Load Frequency Control Design Research Articles

Design of observer-based non-fragile load frequency control for power systems with electric vehicles

This paper establishes an observer-based finite-time non-fragile load frequency control design using electric vehicles for power systems with modeling uncertainties and external disturbances. A state space representation of the addressed power systems together with dynamic interactions of electric vehicles is formulated. A full-order observer-based non-fragile controller is designed to ensure finite-time boundedness and satisfactory finite-time H∞ performance of the considered system. By constructing an augmented Lyapunov–Krasovskii functional and employing Wirtinger-based integral inequality, the required conditions are obtained in terms of linear matrix inequalities. The desired non-fragile load frequency control law is presented via the observer-based feedback approach. Simulations are given to show the effectiveness of the proposed control scheme.

A New Robust Fuzzy-PID Controller Design Using Gravitational Search Algorithm

This paper proposes the design of a novel robust load frequency control (LFC) strategy-based optimised fuzzy-PID controller employing gravitational search algorithm (GSA). The suggested GSA algorithm was applied to optimise the input scaling factors of the fuzzy logic and the PID controller gains. To show the potential of the proposed control methodology, a multi-sources two-area interconnected power system was investigated for the simulation. The considered test system comprises various power generating units from hydro, thermal and nuclear sources in area-1, and power generation from hydro, nuclear and diesel sources in area-2. Initially, the simulation was carried considering a centralised controller for both areas to cope with load changes, and then was extended with decentralised controller. Further, sensitivity analysis was performed to demonstrate the ability of the proposed approach in face of wide changes in system parameters and position of load changes. The frequency deviations and the tie-line power flow change were presented, and the superiority of the proposed control strategy was demonstrated by comparing the results with individual gravitational search algorithm (GSA), fuzzy logic controller (FLC) and with some reported techniques in the literature such as Ziegler-Nichols, genetics algorithm (GA), bacterial foraging optimisation algorithm (BFOA) and particle swarm optimisation (PSO).

Resilient Event-Triggered Output Feedback Control for Load Frequency Control Systems Subject to Cyber Attacks

This paper considers the problem of load frequency control (LFC) design for multi-area power systems. Owing to the multi-area power system with a feature of spatial distribution, it becomes necessary to use the network as a signal transmission medium. The following two problems need to be addressed: 1) the transmission signals transmitted over the communication network are vulnerable to be attacked by adversaries. How to ensure the security of the control system and 2) multi-area power systems have a large amount of data need to be exchanged via the network, how to guarantee the network quality of service and the control performance under the limited network bandwidth. To address these problems, in this paper, a resilient output feedback control strategy in secure means is proposed for LFC systems based on the security criteria. Moreover, a new event triggered mechanism (ETM) is developed, under which the average data releasing rate is much lower than the one using the conventional data transmission mechanism, while it becomes high when the system encounters some external disturbances. To validate the effectiveness of the proposed approach, simulations are performed on a 3-area power system. The results show that the proposed control strategy can maintain the LFC system with a satisfactory control performance in the presence of stochastic cyber-attacks, and the average data releasing rate is of a lower level to save communication and computation resources.

Performance enhancement of a hydro-hydro power system using RFB and TCPS

ABSTRACTThe design of load frequency control (LFC) for the hydro-hydro power system suffers from poor dynamic performance owing to large time constants associated with hydro power generations. The dynamic performance of the hydro-hydro power system can be improved using a thyristor control phase shifter (TCPS) and energy storage battery system. This paper presents a comprehensive study on LFC of an interconnected hydro-hydro power system having TCPS in series with the tie-line and redox flow battery (RBF) at the terminal of one area through few and available state technique, i.e. the output feedback technique. The LFC are designed with the help of few and available states and the performance is judged for typical demand change in the power system area and the results are matched with the LFC obtained via a technique that require all system states, i.e. full state feedback in order to justify the effectiveness of the designed LFC in terms of achieved feedback gains, eigenvalues and the dynamic system responses.Abbreviations: AC: Alternating Current; BESS: Battery Energy Storage System; FACTS: Flexible Alternating Current Transmission System; LFC: Load Frequency Control; RFB: Redox Flow Battery; SSSC: Static Synchronous Series Compensator; SMES: Superconducting Magnetic Energy Storage; TCPS: Thyristor Control Phase Shifter; UPFC: Unified Power Flow Control

