Decentralized Load Frequency Control Research Articles

A Robust Controller Design based on Kharitonov’s Theorem for Frequency Control in an Interconnected Power System

The load frequency control of power systems is often carried out using methods that are dependent on the system load and parameters. Therefore, the controller design is not robust in unforeseen cases such an attack on the power system, variations in system parameters, or changes in load. In such methods, there is a need for an attack detection tool, and moreover, the controller parameters need to be adjusted as the load and power system parameters change. In this paper, Kharitonov's theorem was applied to design a robust decentralized load frequency control for a two-area power system in the presence of electric vehicle fleets as a power source that were targeted by a cyberattack. Furthermore, the robustness of the system against system nonlinearities was demonstrated by testing the efficacy of the controller on both linear and nonlinear systems. The controller design was robust such that there was no need to change the gains of the controller even during an attack. This was compared with the performance of controllers designed using GWO algorithm and fuzzy logic that needed retuning for different case studies with different variations in system parameters, load, or inclusion of a cyberattack to the electric vehicle fleets.

Decentralized Optimized Integral Sliding Mode-Based Load Frequency Control for Interconnected Multi-Area Power Systems

In this paper, a decentralized load frequency control (LFC) is proposed for the frequency regulation of multi-area power systems applying optimized integral sliding mode control (OISMC) scheme. A modified particle swarm optimization (MPSO) algorithm is utilised to optimize the control variables of the proposed controller for improving the performance of frequency response. A comprehensive model of a multi-area power system is developed where each area is considered to power from conventional sources, renewable energy resources (RERs), and electrical vehicle (EV) aggregators. Different types of interconnectors have been considered to tie different power regions. This system is subjected to random generation and loading conditions, as well as model uncertainties, which cause its frequency and area control error (ACE) to deviate from their nominal values. A decentralised OISMC is implemented for the proposed model to keep the frequency variation within the nominal range. Further, a validation study investigates the performance of the proposed control technique in MATLAB simulation environment to mimic the real power system operation. This study includes different test scenarios considering the dynamic events such as variations in load demand, amount of generated power, participation factor of EV reserve, system parameters, disturbances, and time delay. The simulated results support better frequency regulation with the suggested OISMC compared to other alternative control approaches.

LMI-based Decentralized Load Frequency Control of a Hybrid Power System with a Virtual Synchronous Generator and Battery Storage

This paper proposes the participation of wind generation in the decentralized control of load frequency of a hybrid power system consisting of, in addition to wind generation, conventional generation and battery storage. The wind generation is modelled as a ‘Virtual Synchronous Generator (VSG)’ in a separate control area with its own virtual frequency. It has also been proposed to operate the wind generation system in a ‘de-loaded’ mode, thereby allowing it to take part in frequency regulation services. For the purposes of a decentralized control design, the overall system model is decomposed into three subsystems. Static state-feedback control gains are computed by posing the decentralized control problem as a set of linear matrix inequalities (LMIs) subject to structural and stabilizing constraints.

Networked scheduling for decentralized load frequency control

This paper investigates the scheduling process for multi-area interconnected power systems under shared but band-limited networks and decentralized load frequency controllers. To cope with sub-area information and avoid node collision of large-scale power systems, round-robin and try-once-discard scheduling are used to schedule sampling data among different sub-grids. Different from existing decentralized load frequency control methods, this paper studies multi-packet transmission scheme and introduces scheduling protocols to deal with multi-node collision. Considering the scheduling process and decentralized load frequency controllers, an impulsive power system closed-loop model is well established. Furthermore, sufficient stabilization criteria are derived to obtain decentralized output feedback controller gains and scheduling protocol parameters. Under the designed decentralized output feedback controllers, the prescribed system performances have been achieved. Finally, a three-area power system example is used to verify the effectiveness of the proposed scheduling 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.

