The Impact Of Time-delay On Power System Stability

Wide Area Measurement System (WAMS) is based on Global Position System (GPS) and fiber communication technology. It brings new opportunity for power system global stability analysis, operating optimization and coordination control. However, there exist obvious time-delays in WAMS data. And it is well known that time-delay has negative impact on the effectiveness of the global control strategy and coordination controller. So, it is essential to evaluate the impact of time delay in the wide-area power system stability analysis and coordination controller design. Main work of this thesis is as follows:Firstly, impact of the time-delay on power system small signal stability and small signal stability region is deeply discussed. It is a basic requirement for power system to be operating under small signal stability daily. A method to analyze the small signal stability of dynamic system described by Differential Algebraic Equation (DAE) is first derived. Then an optimal based algorithm is given to trace the power system small signal stability region with considering the time delay. Finally, a simple power system is employed to do some verification studies. It is found that the impact of time-delay on power system small signal stability is very complicated. It can bring both negative and positive influences to the small signal stability region. If we can consider both the positive and negative influence of the time-delay in coordination controller design, we can draw more benefit from the wide area control application.Secondly, PSASP (Power system Stability Analysis Software Package) is used to evaluate the impact of time-delay on power system transient stability based on the EPRI-36 (China) system. The following two aspects are considered: 1) Impact of time-delay in the control loop of coordination PSS controller is evaluated based on numerical simulation. It is found that PSS control effectiveness deteriorates with the time-delay increasing. So it is an important issue to properly consider the time-delay impact in coordination PSS controller design; 2) Impact of the data asynchrony from EMS/SCADA system to the on-line stability assessment is discussed. The data asynchrony can be considered as one type of general time-delay. It is found that data asynchrony may cause stability analysis failed under some condition, e.g. power system is under a heavy load. Since the data asynchrony in EMS/SCADA system can not be eliminated easily, it is very important to properly consider its impact on the online monitoring and security assessment. Impact of the time-delay should be properly considered not only for on-line stability monitoring and assessment system constructing but also for coordination controller design under the new wide-area era. We hope our work in this thesis can be helpful for the coming works.