Local and Wide-Area Sliding-Mode Observers in Power Systems

This chapter presents a review of sliding-mode estimation techniques recently proposed by the authors in the area of power systems. The power grid is interpreted as a large-scale system, composed of an interconnection of generator nodes and load nodes. The analysis starts at the local level by considering a single generator node for which two dynamical models are presented. The first model relies on the well-established swing equations, while the second one is a nonlinear and more accurate model accounting for the transient voltage dynamics. Dedicated sliding-mode estimators are proposed to estimate the unmeasured states of a single generator node. In addition, the assessment based on real data is discussed, which employs both the lumped generator node model for the Nordic Power System and the data relevant to the major faults which happened in 2015. Then, the attention is focused on the wide-area level by considering an interconnection of generator nodes and load nodes. A structure-preserving power network dynamical model is presented, which exhibits a differential-algebraic equations (DAE) structure. For this large-scale system, a distributed observer scheme is designed, which combines both the use of a super-twisting-like architecture and iterative algorithms for the algebraic part of the system. The distributed observer scheme is validated by using the IEEE 39 bus benchmark.