Frequency Control Performance Research Articles

On Virtual inertia Application in Power Grid Frequency Control

To achieve a more sustainable supply of electricity, using distributed generators (DGs) utilizing renewable energy sources (RESs) is a promising solution. However, emerging renewable energy based DGs into power grids reduces the total inertia of the system, and hence, the power grid dynamics and performance can be negatively affected. To address these issues, several inverter control methodologies have been recently proposed for the DGs, and some efforts have been done for introducing the concept of virtual inertia and better understanding of dynamic characteristics of power networks in the presence of high penetration of DGs and RESs. The present paper emphasizes some significant points on the importance of inverter-based virtual inertia on the grid frequency regulation, dynamic impacts, and new relevant ideas to improve power grids frequency stability and control performance.

Performance-based maintenance of gas turbines for reliable control of degraded power systems

Abstract Maintenance actions are necessary for ensuring proper operations of control systems under component degradation. However, current condition-based maintenance (CBM) models based on component health indices are not suitable for degraded control systems. Indeed, failures of control systems are only determined by the controller outputs, and the feedback mechanism compensates the control performance loss caused by the component deterioration. Thus, control systems may still operate normally even if the component health indices exceed failure thresholds. This work investigates the CBM model of control systems and employs the reduced control performance as a direct degradation measure for deciding maintenance activities. The reduced control performance depends on the underlying component degradation modelled as a Wiener process and the feedback mechanism. To this aim, the controller features are quantified by developing a dynamic and stochastic control block diagram-based simulation model, consisting of the degraded components and the control mechanism. At each inspection, the system receives a maintenance action if the control performance deterioration exceeds its preventive-maintenance or failure thresholds. Inspired by realistic cases, the component degradation model considers random start time and unit-to-unit variability. The cost analysis of maintenance model is conducted via Monte Carlo simulation. Optimal maintenance strategies are investigated to minimize the expected maintenance costs, which is a direct consequence of the control performance. The proposed framework is able to design preventive maintenance actions on a gas power plant, to ensuring required load frequency control performance against a sudden load increase. The optimization results identify the trade-off between system downtime and maintenance costs as a function of preventive maintenance thresholds and inspection frequency. Finally, the control performance-based maintenance model can reduce maintenance costs as compared to CBM and pre-scheduled maintenance.

Modified group search optimisation‐based comparative performance evaluation of thyristor controlled series capacitor‐based fractional order damping controllers to improve load frequency control performance in restructured environment

This study compares fractional order phase lead-lag controller, fractional order proportional-integral-derivative (FOPID), and tilt-integral-derivative controllers as thyristor controlled series capacitor (TCSC)-based damping controller to improve load frequency control (LFC) performance in a restructured power system. To prepare an efficient ancillary service, a precise formulation for participation of TCSC in tie-line power flow exchange is presented which is compared with the earlier Taylor-based approximated model. The controller parameters are adjusted by employing different evolutionary algorithms. To obtain realistic results under a competitive environment, a diverse-GENCOs multi-DISCOs power system with the generation rate constraint and governor dead-band effects, communication time delay, bilateral contracts, and pool-co transactions is taken into account. Non-linear time-domain simulations demonstrate that the FOPID-based TCSC damping controller in coordination with an integral-type simple LFC can most effectively suppress the area frequency and tie-line power oscillations. Further investigations are performed for uncontracted higher order step and random load demands treated as contract violation scenarios to confirm the superiority of the proposed fractional order controllers-based TCSC–LFC over the Taylor-based TCSC–LFC. The sensitivity analysis is done for a wide range of loading condition and system parameters to compare the robustness of the considered controllers.

Real-time coordination of distributed energy resources for frequency control in microgrids with unreliable communication

The management of distributed energy resources (DER) via control strategies mitigates frequency fluctuations stemming from the volatility of renewable resources and fluctuating power demand. Recently, open communication networks are integrated with the traditional control strategies to overcome the ubiquity of DER system and the lack of dedicated communication infrastructures. However, open networks are exposed to communication degradation and can reduce the control performance. This work investigates the reliability of the integrated DER system and open communication networks, i.e. the cyber-physical microgrid system, with reference to the frequency control in the face of communication degradation. Adequate control strategy is provided by a discrete PID controller tuned via multi-objective particle swarm optimization. The integrated system is tested on a real-time platform with different MAC protocols and open-communication-network architectures to investigate how the communication degradation reduces the frequency control performance. Simulation results demonstrate that transmission delays and packet dropouts jeopardize the ability of the integrated system to maintain the system frequency deviation within bounds. In particular, the use of Ethernet ensures higher reliability as compared to 802.11b/g. Moreover, the impact of interfering traffic and of the percentage of used bandwidth on the PID controller performance reduction is assessed. The optimized PID controller can compensate for communication degradation and uncertainty conditions of the microgrid, and ensures robustness against unknown network configurations.

