Real-time vehicle-to-grid control for frequency regulation with high frequency regulating signal

The large-scale popularization of electric vehicles(EVs)brings the potential for grid frequency regulation.Considering the characteristics of fast response and adjustment of EVs,two control strategies of automatic generation control(AGC)with EVs are proposed responding to two high frequency regulating signals extracted from area control error(ACE)and area regulation requirement(ARR)by a digital filter,respectively.In order to dispatch regulation task to EVs,the capacity of regulation is calculated based on maximum V2G power and the present V2G power of EVs.Finally,simulations based on a two-area interconnected power system show that the proposed approaches can significantly suppress frequency deviation and reduce the active power output of traditional generation units.

The Applications of High-voltage variable frequency speed regulation System in Main Exhauster of Sintering

Main Exhauster is one of the main equipment of sintering production. It needs to consume a lot of electricity. Therefore, the system＇ s reconstruction for energy-saving will effectively reduce electricity for the production. The paper takes an iron and steel enterprise that had successfully transformed the synchronous motors of main exhauster of sintering as an example, which describes the application of high-voltage variable frequency speed regulation system in main exhauster of Sintering, so as to provide a reference for other iron and steel enterprises.

Mechanism of Primary Frequency Regulation for Battery Hybridization in Hydropower Plant

Battery hybridization in hydropower plants is a hydropower flexibility enhancement technology innovation that can potentially expand hydropower’s contributions to the grid,but its fundamental characteristics and influencing mechanisms are still unclear.In this paper,primary frequency regulation(PFR)performance and the mechanism of this new technology are studied.A battery hybridized hydropower plant(BH-HPP)model,based on a field-measured-data-based hydropower plant(HPP)model and a verified battery simplified model,is established.Analysis of system stability and dynamics is undertaken for three different battery control strategies by root locus and participation factor methods.Compared to conventional HPPs,analysis results theoretically reveal BH-HPP can not only accelerate system regulation rapidity but also effectively enlarge HPP stability region during PFR process.Time domain simulation verifies the results and further shows synthetic control has better performance among introduced strategies.Besides,initial design ranges of control parameters considering battery capacity and a renewable energy source scenario case are also discussed.This work could provide theoretical support for flexibility enhancement solutions for hydropower systems.

Optimal Bidding Strategy for PV and BESSs in Joint Energy and Frequency Regulation Markets Considering Carbon Reduction Benefits

Photovoltaic(PV)and battery energy storage systems(BESSs)are key components in the energy market and crucial contributors to carbon emission reduction targets.These systems can not only provide energy but can also generate considerable revenue by providing frequency regulation services and participating in carbon trading.This study proposes a bidding strategy for PV and BESSs operating in joint energy and frequency regulation markets,with a specific focus on carbon reduction benefits.A two-stage bidding framework that optimizes the profit of PV and BESSs is presented.In the first stage,the day-ahead energy market takes into account potential real-time forecast deviations.In the second stage,the real-time balancing market uses a rolling optimization method to account for multiple uncertainties.Notably,a real-time frequency regulation control method is proposed for the participation of PV and BESSs in automatic generation control(AGC).This is particularly relevant given the uncertainty of grid frequency fluctuations in the optimization model of the real-time balancing market.This control method dynamically assigns the frequency regulation amount undertaken by the PV and BESSs according to the control interval in which the area control error(ACE)occurs.The case study results demonstrate that the proposed bidding strategy not only enables the PV and BESSs to effectively participate in the grid frequency regulation response but also yields considerable carbon emission reduction benefits and effectively improves the system operation economy.

Time-delay Correction Control Strategy for HVDC Frequency Regulation Services

With the advancements in voltage source converter(VSC)technology,VSC based high voltage direct current(VSCHVDC)systems provide system operators with a prospective approach to enhance system operating stability and resilience.In addition to long-distance transmission,the VSC-HVDC system can also provide multiple ancillary services,such as frequency regulation,due to its power controllability.However,if a time delay exists in the control signal,the VSC-HVDC system may bring destabilizing influences to the system,which will decrease the system resilience under the disturbance.In order to reduce control deviation caused by time delay,in this paper,a small signal model is first conducted to analyze the impact of time delay on system stability.Then a time-delay correction control strategy for HVDC frequency regulation control is developed to reduce the influence of the time delay.The control performance of the proposed time-delay correction control is verified both in the established small signal model and the runtime simulation in a modified IEEE 39 bus system.The results indicate that the proposed time-delay correction control strategy shows significant improvement in system stability.