Nonlinear decentralized load frequency control of multi‐machine power systems with exponential stability and low L2 gain against load disturbance

AbstractThis paper proposes a novel nonlinear decentralized control method for a class of multi‐machine power systems. The aim is to construct a suitable decentralized feedback control law so as to guarantee that the large‐scale interconnected power system is exponentially stable and robust against load fluctuations. To this end, we propose a novel design algorithm based on the backstepping, which involves five steps and actively utilizes the locally measurable part of the tie‐line power to improve the performance. The effectiveness of the proposed control scheme is demonstrated through extensive simulation studies.

Deterministic Dynamic State Estimation-Based Optimal LFC for Interconnected Power Systems Using Unknown Input Observer

This paper proposes a novel, fully decentralized load frequency control (LFC) approach based on dynamic state estimation (DSE). The proposed approach employs an unknown input observer (UIO) for each power system area for tracking the dynamic states in real time operation. In order to achieve the fully decentralized control approach, the demand fluctuation and tie-line power deviations are modeled as unknown inputs to the UIO of each area. An optimal state feedback control method based on the observed states is used next to control each area separately. This approach reduces the complexity of the designed observer, achieves fully decentralized control, improves the robustness of the controllers, and makes the estimation process highly efficient, accurate, and easy to implement. The applicability of the proposed method is shown on a representative model of four areas interconnected via various transmission links. Simulation results demonstrate the efficiency and accuracy of the designed observer and verify the superiority and robustness of the proposed control approach compared to alternative approaches.

Decentralized Load–Frequency Controller Design for a Single as Well as Multi-area Power System

This paper addresses the application of the proportional–integral–derivative (PID) controller and the proportional–integral–derivative–acceleration (PIDA) controller for decentralized load–frequency control in single- and multi-area power system. In this study, both the controllers are designed via direct synthesis approach. The parameters of the PID controller from direct synthesis approach are obtained by desired pole placement for transient improvement and the frequency response matching near zero frequency for better steady-state behavior. To get the parameters of the PIDA controller, frequency domain approximation of the direct synthesis controller is used. The results obtained by the proposed controllers yield better performance for a single-area as well as the multi-area power system in comparison with the recently reported methods in the literature. It is also observed that the proposed PIDA controller outperforms with respect to the PID controllers. Properly tuned PID controllers provide faster response and further improvement may be obtained by the use of well-tuned PIDA controller in case of load–frequency control of multi-area power system. The proposed controller design method is a good tool in comparison with the prevalent design methods in the literature.

Tustin's technique based digital decentralized load frequency control in a realistic multi power system considering wind farms and communications delays

Abstract This paper presents a digital model of decentralized Load Frequency Control (LFC) using an optimal PID controller-based Particle Swarm Optimization (PSO) in Egyptian Power System (EPS) considering communication delays. The EPS includes both conventional generation units (i.e., non-reheat, reheat, and hydraulic power plants) with inherent non-linearities and wind power, which extracted from Zafarana wind farm, location in Egypt. Thus, the optimal digital controller-based Tustin’s technique is designed for every subsystem of the EPS separately to guarantee the stability of the overall closed-loop system. The performance of the proposed digital model is tested and compared with the analog model under variation in loading patterns, loading conditions, system parameters, wind farm penetration, and communication delays. Results approved that, the proposed digital model can effectively regulate the system frequency and guarantee robust performance under different conditions. Also, it gives a reliable performance at large sampling times, which means a reduction of implementation cost.

Designing Decentralized Load-Frequency Controllers: An Optimization Approach for Synchronous Generators in Islanded Grids

In this article, an optimal decentralized controller is designed for the load-frequency control (LFC) of a multiarea islanded grid with multiple synchronous generation systems. The decentralized controller includes various proportional-integral (PI) controllers that are simultaneously designed and optimized by using a classical descent-direction quasi-Newton (QN)-based technique. Optimal decentralized PI controllers account for the dynamic coupling amid the areas of the islanded grid with no communication links among them required and, hence, improve the frequency control performance. Simulation results confirm the effectiveness of the proposed decentralized PI control approach. The suggested PI controllers have a similar performance to decentralized eighth-order, linear-quadratic-Gaussian (LQG) integral controllers, which are designed in the decentralized servomechanism framework, whereas the proposed decentralized PI controllers have considerably lower-order structures.