Multi-Frequency Control in a Stand-Alone Multi-Microgrid System Using a Back-To-Back Converter

A stand-alone multi-microgrid (MMG) system can be formed by connecting multiple stand-alone microgrids (MGs). In the stand-alone MMG system where the frequencies of each MG system are different, a back-to-back (BTB) converter can be used for interconnecting the adjacent MG system. The frequency control performance of the MMG system can be improved by designing the suitable controller of the BTB converter. This study proposes a multi-frequency control in the BTB converter to improve the performance of frequency regulation in the MMG system. Autonomous power sharing between each MG system is achieved by using the proposed multi-frequency control. The stand-alone MMG system where two stand-alone MG systems with different nominal frequencies are interconnected using the BTB converter is simulated in this study to show the feasibility of the proposed multi-frequency controller. Each stand-alone MG system consists of an inverter-based distributed generator (DG) that uses a grid-forming converter with a conventional frequency droop controller. The inverter-based DG is responsible for the primary frequency control in each MG system. To show the effectiveness of the proposed multi-frequency control, a comparison study of the multi-frequency control and the single frequency control is presented in this study. Simulation results show that the system stability can be improved by using the proposed multi-frequency controller.

Load Frequency Control of Interconnected Power System via Multi-Agent System Method

For the load frequency control (LFC) of the interconnected power system, a two-level coordinated control frame based on multi-agent system is proposed to improve the frequency control performance of the power system. In the control frame, the upper-level agent, in a centralized manner, coordinates the lower-level LFC agents to deal with the conflict between narrowing the area control error and stabilizing the system frequency. The lower-level LFC agents, in the distributed cooperative manner, realize the mutual power support among the neighboring areas to guarantee the frequency stability in an emergency. To verify the validity of the proposed method, the numerical simulations are performed on the three-area interconnected power systems.

Evaluation of Load Frequency Control Performance Based on Standard Deviational Ellipses

This paper discusses new criterion for the evaluation of load frequency control (LFC) performance. The proposed LFC performance evaluation is based on a standard deviational ellipse that characterizes a bivariate relationship between the frequency deviation and the area's interchange power variation. The standard deviational ellipse is evaluated using Tyler's maximum-likelihood estimator, which is distribution-free within the family of elliptical distributions. In addition, a target standard deviational ellipse is proposed, using predefined values for a target frequency bound and the area's frequency bias. The presented approach is based on the accordance of the estimated ellipse with the target ellipse, resulting in several grades for the LFC performance. A comparison of the proposed criterion is made with other LFC performance criteria known from the literature. Extensive measurements were applied, and the obtained results show the correctness of the proposed approach.

Distributed coordination regulation marginal cost control strategy for automatic generation control of interconnected power system

The area-level coordination of regulation capacity by automatic generation control (AGC) is an effective approach to mitigate wind power fluctuations in interconnected power system with high wind penetration. However, the applicability of this method is restricted by the existing AGC strategy. For this reason, power systems in China are experiencing serious wind curtailments to meet the power balance. In this study, a distributed coordination AGC strategy based on regulation marginal cost (RMC) is proposed for coordinating regulation capacity in different areas to remove frequency deviations. Detailed regulating characteristics of the AGC strategy in the existing power systems are discussed. Based on the above analysis, a distributed coordination RMC controller is designed to meet the proposed multi-area coordination rule using a partial primal-dual sub-gradient algorithm. In this proposed controller, the coordination signal containing RMC is exchanged with adjacent controllers through communication networks. The simulation results prove that the distributed coordination RMC strategy can economically coordinate the regulation capacity of an interconnected power system and satisfy the frequency control performance standard.

