Frequency Regulation Of Power Grid Research Articles

A day‐ahead bidding strategy for battery swapping and charging system participating in the regulation market

AbstractThe battery swapping mode is a promising way for electric vehicles (EVs) to participate in power grid frequency regulation. However, the operation mechanism and the uncertainty management in the process still lack research. Aiming at this issue, this paper proposes a day‐ahead bidding strategy for the battery swapping and charging system (BSCS) providing regulation reserve capacity in the ancillary service market. Firstly, a new BSCS‐based regulation model is established. Then, an ambiguity set based on Kullback–Leibler (KL) divergence is used to manage the uncertainty of regulation signals and battery swapping demands. Furthermore, a boundary expectation approach is proposed to turn the problem into robust optimization. Finally, after using the extreme scenario method (ESM) to generate extreme scenarios, a duality‐free column‐and‐constraint generation (C&CG) algorithm is employed to solve the problem. The case studies demonstrate that BSCS can provide economical and robust reserve capacity bidding plans in the day‐ahead market with the proposed strategy. At the same time, the BSCS‐based regulation service is simulated with the battery development trend in the future, and suggestions are given.

A Review of the Application and Development of Flywheel Energy Storage

High power density, high efficiency and low loss are the characteristics of flywheel energy storage, which has broad application prospects in the field of rail transit. This paper introduces the basic structure and principle of flywheel energy storage, analyzes the energy storage density of the rotor in both metal and composite materials, and points out that composite materials such as T1000 fiber/resin have higher strength and lower density. The highest energy density. Finally, the development status of flywheel energy storage in rail transit, civil vehicles and other fields is summarized, and the future development prospects of power grid frequency regulation and uninterruptible power supply are prospected. This paper can provide a reference for in-depth research on flywheel energy storage materials.

Research on the Primary Frequency Regulation Control Strategy of a Wind Storage Hydrogen-Generating Power Station

Wind curtailment and weak inertia characteristics are two factors that shackle the permeability of wind power. An electric hydrogen production device consumes electricity to produce hydrogen under normal working conditions to solve the problem of abandoning wind. When participating in frequency regulation, it serves as a load reduction method to assist the system to rebuild a power balance and improve the wind power permeability. However, due to its own working characteristics, an electric hydrogen production device cannot undertake the high-frequency component of the frequency regulation power command; therefore, an energy storage device was selected to undertake a high-frequency power command to assist the electric hydrogen production device to complete the system frequency regulation. This paper first proposes and analyzes the architecture of a wind storage hydrogen-generating station for centralized hydrogen production with a distributed energy storage, and proposes the virtual inertia and droop characteristic mechanism of the wind storage hydrogen-generating station to simulate a synchronous unit. Secondly, an alkaline electrolysis cell suitable for large-scale engineering applications is selected as the research object and its mathematical model is established, the matching between different energy storage devices and their cooperation in power grid frequency regulation is analyzed, and a super capacitor is selected. A control strategy for the wind storage hydrogen-generating power station to participate in power grid frequency regulation with a wide time scale is then proposed. Using the first-order low-pass filter, the low-frequency component of the frequency regulation power command is realized by an electric hydrogen production device load reduction, and a high-frequency component is realized by the energy storage device. Finally, the effectiveness and rationality of the proposed control strategy are verified by establishing the simulation model of the wind storage hydrogen-generating power station with different initial wind speed states, comparing the system frequency dip values under the proposed multi-energy cooperative control strategy and a single energy device control strategy.

Double-layer AGC frequency regulation control method considering operating economic cost and energy storage SOC consistency

Aiming at the problem of power grid frequency regulation caused by the large-scale grid connection of new energy, this paper proposes a double-layer automatic generation control (AGC) frequency regulation control method that considers the operating economic cost and the consistency of the state of charge (SOC) of the energy storage. At the regional control level, an economically optimized dynamic frequency regulation responsibility distribution between the unit and the energy storage is realized, and the idle time of energy storage is fully used for SOC management to effectively suppress the fluctuation of the energy storage SOC. At the energy storage station level, the cooperative control algorithm is used to ensure that the output and SOC of each energy storage unit are consistent, respectively. The effectiveness of the method is verified by establishing the dynamic model of the unit-storage combined frequency regulation of the regional power grid for simulation and comparison experiments. The method proposed in this paper considers the influence of different disturbance conditions on the AGC frequency regulation responsibility distribution between the unit and the energy storage and fully uses the frequency regulation characteristics of the energy storage's rapid and flexible response. It effectively improves the service life of energy storage and the comprehensive operation efficiency of the system while optimizing the frequency regulation operation cost, improving the frequency regulation performance, and increasing the frequency regulation compensation income.

