Load Frequency Control System Research Articles

LOAD FREQUENCY CONTROL OF INTERCONNECTED POWER SYSTEM GRID INVOLVING WIND AND HYDROPOWER PLANT AND COMPARATIVE ANALYSIS

Power demand is expanding day by day. The greatest test is to give continuous and top-notch power to clients in factor conditions particularly when we interconnect the two areas utilizing power tie-line. To achieve this, the two boundaries should consistently be checked for each condition, these boundaries are Load Distribution and Load Frequency Control (LFC).The primary work of the load frequency control is to regulate the power output of the generator within a specified area with respect to change in system frequency and tie-line power, such as to maintain the scheduled system frequency and power interchange with other areas in a prescribed limit [1][2]. In this paper, the study of LFC system for two areas consisting of Hydropower Plant and Wind Power Plant are carried out. The fuzzy gain scheduled proportional-integral (FGSPI) and fuzzy gain scheduled proportional integral derivative (FGSPID) controllers are designed for load frequency control (LFC) of a two-area interconnected power system. The proposed FGSPI and FGSPID controllers are compared against conventional proportional-integral (PI) controllers and Proportional integral derivation (PID) controllers concerning settling times and peak overshoots of the tie-line power and frequency deviations as performance indices. Comparative analysis indicates that the proposed intelligent controller gives better performance than conventional controllers. Simulations have been performed using Simulink toolbox in MATLAB.

Resilient Adaptive Event-Triggered Load Frequency Control of Network-Based Power Systems against Deception Attacks.

This paper investigates the problem of networked load frequency control (LFC) of power systems (PSs) against deception attacks. To lighten the load of the communication network, a new adaptive event-triggered scheme (ETS) is developed on the premise of maintaining a certain control performance of LFC systems. Compared with the existing ETSs, the proposed adaptive ETS can adjust the number of triggering packets, along with the state changes in the presence of deception attacks, which can reduce the average data-releasing rate. In addition, sufficient conditions can be derived, providing a trade-off between the limited network communication resources and the desired control performance of PSs. Finally, an application case is presented for the PSs to demonstrate the advantages of the proposed approach.

Time delay margins computation for stability of load frequency control in hybrid renewable energy power generation/storage system

In load frequency control (LFC), it is important to transmit control signals from remote terminal units (RTU) to the control center and from the control center to the plant side. Therefore, time delays in signal transmission become unavoidable. These delays reduce the dynamic performance of the LFC system. This paper is dedicated to the delay-dependent stability analysis of the LFC scheme for renewable energy power generation subsystem. The delay margin of the system is analyzed theoretically for different values of inertia, damping factor as well as controller gains. Theoretically obtained results are compared with simulation studies. The relation between the controller gain and the delay margin is investigated. The system studied includes photovoltaic system (PV), ultra-capacitor (UC) bank for energy storage, wind turbine generator (WTG), diesel generator (DG) and fuel cell (FC) system. The upper bound of the delay time, while LFC system is in stable condition, is known as delay margin. Delay margin computations are realized by using an analytical method approach. Proportional-integral (PI) controller is used for controlling proposed power generation storage system. PI Controller parameters are chosen in a wide range to observe the effect of the parameter space on delay margin variation. Simulation studies verify the effectiveness of the proposed method.

Coordinated Frequency Regulation of Smart Grid by Demand Side Response and Variable Speed Wind Turbines

Frequency stability of the power system is impacted by the increasing penetration of wind power because the wind power is intermittent. Meanwhile, sometimes the demand side loads increase quickly to require more power than total power produced. So balancing the active power in the power system to maintain the frequency is the main challenge of the high penetration of wind power to the smart grid. This paper proposes coordination rotor speed control (RSC), pitch angle control (PAC) and inertial control (IC) to control wind turbines, together with demand side response (DSR) participating in frequency regulation to balance active power in the power system. Firstly, the model of a single area load frequency control (LFC) system is obtained, which includes variable-speed wind turbines (VSWT) and DSR containing aggregated air conditioners and plug-in electric vehicles (PEVs). Then the RSC, PAC and IC, which controls wind turbines participating in frequency regulation in the power system, are introduced, respectively. Finally, the coordination of these three methods for wind turbines in different wind speeds is proposed. Case studies are carried out for the single area LFC system with a wind farm and DSR supported grid frequency. Coordination RSC and PAC combined IC are used to control wind turbines with DSR to balance active power in the power system. The proposed method used in the power system with high penetration of wind power and fluctuation of demand load is tested, respectively. Coordinated RSC or PAC with DSR can increase penetration of wind power and reduce peak load.