Perfomance Standard-Compliant Secondary Control: The Case of Chile

The two largest interconections in Chile (SIC and SING) are about to become interconnected. As power balance is a concern in the operation of a power system, it is important to understand the operation of AGC while systems become interconected. In this sense, the performance of the AGC systems after the interconection may change, and the new operating condition may require a change in the parameters of the AGC controllers to comply with performance standards. This work presents an analisis to determine the parameters of the AGC systems in the two interconection to comply with frequency control perfromance standards and minimize the required reserves. In the absence of a Chilean secondary frequency control performance standard, the North American standards are considered. To validate the results, empirically-validated frequency response models of SING and SIC are considered to obtain numerical results.

Load Frequency Control of Multi - area Hybrid Power System by Artificial Intelligence Techniques

paper presents the application of different Artificial intelligence techniques on the tuning of PID controller in a load frequency control system. The algorithms of PSO technique, Genetic algorithm technique, and Artificial Bee Colony technique has been applied on four area power system with six tie lines. The system dynamic model is formulated in state variables form. A comparison between these techniques with different performance indices is presented. The effect of including different types of generating units (i.e. a hybrid power system) on the dynamical performance of a load frequency control is also presented. Three types of control criterion are adopted. Simulation of the applied artificial techniques on a typical hybrid power system has been carried out. It is observed that a hybrid power system can track the load fluctuation quickly.

A Wind Power and Load Prediction Based Frequency Control Approach for Wind-Diesel-Battery Hybrid Power System

A frequency control approach based on wind power and load power prediction information is proposed for wind-diesel-battery hybrid power system (WDBHPS). To maintain the frequency stability by wind power and diesel generation as much as possible, a fuzzy control theory based wind and diesel power control module is designed according to wind power and load prediction information. To compensate frequency fluctuation in real time and enhance system disturbance rejection ability, a battery energy storage system real-time control module is designed based on ADRC (active disturbance rejection control). The simulation experiment results demonstrate that the proposed approach has a better disturbance rejection ability and frequency control performance compared with the traditional droop control approach.

CPS1 Compliance-Constrained AGC Gain Determination for a Single-Balancing Authority

The integration of non-dispatchable generation has increased the need for ancillary services to maintain frequency control performance, and the determination of adequacy to ensure reliability has become an important operating concern. This work determines the AGC gain of a single balancing authority interconnection in order for system frequency to comply with NERC control performance standards, ensuring secondary control adequacy. The particular case of wind expansion is considered, and a simulation of ERCOT is presented to evaluate the performance of the formulation.

Optimal sizing of battery energy storage system in microgrid system considering load shedding scheme

In the past, Battery Energy Storage System (BESS) is used for primary frequency regulation. As developments in batteries progress, advancement in applications of BESS including the implementation in high power penetration is expected. Load shedding is one of frequency control methods during stand-alone operation, and the performance of frequency control improves in combination with BESS. However, without optimal size of BESS, it can cause the oscillations to the system. Thus, this article proposes the feasibility of using optimal BESS with load shedding scheme when the microgrid is disconnected from a main source. In this paper, the analytic algorithm-based DPL (DIgSILENT Programming Language) script is developed and presented to determine the optimal size of BESS with load shedding scheme. Results show that the optimal size of BESS-based analytic algorithm with load shedding scheme can achieve higher performance of frequency control compared to the BESS without optimal size. The optimal sizing method of BESS with load shedding scheme is achieved by using a tool for analysis of industrial, utility and commercial electrical power system called DPL script.

Impact of wind power on control performance standards

As the penetration of wind power continuously increases, the impacts of wind power on frequency control have become of great concern. Frequency control requires real time balance between system generation and load, with system frequency deviation maintained within a certain range. Control Performance Standards (CPS) are indices for evaluating a balancing area’s frequency control performance in an interconnected system. They are important for quantifying the frequency control performance of the interconnected system and the relative distribution of frequency control responsibility among areas. Without mitigating action, the increasing wind power may inhibit a balancing area’s ability to comply with CPS due to variability in power output from wind plants and reduced system frequency response. This paper assesses the impacts of wind power on a balancing area’s frequency control characteristics and studies the wind power impacts on CPS. A two area Automatic Generation Control (AGC) model is used to verify these impacts. AGC changes the valve reference positions of units and restores system frequency to nominal values. Both theoretical study and simulation results show that CPS indices deteriorate as wind power penetration increases. Measures to improve CPS are provided.

