Time-delay exists widely in electric power systems, and is found to have significant effect on the performance of operation and control under certain conditions. It is shown that even a very small delay may destabilize the power system. Therefore, time-delay is of important concern and should be properly handled, especially in the wide-area measurement and control environment. However, only few results about the controller design for power system considering multiple time-delays are reported. In this paper, a multiple time-delayed power system model is constructed with power system stabilizer (PSS) considering time-delays. By using Lyapunov stability theory and linear matrix inequality (LMI) method, two $H_{\infty}$ control schemes are developed for time-varying multiple delayed systems. The proposed controllers guarantee the closed-loop system asymptotic stable with $H_{\infty}$ performance. A two-area four-machine power system and the New England 10-machine 39-bus system are employed to demonstrate the effectiveness of proposed methods. The simulation results verify that the designed controllers can improve the control performance significantly.

Delay-dependent stability control for power system with multiple time-delays

Wide-area damping control system for large wind generation with multiple operational uncertainty

Delay dependent wide area damping controller with actuator saturation and communication failure for wind integrated power system

• Adding an auxiliary function to the Lyapunov function to reduce conservatism of LMI criterion; this leads to increasing delay margin in feasible regions to obtain gains of the output feedback. • Design of bi-level controllers to compensate local and inter-area oscillating modes and to accurately measure related input signals. • Design and modeling of a large-scale power system in the presence of wind power units and MTDC. • Evaluating different uncertainties of power system, wind units, MTDC grid, and communication failure. The main aim of this paper is to design a bi-level damping controller for compensating local and inter-area oscillating modes in the power system. Regarding the need for compensation of time delays in measuring the wide-area signals and transmitting them to the damping controllers, a method is required that can appropriately obtain the controllers’ gains in the presence of signal delays. A robust H ∞ -based criterion is employed in this paper to design a bi-level damping controller. In the proposed design, to reduce conservatism of linear matrix inequality (LMI), an auxiliary function is defined in Lyapunov function. In this function, by including triple adder, reinforced variables, and cross-terms, the conservatism reduction of LMI and preparation of appropriate gains for controllers using state-feedback is fulfilled. The second purpose is to apply the proposed approach on a large-scale power system in the presence of wind power units where transmission of their output power is carried out by multi-terminal DC (MTDC) grid. Regarding the large scale of the power system and control converters in each of the equipment, geometric measurements based on observability and controllability are utilized to acquire accurate damping signals for the input of each controller. Simulations are obtained in different uncertainty scenarios. The results clearly demonstrate robustness of the conducted approach. 

Stability improvement of large-scale power systems including offshore wind farms and MTDC grid aiming at compensation of time delay in sending robust damping signals

Optimal design and control loop selection for a STATCOM wide-area damping controller considering communication time delays

© 2021 The Authors. IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology This paper investigates coordinated design of multiple wide-area damping controllers (WADCs) for damping multiple inter-area oscillations considering communication delays in multiple control loop. Two approaches have been investigated: the sequential approach which uses the stability criteria for single delay and design the WADC independently, and the coordinated approach which employs a less conservative and fast Lyapunov stability criterion for linear system with multiple delays to calculate delay margins simultaneously and coordinately design the multiple WADCs. The sequential approach cannot reveal the interaction among several WADCs loops with multiple delays and may lead to inaccurate delay margins, while the coordinated approach takes into account interactions of delays between different WADC control loops and can result in accurate delay stable region and relationship between delay margins and the WADC gains. Gains of WADCs are determined based on a trade-off between damping performance and delay margin. Case studies are based on the modified IEEE 10-machine 39-bus power system equipped with two FACTS devices and two WADCs. The feasibility and effectiveness of the proposed approach is verified by simulation studies.

Xinmiao Liu

Papers

Coordinated design of delay-dependent wide-area damping controllers considering multiple time delays