Load Frequency Regulation Research Articles

Electric Vehicles Battery Wear Cost Optimization for Frequency Regulation Support

Due to their capacities and quick response, Electric Vehicle (EV) batteries can be used to support a number of power grid services and form a Vehicle-to-Grid (V2G) system. When aggregated and properly managed EV batteries can provide important ancillary services such as peak load levelling and frequency regulation. EVs can also provide various demand response services and help in renewable energy integration. The major challenge for having a wide-scale V2G system to effectively provide the above services is the availability of power which is limited by the battery degradation and the battery cycle life. The battery cycle life is inversely proportional to the charge/discharge cycles the battery goes through during its operation. Therefore, the charge/discharge operation should be optimized to maximize the benefit for both the EV owners and the grid operator. In this paper, we develop an EV charge/discharge optimization model that incorporates frequency regulation and electricity prices from both real and forecasting models into the objective function of the model. We develop a prediction and optimization model to reflect the effects of dynamic and static electricity and regulation prices on the battery cycle life. We present a case study for the charge/discharge scheduling problem utilizing real, predicted regulation and electricity hourly pricing.

Real Time Simulation of Observer Based State Feedback Load Frequency Regulator for Optimally Reduced Power System Model

This paper presents a study of real time simulation of observer based state feedback load frequency regulator for optimally reduced order power system model. The actual system states can be replaced by the observer based states for feedback control design without losing the system stability. State space model of two area interconnected power system model having non-reheat thermal turbine in each area is investigated to develop the proposed control scheme. Moreover, the power system model is optimally reduced with the objective of retaining the dominant characteristics of original system and reducing the complexity and computational burden for the real time simulation of the proposed scheme. Real time simulation is performed on two PC configurations, out of which continuous and discrete time observer based scheme is designed and simulated in non-real time environment on host PC and target PC is used for real time simulation of continuous and discrete time models. It was found that discrete time observer based control scheme for reduced power system model is quite appreciable in terms of dynamic performance and computational burden as compared to continuous time observer based load frequency control for reduced power system model.

Intelligent frequency regulation in the wind integrated control area

Reduction in system inertia due to the higher levels of wind plants in a power system inherently necessitates the frequency regulation investigations and motivates new opportunities for the improvement of active power control techniques. This paper focus on the load-frequency regulation analysis of a control area in the presence of a proposed wind energy technology. The proposed variable speed wind turbine generator model incorporates a dynamic dead-band and moving average frequency filter-based algorithm to provide grid-code compatible power-frequency response. The proposed wind plant model provides better frequency response and increased electrical power generation in comparison to the other frequency responsive wind turbine generator models. This paper also highlights the superiority of gain scheduling concept in fuzzy logic controllers as an improved alternative to various other load frequency controllers under the stochastic conditions in a wind integrated control area.

Potential ancillary services of electric vehicles (vehicle-to-grid) in Indonesia

Many countries committed to promoting eco-friendly transportation by accelerating the adoption of electric vehicles (EVs) in their country due to their beneficial feature, including in Indonesia. The ancillary services by EVs will be one of solution for power system due to their unique characteristic as energy storage. Indonesia is one of the developing countries that has a thousand islands which are mostly not connected to each other. Java-Madura-Bali (JAMALI) system is one of the large systems that has energy mix which is mainly produced by coal-fired power plant and limited energy storage. Large capacity battery from penetrated EVs in the future might be a good opportunity to support the grid, with time mapping for charging and discharging. Duration and period of opportunity can be determined by frequency recognition that has been measured for 1 month. This paper shows the opportunity of parked EVs utilization by releasing and absorbing the electricity for the load leveling and frequency regulation. The impacts of EVs adoption and V2G participation rates, which are motivated by some incentive from Transmission Service Operator (TSO), are analyzed. The results show that controllable charging and discharging behaviors of EVs have led to the idea of EVs utilization for supporting the grid. The feasibility of vehicle-to-grid (V2G) in Indonesian electrical grid is evaluated in this study. The evaluated ancillary services include load leveling and frequency regulation.

