Fast Frequency Regulation Research Articles

Optimal capacity configuration and operation strategy of typical industry load with energy storage in fast frequency regulation

As the potential and competent load-side resources for frequency response and control in modern power grids, typical industrial load can compensate for the deficiency of frequency response capability for new-type power systems. However, the operational flexibility is seriously enforced by the operation conditions uncertainties of industrial load. With “Online Calculation, and Real-time Matching” as the core, based on fuzzy mathematical theory, the coordinated operation strategy of typical industrial loads and energy storage systems (ESS) is proposed to finish fast frequency regulation (FFR) tasks. And an optimal capacity configuration model of industrial loads with ESSs is established to evaluate the whole economic profitability in FFR. Specially, in terms of algorithms, a novel Two-layer Parallel Particle Swarm Optimization and Genetic Algorithm (TPPSGA) is innovatively designed in this manuscript. Comparing with traditional heuristic algorithms, TPPSOGA improves computation speed by 6.84 times. Simulation results show that our proposed strategy can reasonably estimate the frequency capability of industrial load by membership degree function, and prove that the industrial load participating in FFR with the support of ESSs is able to get more revenue and stability than industrial load or ESSs separately is in regulation of FFR. The economic analyze in market price and ESS parameters can help the load agent to screen the suitable-type ESS and its capacity to serve for FFR and enhance the flexibility in load-side frequency regulation.

Fast Frequency Regulation Utilizing Non-Aggregate Thermostatically Controlled Loads Based on Edge Intelligent Terminals

Fast Frequency Regulation Utilizing Non-Aggregate Thermostatically Controlled Loads Based on Edge Intelligent Terminals

Dynamic ancillary services: From grid codes to transfer function-based converter control

Conventional grid-code specifications for dynamic ancillary services provision such as fast frequency and voltage regulation are typically defined by means of piece-wise linear step-response capability curves in the time domain. However, although the specification of such time-domain curves is straightforward, their practical implementation in a converter-based generation system is not immediate, and no customary methods have been developed yet. In this paper, we thus propose a systematic approach for the practical implementation of piece-wise linear time-domain curves to provide dynamic ancillary services by converter-based generation systems, while ensuring grid-code and device-level requirements to be reliably satisfied. Namely, we translate the piece-wise linear time-domain curves for active and reactive power provision in response to a frequency and voltage step change into a desired rational parametric transfer function in the frequency domain, which defines a dynamic response behavior to be realized by the converter. The obtained transfer function can be easily implemented e.g. via a proportional-integral (PI)-based matching control in the power loop of standard converter control architectures. We demonstrate the performance of our method in numerical grid-code compliance tests, and reveal its superiority over classical droop and virtual inertia schemes which may not satisfy the grid codes due to their structural limitations.

Integrated control strategy for 5G base station frequency regulation considering spatio-temporal variations in communication load

The decreasing system inertia and active power reserves caused by the penetration of renewable energy sources and the displacement of conventional generating units present new challenges to the frequency stability of modern power systems. Vast quantities of 5G base stations, featuring largely dormant battery storage systems and advanced communication technology, represent a high-quality fast frequency regulation resource for the power system. This paper proposes a double-layer clustering method for 5G base stations and an integrated centralized-decentralized control strategy for their participation in frequency regulation, considering the variability of available frequency regulation capacity due to spatial and temporal variations in base station communication loads. The proposed capacity model and control methods are evaluated using a case study of a two-machine test system with 10,000 real 5G base stations, demonstrating the effectiveness of the clustering method and the integrated control strategy in improving frequency stability.