Induction Motor Modelling for Load-Frequency Control System

The accuracy of the load-frequency control (LFC) system depends on the accuracy of models used for the components that affect the frequency response. In the conventional LFC system, the frequency-sensitive loads, including induction motors, are simply modeled by the load-damping coefficient. The purpose of this paper is to obtain the fifth-, third- and first-order induction motors models for applying in the LFC system. Also, in this paper, the performance and accuracy of these models on the frequency response in a small-scale stand-alone microgrid are compared. In addition, the effect of system and motor parameters on the frequency response characteristics are investigated. The simulation results point out that the commonly used constant load-damping coefficient model cannot always appropriately reflect the impact of the induction motors on the frequency response. In addition, it is shown that a constant load-damping coefficient cannot present an accurate model for all induction motors when a significant disturbance has occurred in the low-inertia microgrids.

Enhanced Stability Criteria of Network-Based Load Frequency Control of Power Systems with Time-Varying Delays

The stability problem for load frequency control (LFC) of power systems with two time-varying communication delays is studied in this paper. The one-area and two-area LFC systems are considered, respectively, which are modeled as corresponding linear systems with additive time-varying delays. An improved stability criterion is proposed via a modified Lyapunov-Krasovskii functional (LKF) approach. Firstly, an augmented LKF consisting of delay-dependent matrices and some single-integral items containing time-varying delay information in two different delay subintervals is constructed, which makes full use of the coupling information between the system states and time-varying delays. Secondly, the novel negative definite inequality equivalent transformation lemma is used to transform the nonlinear inequality to the linear matrix inequality (LMI) equivalently, which can be easily solved by the MATLAB LMI-Toolbox. Finally, some numerical examples are presented to show the improvement of the proposed approach.

The Bees Algorithm Tuned Sliding Mode Control for Load Frequency Control in Two-Area Power System

This paper proposes a design of Sliding Mode Control (SMC) for Load Frequency Control (LFC) in a two-area electrical power system. The mathematical model design of the SMC is derived based on the parameters of the investigated system. In order to achieve the optimal use of the proposed controller, an optimisation tool called the Bees Algorithm (BA) is suggested in this work to tune the parameters of the SMC. The dynamic performance of the power system with SMC employed for LFC is studied by applying a load disturbance of 0.2 pu in area one. To validate the supremacy of the proposed controller, the results are compared with those of recently published works based on Fuzzy Logic Control (FLC) tuned by Teaching–Learning-Based Optimisation (TLBO) algorithm and the traditional PID optimised by Lozi map-based Chaotic Optimisation Algorithm (LCOA). Furthermore, the robustness of SMC-based BA is examined against parametric uncertainties of the electrical power system by simultaneous changes in certain parameters of the testbed system with 40% of their nominal values. Simulation results prove the superiority and the robustness of the proposed SMC as an LFC system for the investigated power system.

Coordinated intelligent frequency control incorporating battery energy storage system, minimum variable contribution of demand response, and variable load damping coefficient in isolated power systems

Maintaining a generation-demand balance becomes more challenging nowadays due to the limited availability of traditional automatic generation control (AGC) and spinning reserves. In response to this concern, the purpose of the proposed paper is to bridge the gap by introducing battery energy storage system (BESS) control loop in the load frequency control (LFC) system. Furthermore, a minimum variable share of demand response (DR) is utilized as an additional mean to regulate the system frequency. The growing intermittency of controllable loads calls the awareness to incorporate frequency-sensitive loads by considering a variable load-damping coefficient in LFC problem. The presented control scheme demonstrates a stable power operation with the optimal sharing of BESS, dynamic DR, and the supplementary control loop. Moreover, because of the continuous and sudden variations in the demand, adaptive LFC controller is designed using fuzzy logic based on particle swarm optimization (PSO) tuning method. The proposed controller ensures a stable and robust frequency regulation of the system under load fluctuations. In this paper it is revealed that adding the BESS control loop is very effective in enhancing the performance of LFC as it can deliver fast power compensation. The obtained results prove the capability and effectiveness of the proposed method in an isolated power system.