Frequency Regulation of VSC-MTDC System with Offshore Wind Farms

Frequency regulation of voltage source converter-based multi-terminal high-voltage direct current(VSC-MTDC)system with offshore wind farms enhances the frequency stability by compensating the power for a disturbed AC system.However,it is difficult to reasonably allocate frequency-regulation resources due to a lack of coordination mechanisms between wind farms and the MTDC system.Moreover,it is difficult for the frequency control of the wind farms to manage changes in wind speed;and the risk of wind-turbine stalls is high.Thus,based on the kinetic energy of wind turbines and the power margin of the converters,the frequency-regulation capability of wind turbines is evaluated,and a dynamic frequency-support scheme considering the real-time frequency-support capability of the wind turbines and system frequency evolution is proposed to improve the frequency-support performance.A power adaptation technique at variable wind speeds is developed;the active power in the frequency-support stage and restoration stage is switched according to the wind speed.A hierarchical zoning frequency-regulation scheme is designed to use the frequency-regulation resources of different links in the MTDC system with wind farms.The simulation results show that the novel frequency-regulation strategy maintains frequency stability with wind-speed changes and avoids multiple frequency dips.

Communication Resources Allocation for Time Delay Reduction of Frequency Regulation Service in High Renewable Penetrated Power System

The high renewable penetrated power system has severe frequency regulation problems.Distributed resources can provide frequency regulation services but are limited by com-munication time delay.This paper proposes a communication resources allocation model to reduce communication time delay in frequency regulation service.Communication device resources and wireless spectrum resources are allocated to distributed resources when they participate in frequency regulation.We reveal impact of communication resources allocation on time delay reduction and frequency regulation performance.Besides,we study communication resources allocation solution in high renewable energy penetrated power systems.We provide a case study based on the HRP-38 system.Results show communication time delay decreases distributed resources'ability to provide frequency regulation service.On the other hand,allocating more communication resources to distributed resources'communica-tion services improves their frequency regulation performance.For power systems with renewable energy penetration above 70%,required communications resources are about five times as many as 30%renewable energy penetrated power systems to keep frequency performance the same.Index Terms-Communication resources allocation,commun-ication time delay,distributed resource,frequency regulation,high renewable energy penetrated power system.

Decision Aid Model for Private-owned Electric Vehicles Participating in Frequency Regulation Ancillary Service Market

To reduce the difficulty and enhance the enthusiasm of private-owned electric vehicles(EVs) in participating in frequency regulation ancillary service market(FRASM), a decision aid model(DAM) is proposed. This paper presents three options for EV participating in FRASM, i. e., the base mode(BM), unidirectional charging mode(UCM), and bidirectional charging/discharging mode(BCDM), based on a reasonable simplification of users' participating willingness. In BM, individual EVs will not be involved in FRASM, and DAM will assist users to set the optimal charging schemes based on travel plans under the time-of-use(TOU) price. UCM and BCDM are two modes in which EVs can take part in FRASM. DAM can assist EV users to create their quotation plan, which includes hourly upper and lower reserve capabilities and regulation market mileage prices. In UCM and BCDM, the difference is that only the charging rate can be adjusted in the UCM, and the EVs in BCDM can not only charge but also discharge if necessary. DAM can estimate the expected revenue of all three modes, and EV users can make the final decision based on their preferences. Simulation results indicate that all the three modes of DAM can reduce the cost, while BCDM can get the maximum expected revenue.

