Resilient Load Frequency Control of Multi-Area Power Systems Under DoS Attacks

The safety and security of load frequency control (LFC) system are menaced by cyber attacks and physical attacks. Sophisticated attackers can launch cyber-physical attacks (CPAs), in which cyber attacks are used to increase the impacts of physical attacks by sending wrong instructions to the LFC controller. Considering that parameters of cyber attacks in CPAs may be either fixed or variable, a novel detection scheme is designed against two potential CPAs on an LFC system, namely fixed cyber-physical attacks (FCPAs) and variable cyber-physical attacks (VCPAs), respectively. As for FCPAs, dynamic characteristics of Area Control Error (ACE) are utilized to detect the compromised data. Compared with FCPAs, VCPAs are more deceptive. A relation-based (RB) feature extraction method is introduced to distinguish the signals compromised by VCPAs from the normal ones. A detection model that does not require compromised samples is developed with the aid of support vector domain description. In the end, a comprehensive detection scheme is designed to detect both FCPAs and VCPAs on the LFC system.

The hybrid power system is a combination of renewable energy power plants and conventional energy power plants. This integration causes power quality issues including poor settling times and higher transient contents. The main issue of such interconnection is the frequency variations caused in the hybrid power system. Load Frequency Controller (LFC) design ensures the reliable and efficient operation of the power system. The main function of LFC is to maintain the system frequency within safe limits, hence keeping power at a specific range. An LFC should be supported with modern and intelligent control structures for providing the adequate power to the system. This paper presents a comprehensive review of several LFC structures in a diverse configuration of a power system. First of all, an overview of a renewable energy-based power system is provided with a need for the development of LFC. The basic operation was studied in single-area, multi-area and multi-stage power system configurations. Types of controllers developed on different techniques studied with an overview of different control techniques were utilized. The comparative analysis of various controllers and strategies was performed graphically. The future scope of work provided lists the potential areas for conducting further research. Finally, the paper concludes by emphasizing the need for better LFC design in complex power system environments.

The load frequency control (LFC) system is an essential component of the smart grid and is located between cyberspace information and the physical infrastructure. Because the operation of LFC depends on the modern network communication technology, it is vulnerable to network attacks. The false data injection attack (FDIA) injects attack data into the data collected by the LFC system, affecting the control center's calculation and causing errors in the control signals, which affects the stable operation of the power system. For the LFC system, this article builds a cyber-physical model. Based on the model, an FDIA detection and defense mechanism based on the GAN network is proposed. By calculating, contrasting, and replacing the control signals, the proposed method can detect and defend against FDIAs. The experimental results on the two-area interconnected power system, the IEEE 39-bus, and IEEE 118-bus power system show that the proposed defense method can ensure the power system frequency and tie-line power deviation remain within the set value when suffered from FDIA.

[formula omitted] sampled-data load frequency control with time-varying delays considering delay compensation

Resilient load frequency control design: DoS attacks against additional control loop

In this paper, the authors propose an optimal IMC-PID controller design for the Load Frequency Control (LFC) of large-scale power system via model approximation method. The model approximation method uses the Enhanced Differential Evolution (EDE) algorithm to determine an optimal Reduced Order Model (ROM) for the considered large-scale power system by minimizing the performance measure called Integral Square Error (ISE) between their step responses. Later, the LFC design is carried out using an optimal ROM instead of processing with the large-scale power system model. Thus, this simplifies the design, reduces the computational efforts and also helps in determining the lower order controller. An optimal IMC design methodology is proposed by minimizing ISE between the actual output and the reference input responses of the large-scale power system using EDE algorithm. Further, PID controller gains are acquired by least square model matching with the optimal IMC transfer function. The proposed IMC-PID controller design allows a satisfied reference input tracking performance, robustness in disturbance rejection and improves the dynamic stability of the power system. The proposed method is validated by applying it to a single area power system of third-order SISO model and also extended to a centralized two-area thermal–thermal non-reheated power system of a seventh-order MIMO model. The simulation results and the comparison of error performance indices show the efficacy of the proposed method over the significant methods available in the literature.

