A Gain Scheduling Approach to the Load Frequency Control in Smart Grids

As an indispensable technology that enables smart grid operations, the two-way communication networking technology greatly facilitates the vast amount of information exchange involved in the operations. However, this technology also makes it challenging to ensure the reliability and stability of smart grids. It is well-known that communication networks, especially wireless networks, are unreliable because of communication delays and random communication failures. If these factors are not properly considered in the control scheme of a smart grid, they may degrade the dynamic performance of a power system and/or even make the entire power system unstable. In this thesis, two important issues related to the effects of these unreliable network-associated factors on the load frequency control of smart grids are investigated. One of them is that how communication delays can affect the load frequency control of low-voltage microgrids. To study this issue, a thorough small-signal analysis is presented for an islanded microgrid. By conducting this analysis, the maximal communication delay below which the microgrid can maintain stable (usually defined as a delay margin) is determined and its relationships with secondary frequency control gains are identified. To improve the robustness of the microgrid to communication delays, a gain scheduling method is proposed for the load frequency control. Simulation results of the Canadian urban benchmark distribution system verify the correctness of the small-signal analysis results and the effectiveness of the proposed gain scheduling load frequency control. The other is that how communication failures can influence the load frequency control of high-voltage largely interconnected power grids. To investigate this issue, two particular scenarios that can result in communication failures are considered, including cognitive radio networks and denial of service attacks. By modeling power systems with communication failures as linear switched systems, the effects of these two scenarios on the load frequency control of largely interconnected power systems are respectively analyzed. To compensate the effects of the communication failures, a distributed gain scheduling method is also proposed for the load frequency control. Simulation results of a four-area interconnected power system show the proposed gain scheduling control can greatly improve its robustness to communication failures.