Experimental and numerical simulation research on flow characteristics of model pump-turbine in four-quadrant operating quadrants

Owing to the need for power grid peak regulation and frequency regulation, the pumped storage unit has to undergo frequent working condition conversion, and the pump turbine runs across the four quadrants of the full characteristics during the transition. This study used the full flow numerical simulation and particle imaging velocimetry test to examine the internal flow of three guide vane openings. Consequently, the evolution law of the internal flow characteristics of the pump turbine was obtained. According to our results, in the high-efficiency areas of the turbine and the pump, the runner and guide vane areas flowed steadily, whereas, under other unsteady conditions, there was a vortex structure between the runner area and the vane area. Except for the pump-braking mode, all the most unstable flow areas appeared in the vaneless space. The flow in the runner channel was most unstable in pump-braking mode. Finally, we obtained test images of different operating points in the four-quadrant operating area as well as vortex motion trends.

Optimal Coordinated Frequency Regulation of Renewable Energy Systems via an Equilibrium Optimizer

With the urgency of environmental protection, wind power and photovoltaic (PV) projects are continued to be implemented, and the proportion of renewable energy in the power grid will be higher and higher. Therefore, wind power and PV also began to participate in the regional power grid frequency regulation (FR) and have gradually replaced the role of thermal power units in the power grid. To study the characteristics of renewable energy in frequency modulation, an automatic generation control (AGC) model of wind power and photovoltaic participating in the power grid FR is established. At the same time, an equilibrium optimization is proposed to allocate the total power in real-time so as to improve the FR performance by quickly obtaining the optimal power distribution scheme. The simulation results of the proposed model show that the proposed method is feasible. At the same time, the proposed method is compared with the genetic algorithm (GA), which proves the superiority of the proposed method.

Coordinated control strategy of multi-type power coupling system participating in primary frequency regulation of AC-DC hybrid power grid

Wind power, photovoltaic (PV) power, thermal power and hydropower are connected to AC-DC power grid through the same power coupling point, which is common in North China. Such physical properties make it possible for multiple types of power sources to form a coupling system and behave as a large integrated power supply. How the coupling system participate in the primary frequency regulation (PFR) is a problem worthy of investigation. However, there is a lack of research in this field by now. In this paper, a coordinated control strategy of coupling system participating in PFR is proposed, that is, each power source separately measures the frequency and carries out PFR; the central controller of the coupling system is responsible for receiving related information of each power source, calculating and issuing the key parameters for each power source, such as the frequency control gain. A test system is established based on the actual regional power grid in Liaoning province, China. The simulation results under typical operating conditions verify the effectiveness of the proposed control strategy, which can realize the coordination of multiple power sources on the basis of ensuring the overall frequency regulation rapidity of the coupling system.

Sliding Mode Observer-Based Finite Time Control Scheme for Frequency Regulation and Economic Dispatch in Power Grids

In this brief, a novel sliding mode (SM) observer-based scheme is proposed to achieve frequency regulation and economic dispatch (ED) in power grids composed of interconnection of generators and load buses. The ED problem is addressed in two steps. Assuming only the voltage phase angles are measured, in the first step a network of heterogeneous SM observers, suitably interconnected in a distributed fashion, is created to estimate both frequency deviations and unknown power levels associated with each bus. In the second step, the observer scheme is coupled with an SM control strategy which is able to reach the optimal value of the control input in each generator bus in finite time. The scheme is assessed via the IEEE 39 bus benchmark, and a comparison with existing control methods is provided.

