An Haiyun

An improved power system stability criterion with multiple time delays

Since there exist significant time delays in the data of phasor measurement unit (PMU) and wide-area measurement system (WAMS), to evaluate their impact is very important for power system online stability assessment and controller design in the wide-area environment. In this paper, we use Lyapunov stability theory and linear matrix inequality (LMI) method to analyze the impact of time delays on power system stability. An improved delay-dependent stability criterion for power system stability analysis with multiple time delays is presented. Based on Lyapunov-Krasovskii theory, a proper Lyapunov functional is firstly constructed. And, in deduction of its derivative function along the system trajectory, some necessary slack variables are introduced so as to reduce the method conservativeness. Then the derivative function is expressed as a set of linear matrix inequalities, which can be easily solved with LMI toolboxes in Matlab or Scilab. Finally, a typical two-dimension time-delayed system and WSCC 3-generator-9-bus system with two time delays are employed to validate the method effectiveness. It is revealed that the presented method is correct, effective and with less conservativeness. Work of this paper is helpful for power system stability assessment and control with considering time delays under wide-area environment.

ON an improved delay-dependent robust stability criterion and application to power system statbility analysis with time delays

In this paper, Lyapunov stability theory and linear matrix inequality (LMI) method are used to analyze the delay-dependent robust stability of power systems with multiple time delays. An improved delay-dependent robust stability criterion for power system with multiple time delays is presented. A proper Lyapunov functional is firstly constructed based on Lyapunov-Krasovskii theory. And, in the deduction of its derivative function along the system trajectory, some necessary slack variables are introduced so as to reduce its conservatism. Then the method is applied to the robust stability analysis for power system with time-varying delays and uncertainties. It can be found the present method is correct, effective and with less conservatism.

Research on power system self-adaptive islanding based on real-time measured data

It is possible to prevent collapse of the whole post-fault power system, which is in unstable condition, by islanding control method to calm down system oscillation. Finding out the out-of-step modes is the key step of islanding control. A fast out-of-step detection method based on real-time measured data is presented in this paper. In this paper, the voltage phase angle of each branch and the active power through each branch is measured. Then, the out-of-step mode is determined when the out-of-step branch forms a cut-set. Finally, the islanding boundary is found based on the out-of-step mode and proper islanding boundary searching method. The method presented can be easily carried out and the result is found real-time. Simulation on IEEE 118-bus power system shows that the proposed method is effective.