Grid Services Research Articles

Dynamic Response Analysis on a 9-Kw Vrfb Test Facility

An industrial-scale Vanadium redox flow battery test facility (IS-VRFB) in operation at the Electrochemical Energy Storage and Conversion Laboratory of University of Padua aims at exploring the technological developments from VRFB laboratory testbeds to grid scale VRFB systems. The 40-cell 600-cm2 active-area stack and two 550-L tanks provide a power of 9 kW and an energy 27 kW h. An AC/DC bidirectional static converter that controlled by the battery management system (BMS) provides the electric power conditioning during charge and discharge with currents up to 75 A and a variable passive load allows high-current discharges up to 600 A. The plant is fully instrumented with electrical and thermo-fluid dynamic probes and the in-house LabVIEW-based BMS provides acquisition, processing and control functions. Since VRFBs are capable of fast response times and can provide fast grid services, such as frequency regulation, it is quite important characterizing their transient behavior. Nerveless, extensive experimental campaigns for investigating the fast response of a large-scale VRFB systems, are largely missing, especially in term of fast time-domain analysis. This presentation is an early contribution in such regard, in view of real large-scale applications of the VRFB technology. Two different time intervals involving different phenomena occurring in the cell have been analysed. Initially, the first 20 ms after battery powering were acquired using an oscilloscope with a sample rate of 2 GHz. Secondly, the first 120 s were explored by means of the BMS acquisition system a sampling rate of 1.25 Hz. In order to widely explore the fast response capability, different conditions were examined by varying state of charge (SOC), flow rate (Q), and current (I). The oscilloscope analyses revealed a “peak transient” time interval during which both current and voltage undergo large variations, up to 50%. During this interval, lasting few milliseconds, no reliable current and voltage value can be provided by the battery. In the longer timescale, different behaviors occurred depending on the Q, SOC, and I. The higher Q and SOC, the shorter the transient before a steady-state condition was achieved, with both current and voltage constant in time (Fig.1a). Preliminary analysis demonstrated the suitability of the model of Fig.1b to predict the stack dynamic response. Modelling resorted to experimental data obtained from a multichannel Electrochemical Impedance Spectroscopy (EIS) analyzer, tailored for IS-VRFB and capable of operating in the range 0─10 kHz with bias currents up to 400 A.

(Invited) Advanced Intermediate Temperature Na-Metal Halide Batteries for Grid Applications

Developing battery systems that are inexpensive, enduring, and safe is essential for integrating renewable energy sources such as solar and wind power into the electricity grid and providing valuable grid services such as frequency regulation, peak shaving, and arbitrage. In this regard, Na-based batteries are promising candidates because they use naturally abundant sodium (Na) as the charge carrier, which can potentially reduce the materials cost and support multiple energy storage applications. Among various Na-based batteries developed to date, thorough investigations have been done on high-temperature (~300°C) Na-metal halide (Na-MH) batteries, which offer long cycle life and superior safety. In particular, the tubular sodium-nickel chloride (Na-NiCl2 or Zebra) battery has been commercialized and found wide application in the telecom and oil/gas industries. However, the high operating temperature and cost of the Zebra battery has hindered its further market penetration. Recently, the research of Na-MH battery has been focusing on the development of battery technologies operated at intermediate temperature (< 200oC), which has several advantages including simple cell architectures, improved thermal management, lower operating temperature, and lower manufacturing cost over high temperature Na based batteries. Here, we will introduce the mechanism of battery degradation, the development of advanced low-cost cathode materials, long-term cycle results, and the current status and prospects of scale up this promising battery technology.

(Invited) Low-Cost and High Rate Na-FeCl2 Batteries for Large Scale Energy Storage Applications

Developing battery systems that are inexpensive, enduring, and safe is essential for integrating renewable energy sources such as solar and wind power into the electricity grid and providing valuable grid services such as frequency regulation, peak shaving, and arbitrage. In this regard, Na-based batteries are promising candidates because they use naturally abundant sodium (Na) as the charge carrier, which can potentially reduce the materials cost and support multiple energy storage applications. Among various Na-based batteries developed to date, thorough investigations have been done on high-temperature (~300°C) Na-metal halide (Na-MH) batteries, which offer long cycle life and superior safety. In particular, the tubular sodium-nickel chloride (Na-NiCl2 or Zebra) battery has been commercialized and found wide application in the telecom and oil/gas industries. However, the high operating temperature and cost of the Zebra battery has hindered its further market penetration. Considering constraints of the Ni-based cell chemistry, it is highly desirable to develop an alternate cathode for Na-MH batteries towards next-generation energy storage applications. This pursuit, unsurprisingly, led us to the Fe/NaCl cathode. In this study, we present an advanced Na-FeCl2 battery with unprecedented high-rate performance and low cost for stationary energy storage applications. Operated at an extremely high current density of 33.3 mA/cm2 at 190°C, the cell can output 74% of its total capacity—a capacity retention double that of IT Na-NiCl2 cells. The origin of the high rate capability of Na-FeCl2 batteries was elucidated by means of comprehensive phase/structure analysis and electrochemical/electroanalytical characterizations. Moreover, Fe particle pulverization originating from liquid-phase reactions was determined to be the major source of capacity fading during long-term cycling. Accordingly, we designed a unique cathode with Ni additive, which delivered a high discharge specific energy density of over 295 Wh/kg for 200 cycles at C/5 with almost no capacity fading.