Corrigendum: Power Grid Frequency Regulation Strategy for Photovoltaic Plant Based on Multiobjective Harris Hawks Optimization

In the published article, there was an error in affiliation 1. Instead of “School of Mechatronics Engineering, Zhengzhou University of Aeronautics, Zhengzhou 450046, China*”, it should be “**Zhengzhou University of Aeronautics, Zhengzhou 450046, China**”. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.

Application of flow battery energy storage system at the end of rural power grid

The mobile energy storage power station based on the all vanadium flow battery has many advantages such as flexible layout, adjustable power capacity and high application efficiency. It can achieve effective support for active and reactive power at the end of the rural power grid and voltage and frequency regulation, and comprehensively improve the power supply capacity and quality of the end of the rural power grid. In order to select suitable application demonstration points to verify the above functions, a survey was conducted on the low voltage at the end of the rural power grid. Based on the experience of local staff and the comprehensive geographic factors of local monitoring system data, the end of a certain rural power grid was selected as the pilot area. The capacity of the transformer in the distribution station area was 50kW to supply power to approximately 50 households. The 50kW/100kWh all vanadium redox flow battery was selected as the energy storage system.

The Strategy of Considering the Participation of Doubly-Fed Pumped-Storage Units in Power Grid Frequency Regulation

Facing the challenges of grid stability brought by the large-scale access of new energy to the grid, as one of the important means of frequency regulation of the grid, the doubly-fed pumped-storage units (DFPSU) have great practical significance in the study of the joint frequency regulation strategy with the thermal power unit (TPU). In order to reduce the frequency regulation pressure on the grid caused by the large-scale entry of new energy sources, this paper proposes a joint frequency regulation strategy for the TPU and DFPSU. Based on establishing the optimal scheduling model of the system, taking into account the minimum total operating cost and the optimal time as goals, the chaotic particle swarm optimization (CPSO) is proposed to solve the model. Finally, through MATLAB simulation, the relevant examples are studied and analyzed, and the simulation results verify that the joint frequency regulation strategy in this paper can effectively improve the frequency regulation performance of the unit and the operation economy is good.

Multi-Objective Mayfly Optimization-Based Frequency Regulation for Power Grid With Wind Energy Penetration

With the continuous development of society and under the background of sustainable development and resource conservation, the proportion of renewable energy in the global energy structure is increasing. At the same time, wind power has been widely used in many regions of the world because wind power technology is more advanced and mature than other renewable energy sources. In addition, with a large number of wind turbines connected to the grid, it not only helps automatic generation control (AGC) of power systems but also brings new challenges and difficulties. In this study, a multi-source cooperative control model of wind power participating in AGC frequency regulation is established to solve the dynamic problem of power distribution from real-time total power command to different AGC units. This study presents an optimal AGC-coordinated control method based on the multi-objective mayfly optimization (MMO) algorithm, which makes the fitting degree of power command output and actual output curve high and the adjustment mileage payment minimum, so as to achieve the best AGC performance. Finally, the simulation results show that this method can effectively decrease the total power deviation and adjustment mileage payment in the multi-source-coordinated control of AGC.

Power Grid Frequency Regulation Strategy for Photovoltaic Plant Based on Multi-Objective Harris Hawks Optimization

To settle the issue of balance between two objectives, i.e., photovoltaic (PV) power station output power maximization and frequency regulation (FR) signals response, a novel PV reconfiguration strategy is proposed in this work, which maximizes the output power through PV reconfiguration, and meanwhile utilizes the energy storage system (ESS) to decrease the PV plant generated power’ deviation from FR signals. Above all, a model of PV-storage power station reconfiguration is designed to minimize the power bias of both rated power and FR signals. Then, the multi-objective Harris hawks optimization (MHHO) is used to obtain the Pareto front which can optimize the above two objectives due to its high optimization efficiency and speed. Subsequently, the optimal compromise solution is selected by the decision-making method of VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR). Aiming to substantiate the efficacy of the proposed technique, the case studies are carried out under partial shading condition (PSC) with constant and time-varying FR signals. The simulation results show that, compared with the situation without optimization, the power deviations of the two objectives are reduced by 25.11 and 75.76% under constant FR signals and 23.27 and 55.81% under time-varying FR signals by proposed method, respectively.