Load frequency regulation using observer based non-linear sliding mode control

In this paper, the generalized extended state observer (GESO) and non-linear sliding mode control (SMC) are merged together to study the frequency deviation problem in multi-area power system. In study, the GESO is used not only for state and disturbance estimation but also for disturbance rejection of the system. The said observer ensures accurate estimation of the actual states leading to convergence of estimation error to zero. The non-linear SMC is used to increase the damping ratio of the system whenever, any perturbations occurs. The proposed observer based controller is compared with an existing two-layer active disturbance rejection control (ADRC) and also validated on large power system at random load disturbance. Further, the proposed controller performance is tested on the minimum and non-minimum phase systems. In addition to fast response in terms of settling time and reduced over/undershoots, the proposed control scheme satisfactorily compensates the disturbance in the system. The proposed scheme is further tested in the presence of power system non-linearities such as generation rate constraints and governor dead-band. The simulation results illustrate the robustness of proposed controller when subjected to load disturbances and non-linearities.

Distributed Model-Based Control and Scheduling for Load Frequency Regulation of Smart Grids Over Limited Bandwidth Networks

An integrated model-based control and scheduling scheme is proposed for the load frequency control (LFC) of large-scale power systems under the distributed structure and uncertainties. Specifically, the limited bandwidth constraint is considered when state observation is exchanged over shared communication networks. Each area controller uses the explicit models of its own and neighboring areas to predict state observations when the actual one is not available. At each transmission instant, the state observation of the scheduled area is broadcasted to the relevant areas and the model-based controllers are partially updated. By properly scheduling the transmission sequence and intervals, the stability of the power system can be guaranteed with a substantial reduction of the bandwidth usage and this is proven by performing a thorough theoretical analysis. Simulation results of a four-area power system verify that the proposed distributed model-based control scheme integrated with a proper scheduling strategy can greatly enhance the performance and the resiliency to parameter uncertainty in large-scale power systems.

Multi-Area Hydrothermal Interconnected Load Frequency Control with Double-Fed Induction-Generator-Based Wind Turbine via Improved Harmony Algorithm

The main purpose of this research is to allow doubly fed induction generator (DFIG) to participate effectively in interconnected power systems load frequency control via improved harmony algorithm (IHA). In order to tune the parameters of the PI controllers without considering the complexity associated with the modeling of the power system, the corresponding optimization problem is formulated in terms of an objective function, which represents the norm of the closed-loop area control error signal. A three-area interconnected power system subjected to major disturbances is investigated to verify the effectiveness of the developed algorithm of DFIG wind turbine participation in load frequency regulation. Time domain simulation results are presented to prove the improved performance of the developed IHA-based controller compared with genetic algorithm, simulated annealing, and a conventional integral controller. The results show that the developed IHA controller has better behavior over other algorithms in terms of settling times and other indices.

EVs for frequency regulation: cost benefit analysis in a smart grid environment

Vehicle-to-grid systems facilitate efficient and reliable integration of electric vehicle (EV) into the smart grid. This integration helps provide various services such as peak load levelling, frequency regulation (FR) and other ancillary services that provide notable benefits to utilities. In addition to the benefits to the utilities, EV owners may also benefit from providing these ancillary services to the grid. In this study, a comprehensive assessment of the economic benefits of using EVs to support FR service to the power grid is developed. The limitations for providing such services to the grid are evaluated. The number of the charge and discharge cycles of the EV battery is estimated based on a realistic semi-logarithmic model. Finally, the estimates are used to calculate the battery degradation cost for providing FR and estimate the safe amount of power that EVs can supply with adequate consideration for daily driving requirements.

Optimal sliding mode control for frequency regulation in deregulated power systems with DFIG-based wind turbine and TCSC–SMES

In this article, disrupted oppositional learned gravitational search algorithm (DOGSA)-optimized sliding mode control (SMC) is proposed for the load frequency regulation problem in deregulated power system including flexible alternating current transmission system devices, namely thyristor-controlled series capacitor (TCSC) and superconducting magnetic energy storage (SMES) without and with doubly fed induction generator (DFIG) wind turbine. Initially, the performance of the proposed control scheme is compared with genetic algorithm-tuned integral controller reported in the literature for two-area interconnected power system with TCSC in tie-line under deregulated environment. Further, the SMES unit is also considered in one of the areas and the system performance is analyzed and found to be better with the combination of optimized SMC and TCSC–SMES for unilateral, bilateral as well as contract violation cases in comparison with system with optimal SMC and TCSC and also with the controller reported in the literature. The potential of the proposed schemes is further analyzed and studied in the presence of nonlinear constraints, namely generation rate constraint, governor deadband and time delay which are present in the real-time power system. From the simulation results, it is deduced that the optimal SMC-generated control signal eliminates the chattering problem in the controller output. Also, the combination of TCSC and SMES improves the transient performance of the system. Thus, the frequency regulation in deregulated power system has been performed using the DOGSA-tuned SMC and also investigated the coordinated action of TCSC–SMES with inclusion of DFIG wind turbine in both the control areas of the system.

