Cyberphysical Challenges of Transient Stability and Security in Power Grids

Abstract:

Motivation: Power transmission networks underpin our way of life and are at the center of the transformation of the US energy system. "Keeping the lights on" as we transform an already large and complicated power system is a fundamental challenge for cyber- physical engineering. Future power networks will be instrumented with synchrophasor measurement units, communication infrastructures and distributed computing, and are therefore prototypical examples of cyber-physical systems with tightly coupled compu- tational and physical resources. Our team integrates expertise in power networks, fault detection, cyber security, control systems, distributed and multi agent systems, and net- work science.

Our focus: To develop new principles that integrate physical and cyber aspects into a unified theory, we focus on the problem of detecting and avoiding fast instabilities of power networks that can cause blackouts. We propose novel approaches to analyze these dynamic instabilities and to design cyber-physical control methods to mitigate them. The controls must perform robustly in the presence of variability and uncertainty in genera- tion, loads, communications, and the operating state, and during abnormal states caused by natural faults or malicious attacks.

Highlights

• Transient stability is the ability of the entire power grid to stay synchronized to- gether at 60 Hz. Almost exact conditions for transient stability have been obtained in terms of the spread of natural frequencies of generators (oscillators) and the cou- pling provided by the power grid, and this has been published in the PNAS journal. The next step is to use the conditionst to understand and design controls to help prevent instability
• Electromechanical grid oscillations occur, for example, when voltages in Arizona slowly swing at about 1 Hz relative to voltages Canada. We have published an ana- lytic formula for the damping of these harmful oscillations by redispatching gener- ators based on measurements of the patterns of oscillations and power flows. (Some other researchers thought this impossible.) The next step is to formulate a practical algorithm based on synchrophasor measurements to suppress the oscillations.
• Power grid operation relies on voluminous sensor data and is robust to errors to some extent but not to cyber attacks. We designed an anomaly detector which minimizes the "worst-case" probability of error against all possible manipulations of up to n sensor measurements. We proved a necessary condition for the detector to be optimal and derived a heuristic detector, which is asymptotically optimal.
• Florian Do" rfler graduated with a PhD from UCSB and joined the faculty at UCLA. Iowa State visitor Sarai Mendoza graduated with PhD in Physics from Universidad Michoacana, Mexico, and will continue work on the project as a postdoc.

A general insight: we learned the importance of finding simple conditions summarizing intricate physics and engineering that can give actionable information to enable cyberphysical controls.