Implementation and Assessment of a Decentralized Load Frequency Control: Application to Power Systems with High Wind Energy Penetration

This paper describes and assesses a decentralized solution based on a wireless sensor-actuator network to provide primary frequency control from demand response in power systems with high wind energy penetration and, subsequently, with relevant frequency excursions. The proposed system is able to modify the electrical power demand of a variety of thermostatically-controlled loads, maintaining minimum comfort levels and minimizing both infrastructure requirements and primary reserves from the supply side. This low-cost hardware solution avoids any additional wiring, extending the wireless sensor-actuator network technology towards small customers, which account for over a 30% share of the current power demand. Frequency excursions are collected by each individual load controller, considering not only the magnitude of the frequency deviation, but also their evolution over time. Based on these time-frequency excursion characteristics, controllers are capable of modifying the power consumption of thermostatically-controlled loads by switching them off and on, thus contributing to primary frequency control in power systems with higher generation unit oscillations as a consequence of relevant wind power integration. Field tests have been carried out in a laboratory environment to assess the load controller performance, as well as to evaluate the electrical and thermal response of individual loads under frequency deviations. These frequency deviations are estimated from power systems with a high penetration of wind energy, which are more sensitive to frequency oscillations and where demand response can significantly contribute to mitigate these frequency excursions. The results, also included in the paper, evaluate the suitability of the proposed load controllers and their suitability to decrease frequency excursions from the demand side in a decentralized manner.

H-Infinity Loop-Shaping Controller for Load Frequency Control of a Deregulated Power System

Load frequency control is an essential component of Automatic Generation Control of power systems. Deregulated power system isa highly complex and uncertain system because of multiple bilateral transactions taking place. This necessitates the use of advanced robust controllers for load frequency control. A decentralized load frequency controller using H-infinity based loop-shaping method is suggested for a two area deregulated non-reheat thermal power system in this paper. The connections between each control area with the rest of the system as well as the contracts existing in a deregulated system are treated as input disturbance signals to achieve decentralization. Dynamic responses for three contract cases of operation in a deregulated system using the H-infinity controller are obtained.

Decentralized load frequency control for two-area interconnected power system

This paper proposes a decentralized output feedback control scheme applied to two-area interconnected power system. Thecontroller synthesis problem is formulated as the scaled H∝ control problem and a new LMI-based algorithm is proposed tocompute the decentralized controller. The proposed controller provides robustness with regard to parametric uncertainties andalso attenuates bounded exogenous disturbances in the sense of L 2-gain. Simulation results clearly show the effectiveness ofdeveloped decentralized output feedback control scheme.

Decentralized ADRC for LFC in Deregulated Environments

Active disturbance rejection control (ADRC) method is investigated in this paper to design decentralized load frequency controllers (LFC) for deregulated multi‐area power systems. ADRC can treat the connections among control areas and the effects of possible contracts as new disturbance signals, and uses an extended state observer (ESO) to estimate and compensate them quickly. Thus, it can achieve good disturbance rejection performance and is a good candidate for LFC design. Simulation results for a three‐area power system show that the proposed method is simple to apply in practice and good performance can be achieved.