Improved load frequency control of power system using LMI based PID approach

In this paper an approach for designing an optimum gain of Proportional integral derivative (PID) controller subject to Linear matrix inequality (LMI) constraints for load frequency regulation of single area and multi-area power system is presented. The LMI based PID control reduces the required control effort while assuring that pre-defined design conditions for dynamic response of system like settling time, overshoot and Integral square error. Further a subset of complex plane with respect to the design conditions is mapped onto a stability region in the coefficient space of the characteristic polynomial. Next, the stability region in the polynomial coefficient space defines LMI as a constraint, which is used to find the optimum gain of PID controllers. A series of simulations results are performed for efficacy of proposed design approach especially for dynamic response of single area and multi-area power system which is superior in comparison to other design method obtained from literature. The simulation results demonstrate that the designed controller can effectively restrain the impact of variation in system parameters and load disturbance.

Hybridized gravitational search algorithm tuned sliding mode controller design for load frequency control system with doubly fed induction generator wind turbine

SummaryIn this paper, the load frequency regulation problem of 2‐area interconnected power system is resolved using the sliding mode control (SMC) methodology. Interconnected 2‐area power systems with and without doubly fed induction generator wind turbines are considered for implementing the proposed optimal control methodology. Here, a heuristic gravitational search algorithm (GSA) and its variants such as opposition learning–based GSA (OGSA), disruption‐based GSA (DGSA), and disruption based oppositional GSA (DOGSA) are employed to optimize the switching vector and feedback gains of SMC. In order to overcome the inherent chattering problem in SMC, the control signals are considered in the objective function. The robustness of optimized SMC is analyzed by the inclusion of nonlinearities such as generation rate constraint (GRC), governor deadband, and time delay during the signal processing between the control areas, which are present in the real‐time power system. The insensitiveness of the optimal controller is shown by variation in system parameters like loading condition, speed governor constant, turbine constant, and tie‐line power coefficient. Further, the optimal SMC has been studied with significant load variations and wind power penetration levels in the control areas. The potential of proposed SMC design with chattering reduction feature is shown and validated by comparing the results obtained with the other reported methods in the literature.

Novel Quasi-Decentralized SMC-Based Frequency and Voltage Stability Enhancement Strategies Using Valve Position Control and FACTS Device

This paper proposes a novel sliding mode control (SMC) strategy for load frequency and voltage control in a complex power system under electrically faulty conditions. The load frequency regulation is achieved by changing the valve position of generators, while the bus voltage regulation is realized with the utilization of a popular FACTS device, Static Var Controller. Inter-area tie-line power is taken into consideration in the load frequency control so as to maintain the obligations of importing/exporting active power from/to connecting areas. The proposed control method thus operates in a quasi-decentralized manner, utilizing local frequency and voltage signals, as well as inter-area tie-line power information. An improvement is then made to the originally proposed SMC scheme to suppress its inherent fluctuations. The proposed enhanced SMC is easy to implement, and compared with conventional PI controllers, it produces superior performances in regulating frequencies and magnitudes of bus-bar voltages.

주파수조정용 에너지저장장치 운전제어 기술의 개발과 계통연계 자동제어 운전

Grid-connected, large-capacity energy storage systems (ESS) can be used for peak load supply, frequency regulation, and renewable energy output smoothing. In order to confirm the capability of battery ESS to provide such services, 4MW/ 8MWh battery ESS demonstration facility was built in the Jocheon substation on Jeju Island. The frequency regulation technology developed for the Jocheon demonstration facility then became the basis for the 28MW and 24MW frequency regulation ESS facilities installed in 2014 at the Seo-Anseong and Shin-Yongin substations, respectively. The operation control systems at these two facilities were continuously improved, and their successful commercialization led to the construction of additional ESS facilities all over Korea in 2015. In seven (7) locations nationwide (e.g., Shin-Gimje and Shin-Gyeryeong), a total of 184 MW of ESS had been commercialized in 2016. The trial run for the new ESS facilities had been completed between April and May in 2016. In this paper, results of the trial run from each of the ESS facilities are presented. The results obtained from the Seo-Anseong and Shin-Yongin substations during a transient event by a nuclear power plant trip are also presented in this paper. The results show that the frequency regulation battery ESS facilities were able to quickly respond to the transient event and trial run of ESS is necessary before it is commercialized.

