Real time PMU-based stability monitoring

Zijie Lin

The purpose of this thesis is to develop PMU-based, real-time, wide area stability monitoring algorithms for the power grids using different methods and approaches. Phasor Measurement Units (PMUs) are increasingly available on power grids due to the significant investment in recent years. As a result, a priority in industry is to extract critical information from the increasing amount of PMU data for operation, planning, protection, and control. This research proposes enhanced algorithms for real time stability monitoring in a control center environment: the waveform analysis to extract the "trending" information of system dynamics embedded in Lyapunov exponents. The algorithm will help build a complete model for predicting system stability, which can help to avoid cascading failures and enhance system security. A PMU-based online waveform stability monitoring technique is proposed based on the Maximum Lyapunov Exponent (MLE). The main idea of the MLE technique is to calculate MLE as an index over a finite time window in order to predict unstable trending of the operating conditions. Significant progress has been made to improve the accuracy of MLE technique. Firstly, state calculator is applied to improve the MLE accuracy by introducing real time monitoring measurement into the computation. Secondly, the power system model is greatly improved by adopting a dynamic structure-preserving load model. This model takes into account the dynamics of P and Q load with respect to the frequency/voltage variations. The purpose is to extend the MLE technique to voltage stability analysis as well as rotor angle stability. Based on this model, the system can be represented by a set of differential equations, which is used for MLE calculation. The power network topology is preserved. Thirdly, parameters for the model are identified from the results of time domain simulation based on their importance. Finally, the methods to save memory and to improve the calculation speed are also discussed. The proposed methods are validated by time-domain simulation of the122-bus Mini-WECC system and the15000-bus PJM system model.

Real time PMU-based stability monitoring

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