Efficient and robust data availability solution for hybrid PLC/RF systems

Recently, many efforts have been made by researchers, standardization organizations, telecommunication industries and energy providers, in order to realize robust and efficient communication in Smart Grids. To meet these requirements, a new generation of Narrow-Band Power Line Communication (NB-PLC) protocols have been proposed. The main advantage of PLC systems is that they require no additional costs in terms of deployment and wiring since the existing power cables can be used to transmit power and data, simultaneously. The PLC technology has many applications within Smart Grids such as advanced metering infrastructure, distributed automation, street light control, and public charging. One popular PLC standard is the Power-line Related Intelligent Metering Evolution (PRIME). This technology enables different types of Smart Grid services over electricity distribution networks. In PRIME, the security is implemented at the data link layer and it targets data confidentiality and message authentication, but not data availability. In this paper, we propose an efficient and robust security solution to guard against availability and confidentiality attacks. The main goal of the proposed solution is to enhance the security and reliability of PLC communication among end nodes with minimum overhead in terms of resources, complexity and latency. The solution is based on the Information Dispersal Algorithm (IDA) and the physical characteristics of PLC channels. In particular, end nodes benefit from a shared working key and the random channel parameters to derive the cryptographic primitives that are used in the proposed scheme. The security and performance tests showed that the proposed solution introduces a low overhead while offering a high degree of availability and reinforcing confidentiality.

Possible Power Quality Ancillary Services in Low-Voltage Grids Provided by the Three-Phase Damping Control Strategy

The share of renewable energy is increasing because of environmental concerns and favorable economic conditions. The majority of the distributed energy resources, connected to the low-voltage grid, are inverter-connected units. These inverters are controlled by using specially developed control strategies to determine the power injection between the primary source and the grid. In the past, the connection of distributed energy resources was based on the connect-and-forget principle, but this approach leads to severe power quality problems. Nowadays, more sophisticated control strategies need to be developed, so that ancillary services can be provided to the distribution system operator, which will allow further increase of renewable share in the distribution grids. This article examines the technical capabilities of the three-phase damping control strategy to provide ancillary services to the distribution system operator. Besides the three-phase damping control strategy, the article also compares the classical positive-sequence control strategy. Active power drooping and reactive power exchange are combined with these control strategies and the effect on the annual energy production, power quality, and grid performance is assessed. The simulations are conducted on a Matlab/OpenDSS platform in a time series simulations.

Vehicle-to-grid technology and its suitability for the Moroccan national grid

Thanks to the technological advances in electronic devices and bidirectional power inverters, electric vehicles (EVs) are no longer viewed as just transportation tools. Rather, they could also serve as electric storage units for the grid and supply ancillary services within the framework of vehicle to grid (V2G) technology. Following the successful implementation of this emerging technology in several countries such as Germany and Spain, numerous scientific papers and research activities are addressing the use of V2G via plug-in cable energy transfer or inductive wireless charging. This paper investigates the suitability of such technology for the Moroccan national grid. It outlines the state of art of the V2G technology together with the current status of the country's power grid. Furthermore, the paper takes into consideration the evolution of the EV market in the country as well as the EV charging infrastructure deployed within its territories. Moreover, a survey on the services that the V2G could provide is presented. Finally, the authors conclude that the V2G would be very beneficial for the national power grid, providing up to 7.7 GW of controllable, and mobile loads by 2030, as well as for the EV owners once the recommended incentives are put in place.

A Review and Categorization of Grid-Interactive Efficient Building Technologies for Building Performance Simulation

Abstract Buildings of the future are expected to not only be energy efficient but also able to offer grid services through implementation of demand-side management strategies by utilizing existing and new technologies that enhance electrical load flexibility. With the high penetration of variable renewables, grid operators have to balance between variable supply with controllable and adaptable demand. This article reviews the current literature on grid-interactive efficient buildings (GEBs) that can provide grid services. In particular, the review identifies categories and examples of measures and technologies that are suitable for GEBs using various criteria. These criteria include demand-side management strategies, potential to provide grid services, technology maturity, as well as ability to model the technologies to perform detailed analyses and assessments in whole-building simulation software.