Quantifying electric vehicle battery degradation from driving vs. vehicle-to-grid services

Abstract The risk of accelerated electric vehicle battery degradation is commonly cited as a concern inhibiting the implementation of vehicle-to-grid (V2G) technology. However, little quantitative evidence exists in prior literature to refute or substantiate these concerns for different grid services that vehicles may offer. In this paper, a methodology is proposed to quantify electric vehicle (EV) battery degradation from driving only vs. driving and several vehicle-grid services, based on a semi-empirical lithium-ion battery capacity fade model. A detailed EV battery pack thermal model and EV powertrain model are utilized to capture the time-varying battery temperature and working parameters including current, internal resistance and state-of-charge (SOC), while an EV is driving and offering various grid services. We use the proposed method to simulate the battery degradation impacts from multiple vehicle-grid services including peak load shaving, frequency regulation and net load shaping. The degradation impact of these grid services is compared against baseline cases for driving and uncontrolled charging only, for several different cases of vehicle itineraries, driving distances, and climate conditions. Over the lifetime of a vehicle, our results show that battery wear is indeed increased when vehicles offer V2G grid services. However, the increased wear from V2G is inconsequential compared with naturally occurring battery wear (i.e. from driving and calendar ageing) when V2G services are offered only on days of the greatest grid need (20 days/year in our study). In the case of frequency regulation and peak load shaving V2G grid services offered 2 hours each day, battery wear remains minimal even if this grid service is offered every day over the vehicle lifetime. Our results suggest that an attractive tradeoff exists where vehicles can offer grid services on the highest value days for the grid with minimal impact on vehicle battery life.

V2G 전기자동차의 부하관리 자원 활용을 위한 적정 지원금 산정에 관한 연구

Recently, various energy efficiency optimization activities are ongoing globally by integrating conventional grids with ICT (Information and Communication Technology). In this sense, various smart grid projects, which power suppliers and consumers exchange useful informations bilaterally in real time, have been being carried out. The electric vehicle diffusion program is one of the projects and it has been spotlighted because it could resolve green gas problem, fuel economy and tightening environmental regulations. In this paper, the economics of V2G system which consists of electric vehicles and the charging infrastructure is evaluated comparing electric vehicles for V2G with common electric vehicles. Additional benefits of V2G are analyzed in the viewpoint of load leveling, frequency regulation and operation reserve. To find this benefit, electricity sales is modeled mathematically considering depth of discharge, maximum capacity reduction, etc. Benefit and cost analysis methods with the modeling are proposed to decide whether the introduction of V2G systems. Additionally, the methods will contribute to derive the future production and the unit cost of electric vehicle and battery and to get the technical and economic analysis.

CONTRIBUCIÓN DE UNA CENTRAL REVERSIBLE CON BOMBEO A VELOCIDAD VARIABLE A LA REGULACIÓN FRECUENCIA-POTENCIA DE UN SISTEMA AISLADO

The development of renewable energies is growing in recent years, promoted by many governments in response to climate change. The main drawbacks of renewable energies, come from uncertainty and variability in the short term of wind and solar radiation. For many years, pumped storage power plants have become one of the most important means to cover the lack of regulation, characteristic of aforementioned renewable energies. In addition, pumped storage power plants can nowadays be operated with variable speed, thanks to last decades improvements in electronic frequency converters. Converters are usually limited by electrical magnitudes (voltages or currents) but in some cases hydraulic limits can be more restrictive, as in high head power plants. The main objective of this work is to study the influence of a pumped storage power plant with variable speed on an isolated system, and to analyze how the hydraulic limits of the reversible turbine in pumping mode reduces the power plant regulation capacity. For this purpose, a dynamic model of the power plant and the isolated system has been developed by means of Matlab/Simulink. Some simulations are carried out and it is indeed stated that hydraulic characteristics constrain the possibility of the pumped storage power plant, to offer load-frequency regulation in the secondary market. Keywords: Pumped storage power plant, variable speed, load-frequency control, hydraulic stability limit, long penstock, simulation model

Load Voltage and Frequency Regulation in PMSG based Standalone Wind Energy Conversion System

Stand alone variable speed wind energy conversion system with PMSG is proposed in this paper. Two back to back VSCs are connected to interface PMSG with load. Constant voltage in DC link between two VSCs can be maintained constant by using a battery energy storage system (BESS). BESS is efficient to maintain load voltage and frequency to be regulated during variable wind speed conditions. MPPT based vector controlling is used to control generator side converter to maintain unity power factor at PMSG which improves generated power and efficiency. Load side converter is controlled to maintain regulated voltage and frequency at load side. Simulations are performed using MATLAB/SIMULINK to check effectiveness of control strategies. Performance is checked with increase in wind speed; decrease in wind speed and with unbalanced/non linear loads.