Engineering Fastest Control: A New Process Control Method for Thermal Power Units

The intermittent and volatile nature of wind power generation necessitates thermal power units to provide deep-peak shaving and fast frequency regulation services within the same grid. However, the current proportional integral differential (PID) control performance in the process control foundation of thermal power units falls short of meeting these requirements. Despite the lack of comprehensive research on engineering fastest control (EFC), this article aims to address this gap by studying and analyzing the mechanism and physical defects of the fast tracking filter (FTF), the output tracking input characteristics of EFTF reconstructed by FTF engineering, and the control performance of the constructed EFC. Through mathematical calculation analysis, simulation experiments, and real-world engineering practice, it is concluded that EFC surpasses the limitations of PID control performance and effectively enhances feedback control performance. As a result, it is deemed suitable for process control in thermal power units.

Optimization of the Fast Frequency Regulation Strategy for Energy Storage-Assisted Photovoltaic Power Stations

Photovoltaic (PV) power generation is characterized by randomness and intermittency, resulting in unpredictable fluctuations in output power. This presents a significant challenge to the stable operation of the grid. To address this issue, the integration of energy storage systems provides a solution to mitigate the volatility of PV output, ensuring stability and precise control. In this study, we propose an ASS-Elman-based equivalent droop control strategy for PV power stations participating in grid frequency regulation. Furthermore, a joint PV-energy storage frequency regulation system is developed. For energy storage power stations actively engaged in grid frequency regulation, we employ an adaptive droop control strategy to enhance the traditional droop control method by incorporating additional frequency control strategies. We validate the effectiveness of the proposed strategies through simulation using MATLAB/SIMULINK. The results demonstrate that these strategies maximize the potential of energy storage and PV systems to comprehensively regulate frequency and significantly improve primary frequency regulation performance.

Koopman model predictive control based load modulation for primary frequency regulation

AbstractConventional power systems function under the assumption that loads are uncontrollable, and that the generation control is the primary means of preserving system voltage, frequency, and stability. Thanks to recent advancements of power electronics technology and communication schemes, demand‐side resources are now capable of providing fast frequency regulation. Controllable loads can provide upward/downward reserve during frequency excursions. In this paper, the authors consider collective contribution of large clusters of controllable loads which modulate their aggregate demand power to regulate the primary frequency. Koopman model predictive control is designed to handle local frequency variations caused by various disturbances at each load bus, considering uncertain load models. The efficacy of the proposed method has been validated using the New‐England power system considering two scenarios, namely, load variation, and generation outage.

Manage Real-Time Power Imbalance With Renewable Energy: Fast Generation Dispatch or Adaptive Frequency Regulation?

Manage Real-Time Power Imbalance With Renewable Energy: Fast Generation Dispatch or Adaptive Frequency Regulation?

Fast Frequency Regulation From a Wind Farm-BESS Unit by Model Predictive Control: Method and Hardware-in-the-Loop Validation

The integration of Renewable Energy Sources (RES) into the power system requires an upgrade of the adopted management and control solutions. Focusing on frequency regulation, the same RES, as well as loads, both possibly coupled with energy storage systems, are called to provide a contribution through suitable regulation services. In this context, this paper proposes a control strategy for enabling a unit composed by a Wind Farm and Battery Energy Storage Systems (BESSs) to provide a fast frequency regulation service. The control is based on Model Predictive Control technique, whereas the regulation service is defined according to the technical requirements of the Italian Transmission System Operator (TSO). The approach is also tested via Hardware-In-the-Loop simulations. More specifically, tests are carried out by implementing the control algorithm on a Raspberry Pi board that communicates with a real BESS and with a real-time simulator implementing a benchmark power system. The validation results prove the practical effectiveness of the proposed control method since they demonstrate that the designed algorithms can be implemented on a low-cost hardware and applied, without computational and communication issues, in a real-field framework.