False data injection attacks (FDIAs) against the load frequency control (LFC) system can lead to unstable operation of power systems. In this paper, the estimation problem of the FDIAs for the LFC system in the presence of external disturbances is investigated. The LFC system model under FDIAs against frequency and tie-line power measurements is established. Then an attack estimation scheme combining the attack observer (AO) and technique is proposed to minimize the effect of external disturbance on estimation errors. The uniform boundedness of the state and attack estimation errors is proved using Lyapunov stability theory. Finally, a two-area interconnected power system is simulated to demonstrate the effectiveness of the proposed attack estimation algorithms.

Information and communication technology tremendously facilitates the operation efficiency and economy of modern power systems in recent years. However, risks such as bandwidth constraints and malicious attacks threaten the secure load frequency control (LFC) of power systems. To mitigate such risks, this paper proposes distributed observer-based event-triggered LFC schemes for multi-area power systems under cyber attacks. Considering the practical situation that only local system output information may be available, distributed observer-based LFC schemes are designed. Meanwhile, to reduce the communication burden, an event-triggered mechanism is adopted to design control laws, where both static and dynamic event-triggered approaches are taken and the dynamic one is proved to be more economical in terms of control cost. Verifiable sufficient conditions are established to guarantee the stability of the closed-loop system in the presence of cyber attacks and the controller gains are explicitly derived. Finally, validation studies on a three-area interconnected power system are carried out to demonstrate the proposed control schemes. Note to Practitioners—Load frequency is a crucial index for evaluating the quality of electric energy and thus LFC has brought considerable attention in the area of power systems control. Although many achievements have been made on the LFC of multi-area power systems, the risks such as bandwidth constraints and malicious attacks affect the normal operation of LFC due to the interconnection between different power systems. To deal with these risks, this paper focuses on designing event-triggered LFC to guarantee the stability of the frequency deviation while reducing the communication burden and mitigating cyber attacks. More importantly, the proposed event-triggered LFC is designed based on an observer and can be implemented in a distributed manner, which is relatively practical in real applications. The results presented in this paper aim to provide a helpful reference for stable and secure LFC design of multi-area power systems, such that the corresponding application research can be promoted.

Numerous control methods based on modern control theory have been proposed to improve the load frequency control (LFC) characteristics of power systems. These control methods generally regard the load frequency control system as a linear system model. Furthermore, complicated mathematical equations have to be solved to determine control laws. However, realistic power systems are nonlinear, i.e., the nonlinearities of tie‐lines connecting between the control areas and of generation rate constraints of power plants exist. Consequently, it is considered that the design of controllers is difficult.In this paper, the application of fuzzy control to the load frequency control system is proposed to solve the forementioned problems. The proposed control first, to satisfy the load frequency control requirements, estimates power demand variations of the control areas and uses them as the output set‐point values of power plants, instead of using an integral‐type controller. Next, to improve stability and optimality of the nonlinear load frequency control system using the fore‐mentioned output set‐point control method, the proportional‐type fuzzy control considering a computation time‐delay is implemented. Parameters of the proposed fuzzy controller are determined by minimizing the integral square of the area control error (ACE) to ensure optimality of the system.

In this paper we present an approximate model for load frequency control system with time delay. The load frequency control is one of the conventional power system control problems. In order to secure the stability of the grid the frequency must remain within its limited range which is achieved through the load frequency control. The load frequency control signals experience time delay that could destabilize the power systems. The presence of the time delay complicates the analysis of the load frequency control system. In this paper we present a stability method based on the Direct Frequency Response approximation for the time delay. This approximation transforms the transcendental time delay equation into linear equation. This results in a simple stability criterion for the loadfrequency control system with time delay. A one-area load frequency control system is chosen as a case study. The effectiveness of the proposed approximation has been tested through simulation and comparison with the published research work. By tracking the eigenvalues or using Routh's criterion the maximum delay margin can be estimated. The proposed stability criterion has been compared with the most recent methods and showed it is merit. The range of the PI controller parameters for a given time delay can be determined which is very important in practice.