Integrated Frequency-constrained Scheduling Considering Coordination of Frequency Regulation Capabilities from Multi-source Converters

As the proportion of renewable energy(RE)increases,the inertia and the primary frequency regulation(FR)capability of the power system decrease.Thus,ensuring frequency security in the scheduling model has become a new technical requirement in power systems with a high share of RE.Due to a shortage of conventional synchronous generators,the frequency support of multi-source converters has become an indispensable part of the system frequency resources,especially variable-speed wind turbine generation(WTG)and battery energy storage(BES).Quantitative expression of the FR capability of multi-source converters is necessary to construct frequency-constrained scheduling model.However,the frequency support performance of these converter-interfaced devices is related to their working states,operation modes,and parameters,and the complex coupling of these factors has not been fully exploited in existing models.In this study,we propose an integrated frequency-constrained scheduling model considering the coordination of FR capabilities from multi-source converters.Switchable FR control strategies and variable FR parameters for WTG with or without reserved power are modeled,and multi-target allocation of BES capacity between tracking dispatch instruction and emergency FR is analyzed.Then,the variable FR capabilities of WTG and BES are embedded into the integrated frequency-constrained scheduling model.The nonlinear constraints for frequency security are precisely linearized through an improved iteration-based strategy.The effectiveness of the proposed model is verified in a modified IEEE 24-bus standard system.The results suggest that the coordinated participation of BES and WTG in FR can effectively reduce the cost of the scheduling model while meeting frequency security constraints.

Control of Virtual Synchronous Generator for Frequency Regulation Using a Coordinated Self-adaptive Method

Power inverter adopting virtual synchronous generator(VSG)control can provide inertia support for distributed generation systems.However,it cannot take into account the dynamic regulation characteristics of frequency.Thus,when the system encounters a sudden change in load or disturbance,the dynamic process of frequency regulation will be greatly influenced.In view of this issue,an improved VSG control strategy based on a coordinated self-adaptive(CSA)method is proposed.The time domain analysis method is used to study the influences of virtual inertia and damping parameter perturbation on the system steady and dynamic performances.Furthermore,in order to make the control strategy suitable for large load changes and suppress frequency variations beyond the limit,the secondary frequency modulation is introduced into the control loop.Through the coordinated adaptive control of virtual inertia,virtual damping and frequency modulation,the dynamic performance of vSG frequency regulation can be obviously improved.Simulation and experiment results have verified the effectiveness of the proposed CSA control strategy.

A Parallel-type Load Damping Factor Controller for Frequency Regulation in Power Systems with High Penetration of Renewable Energy Sources

Renewable energy sources(RESs)are rapidly devel-oping and their substitution for traditional power generation poses significant challenges to the frequency regulation in power systems.The load damping factor D characterizes the active power of load that changes with power system frequency,which is an important factor influencing the frequency response.However,the value of D is small,resulting in the limitation in frequency regulation of the power system.This paper proposes a parallel-type load damping factor controller to enhance load damping factor by utilizing static var generators(SVGs)in substations.Additionally,it discusses the configuration method for the relevant parameters of the controller,evaluates its frequen-cy regulation capability,investigates the impact of large-scale application of the controller on static and dynamic loads,and conducts a comprehensive evaluation of the impact of the damping factor control process on the voltage stability of the main grid.The large-scale application of the proposed controller can significantly improve the frequency regulation capability,and almost have no influence on the working status of the load.It can also significantly improve the dynamic performance of system frequency.The proposed controller can provide technical support for the frequency regulation of new power systems with high proportion of RESs.

Decentralized Primary Frequency Regulation for Hybrid Multi-terminal Direct Current Power Systems Considering Multi-source Enhancement

Hybrid multi-terminal direct current(MTDC)transmission technology has been a research focus,and primary frequency regulation(FR)improvement in the receiving-end system is one of the problems to be solved.This paper presents a decentralized primary FR scheme for hybrid MTDC power systems considering multi-source enhancement to help suppress frequency disturbance in the receiving-end systems.All the converters only need local frequency or DC voltage signal input to respond to system disturbance without communication or a control center,i.e.,a decentralized control scheme.The proposed scheme can activate appropriate power sources to assist in FR in various system disturbance severities with fine-designed thresholds,ensuring sufficient utilization of each power source.To better balance FR performance and FR resource participation,an evaluation index is proposed and the parameter optimization problem is further conducted.Finally,the validity of the proposed scheme is verified by simulations in MATLAB/Simulink.