Control approach to the load frequency regulation of a Generation IV Lead-cooled Fast Reactor

One of the most pressing issues in the study of the power generation and distribution is the characterization of the grid behavior, whether a relevant fraction of the connected power plants relies on Renewable Energy Sources. Indeed, because of the discontinuous power supply and the limited presence of energy accumulators, concerning power imbalances may take place on the grid. The power plants ensuring high reliability performance should be ready to feed the loads when the Renewable Energy Sources are not available. In order to ensure the grid stability and the sustainability of nuclear energy, the possibility of operating Generation-IV nuclear reactors in a flexible way should be considered, i.e., the Nuclear Power Plants should adjust the mechanical power produced so as to comply with the sudden grid frequency variations. In the present work, this opportunity is assessed for the Lead-cooled Fast Reactors, adopting the Advanced Lead Fast Reactor European Demonstrator (ALFRED) as a representative of Lead-cooled Fast Reactor technology. For this reactor concept, because of the large thermal inertia that characterizes the system, the adoption of the “reactor-follows-turbine” scheme (currently employed in the Pressurized Water Reactors) is not feasible. An alternative solution is proposed, i.e., the set-point for the thermal power produced in the core is kept constant at the nominal value (or slowly variable), and the set-point for the mechanical power available to the alternator is adjusted according to the load demands. In order to assess the performance of the developed control scheme, two case studies are simulated. In the first one, a frequency profile of the synchronous Continental European grid is provided. In the second simulation, the possibility of performing the islanding operational transient is evaluated. Such an operational transient needs the connected power plants to perform relevant power variations in few seconds in order to deal with the abrupt change in the grid powered configuration. The simulation outcomes show that the proposed control scheme allows achieving prompt mechanical power variations. As for the quantitative results, in both simulations the frequency value is maintained below the upper safety threshold (50.8Hz). On the other hand, the control scheme complies with the technological constraints set for the safe operation of the primary circuit of the ALFRED reactor. In particular, the Balance of Plant pressure-induced feedbacks on the primary circuit dynamics are effectively dampened, i.e., the temperature in the cold leg is effectively maintained close to its set-point (i.e., 400°C) and the plant is almost insensitive to the variations of the grid power demands.

An Effective Power Management Strategy for a Wind–Diesel–Hydrogen-Based Remote Area Power Supply System to Meet Fluctuating Demands Under Generation Uncertainty

This paper addresses power management strategies, including technical issues and control methodologies, for a wind-dominated hybrid remote area power supply (RAPS) system. The system consists of a doubly fed induction generator, a diesel generator, a hydrogen-based generation scheme, and mains loads. The goal is to maximize power extraction from the wind generator under generation uncertainty. For active power management, a hydrogen-based generation scheme consisting of an electrolyser and a fuel cell system is integrated to the RAPS system. Developed control strategies contribute to achieve the following objectives: 1) load side voltage and frequency regulation; 2) maximum power extraction from wind; and 3) regulating diesel generator operation at low load conditions. Simulation studies with a real-life data set are used to evaluate the proposed architecture and prove the control objectives, and it has been observed that all the proposed objectives are met within satisfactory limits.

Contribution of a hydraulic short-circuit pumped-storage power plant to the load–frequency regulation of an isolated power system

In this paper, the contribution of a hydraulic short-circuit pumped-storage power plant (HSCPSPP) to the load–frequency regulation (LFR) of an isolated power system has been further analyzed by means of simulations. For this purpose, a simulation model has been developed that considers the AGC system and both the synchronized thermal units’ and the HSCPSPP’s response to frequency deviations and power set-point signals sent by the AGC system. The frequency deviation of the power system and the electromechanical behavior of the HSCPSPP have been modeled by using commonly accepted approaches for studies on long-term dynamics of power systems. The behavior of the penstock has been considered through an elastic water column model. The simulations results demonstrate that the HSCPSPP has a large flexibility and that can contribute to a great extent to the LFR of the system, while fulfilling the requirements established by the TSO and preserving the plant safety.