Toward a Retail Market for Distribution Grids

Modern active distribution grids are characterized by the increasing penetration of distributed energy resources (DERs). Proper coordination and scheduling of these DERs requires a local retail market which can operate at the distribution grid level. In this paper, we propose a retail market for optimally managing and scheduling DERs, and coordinating ancillary services in a distribution grid. Our proposed retail market leverages a recently proposed distributed proximal atomic coordination (PAC) algorithm which has several advantages over other distributed algorithms, with reduced local computational effort and enhanced privacy. We describe how the market can be implemented using a Distribution System Operator (DSO), whose representatives are located at the primary feeder level and workers are located at the substation level, and how the DSO will interact with the Wholesale Electricity Market. Finally, we extensively validate the performance of the proposed retail market via simulations of three networks: a real distribution grid in Tokyo, a balanced IEEE 123-bus distribution grid, and a modified IEEE 13-bus network. Our results show that the proposed market is practical and can be easily implemented in distribution grids, resulting in optimal real-time scheduling of DERs and compensation in the form of distributed locational marginal prices.

Distributed Generation: Leveraging for Grid Services [In My View

In the past two decades. significant progress has been made to deploy distributed energy resources (DERs) in California. The Golden State (as California is nicknamed) now has a much more open planning process where DERs can be utilized for grid services. With the tools and processes already instituted and given the quantity and size of the aggregated deployment, many people believe DERs should be providing these services and enabling utilities to defer large quantities of traditional infrastructure investment.

Standby thermal management system for a kW-class vanadium redox flow battery

Standby is a condition that may occur several times and for long periods in the operation of a redox flow battery for energy storage services in electrical grids (from a national grid down to smart grids, microgrids, …), so that the efficient operation of these batteries calls for specific standby management procedures, capable of minimizing losses while avoiding solutes precipitation. This paper describes the characteristics of a standby thermal management system capable of performing these tasks with high efficiency. Its design resorts to an experimental and numerical investigation that made use of a cell-resolved dynamic thermal model, determining the stack voltage, self-discharge and temperature evolutions. Two different standby modes were analyzed: one with no electrolyte flow (named “swamped standby mode”) and the other with a small electrolyte cooling flow rate (named “streamed standby mode”). In addition, the critical conditions which may lead to V(V) precipitation were identified based on published experimental data. As regards the swamped standby mode, an advanced strategy consisting of smart intermittent washings was designed and tested on a kW-scale vanadium redox flow battery system, showing a dramatic reduction of self-discharge losses compared to a conventional fixed periodic washing. As regards the streamed standby mode, the optimal value of the cooling electrolyte flow rate that minimizes self-discharge was identified. With respect to the swamped one, the streamed standby mode ensures the battery readiness to provide fast power service in safe conditions. To the best of the authors’ knowledge, this is the first work in which such thermal management strategy during standby, supported by experimental validation on a kW-class vanadium redox flow battery, is presented.

Grid Integration as a Strategy of Med-TSO in the Mediterranean Area in the Framework of Climate Change and Energy Transition

The paper presents a survey on the situation in terms of solutions for grid integration throughout the Mediterranean area in the framework of climate change and energy transition. The objective of the study is focused on Mediterranean region connectivity initiatives in the context of the broader vision of an interconnected European–Mediterranean (Euro–Med) power system for a future low-carbon energy system as the fundamental objective of Med-TSO, the Association of the Mediterranean Transmission System Operators (TSOs) for electricity. The analysis examines how the power grid connectivity evolves from now on to 2030, describing the progress made to date in integrating the power grids of the Mediterranean region as well as the future possibilities for a more integrated power grid covering the whole region. The research, conducted within Mediterranean Project II of Med-TSO, includes an overview on the current situation of the interconnections and the proposal for the 2030 interconnections Master Plan, coherent with the national development plans (NDPs) and shared energy scenarios for the whole region at the same horizon of 2030. It conducts an assessment of the gap between the current and the 2030 expected situation, taking into account the energy transition toward 2030 objectives resulting from the achievements of climate change pledges, local governmental policies and EU strategy for neighboring countries and Africa. The solutions survey includes technical solutions, procedures and rules to improve systems’ integration and increase regional electricity exchanges in Med-TSO countries, and is aimed at achieving a higher quality of services and better efficiency of energy supply in Med-TSO member countries in the framework of the expected energy transition. The main scope is to present solutions that will be made available due to maturity and experience in the coming decade, specifically: high voltage direct current (HVDC) transmission technologies, energy storage, sectors coupling, smart grid technologies and services, inter-TSO and transmission–distribution cooperation platforms, etc. The article presents two case studies: the island paradigm and a new cross-border interconnection project of common interest. Finally, the post-pandemic core role of TSOs, which has become more relevant than ever, is transformed into a key-enabler of energy transition towards a sustainable, resilient and innovative climate-neutral recovery.

