Mayhorn, Ebony T (2015-08). Optimal Coordination of Distributed Energy Resources in Isolated Power Systems: A Cross-Time Scale Perspective. Doctoral Dissertation.
Thesis
This dissertation investigates the problem of optimally coordinating distributed energy resources (DERs) in isolated power systems. It is motivated by the recent efforts worldwide of integrating large amounts of renewable generation into power grids to provide more sustainable electricity services. The increased penetration of renewable generation presents challenges for power systems operations due to increased variability and uncertainty occurring at multiple time scales. The challenge of coordinating resources cost effectively while ensuring adequate technical performance is even more pronounced in isolated power systems that are vulnerable to disturbances because of low inertia and limited generation capacity. Tertiary control approaches have been proposed for managing resources economically and all approaches assume time scale separation exists with lower level secondary and/or primary controls. Some works have mentioned that tertiary controls should be executed faster (i.e., seconds). However, if tertiary controls are executed faster, so as to interact with lower level control actions, this could cause exacerbated technical performance (e.g., frequency performance). The effect of dispatching at shorter time scales, on technical performance, has not yet been investigated. In this work, such cross-coupling among different time scales is considered, and an optimal coordination (OC) strategy for isolated microgrid systems with a mix of DERs is proposed. The goals of the OC strategy are to simultaneously minimize operating costs of diesel generators and maximize the utilization of wind generation, while considering equipment life of DERs, physical limitations on the individual controllable resources and maintain adequate frequency performance. Time scale coupling between the OC strategy and primary controls was investigated along with key parameters affecting tertiary control performance. The effectiveness of the OC strategy is evaluated in terms of frequency, economic and computational performance under realistic scenarios. To capture the impact on frequency performance, simulations were performed on a dynamical model of an isolated microgrid system. Results suggest that the proposed approach is generalizable towards designing multi-time scale optimal coordination strategies for isolated power systems to satisfy both economic and operational objectives. Recommendations are given on extending the approach to other types of isolated power systems with different variability and uncertainty characteristics.
This dissertation investigates the problem of optimally coordinating distributed energy resources (DERs) in isolated power systems. It is motivated by the recent efforts worldwide of integrating large amounts of renewable generation into power grids to provide more sustainable electricity services. The increased penetration of renewable generation presents challenges for power systems operations due to increased variability and uncertainty occurring at multiple time scales. The challenge of coordinating resources cost effectively while ensuring adequate technical performance is even more pronounced in isolated power systems that are vulnerable to disturbances because of low inertia and limited generation capacity. Tertiary control approaches have been proposed for managing resources economically and all approaches assume time scale separation exists with lower level secondary and/or primary controls. Some works have mentioned that tertiary controls should be executed faster (i.e., seconds). However, if tertiary controls are executed faster, so as to interact with lower level control actions, this could cause exacerbated technical performance (e.g., frequency performance). The effect of dispatching at shorter time scales, on technical performance, has not yet been investigated.
In this work, such cross-coupling among different time scales is considered, and an optimal coordination (OC) strategy for isolated microgrid systems with a mix of DERs is proposed. The goals of the OC strategy are to simultaneously minimize operating costs of diesel generators and maximize the utilization of wind generation, while considering equipment life of DERs, physical limitations on the individual controllable resources and maintain adequate frequency performance. Time scale coupling between the OC strategy and primary controls was investigated along with key parameters affecting tertiary control performance.
The effectiveness of the OC strategy is evaluated in terms of frequency, economic and computational performance under realistic scenarios. To capture the impact on frequency performance, simulations were performed on a dynamical model of an isolated microgrid system. Results suggest that the proposed approach is generalizable towards designing multi-time scale optimal coordination strategies for isolated power systems to satisfy both economic and operational objectives. Recommendations are given on extending the approach to other types of isolated power systems with different variability and uncertainty characteristics.