Extended dissipativity-based non-fragile control for multi-area power systems with actuator fault

ABSTRACTThis paper addresses the issue of reliable load frequency control design of an uncertain multi-area power system with constant time delays and disturbances via non-fragile sampled-data control approach. In particular, the parameter uncertainties are assumed to be randomly occurring which are described by the Bernoulli distributed sequences. By constructing a suitable Lyapunov–Krasovskii functional together with Wirtinger-based inequality, a new set of sufficient conditions in terms of linear matrix inequalities is obtained to ensure the asymptotic stability and extended dissipativity of the multi-area power system not only when all actuators are operational, but also in case of some actuator failures. Finally, simulation results are conducted to validate the effectiveness of the proposed control design technique.

MVO Algorithm Based LFC Design of a Six-Area Hybrid Diverse Power System Integrating IPFC and RFB

Flexible alternating current transmission system devices and energy storage devices have great potential to support frequency regulation in power system. Hence, the impact of interline power flow controller unit and redox flow battery unit in the load frequency control (LFC) of six-area power system having different power plant units has been investigated in this paper. The multi-verse optimizer (MVO) is proposed to tune the parameters of the proportional–integral and derivative (PID) controller. Further, the efficacy of the multi-verse optimizer tuned proportional–integral (PI) controller is also equated with the recently developed sine-cosine algorithm tuned PI controller in the investigated power system. The encouraging role of interline power flow controller (IPFC) unit and redox flow battery (RFB) unit has been confirmed for system frequency and tie-line power regulation. The investigation validated that multi-verse optimizer based proportional–integral–derivative controller with an interline power flow controller unit and redox flow battery unit give better dynamic response during sudden load disturbances.

Equivalent input disturbance‐based robust LFC strategy for power system with wind farms

Due to the intermittent power generation, wind farms integrated into the grid may cause a problem of large frequency fluctuation, when the capacity of load frequency control (LFC) is not enough to compensate the unbalance between the generation and the load demand. In this study, a new robust LFC strategy against load disturbance and wind power fluctuation is proposed to improve the disturbance-resistant performance of the power system with wind farms. First, a simplified model of the power system with wind farms is established without considering the accurate model information. Then, a control scheme based on the compensation of equivalent input disturbance (EID) is introduced, and a method of EID estimation is presented. The robust LFC design addresses various disturbances and internal/external uncertainties of power systems. Finally, to evaluate the effectiveness of the proposed method, two case studies are carried out and the performance comparisons with the classical proportional–integral–derivative control scheme are used to confirm the proposed method.

Auxiliary‐function‐based double integral inequality approach to stability analysis of load frequency control systems with interval time‐varying delay

A new approach is presented for the stability problem of one-area and multi-area load frequency control (LFC) scheme with time delays in this study. Novel stability criteria with delay dependency in terms of linear matrix inequalities for LFC systems are derived by an augmented Lyapunov–Krasovski functional with triple integral terms. The LFC design takes the interval time-varying communication delays into account and the load disturbance is mathematically modelled as a norm-bounded non-linear function. This study suggests a new class of inequality for double integral of quadratic functions via intermediate auxiliary functions, which produce more tighter bounds than what Wirtinger's double integral inequality produces. Case studies are carried out to illustrate the validity of the proposed delay-dependent proportional–integral-based output feedback design method.

PI Controller Based Load Frequency Control Approach for Single-Area Power System Having Communication Delay

The modern power systems are becoming complicated day by day because of the delays introduced by the communication networks. Due to this reason, the traditional load frequency control (LFC) design scheme depicts a destabilizing impact and an unacceptable performance. Therefore, this paper proposes an analytico-graphical approach for designing PI controller for a single-area LFC system having communication delay. The concept is based on extracting stability region in parameter space (kp,ki) with predefined gain and phase margins. Further, the values of optimal kp and ki are selected using integral error criterion. The proposed scheme gives faster disturbance rejection response as compared to the recently developed LFC scheme. The controller also works well when the system parameters are perturbed from their nominal values.