Maiden Application of Fuzzy-2DOFTID Controller in Unified Voltage-Frequency Control of Power System

This article presents an amalgamated pattern of automatic load frequency control (ALFC) and automatic voltage regulator (AVR) system in a three-area interconnected power system using the Fuzzy two-degree-of-freedom tilt-integral-derivative controller (F2DOFTID). The multi-area system includes single-stage reheat thermal plants and Solar Thermal Power Plant (STPP) in Area-1 and Heavy-Duty Gas Turbines (HDGT) in Area-2 and Area-3. An incipient attempt is made to incorporate the HDGT plant in amalgamated control of the power system. Relevant generation rate constraints (GRC) and Governor Dead Band (GDB) are rendered for thermal plants. In both ALFC and AVR systems of all areas, a first attempt is made to implement an F2DOFTID controller to alleviate the frequency and voltage deviations. In this investigation, an algorithm named Harris Hawks Optimization (HHO) is efficaciously used to accomplish optimal controller parameters. Concerning all time-domain behaviors, F2DOFTID controller performance is superior relative to the TID and 2DOFTID controller. The AVR effect proclaims a substantial improvement in system dynamics. In this amalgamated scenario, the aftermath of the high voltage direct current (HVDC) tie-line and the usage of energy storage devices such as ultra-capacitors (UC) are found superlative in the amelioration of system performance. Similarly, by modifying the generator parameters and synchronizing coefficients, the robustness of the proposed controller is measured, which signifies that obtained controller parameters during nominal conditions are resilient enough and not to be altered. Eventually, the system is also studied in OPAL-RT OP 4510 RT Lab hardware set-up for real-time analysis.

Evaluation of Delays-based Stability of LFC Systems in the Presence of Electric Vehicles Aggregator

In the integrated electrical systems, frequency control service considering the electric vehicle (EV) aggregators could lead to time-varying delay in load frequency control (LFC) schemes. These delays influence the LFC system efficiency, and in some situations, the lack of a clear choice of a control strategy considering the time-varying delays causes power system instability. Thus, this paper illustrates different time-varying delays based on the stability of an LFC system in the EV aggregators presence. The LFC's delay-dependent stability study is executed for finding the stability region and, stability criteria is suggested using the linear matrix inequality (LMI) method and Lyapunov-Krasovskii theory. Also, Wirtinger-based improved inequality and bounding lemma are applied to compute the greatest allowable delay in the LFC system, including the EV aggregators.

Distributed frequency emergency control with coordinated edge intelligence

Developing effective strategies to arrest grid frequency drop in case of severe contingencies is an important requirement. While distributed responsive loads for primary frequency control have been studied in the literature, the coordination of the distributed loads relies on high-speed communication or centralized frequency threshold setting. They might be cost-prohibitive or not sufficiently fast in severe contingencies, like the fault of ultrahigh voltage direct current (UHVDC) lines in China. In this paper, a local power loss ∆P estimation approach for frequency emergency control is proposed, and the coordination of the distributed loads is achieved by the edge intelligence and Internet-of-Things (IoT) technologies. The proposed approach can enable the distributed loads to provide fast and accurate frequency support to power grids. The parameter-setting in the control center and decision-making at the edge level for the proposed approach are described in detail. Based on a typical IEEE test system and a real bulk power system in China, numerical simulations and hardware experiments are conducted to verify the frequency support performance of the proposed approach. Further, a direct load frequency control system named Grid Sense implemented in China is explicitly described, and the real-world issues for implementing the proposed approach are analyzed.