Decentralized load frequency control in an interconnected power system using Coefficient Diagram Method

This paper presents a new load frequency control (LFC) design, using the Coefficient Diagram Method (CDM) in a multi-area power system. The CDM controller has been designed to reduce the effect of uncertainties owing to variations in the parameters of governors and turbines as well as load disturbance. Each local area controller is designed independently, such that, stability of the overall closed-loop system is guaranteed. The CDM structure is built on the frequency response model of multi-area power system, and physical constraints of the governors and turbines are considered. Digital simulations for both two and three-area power systems are provided to validate the effectiveness of the proposed scheme. From the simulation results it is shown that, considering the overall closed-loop system performance with the proposed CDM technique, robustness is demonstrated in the face of uncertainties due to governors and turbines parameters variation and loads disturbances. A performance comparison between the proposed controller, model predictive controllers (MPC), and a classical integral control (I) scheme is carried out, confirming the superiority of the proposed CDM technique.

Genetic algorithm tuned IP controller for Load Frequency Control of interconnected power systems with HVDC links

Abstract A new design of decentralized Load Frequency Controller for interconnected thermal non-reheat power systems with AC-DC parallel tie-lines based on Genetic Algorithm (GA) tuned Integral and Proportional (IP) controller is proposed in this paper. A HVDC link is connected in parallel with an existing AC tie-line to stabilize the frequency oscillations of the AC tie-line system. Any optimum controller selected for load frequency control of interconnected power systems should not only stabilize the power system but also reduce the system frequency and tie line power oscillations and settling time of the output responses. In practice Load Frequency Control (LFC) systems use simple Proportional Integral (PI) or Integral (I) controller. The controller parameters are usually tuned based on classical or trial-and-error approaches. But they are incapable of obtaining good dynamic performance for various load change scenarios in multi-area power system. For this reason, in this paper GA tuned IP controller is used. A two area interconnected thermal non-reheat power system is considered to demonstrate the validity of the proposed controller. The simulation results show that the proposed controller provides better dynamic responses with minimal frequency and tie-line power deviations, quick settling time and guarantees closed-loop stability margin.

Dynamic Performance Evaluation of Decentralized Load Frequency Controllers for Interconnected Thermal Power System with Parallel AC-DC Tie-lines: A Comparative Study

Dynamic Performance Evaluation of Decentralized Load Frequency Controllers for Interconnected Thermal Power System with Parallel AC-DC Tie-lines: A Comparative Study

LOAD FREQUENCY CONTROL IN CO-ORDINATION WITH FREQUENCY CONTROLLABLE HVDC LINKS USING FUZZY LOGIC CONTROLLER

In this paper decentralized load frequency control (LFC) for suppression of oscillations in multi-area power systems using fuzzy logic controller was studied. A three area system is cons idered in which areas 1 and 2 and areas 1 and 3 are connected by HVDC transmission links and areas 2 and 3 are connected by normal AC tie-line. The performance of the fuzzy logic controller is compared with the conventional PI controller and the simulat ion results shows that fuzzy logic controller is ve ry effective enhancing better damping performance in non-linear conditions.

Robust analysis of decentralized load frequency control for multi-area power systems

Robust analysis for decentralized load frequency control (LFC) for multi-area power systems is studied in this paper. It is observed that such an analysis can be decomposed into two steps considering the inherent structure of a multi-area power system: robustness analysis against the parametric variations in local-area power systems and robustness analysis against the structure and/or magnitude variations in the tie-line power flow network. A detailed structured singular value method is proposed for local-area robustness analysis, and an eigenvalue method is derived for tie-line robustness analysis. The proposed method is then applied to a four-area power system and the results show that the method is convenient and useful for decentralized load frequency control of multi-area power systems.

Decentralized Load-Frequency Control of Large-Scale Nonlinear Power Systems: Fuzzy Overlapping Approach

This paper develops a design methodology of a decentralized fuzzy load-frequency controller for a large-scale nonlinear power system with valve position limits on governors. The concerned system is locally exactly modeled in Takagi-Sugeno's form. Sufficient design condition for uniform ultimate boundedness of the closed-loop system is derived based on the overlapping decomposition. Convergence of all incremental frequency deviations to zero is also investigated. A simulation result is provided to visualize the effectiveness of the proposed technique.