Distributed Automatic Load-Frequency Control with Optimality in Power Systems

Abstract

With the increasing penetration of renewable energy resources, power systems face new challenges in balancing power supply and demand and maintaining the nominal frequency. This paper studies load control to handle these challenges. In particular, a fully distributed automatic load control (ALC) algorithm, which only needs local measurement and local communication, is proposed. We prove that the load control algorithm globally converges to an optimal operating point which minimizes the total disutility of users, restores the nominal frequency and the scheduled tie-line power flows, and respects the load capacity limits and the thermal constraints of transmission lines. It is further shown that the asymptotic convergence still holds even when inaccurate system parameters are used in the control algorithm. In addition, the global exponential convergence of the reduced ALC algorithm without considering the capacity limits is proved and leveraged to study the dynamical tracking performance and robustness of the algorithm. Lastly, the effectiveness, optimality, and robustness of the proposed algorithm are demonstrated via numerical simulations.

A hierarchical control scheme for optimal secondary frequency regulation with on-off loads in power networks

“…Remark 1: An issue of implementability may be raised due to the requirement for demand measurements in the Primal-Dual scheme (5). This issue have been extensively considered in the literature [16], [32], [19], [33], [34], where schemes with different information structures have been proposed to relax the load measurements requirement. Note that exact knowledge of the demand is not required for the stability properties of the power system, presented below, to hold.…”

Distributed Optimal Frequency Control for Integrated Energy Systems with Electricity and Heat

“…where i  is the virtual phase angle [12] to eliminate the measurement of real phase angle i III. THE DISTRIBUTED OPTIMAL FREQUENCY CONTROL ALGORITHM In this section, a fully-distributed algorithm is proposed to solve the OLFC problem (6) based on the reverse engineering [11]- [13]. The derivation process includes three steps: 1) derive Lagrangian function; 2) apply partial primal-dual gradient method derive a distributed control scheme; 3) propose the implementation framework of the scheme.…”

“…Nevertheless, some reliability constrains such as load power and line power flow limits are not considered. Based on reverse engineering, [11]- [13] designed a distributed load-side control scheme to restore frequency with optimality, line thermal limit and convergence guaranteed under inaccurate coefficient, where [13] realized the fully distributed algorithm with only neighborhood communication and did not need accurate measurement of parameters. However, above methods face challenges in the IES because load-side electric power could depend on its heat demand.…”

“…In this paper, we propose a distributed load-side frequency control method for DERs with system-wide optimality ensured in the transmission level of IES, which is applied in secondary control. To be more specific, physically, our EPS frequency regulation considers constraints and flexibility from the DHS, and power load limits and line flow limits are also included; mathematically, detailed models of load-side DER and heat system are considered in the optimal control problem compared with [11]- [13]. It is also noteworthy that our method 1) only needs neighborhood and local information and is a fully distributed method, and 2) is robust to inaccurate coefficients and globally asymptotically stable.…”

A distributed scheme for secondary frequency control with stability guarantees and optimal power allocation

“…Literature survey: There are many recent studies associated with stability and optimality in distributed secondary frequency control. A common approach is to involve control schemes with dynamics that follow from a primal/dual algorithm associated with some optimal power allocation optimization problem [7,11,[13][14][15][16][17][18][19][20]. This approach allows to take into account economic considerations along with the objectives of secondary frequency control.…”