Regulation Adequacy Analysis Under High Wind Penetration Scenarios in ERCOT Nodal

The significant expansion of wind power capacity in the Electric Reliability Council of Texas (ERCOT) will increase the amount of ancillary services (AS) necessary to maintain ERCOT system frequency targets. This paper analyzes ERCOT regulation adequacy from a simplified dynamical model of ERCOT validated by empirical data. The model includes a representation of system frequency response characteristics; a stochastic, empirical-based model of wind power expansion; and a model of net load forecast error based on current performances. The simulation uses current ERCOT methodology for determining regulation, and NERC Balancing Authority Standards to examine frequency control performance.

Active fault tolerant control for a class of linear time-delay systems in finite frequency domain

This article deals with the problem of active fault tolerant control (AFTC) for a class of linear time-delay systems in a finite frequency domain. A new ℋ∞ controller in generalised internal model control architecture with an observer-based fault estimator is proposed for the AFTC system. Based on online fault estimation and accommodation, the closed-loop system stability and ℋ∞ performance for both fault free and faulty cases are guaranteed. With the aid of the generalised Kalman–Yakubovich–Popov lemma for time-delay systems, sufficient conditions on the existence of such an AFTC system ensuring simultaneous finite frequency estimation and control performance are derived. The calculation procedure of the parameter matrices of the fault estimator and ℋ∞ controller is also proposed. Finally, a numerical example is given to illustrate the effectiveness of the proposed method.

On the Performance of an Automatic Frequency Control Loop in Dissimilar Fading Channels in the Presence of Interference

Two effects of a single interference on the performance of an automatic frequency control (AFC) loop are explained, and two measures, average switching rate and mean time to loss of lock, are presented to capture the impact of each effect. These measures are derived in closed-form expressions and single integral formulas in dissimilar fading channels with Rayleigh, Rician, and Nakagami-m distributions. The general case of modulated carriers as well as different special cases are considered. Numerical examples are provided to illustrate the effects of different fading scenarios on the performance of an AFC. The effect of maximum Doppler frequency on the performance of the AFC is also investigated.

Designing an Energy Storage System Fuzzy PID Controller for Microgrid Islanded Operation

Recently, interest in microgrids, which are composed of distributed generation (DG), distributed storage (DS), and loads, has been growing as a potentially effective clean energy system to mitigate against climate change. The microgrid is operated in the grid-connected mode and the islanded mode according to the conditions of the upstream power grid. The role of the energy storage system (ESS) is especially important to maintain constant the frequency and voltage of an islanded microgrid. For this reason, various approaches for ESS control have been put forth. In this paper, a fuzzy PID controller is proposed to improve the frequency control performance of the ESS. This fuzzy PID controller consists of a fuzzy logic controller and a conventional PI controller, connected in series. The fuzzy logic controller has two input signals, and then the output signal of the fuzzy logic controller is the input signal of the conventional PI controller. For comparison of control performance, gains of each PI controller and fuzzy PID controller are tuned by the particle swam optimization (PSO) algorithm. In the simulation study, the control performance of the fuzzy PID was also tested under various operating conditions using the PSCAD/EMTDC simulation platform.

Demand as Frequency Controlled Reserve

Relying on generation side alone is deemed insufficient to fulfill the system balancing needs for future Danish power system, where a 50% wind penetration is outlined by the government for year 2025. This paper investigates use of the electricity demand as frequency controlled reserve (DFR), which has a high potential and can provide many advantages. Firstly, the background of the research is reviewed, including conventional power system reserves and the demand side potentials. Subsequently, the control logics and corresponding design considerations for the DFR technology have been developed and analyzed, based on which simulation models have been built using the DIgSILENT Power Factory. The simulation studies of different scenarios confirm that the DFR can provide reliable performance of frequency control. Furthermore, relevant issues regarding implementing DFR in reality have been discussed.

Introduction of Generator Unit Controller and Its Tuning for Automatic Generation Control in Korean Energy Management System (K-EMS)

Automatic generation control (AGC) is an important function for load frequency control, which is being implemented in Energy Management System (EMS). A key feature of AGC is to back up governors to enhance the performance of frequency control. The governor regulates system frequency in several to ten seconds, while the droop control concept results in steady-state control error. AGC is a supplementary tool for compensation of the steady-state error caused by the droop setting of the governors. As the AGC target is delivered to each generator as an open loop control target, the generator output is not guaranteed to follow the AGC target. In this paper, we introduce generating unit controller (GUC) control block, which has the purpose of enabling the generator output to track the AGC target while maintaining the governor performance. We also address the tuning methods of GUC for better performance of AGC in the Korea Energy Management System (K-EMS).