Random transmission delay and packet loss may cause load frequency control (LFC) performance degradation or even instability in interconnected power systems. Traditional robust methods mainly focus on guaranteeing the asymptotic stability with pre-estimate a maximum delay case. As a result, the designed controller cannot satisfy the actual operational requirements completely since the improper network performance estimation. In this paper, based on jump system theory, the state-space model for LFC system with the different transmission delay is established as the jumping decision variable, which describes the possible dynamics of the networked LFC system with the bounded time delay. Secondly, in order to avoid the defect of conservative or optimistic design caused by imprecise pre-set delay, the upper boundary of the transmission delay in the power communication system is calculated by deterministic network theory. Furthermore, the asymptotic stability constraints in bilinear matrix inequality forms are deduced via construction of a Lyapunov function. Moreover, to reduce the peak value, peak time and setting time of frequency deviations caused by power mismatches, an iterative optimization algorithm is proposed to obtain the optimal feedback matrix. Simulation studies with two-area and five-area interconnected power systems show that the proposed method can avoid optimistic or conservative design effectively while the stability and dynamic performance can be ensured simultaneously.

Malicious traffic attack can prolong the transmission delay of normal data flows by exhausting the limited bandwidth with injecting numerous invalid data packets. For the networked load frequency control (LFC) systems, the traffic attacks can cause the control performance deterioration or even instability. In this paper, an adaptive LFC scheme where the controller gains can be flexibly adjusted according to the attack intensities is proposed. Firstly, to quantitatively evaluate the impact of traffic attacks on the network transmission performance, the relationship between attack intensity and transmission delay bounds of normal data flows in multi-hop transmission process is well revealed based on deterministic network calculus. Secondly, to alleviate the adverse impacts of traffic attacks and improve the control performance under low-level attack intensities, the studied systems are described as a series of subsystems with the actual transmission delays of normal data flows as the switching decisions. Thirdly, a controller bank corresponding to all the attack intensities is elaborately constructed. The constraints and update criteria of each controller in the bank are strictly deduced in the switching control framework. Finally, the effectiveness of the proposed adaptive method is verified by four case studies.

In multiarea power systems, by preempting the transmission resources, denial-of-service (DoS) attacks may cause continuous packet losses in communication network and correspondingly make a performance degradation or even instability of the load frequency control (LFC) system. In this paper, a LFC scheme resilient to DoS attacks is developed. First, the dynamic boundary behaviors of data flow transmitted among multiple switches in normal no-DoS attack scenarios are described by using deterministic network calculus. Then, the analytic relationships among the upper transmission delay bound and key network parameters (e.g., packet size, forwarding rate, and hops) are deduced. Second, considering that the influences of bounded transmission delays on control instructions, the dynamics of closed-loop LFC systems are described as a series of subsystems with actual delays as the jumping decision variables. The established jumping model clearly demonstrates the dynamic evolution process of LFC systems under DoS attacks and stochastic delays. The $H_{\infty }$ -stabilization criteria considering parameter uncertainties are further deduced by using the Lyapunov theory and a constrained optimization algorithm is developed. Finally, case studies show the effectiveness of the proposed method.

With the deep coupling between the electrical power systems and cyber systems, there is a increasingly detrimental effect of the communication delays and packet losses on the load frequency control (LFC) performance. Traditional methods mainly focus on guaranteeing the asymptotic stability in maximum delay case but ignore improving the system dynamic performance. The resulting designed controller cannot satisfy the actual operational requirements completely. Hence, this paper investigates a novel decentralized LFC strategy based on switching control theory. First, the networked LFC system is modelled as a series of subsystems with transmission delay as the switching decision variable. Compared with the existing modelling methods, our modelling approach can depict the influences of time delay and packet loss on system dynamics more accurately. Second, a memoryless state-feedback control design scheme is proposed. Design constraints are deduced by constructing a Lyapunov function and then presented in a bilinear matrix inequality form. To improve the system dynamic performance in power mismatch and communication change case, an iterative linear matrix inequality (LMI) algorithm is proposed. Finally, simulation results illustrate that our proposed method can restore the frequency deviation to zero quickly.

Load frequency control (LFC) is an effective method to maintain frequency stability in power systems. With the large‐scale application of wide‐area measurement system (WAMS), impacts of unexpected physical faults and malicious cyber attacks on the frequency deviation damping performance of LFC systems cannot be ignored anymore. Different from the traditional robust‐based design methods, which assume that the operating parameters vary within a small range, physical and cyber failures may cause the significant structural or parametric changes in LFC system. Hence, a system parameter‐free active fault‐tolerant control (AFTC) strategy for LFC is proposed. First, a bank containing a series of controllers is predesigned to stabilize all the possible operation scenarios. Second, a zero trial‐and‐error selection scheme, which does not depend on prior system parameters is well‐designed to select the most matching controller. To enhance the fault‐tolerant ability in case of unmodeled faulty situations, an expansion scheme without any prior faulty information is proposed. Finally, simulation results of a three‐area‐interconnected power system show that our proposed method can ensure the smooth transition of LFC system under physical/cyber failures, thereby the reliability of power grid operation can be enhanced.