Optimal Frequency Regulation in AC Mobile Power Grids Exploiting Bilinear Matrix Inequalities

By day-to-day improvement in a microgrid (MG) control, frequency regulation in the shipboard alternating current (ac) MGs has received much interest in the past decade. The shipboard MGs involve renewable energy sources (RESs) that are unable to produce reliable and constant energy. This important fact vividly demonstrates the requirement of modern frequency regulation techniques. This article proposes a novel dynamic output feedback controller (DOFC) for load frequency control (LFC) in a sample shipboard MG. The considered ac MG involves fuel cell, gas turbine, and diesel generator as the controllable power generators; photovoltaic array and sea wave energy converter as the renewable energy sources; and batteries and flywheels as the storage units. The existing approaches almost exploit linearization for solving the problem, which imposes restrictions on the problem and raises conservative constraints resulting in shrinking the solution space. This article suggests a simple approach that effectively reduces such limitations through the formulation of sufficient conditions on the controller design in the form of bilinear matrix inequalities (BMIs). This consequences in a more exact solution compared to the previous methods. To show the merits of the developed approach, OPAL real-time (RT) simulations are executed, and the results are compared to the other state-of-the-art-methods that prove the efficacy of the suggested approach. Also, the results of our proposed method (DOFC; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n=2$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n=3$ </tex-math></inline-formula> ) are compared to the typical <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {H}_{\infty }$ </tex-math></inline-formula> optimization, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu }$ </tex-math></inline-formula> -synthesis, fuzzy type-1, and intelligent-PI methods. The comparisons between norms of the frequency deviation verify the efficacy of the proposed controller in this article.

Multi-source Optimal Coordinated Frequency Regulation for Power Grid with High Penetration of Renewable Energy

Multi-source Optimal Coordinated Frequency Regulation for Power Grid with High Penetration of Renewable Energy

Wind Power Deterministic Prediction and Uncertainty Quantification Based on Interval Estimation

Abstract With the increasing penetration of wind power into modern power systems, accurate forecast models play a crucial role in large-scale wind power consumption and power system stability. To improve the accuracy and reliability of ultrashort-term wind power prediction, a novel deterministic prediction model and uncertainty quantification with interval estimation were proposed in this study. In consideration of the dynamic characteristics of a generator and conditional dependence, the generator rotor speed and pitch angle were regarded as the indicators of the dynamic characteristics of the generator, and light gradient boosting machine (LGBM) with a Bayesian optimization method was explored to build the deterministic prediction model. Considering the conditional dependence between output power and forecast error, a fuzzy C-means clustering method was used to cluster forecast errors into different clusters, and the best error probability distribution was obtained by fitting the error histogram with nonparametric kernel density estimation. Prediction intervals at different confidence levels were calculated, and the error uncertainty was quantified. A case study was conducted to compare prediction accuracy and reliability by using the present and proposed methods. Results demonstrate that the LGBM deterministic prediction model combined with Bayesian optimization has better prediction accuracy and lower computational cost than the comparative models, specifically when the input features are high-dimensional big data. The nonparametric estimation method with conditional dependence is reliable for interval prediction. The proposed method has a certain reference value for wind turbines participating in frequency regulation and power control of power grid.

Primary frequency regulation in power grids with on–off loads: Chattering, limit cycles and convergence to optimality

Load side participation can provide valuable support to the power network in case of urgencies. On many occasions, loads are naturally represented by on and off states. However, the use of on–off loads for frequency control can lead to chattering and undesirable limit cycle behavior, which are issues that need to be resolved for such loads to be used for network support This paper considers the problem of primary frequency regulation with ancillary service from on–off loads in power networks and establishes conditions that lead to convergence guarantees and an appropriate power allocation within the network. In particular, in order to assist existing frequency control mechanisms, we consider loads that switch when prescribed frequency thresholds are exceeded. Such control policies are prone to chattering, which limits their practicality. To resolve this issue, we consider loads that follow a decentralized hysteretic on–off policy, and show that chattering is not observed within such a setting. Hysteretic loads may exhibit, however, limit cycle behavior, which is undesirable. To address this, we propose an adapted hysteretic control scheme for which we provide convergence guarantees. Furthermore, we consider a mixed-integer optimization problem for power allocation and propose a suitable design of the control policy such that the cost incurred at equilibrium is within ϵ from the optimal cost, providing a non conservative value for ϵ. The practicality of our analytic results is demonstrated with numerical simulations on the Northeast Power Coordinating Council (NPCC) 140-bus system.