Impact of electric vehicles fast frequency regulation and charging strategies on grid frequency stability

With the gradual reduction of grid inertia, system sensitivity to load unbalances is increasing, compromising frequency stability. To face this problem, faster frequency regulation resources are required. In this context, vehicle-to-grid (V2G) is one of the concepts that is suggested for this purpose. When electric vehicles (EVs) are parked, their batteries can be used as distributed energy storage systems (EESs), injecting and absorbing power faster than conventional generation units (CGUs). The goal of this paper is to analyse the impact of fast frequency regulation of EVs in a small-scale grid, under sudden load variations. In this paper, the effect of charging strategies (CSs) is addressed, as they have a direct impact on the magnitude of the EV fleet regulation. In this way, different CSs can be used to achieve symmetrical up and down regulation, or to maximize one of them. The effect of the EV fleet dynamics in the frequency transient is also studied. The speed of response, and hence, the frequency transient, are influenced by these dynamics. The focus of the analysis will be the communication delay between the EV fleet and the central controller.

Distributed optimal power sharing strategy for wind farm fast frequency regulation based on EBCC

The wind farm (WF) provides fast frequency regulation (FFR) has become a consensus in low-inertia power systems. However, the optimal power sharing within the large-scale WF during the FFR process is intractable. Inspired by the intrinsic similarity between the information flow and the power flow, this paper proposes a distributed power sharing control for the FFR of the large-scale WF based on the idea of equation-based congestion control (EBCC). Concretely, a global congestion index, reflecting the deviation between the output power and the FFR order of the WF, is introduced for power tracking at the WF level. Besides, a local congestion index, which implies the operating cost of each WT, is constructed to reduce the operating cost of the WF. Then, the power sharing of each WT is determined locally. The distributed control significantly reduces the computational and communication burden, which makes the proposed method suitable for the large-scale WF, as well as meeting the demand of FFR. Moreover, the robustness to varying operating conditions makes the method practical and attractive. Finally, the effectiveness of the proposed method is verified under various scenarios by simulations.

Twin Delayed Deep Deterministic Policy Gradient (TD3) Based Virtual Inertia Control for Inverter-Interfacing DGs in Microgrids

Environmental and energy security concerns lead to the continuous displacement of traditional fossil fuel-based power generation to power electronics interfaced distributed generations (DGs). Increasing penetration of renewable energy sources and the substitution of synchronous generators with power electronic converters have resulted in reduced power system inertia and damping. This causes large frequency deviations and a higher rate of change of frequency. The fast and flexible nature of the energy storage system with a designed controller can achieve frequency stability in low inertia microgrids (MGs). The conventional proportional-integral-based virtual inertia controller is unable to eliminate frequency instability in low inertia MG. To enhance frequency stability, this article proposes a virtual inertia emulation strategy using a twin delayed deep deterministic policy gradient (TD3) algorithm for fast frequency regulation of MGs with inverter-based DGs. A comparative analysis of the TD3 scheme and the conventional method is made. The results show that the TD3-based virtual inertia control provides better tracking with a 56.6% reduction in frequency deviation and faster transient recovery than the conventional virtual inertia control against a broad range of operational scenarios. Performance metrics and simulation results are shown to demonstrate the feasibility of the proposed control scheme.

Participation of DERs to the Bottom-Up Power System Frequency Restoration Processes

This paper studies the transient behavior and frequency stability of a grid with a large share of distributed energy resources (DERs) during a bottom-up restoration process. This work is motivated by a real-world restoration process, during which the tripping of the DER frequency protections led to the frequency instability and finally to the collapse of the system. The main contribution of the paper is the proposal of a DER control strategy based on the estimation of the rate of change of frequency and fast frequency regulation. A comprehensive stochastic analysis in time domain shows that the proposed control effectively prevents the occurrence of the instability during the restoration process.