Frequency Regulation of Alternating Current Microgrid Based on Hierarchical Control Using Fuzzy Logic

An alternating current(AC)microgrid is a system that integrates renewable power,power converters,controllers and loads.Hierarchical control can manage the frequency of the microgrid to prevent imbalance and collapse of the system.The existing frequency control methods use traditional proportion integration(PI)controllers,which cannot adjust PI parameters in real-time to respond to the status changes of the system.Hierarchical control driven by fuzzy logic allows real-time adjustment of the PI parameters and the method used a two-layer control structure.The primary control used droop control to adjust power distribution,and fuzzy logic was used in the voltage loop of the primary control.The secondary control was added to make up for frequency deviation caused by droop control,and fuzzy logic was used in the secondary frequency control to deal with the dynamic change of frequency caused by the disturbances of loads.The proposed method was simulated in Matlab/Simulink.In the primary control,the proposed method reduced the total harmonic distortion(THD)of two cycles of the output voltage from 4.19%to 3.89%;in the secondary control,the proposed method reduced the frequency fluctuation of the system by about 0.03 Hz and 0.04 Hz when the load was increased and decreased,respectively.The results show that the proposed methods have a better effect on frequency maintenance and voltage control of the AC microgrid.

Reliability Assessment of Interconnected Power Systems with HVDC Links Considering Frequency Regulation Process

With various components and complex topologies,the applications of high-voltage direct current(HVDC)links bring new challenges to the interconnected power systems in the aspect of frequency security,which further influence their reliability performances.Consequently,this paper presents an approach to evaluate the impacts of the HVDC link outage on the reliability of interconnected power system considering the frequency regulation process during system contingencies.Firstly,a multi-state model of an HVDC link with different available loading rates(ALRs)is established based on its reliability network.Then,dynamic frequency response models of the interconnected power system are presented and integrated with a novel frequency regulation scheme enabled by the HVDC link.The proposed scheme exploits the temporary overload capability of normal converters to compensate for the imbalanced power during system contingencies.Moreover,it offers frequency support that enables the frequency regulation reserves of the sending-end and receiving-end power systems to be mutually available.Several indices are established to measure the system reliability based on the given models in terms of abnormal frequency duration,frequency deviation,and energy losses of the frequency regulation process during system contingencies.Finally,a modified two-area reliability test system(RTS)with an HVDC link is adopted to verify the proposed approach.

Experimental study on f-ω regulation model under abnormal methane emission

In view of the difficulty of automatic adjustment, the recovery lag and the major accident potential of the mine ventilation system, an experimental model of the pipe net was established according to the typical one mine and one working face ventilation system of Daliuta coal mine. Using the best uniform approximation method of Chebyshev interpolation to fit the fan performance curve, we experimentally determined fan characteristics with different frequencies and establish the data base for the curves. Based on ventilation network monitoring theory, we designed a monitoring system for ventilation network parameter monitoring and fan operating frequency automatic control. Using the absolute methane emission quantity to predict the air quantity requirement of branch and fan frequency, we established a f-ω regulation model based on fan frequency and absolute methane emission quantity. After analysing methane emission and distribution characteristics, using CO_2 to simulate the methane emission characteristics from a working face, we verified the correctness and rationality of the f-ω regulation model. The fan operation frequency is adjusted by the method of air adjustment change with methane emission quantity and the curve searching method after determining air quantity requirements. The results show that the air quantity in a branch strictly changes according to the f-ω regulation model, in the airincreasing dilution by fan frequency regulation, the CO_2 concentration is limited to the set threshold value. The paper verifies the practicability of a frequency regulation system and the feasibility of the frequency adjustment scheme and provides guidance for the construction of automatic frequency conversion control system in coal mine ventilation networks.

Frequency-constrained Unit Commitments with Linear Rules Extracted from Simulation Results Considering Regulations from Battery Storage

Heavy renewable penetrations and high-voltage cross-regional transmission systems reduce the inertia and critical frequency stability of power systems after disturbances.Therefore,the power system operators should ensure the frequency nadirs after possible disturbances are within the set restriction,e.g.,0.20 Hz.Traditional methods utilize linearized and simplified control models to quantify the frequency nadirs and achieve frequency-constrained unit commitments(FCUCs).However,the simplified models are hard to depict the frequency responses of practical units after disturbances.Also,they usually neglect the regulations from battery storage.This paper achieves FCUCs with linear rules extracted from massive simulation results.We simulate the frequency responses on typical thermal-hydro-storage systems under diverse unit online conditions.Then,we extract the rules of frequency nadirs after disturbances merely with linear support vector machine to evaluate the frequency stability of power systems.The algorithm holds a high accuracy in a wide range of frequency restrictions.Finally,we apply the rules to three typical cases to show the influences of frequency constraints on unit commitments.

