Enhanced protection and control strategies for improving power system transient stability
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Due to the expensive cost of expanding transmission lines, power systems are operated closer to their stability margins. Consequently, stability becomes a challenging problem in the operation of power systems. Interconnected power systems should tolerate large disturbances such as short circuit faults on transmission lines, unexpected outage of generating units, or loss of large loads. Different methodologies have been proposed for enhancing the transient stability of power systems. Developing a controller for improving the transient stability of power systems has dilemma in the architecture, centralized or decentralized control approaches. A centralized controller requires fast communication systems that enable collection of data from different locations throughout the network and fast computing power hosted at a control center which increases the complexity of implementing the controller. By contrast, decentralized approaches can be implemented locally using only local measurements. This dissertation presents a centralized controller approach based on model predictive control (MPC) that enhances transient stability of power systems by determining the optimal control actions for the output powers of the energy storage units. To enhance the performance of the controller in the presence of exogenous disturbances and modeling uncertainty, a controller modeled after tube-based MPC is developed. Moreover, this dissertation introduces a decentralized tube-based MPC to provide coordinated control of excitation and steam turbine of the synchronous generators that explicitly take into account the physical constraints of the actuators. Furthermore, after a major disturbance, power system’s response is highly dependent on protection schemes and system dynamics. Improving a power system’s situational awareness requires accurate and simultaneous modeling of both protection schemes and dynamic characteristics in the power system’s analysis tools. Historical information and ex-post analysis of blackouts reaffirms the critical role of protective devices in cascading events, thereby reinforcing the necessity to represent protective schemes in transient stability studies. Another goal of this study is to investigate the importance of modeling protection systems during transient stability studies, as well as identify and represent critical protective relays in bulk transmission systems. In addition, this dissertation proposes a novel loss of excitation detection technique in order to prevent relay mis-operations during power swings.