A simulation study for assessing the impact of energy storage systems for Fast Reserve with additional synthetic inertia control on the Continental Europe synchronous area

This article shows the results of a simulation study on the application of battery storage systems for providing fast frequency regulation (the so-named Fast Reserve) with additional synthetic inertia control. The aim of the study is to assess the impact of the extension of the regulation provided by the FRUs to all the Continental Europe synchronous grid, with the same power proportions of the first Italian FRU auction. The simulations are conducted in two different scenarios: a base one related to 2020 and a future one related to 2040 and based on ENTSO-E projections for load and generation. The results show that, for the reference incident of 3000 MW, the frequency quality parameters in 2040 are significantly worse than those in 2020 but, with the injection of the FRUs with additional synthetic inertia control, there is an improvement both in dynamic and steady-state conditions. The study shows how 2040 frequency parameters can become comparable with the current ones if minimum shares of fast reserve and synthetic inertia are provided to improve the stability of the grid. Finally, starting from the incident that occurred on the 8th of January 2021, it is shown by simulations how FRUs can support the grid also during a system split.

Coordinated Control of a Wind Turbine and Battery Storage System in Providing Fast-Frequency Regulation and Extending the Cycle Life of Battery

Fast-frequency regulation (FFR) is becoming a key measure to enhance the frequency stability of power systems as the penetration of renewables and power electronics continues to grow and the system inertia declines. Although different control methods have been proposed to provide a wind turbine generator (WTG) with a limited capability of virtual inertia and frequency support, the coordination between the WTG and a battery energy storage system (BESS), as well as the potential optimization benefits, have not been fully studied. This study proposes a coordinated control of WTG and BESS that provides FFR to the AC system and at the same time extends the cycle life of the battery. First, a cost effective and SOC-based FFR strategy of BESS alone was proposed. Then, a coordinated FFR method for the WTG–BESS hybrid system under all wind speeds was proposed by analyzing the operational characteristics of WTG. The proposed coordinated strategy improves the FFR performance with a longer cycle life and lower cost of battery under different operating conditions. Simulation results based on varying wind speeds indicate that the proposed FFR strategy raises the frequency nadir and avoids the frequency secondary dip.

Multi-objective control of isolated power systems under different uncertainty approaches

This paper proposes and compares a set of multi-objective supervisory controllers for an isolated power system including a gas turbine operating in load following mode as a dominant source of generation, a battery energy storage system, and stochastic renewable generation. It analyzes their capability to coordinate the gas turbine and energy storage to provide isochronous speed control, achieving fast frequency regulation for the local grid, while the gas turbine can still operate with minimum deviation from its optimal loading and the storage system can follow a pre-scheduled reference state of charge trajectory. In more detail, we consider and compare different control strategies to handle model and disturbance uncertainties, including stochastic model predictive control under various parametrizations of the scenario approach, and robust control under the H∞ paradigm. The various controllers are compared against a benchmark, i.e., a deterministic predictive control strategy. Instead of point-to-point comparisons for some arbitrary cases (i.e., worst-case or expected), empirical distributions of the controller’s performance for the whole probability spectrum are derived, leading to more accurate and representative comparisons. The analyzed performance indicators are nominal dynamic performance, constraint violation probabilities, and expected system operation performance. The results indicate the clear superiority of stochastic control over both robust and deterministic control in dealing with both parametric and disturbance uncertainty. Moreover, choosing an appropriate parametrization is shown to be essential to achieve both good nominal performance and lower violations probability, indicating that the superiority of stochastic control comes with the drawback of needing user-defined tuning from the designer.

Fast Frequency Regulation Method for Power System With Two-Stage Photovoltaic Plants

The full utilization of solar energy is of great significance in reducing carbon emissions and alleviating environmental problems. Fast frequency regulation plays an important role in the power system with grid-connected two-stage photovoltaic (PV) plants. The presented fast frequency regulation method is composed of droop control, virtual inertia control and de-loading control. This work focuses on improving droop control and virtual inertia control for PV plants connected to grid. Due to non-Gaussian disturbance induced by solar irradiance, an adaptive control strategy is proposed by minimizing an improved performance index which combines the mean square error (MSE) and the minimum error entropy (MEE) criteria. Based on the collected frequency deviation series data, the entropy of the frequency deviation is estimated with the aid of a quantizer. The droop control coefficient and inertia gain are then solved by an improved gravitational search algorithm (IGSA). Finally, the effectiveness of the proposed strategy is testified by an illustrative power system with a two-stage grid-connected PV plant.

