Power system transient stability assessment (TSA) and control is a complex problem. TSA from the perspective of individual machine Kimbark curves forms a distinctive approach. On the other hand, transient stability constrained optimal power flow (TSC-OPF) has been adopted widely for determining preventive control actions against transient instabilities under a given contingency. This paper presents a strategy for transient stability control, which mainly integrates the concepts of individual machine methods based TSA and global TSC-OPF. The proposed workflow is mainly based on the most severely disturbed machines (MDM) and their critical trajectories. These are utilized in deciding the number of TSC-OPF transient stability constraints, the minimum upper time limit for TSC-OPF solution interval, and security-based transient stability constraint of individual machines. Further, the application of the proposed method is explained with respect to stabilization of three different transient instability scenarios viz., transient instability originates from first swing instability, transient instability originates from multi swing instability but leads to first swing instability as fault duration increases, and transient instability originates from multi swing instability, but never leads to first swing instability as fault duration increases. IEEE 39 bus and 118 bus test system are considered for testing the proposed control strategy. The proposed approach, which expresses the transient stability constraints in global TSC-OPF in terms of some selective machine (i.e MDMs) critical trajectories not only forms a distinctive approach but also provide a smooth reconciliation between economy of operation and security level while ensuring transient stability under a given contingency.
Preventive control actions for enhancing the transient stability of power system ensures the system stability under a given contingency. Generation rescheduling through stability constrained optimal power flow (TSC-OPF) is one of the widely adopted preventive control scheme. This study reports an approach for enhancement of transient stability using global transient stability constrained optimal power flow (TSC-OPF) methods. The proposed approach uses individual machine equal area criterion framework (IMEAC), which is a direct time-domain approach for transient stability analysis, to carry out two important functional aspects of TSC-OPF methods: first, individual machine Kimbark curves (IMKC) are used to perform the transient stability analysis; second, IMKC around the critical clearing time (CCT) are used to identify most severely disturbed machines (MDM) for the given contingency. Further, the critical trajectories of these MDMs are utilized in forming reference transient stability constraints, at only one particular time step of integration. In such manner, transient stability constraints are modified at each iteration of TSC-OPF, so that they represent the dynamic response of the power system efficiently, while operating condition is improving through TSC-OPF iterations. Numerical examples demonstrate the effectiveness and main properties of the proposed approach.
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