approximation. The validity of this method is verified on a two-area four-machine system.