This paper presents a damping based stability analysis of a time delayed single-area load frequency control (LFC) system with plug-in Electric Vehicles (EVs) Aggregator by employing a graphical method. The proposed technique computes all the stabilizing gain values of Proportional Integral (PI) controller of the LFC with plug-in EVs (LFC-EVs) system. The proposed method relies on identifying stability region and the stability boundary locus in the PI controller parameter plane having user defined relative stability. These damping based stability regions are obtained and the accuracy of their Complex Root Boundary (CRB) and Real Root Boundary (RRB) is validated by an independent algorithm and time-domain simulations. Moreover, a simple and effective analytical approach known as Weighted Geometrical Center (WGC) is used for tuning the stabilizing controller parameters to achieve better system performance.

Event-triggered load frequency control of Markovian jump interconnected power systems under denial-of-service attacks

Numerous control methods based on modern control theory have been proposed to improve the load frequency control (LFC) characteristics of power systems. These control methods generally regard the load frequency control system as a linear system model. Furthermore, complicated mathematical equations have to be solved to determine control laws. However, realistic power systems are nonlinear, i.e., the nonlinearities of tie-lines connecting between the control areas and of generation rate constraints of power plants exist. Consequently, it is considered that the design of controllers is difficult. In this paper, the application of fuzzy control to the load frequency control system is proposed to solve the forementioned problems. The proposed control first, to satisfy the load frequency control requirements, estimates power demand variations of the control areas and uses them as the output set-point values of power plants, instead of using an integral-type controller. Next, to improve stability and optimality of the nonlinear load frequency control system using the fore-mentioned output set-point control method, the proportional-type fuzzy control considering a computation time-delay is implemented. Parameters of the proposed fuzzy controller are determined by minimizing the integral square of the area control error (ACE) to ensure optimality of the system.

This research presents a load frequency control (LFC) system with demand response (DR) studied for robust stability analysis based on gain and phase margins (GPMs) utilizing a fractional-order proportional-integral (FOPI) controller. Electric power systems contain many parametric uncertainties. FOPI controller gains are adjustable parameters and can be designed to provide the desired frequency control and dynamic performance. Therefore, in this article, the robust stability regions containing a set of robust FOPI controller gains are designed for the range model of the load frequency control system using Kharitonov’s theorem, considering the uncertainties in the LFC-DR system parameters and the time delay. Further, the robust performance of the interval LFC-DR system in terms of design features, including GPMs, is investigated. Simulation studies indicate that GPM parameters provide a better dynamic performance in terms of fast damping of oscillations, less settling time, and overshoot time for the interval LFC-DR system.

Automatic generation control (AGC) and load frequency control (LFC) are very important parts of the power systems in order to provide reliable and quality power supply to the end users. Load variations can lead to the deviation generated power frequency which ultimately can destabilize the entire power system. Here comes the LFC for rescue by maintain the power frequency at desired value. In LFC, area controllers are used to perform this task. In this work, three area interconnected LFC system has been used for simulation purpose. Fractional order proportional integral (FOPI) controllers were used as an area controller in order to mitigate the effect of load variation in power system. In order to optimize the parameters of FOPI controllers, three optimization algorithms namely genetic algorithm (GA), particle swarm optimization (PSO) and water cycle algorithm (WCA) have been used. Performance comparison between optimized FOPI controllers using these algorithms has also been performed. Comparative analysis shows that the WCA optimization performed better than the other two GA and PSO algorithms. LFC system was simulated on MATLAB with the load disturbance of 0.01 p.u. in all areas at the same time.KeywordsLoad frequency controlOptimizationITAEPower systemsWater cycle algorithm