Robust PID Load Frequency Controller Design with Specific Gain and Phase Margin for Multi-area Power Systems

In interconnected power systems, the load frequency control (LFC) is considered a hugely beneficial ancillary service. The goal of the LFC in an interconnected power system is to limit the frequency of each area within certain bounds and to maintain the tie-line power flows within some pre-specified latitudes by balancing the power outputs of the generators so as to satisfy ever changing load demands. In the classical control theory, PID controller is said to be robust if it provides some specific gain and phase margin. In this paper, a novel methodology is proposed for the robust PID controller design having specific gain and phase margins for LFC in a multi-area power system. The proposed technique is based on stability boundary locus and PID controllers are designed for four-area power system having different types of turbines. The simulations are carried out using MATLAB and effectiveness of the proposed methodology is verified by the comparison with a recently published approach.

New Stability Criteria of Delayed Load Frequency Control Systems via Infinite-Series-Based Inequality

A new approach is proposed for the stability problem of delayed load frequency control (LFC) scheme with fixed and time-varying delay cases included in the current paper. New stability criteria with delay dependence in terms of linear matrix inequalities for LFC systems are derived by a novel augmented Lyapunov–Krasovski (L–K) functional. Our proof deployment for system stability of power grids employs the further improved integral inequality in the form of infinite series, which turns out to be less conservative than Wirtinger's inequality that encompasses Jensen inequality. Simulation case studies are carried out to show the effectiveness and superiority of the presented delay-dependent PI-type LFC design scheme.

Resilient Event-Triggering $H_{\infty }$ Load Frequency Control for Multi-Area Power Systems With Energy-Limited DoS Attacks

This paper investigates a resilient event-triggering H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> load frequency control (LFC) for multi-area power systems with energy-limited Denial-of-Service (DoS) attacks. The LFC design specifically takes the presence of DoS attacks into account. First, an area control error dependent time delay model is delicately constructed for multi-area closed-loop power systems. Second, a resilient event-triggering communication (RETC) scheme is well designed, which allows a degree of packet losses induced by DoS attacks and has the advantage of improving the transaction efficiency. Then, by using the Lyapunov theory, two stability and stabilization criteria for the multi-area power systems are derived under consideration of the energy-limited DoS attacks. In these criteria, the relationship between the allowable DoS attack duration and the resilient event-triggering communication parameters are clearly revealed. Moreover, an algorithm is also provided to obtain the RETC parameters and the LFC gains simultaneously. Finally, a case study shows the effectiveness of the proposed method.

Non‐linear recurrent ANN‐based LFC design considering the new structures of Q matrix

This paper presents the design of a non-linear recurrent artificial neural network (ANN) based load frequency control (LFC) of a two-area power system interconnected via HVDC tie-line in parallel with EHVAC line. The control design is based on the combination of robust LFC and optimisation of recurrent ANN so that designed LFC scheme is suitable to handle the diverse operating conditions of power system. The various structures of the state cost weighting matrix ( Q ), i.e. controllability and observability aspects which affect the dynamics of the power system are used for the LFC design. The feedback gains achieved by the implementation of robust LFC using the different structures of Q are used to effectively train the recurrent ANN-based LFC design and its performance is analysed with and without system non-linearity's for 1% step load disturbance in one of the control areas to show the superiority of one design over the others. The closed-loop system eigenvalues obtained for the system ensure the system stability. Furthermore, the recurrent ANN-based LFC performance is evaluated for the diverse system operating conditions and compared with multi-layer perceptron (MLP) ANN-based and conventional PI control schemes to demonstrate the effectiveness of proposed LFC design scheme.

QFT based Robust Load Frequency Controller Design for Multi-Area Power System

QFT based Robust Load Frequency Controller Design for Multi-Area Power System

Firefly algorithm-based load frequency controller design of a two area system composing of PV grid and thermal generator

In this paper, firefly algorithm (FA) for optimal tuning of PI controllers for load frequency control of hybrid system composing of photovoltaic (PV) system and thermal generator is introduced. Also, maximum power point tracking of PV is considered in the design process. The block diagram of the hybrid system is performed. To robustly tune the parameters of controllers, a time domain-based objective function is established which is solved by the FA. Simulation results are presented to show the improved performance of the suggested FA-based controllers compared with genetic algorithm (GA). These results show that the proposed controllers present better performance over GA in terms of settling times and different indices.