The effect of demand response control on stability delay margins of load frequency control systems with communication time-delays

This paper studies the effect of dynamic demand response (DR) control on stability delay margins of load frequency control (LFC) systems including communication time-delays. A DR control loop is included in each control area, called as LFC-DR system and Rekasius substitution is utilized to identify stability margins for various proportionalintegral (PI) gains and participation ratios of the secondary and DR control loops. The purpose of Rekasius substitution technique is to obtain purely complex roots on the imaginary axis of the time-delayed LFC-DR system. This substitution first converts the characteristic equation of the LFC-DR system including delay-dependent exponential terms into an ordinary polynomial. Then the well-known Routh-Hurwitz stability method is applied to find those imaginary roots and the corresponding stability delay margin known as maximal time-delay. Delay margin results indicate that the inclusion of DR control loop significantly increases stability delay margin and improves the frequency dynamic behavior of the LFC system including time-delays. Theoretical stability margins are confirmed by a proven algorithm, quasi-polynomial mapping-based root finder (QPmR) algorithm and time-domain simulations

Fast valving automation setting using HRTSim

Abstract At present, due to the increase and significant complication of the electric power system (EPS), the task of maintaining the stability of the EPS is becoming increasingly important. Due to the fact that, in case of significant disturbances in the EPS, the processes occurring can lead to large synchronous swings of the generating equipment or loss of stability. When disconnecting the intersystem communication or a powerful load in the excess part of the EPS, an emergency excess of generated active power occurs, as a result, the frequency begins to increase, and the load-frequency control system is not able to cope with such an accident, due to its slowness. In this case, it is necessary to use the means of emergency automation to eliminate the surplus of active power. One of the most effective methods is fast valving automation. However, its effectiveness directly depends on the quality of its setting - which is a rather difficult task, since for its implementation, a complete mathematical model of the turbo-generator is required, taking into account its control systems and boiler unit.

Impact of electric vehicles aggregators with communication delays on stability delay margins of two-area load frequency control system

This paper investigates the impact of electric vehicles (EVs) aggregator with communication time delay on stability delay margin of a two-area load frequency control (LFC) system. A frequency-domain exact method is used to calculate stability delay margins for various values of proportional-integral (PI) controller gains. The proposed method first eliminates the transcendental terms in the characteristic equation without using any approximation and then transforms the transcendental characteristic equation into a regular polynomial using a recursive approach. The key result of the elimination process is that real roots of the new polynomial correspond to imaginary roots of the transcendental characteristic equation. With the help of new polynomial, delay-dependent system stability and root tendency with respect to the time delay is determined. An analytical formula is then developed to compute delay margins in terms of system parameters. The qualitative impact of EVs aggregator on stability delay margins is thoroughly analysed and the results are verified by time domain simulations and quasi-polynomial mapping-based root finder (QPmR) algorithm.

Delay-dependent Stability Analysis Considering Dynamic Demand Response and Electric Vehicle Aggregator Integration in Two-Area Load Frequency Control Systems

Delay-dependent Stability Analysis Considering Dynamic Demand Response and Electric Vehicle Aggregator Integration in Two-Area Load Frequency Control Systems

A Novel Rekasius Substitution Based Exact Method for Delay Margin Analysis of Multi-Area Load Frequency Control Systems

Time delays are inevitable in load frequency control (LFC) of the power system, especially in a deregulated system where open communication networks are more favorable than the dedicated ones. However, extensive delays may affect the stability of a system. In this paper, an exact frequency-domain method for calculating the delay margin of LFC systems is presented, which is likely to be used to assess a system's stability caused by time-delays and guide the controller design. Firstly, a dynamic model of load frequency control systems is established, described by delay differential and algebraic equations (DDAEs). The Rekasius substitution is then employed to eliminate the transcendental terms in the characteristic equation without making any approximation. Afterward, an eigenvalue perturbation theory is introduced to transform the problem of calculating the delay margin into solving a series of one-dimensional nonlinear equations. Since only equivalent transforms are involved in the whole process, the delay margins obtained by the proposed method are exact. Finally, a two-area and a three-area deregulated LFC systems are applied to verify the correctness and efficiency of the proposed method.

