8 research outputs found
Distributed Optimal Frequency Control Considering a Nonlinear Network-Preserving Model
This paper addresses the distributed optimal frequency control of power
systems considering a network-preserving model with nonlinear power flows and
excitation voltage dynamics. Salient features of the proposed distributed
control strategy are fourfold: i) nonlinearity is considered to cope with large
disturbances; ii) only a part of generators are controllable; iii) no load
measurement is required; iv) communication connectivity is required only for
the controllable generators. To this end, benefiting from the concept of
'virtual load demand', we first design the distributed controller for the
controllable generators by leveraging the primal-dual decomposition technique.
We then propose a method to estimate the virtual load demand of each
controllable generator based on local frequencies. We derive incremental
passivity conditions for the uncontrollable generators. Finally, we prove that
the closed-loop system is asymptotically stable and its equilibrium attains the
optimal solution to the associated economic dispatch problem. Simulations,
including small and large-disturbance scenarios, are carried on the New England
system, demonstrating the effectiveness of our design
Load and Renewable-Following Control of Linearization-Free Differential Algebraic Equation Power System Models
Electromechanical transients in power networks are mostly caused by mismatch
between power consumption and production, causing generators to deviate from
the nominal frequency. To that end, feedback control algorithms have been
designed to perform frequency and load/renewables-following control. In
particular, the literature addressed a plethora of grid- and frequency-control
challenges with a focus on linearized, differential equation models whereby
algebraic constraints (i.e., power flows) are eliminated. This is in contrast
with the more realistic nonlinear differential algebraic equation (NDAE)
models. Yet, as grids are increasingly pushed to their limits via intermittent
renewables and varying loads, their physical states risk escaping operating
regions due to either a poor prediction or sudden changes in renewables or
demands -- deeming a feedback controller based on a linearization point
virtually unusable. In lieu of linearized differential equation models, the
objective of this paper is to design a simple, purely decentralized,
linearization-free, feedback control law for NDAE models of power networks. The
objective of such controller is to primarily stabilize frequency oscillations
after a large, unknown disturbance in renewables or loads. Although the
controller design involves advanced NDAE system theory, the controller itself
is as simple as a decentralized proportional or linear quadratic regulator in
its implementation. Case studies demonstrate that the proposed controller is
able to stabilize dynamic and algebraic states under significant disturbances.Comment: 13 pages, 6 figures, 2 table