Revenue Stacking for BESS: Fast Frequency Regulation and Balancing Market Participation in Italy

Battery energy storage systems (BESS) are considered a relevant flexible resource for supporting the balancing of a RES-penetrated power grid. Since their cost structure is characterized by very high capital costs, it is of utmost importance to ensure efficient and effective operations from a techno-economic perspective. The possibility of services (and revenues) stacking is one of the most discussed optimization solutions. The present work provides a novel approach for BESS modeling, including the stacking of two diverse ancillary services, a dedicated balancing market bidding model, and a state-of-charge management strategy. Fast frequency regulation is proposed as a power-based service, requiring large ramping capability, but asking BESS activation just for a limited amount of time. For the remainder, BESS power can be traded on balancing market (BM): energy-based services, such as tertiary regulation, could be effectively coupled with power-based, fast regulations, increasing the economic attractiveness of investments in BESS. The case of fast reserve (FR), a new high-speed frequency response service proposed by the Italian TSO in Italy, is assessed in this study. FR provision foresees a capacity-based remuneration (k€/MW/year) and requires to ensure 1000 hours per year of availability. After assessing its cost-effectiveness as a stand-alone service, a sequential multiservice strategy is proposed, where BESS provides FR for 1000 hours, while for the rest of the time it is dedicated to the provision of replacement reserve (RR). Performances of BESS are evaluated considering the reliability of the provision, its operational efficiency, and investment’s economics. Performed tests demonstrate how, within the current Italian regulatory framework, the investment’s rate of return improves thanks to the multiservice approach. In particular, while maintaining a proper reliability, the minimum acceptable remuneration from FR yearly auctions decreases by 13%; at the same time, self-dispatching of energy through BM calls reduces the need to purchase energy on day-ahead market and keeps BESS state-of-charge far from saturation regions, thus also increasing its lifetime.

A variable parameter control method for charging pile load aggregator to participate in the fast frequency market

Abstract With the access of large-scale new energy sources, fast frequency regulation resources of the power system are scarce. A variable parameter control method for charging pile load aggregator to participate in the fast frequency market is proposed in this paper. It is that charging pile load aggregator actively adjusts the active power according to the frequency of the local power system, and the response speed is within 0-2 seconds. In addition, the variable parameter control method proposed in this paper specifically controls the power of charging pile according to the speed and amplitude of frequency drop, which has strong pertinence and simple control scheme, and further improves the frequency stability of the power grid.

Analysis and Design of Inertia for Grid-Tied Electric Vehicle Chargers Operating as Virtual Synchronous Machines

Renewable energy resources (RES), e.g., solar photovoltaic (PV), wind energy, and electric vehicles (EVs) are extensively integrated into modern power electronics-based power systems due to their sustainable and environmentally friendly features. This has gradually reshaped the frequency regulation structure of power systems. Specifically, the duty of frequency regulation, previously supported by synchronous generators, will be taken over by grid-tied power converters (such as EV chargers), which can be controlled as virtual synchronous machines (VSMs) to mimic the inertial response of synchronous generators. However, being different from synchronous generators, VSMs enable fast frequency regulation. As a consequence, it is identified in this paper that the elimination of frequency oscillations is possible. Therefore, instead of simply increasing inertia for oscillations suppression, the desirable inertia coefficient can be different for various cases. In order to illustrate this point, relationships between several important performance indices, such as the rate-of-change-of-frequency, frequency nadir, overshoot, settling time, and inertia coefficient, are analyzed in detail. Furthermore, a straightforward method for designing the optimal inertia coefficient for VSMs is put forward. Finally, experiment results obtained from a 1-kW three-phase VSM prototype are demonstrated to validate the effectiveness of the theoretical analysis and proposed design method.