A deep asynchronous actor‐critic learning‐based event‐triggered decentralized load frequency control of power systems with communication delays

AbstractThis article proposes a novel asynchronous advantage actor‐critic (A3C) learning‐based dynamic event‐triggered mechanism for the decentralized load frequency regulation to alleviate the local‐area communication burden and influence of the load fluctuations. The proposed dynamic event‐triggered mechanism applies the A3C algorithm to optimally adjust the threshold of the event‐triggered function in real time. In the A3C algorithm framework, the long short‐term memory (LSTM) network is used to estimate the policy function and value function. First, for each control area, a novel model of the decentralized load frequency control (LFC) system is established to design the event‐triggered communication mechanism and deal with the communication delay simultaneously. Then, based on the Lyapunov stability theory, the controller gain parameters of the decentralized LFC system and the margins of the even‐triggering thresholds are derived by solving a series of linear matrix inequalities (LMIs). Finally, a three‐area and four‐area power systems are used to evaluate the proposed decentralized LFC method. Simulation results show that the proposed method can greatly reduce the data transmission times and preserve a satisfactory system performance.

Hierarchical-Attention-Based Defense Method for Load Frequency Control System Against DoS Attack

The deployment and operation of load frequency control (LFC) systems rely on the latest network and communication technologies. This exposes it to network attacks, such as DoS attacks, which affect the running of the system. In order to offset the impact of DoS attacks, this article proposes a data prediction-based defense method. First, the cyber–physical model of LFC is constructed to derive the frequency. Based on the model, a prediction model organically combined with the hierarchical attention network is applied to restore missing measurements. Then the proposed method can detect and eliminate the impact of DoS attacks by comparing and replacing the measurements, rather than adopting flexible LFC strategies. Finally, simulation experiments are carried out on three different power generation systems. The results prove that the suggested method can effectively resist DoS attacks.

Robust Load Frequency Control Using Fractional-order TID-PD Approach Via Salp Swarm Algorithm

To preserve frequency and tie-line power flow within a tolerable range in modern intricate and renewable energy sources (RES) integrated power system, an intelligent, expert, and robust load frequency control (LFC) scheme is requisite. This paper proposes a new load frequency control (LFC) approach using a dual-stage controller composed of fractional-order tilted-integral-derivative (TID) and integer-order proportional-derivative (PD) controllers. The recently developed salp swarm algorithm has tuned the parameters of the controller. The proposed scheme exhibits robustness and fast disturbance rejection performance because the tilted-integral-derivative controller is structured in a fractional-order framework, and transient response is improved due to the proportional-derivative controller. The overall activity of the LFC has been further upgraded by incorporating the flexible AC transmission system (FACTS) device namely thyristor-controlled phase shifter (TCPS) unit and energy storage system called redox flow battery (RFB) units. The proposed control approach is applied to diverse types of multi-area multi-source power systems with thermal, hydro, and wind turbine units along with nonlinear functions namely generation rate constraint (GRC), governor dead band (GDB), and communication delay (CD). The simulation results yield improved frequency regulation activity with and without TCPS and RFB using the proposed control approach when compared with the recently developed LFC approaches. Sensitivity analysis also established the robustness of the proposed control approach.

HHO-based Model Predictive Controller for Combined Voltage and Frequency Control Problem Including SMES

This paper discusses the modelling and control of a combined load frequency control (LFC) and automatic voltage regulator (AVR) system for a multi-area power system network with each generating area includes thermal, diesel, and solar thermal power plant. Superconducting magnetic energy storage is incorporated with the LFC loop to provide auxiliary control against instantaneous changes in active power demand. Model Predictive Controller (MPC) has been employed in this study to improve the performance of AVR and LFC loops, and controller weights are fine-tuned with the help of Harris Hawks Optimization (HHO) approach. The effectiveness of the proposed MPC-HHO algorithm has been examined by comparing its transient performance indices with that of conventional MPC, PID, FOPID, fuzzy PID, integral double derivative with derivative filter controller as well as Particle Swarm Optimization and Sine Cosine Algorithm based Model Predictive Controllers. The proposed MPC-HHO controller gives superior results than the above-mentioned controllers.