Performance assessment of grid-forming and grid-following converter-interfaced battery energy storage systems on frequency regulation in low-inertia power grids

Power systems with large shares of converter-interfaced renewables may be characterized by low grid inertia due to the lack of frequency containment provided by synchronous generators. Battery energy storage systems (BESSs), which can adjust their power output at much steeper ramping than conventional generation, are promising assets to restore suitable frequency regulation capacity levels. BESSs are typically connected to the grid with a power converter, which can be operated in either grid-forming or grid-following modes. This paper quantitatively assesses the impact of large-scale BESSs on the frequency containment of low inertia power grid and compares the performance of grid-forming and grid-following control modes. Numerical results are provided considering a detailed dynamic model of the IEEE 39-bus system where fully characterized models of stochastic demand and generation are taken into account. In order to assess the performance of the BESS control modes in a practical operative context, daily long simulations are considered where reserve levels for frequency containment and restoration are allocated considering the current practice of a transmission system operator in Europe. Numerical analyses on various metrics applied to grid frequency show that grid-forming outperforms grid-following converter control mode. • Grid-forming vs grid-following converter-interfaced BESS in low-inertia power grids. • Quantification of system frequency containment via 24-hour time-domain simulations. • Coupling of real-time simulation with day-ahead energy and reserve schedules. • Definition of realistic grid operational scenario • Frequency containment and restoration reserves allocated by considering nowadays procedures adopted by TSOs.

Numerical investigation of dynamic characteristics for expansion power generation system of liquefied air energy storage

Liquefied air energy storage (LAES), as a type of compressed air energy storage, has comprehensive advantages. It is suitable for various situations regarding electric energy storage, such as generation, transmission, and user-side applications. It is necessary to learn the operating characteristics of LAES for safe, stable, and controllable operations. In this study, a dynamic model of a 12.5 MW LAES system is established and used to simulate various operating conditions in the expansion phase. The results show that the startup period and rotating speed overshoot of the expander affect each other during the startup process. This can be balanced using a segmented startup scheme, so that the rotating speed overshoot can be controlled within a permissible safe range while shortening the startup period as much as possible. When the segmented startup scheme is “9000 rpm/min–3000 rpm/min,” the startup time is shortest, at 145 s. A ±0.03 Hz dead zone for frequency regulation is considered in the application of the LAES system to the primary frequency regulation of power grid to avoid frequent regulation of the control system, and the primary frequency regulation process is controlled to be within 20 s, meeting the requirements of the power grid. As the action of the emergency closing valve of the protection system in the process of power generation is triggered by the off-grid of the expansion generator owing to an unexpected event, the delay time of the valve action must be controlled to remain within the permissible safe range. This ensures that the expansion generator is safe, and avoids the rotor over-speed caused by the delay of the valve action. The dynamic model and its simulation results can be used to support operation control strategies for LAES systems for primary frequency regulation.

A Novel Control Strategy for the Frequency and Voltage Regulation of Distribution Grids Using Electric Vehicle Batteries

In this study, a double-loop control strategy is proposed for power grid frequency and voltage regulation using plug-in electric vehicles (PEVs) connected to the grid through a three-level capacitor clamped inverter. The frequency and voltage regulation problem is first formulated using vector space analysis and phasor diagrams to find the boundaries and constraints in terms of the system parameters. The derived formulas are then utilized to design a double-loop controller using an exclusive phase detector control loop and a novel pulse width modulation (PWM) scheme to effectively regulate the frequency and voltage of the grid. The effectiveness and feasibility of the proposed control strategy are evaluated through simulation and experimental studies. This approach can benefit both the customers and the grid operator, as it facilitates utilizing the batteries of the connected PEVs to supply a portion or all of the active and reactive power demand, hence regulating the frequency and voltage of the grid. The extent to which active and reactive power can be supplied depends on the number of PEVs connected to the local grid.