A comprehensive review of wind power based power system frequency regulation

Wind power(WP)is considered as one of the main renewable energy sources(RESs)for future low-carbon and high-cost-efficient power system.However,its low inertia characteristic may threaten the system frequ-ency stability of the power system with a high penetration of WP generation.Thus,the capability of WP participating in the system frequency regulation has become a research hotspot.In this paper,the impact of WP on power system frequency stability is initially presented.In addition,various existing control strategies of WP participating in frequency regulation are reviewed from the wind turbine(WT)level to the wind farm(WF)level,and their perfor-mances are compared in terms of operating principles and practical applications.The pros and cons of each control strategy are also discussed.Moreover,the WP combing with energy storage system(ESS)for system frequency regulation is explored.Furthermore,the prospects,future challenges,and solutions of WP participating in power system frequency regulation are summarized.

Wind-farm and hydrogen-storage co-location system optimization for dynamic frequency response in the UK

The continuous development of hydrogen-electrolyser and fuel-cell technologies not only reduces their investment and operating costs but also improves their technical performance to meet fast-acting requirements of electrical grid balancing services such as frequency-response services.In order to project the feasibility of co-locating a hydrogen-storage system with a wind farm for the dynamic regulation frequency-response provision in Great Britain,this paper develops a modelling framework to coordinate the wind export and frequency responses to the main grid and manage the interaction of the electrolyser,compressor,storage tank and fuel cell within the hydrogen-storage system by respecting the market mechanisms and the balance and conversion of power and hydrogen flows.Then the revenue of frequency-response service provision and a variety of costs induced by the hydrogen-storage system are translated into the net profit of the co-location system,which is maximized by optimizing the capacities of hydrogen-storage-system components,hydrogen-storage levels that guide the hydrogen restoration via operational baselines and the power interchange between a wind-farm and hydrogen-storage system,as well as the capacities tendered for low-and high-frequency dynamic regulation services.The developed modelling framework is tested based on a particular 432-MW offshore wind farm in Great Britain combined with the techno-economics of electrolysers and fuel cells projected for 2030 and 2050 scenarios.The optimized system configuration and operation are compared between different operating scenarios and discussed alongside the prospect of applying hydrogen-storage systems for frequency-response provision.

＂One-for-several＂ rotor VVVF Technique apply to water injection station

In the process of oilfield water injection volume of injection allocation often appear with the pump displacement situation does not match, the widespread adoption of stator frequency technology allows the pump displacement and volume of injection allocation phase matching. But the technology in pump class load application speed range is limited, there is still a reflux valve control blind area,＂ turn off undead＂ problem. ＂ One-for-several＂ rotor frequency Technique in water injection station application, solved the control blind area problem, the full realization of the variable frequency close return voltage injection, at the same time, the successful implementation of the slip power efficient feedback. Stable water injection pressure of the system, and the electric energy is saved, satisfy the oilfield high efficiency, fine water needs, has a high application value.

Assessment and Enhancement of FRC of Power Systems Considering Thermal Power Dynamic Conditions

Frequency stability and security have been a vital challenge as large-scale renewable energy is integrated into power systems.In contrast,the proportion of traditional thermal power units decreases during the decarbonization transformation process,resulting in poor frequency support.This paper aims to explore the potential of frequency regulation support,dynamic assessment,and capacity promotion of thermal power plants in the transition period.Considering the dynamic characteristics of the main steam working fluid under different working conditions,a nonlinear observer is constructed by extracting the main steam pressure and valve opening degree parameters.The real-time frequency modulation capacity of thermal power units can provide a dynamic state for the power grid.A dynamic adaptive modification for primary frequency control(PFC)of power systems,including wind power and thermal power,is proposed and improved.The power dynamic allocation factor is adaptively optimized by predicting the speed droop ratio,and the frequency modulation capability of the system is improved by more than 11%under extreme conditions.Finally,through the Monte Carlo simulation of unit states of the system under various working conditions,the promotion of the frequency regulation capacity with high wind power penetration(WPP)is verified.