Comparative performance evaluation of fractional order controllers in LFC of two-area diverse-unit power system with considering GDB and GRC effects

In this paper, fractional order proportional-integral-derivative (FOPID) and tilted-integral-derivative (TID) controllers are applied in the design of load frequency controller (LFC). Tuneable parameters are adjusted via an improved particle swarm optimization algorithm which is powered by chaotic parameter and crossover operator to find a globally optimal solution. The FOMCON toolbox is employed within MATLAB/Simulink for implementing fractional order modeling and control. A two-area diverse-unit power system is examined considering the physical constraints of generation rate constraint and governor dead band. Comparative evaluations demonstrate that the FOPID-based LFC achieves the greatest dynamic performance under different load disturbance patterns. Sensitivity analysis is carried out to demonstrate the robustness of the proposed LFCs under wide variations in the system loading condition and parameter.

Internal Model Based Load Frequency Controller Design for Hybrid Microgrid System

The increase of power demand exponentially over the past decade in developing countries has necessitated the integration of different types of renewable energy sources into the utiligy grids which were earlier running with fossil fuel fired units. Renewable energy sources are integrated with these generating plants since it is economical and pollution free. Power generation through these types of generating plants comprise of a combination of intermittent renewable sources like wind, solar and other generating sources like diesel generators, fuel cells. Also, because of the weak inertial nature of the renewable sources used in microgrid, it is much more important to regulate the system frequency closer to the nominal values. This paper explores the development of an Internal Model based controller approach for better frequency regulation in a hybrid microgrid. Two different cases are examined to validate the robustness of IMC based controller design.

Design of Robust Load Frequency Controller for Multi-Area Interconnected Power System Using SDO Software

The response of the load frequency control problem in multi-area interconnected electrical power system is much more complex with increasing size, changing structure and increasing load. This paper deals with Load Frequency Control of three area interconnected Power system incorporating Reheat, Non-reheat and Reheat turbines in all areas respectively. The response of the load frequency control problem in a multi-area interconnected power system is improved by designing PID controller using different tuning techniques and proved that the PID controller which was designed by Simulink Design Optimization (SDO) Software gives the superior performance than other controllers for step perturbations. Finally the robustness of controller was checked against system parameter variations..

Robust overlapping load frequency output feedback control of multi-area interconnected power systems

This paper presents a new approach to the design of robust proportional-integral (PI) load frequency controller (LFC) with overlapping structure in the presence of generation rate constraint (GRC) and time-varying communication delays. The power system is decomposed into overlapping areas with tie-lines being the overlapping (shared) parts between the areas. The overlapping LFC design is based on the expansion-contraction principles, where the power system is first expanded in such a way as to decouple the areas from each other. Then, for obtaining an appropriate level of performance, robust local stabilising PI controllers are designed for each of the decoupled areas using an iterative linear matrix inequality (ILMI) algorithm such that asymptotic stability with a minimal H∞ performance level is achieved. Finally, the designed robust local H∞ controllers are contracted (transformed) to a robust overlapping LFC for implementation on the multi-area power system. Although the approach is applicable to multi-area power systems, a time-delay three-area interconnected power system experiencing communication delays is considered in this paper. Simulation results under different scenarios clearly illustrate an improved performance obtained with the overlapping structured LFC of this paper compared with existing decentralized LFCs.

Tie-Line Bias Control Applicability to Load Frequency Control for Multi-Area Interconnected Power Systems of Complex Topology

The tie-line bias control (TBC) method has been widely used in the load frequency control (LFC) of multi-area interconnected systems. However, it should be questioned whether the conventional TBC can still apply to LFC when considering the complication of structures of power systems. LFC, in essence, is to stabilize system frequency/tie-line power by controlling controlled outputs’ area control error (ACE). In this paper, relations between LFC control variables and controlled outputs are expressed as a system of equations, based on which an exemplary ring network is studied. Sufficient and necessary conditions for TBC applicability is presented, and a novel LFC mode is proposed for a general ring network where TBC cannot work. Finally, TBC applicability to multi-area systems with general topology is studied, and a general LFC mode is proposed for systems where TBC is not definitely applicable, thus rendering routines that may guide LFC design of future power systems with more complex topologies.