Grid-Feeding Inverter With Simplified Virtual Synchronous Compensator Providing Grid Services and Grid Support

This paper proposes the enhancement of the control of a grid-connected inverter by a simplified virtual synchronous compensator (S-VSC) model working in parallel with the traditional inverter current control loops. The goal of the integration of this model into the inverter control scheme is to provide grid services, such as virtual inertia behavior, current harmonic compensation, as well as reactive grid support during faults. The S-VSC is only in charge of providing the aforementioned services, working, therefore, always at a low power level. On the other hand, the main power references are sent directly to the inverter control loops. This way, a more stable and damped operation of the inverter is obtained. The proposed structure has been implemented on a 15 kVA grid-connected inverter for experimental validation.

State description of cyber-physical energy systems

The integration of ICT into power systems has increased the interdependencies between the two systems. The operation of power system depends on several ICT-enabled grid services which manifest the interdependencies. ENTSO-E system state classification is a tool that is widely used by operators to determine the current operational state of the power system. However, it does not adequately describe the impact of ICT disturbances on the operation of the power system. Despite their interconnections, the operational states of both systems have been described separately so far. This paper bridges the well-established ENTSO-E systems state classification with an ICT system state classification, forming a new model considering the state classification of the ICT-enabled grid services. The model is developed by first identifying the ICT-enabled services, remedial actions and the respective performance requirements that are required by the power system. Then the states of these services are specified based on the supporting ICT system. The resulting joint state description shows how performance degradation of ICT-enabled services (introduced by disturbances) can affect the operation of the interconnected power system. Two case studies of such ICT-enabled services, namely state estimation and on-load tap changer control, are investigated in terms of how their operational states affect the states of the power system. A third case study highlights the interdependencies that exist between the services. These case studies demonstrate the interdependencies that exist between power and ICT systems in modern cyber-physical energy systems, thus highlighting the usage of a unified system state description.

Degradation of electric vehicle lithium-ion batteries in electricity grid services

Repurposing retired electric vehicle lithium ion batteries into stationary electricity grid storage will increase their utilization and correspondingly reduce their environmental footprint prior to recycling. In this work, we investigated the performance characteristics of leading commercial cell types repurposed into electricity grid services. Two different positive active materials were compared: (1) a lithium nickel manganese cobalt oxide blended with lithium manganese oxide (LiNiMnCoO2+ LiMn2O4, termed ``NMC+LMO'') and (2) lithium iron phosphate (LiFePO4, termed ``LFP''). The bulk electricity service of energy arbitrage and the ancillary power electricity service of frequency regulation were tested. Performance was evaluated for energy capacity degradation and round-trip energy efficiency throughout cycle life. Half cell testing and electrochemical voltage spectroscopies were used to investigate the origin of degradation. The results gave useful insight into which chemistries are most appropriate for repurposing into which electricity grid service application. It was found that energy arbitrage service degrades energy capacity approximately twice as fast as frequency regulation service. NMC+LMO degrades approximately twice as fast as LFP. The main energy capacity degradation mechanism comes from loss of lithium inventory. We note that inter-cell capacity degradation differences appear to be a function of overall degradation level. Consequently, the battery management system for repurposed applications must have greater ability to manage inter-cell differences than factory electric vehicle systems. NMC+LMO was more energy efficient than LFP (96% vs 94%) and no degradation of energy efficiency was noted over the first 1200 complete cycle equivalents. This indicates that the thermal management systems applied for electric vehicle purposes is sufficient for repurposed applications. The choice of chemistry type thus depends on the service conducted as some services do not demand long life and some are insensitive to the cost of energy inefficiencies.

A Lightweight Authentication Scheme for V2G Communications: A PUF-Based Approach Ensuring Cyber/Physical Security and Identity/Location Privacy

Vehicle-to-grid (V2G) technology has become a promising concept for the near future smart grid eco-system. V2G improves smart grid resiliency by enabling two-way communication and electricity flows while reducing the greenhouse gases emission. V2G practicality and stability is strongly based on the exchanged data between electrical vehicles (EVs) and the grid server (GS). However, using communication protocols to exchange vital information leads grid to being vulnerable against various types of attack. To prevent the well-known attacks in V2G network, this paper proposes a privacy-aware authentication scheme that ensures data integrity, confidentiality, users’ identity and location privacy, mutual authentication, and physical security based on physical unclonable function (PUF). Furthermore, the performance analysis shows that the proposed scheme outperforms the state-of-the-art, since EVs only use lightweight cryptographic primitives for every protocol execution.

Optimal Energy Dispatch Controller for Fuel Cell-Integrated Multi-Zone Building

Abstract Stationary fuel cells provide potential opportunities for energy savings when integrated with buildings. Through smart dispatch of both electrical power and heat generated by the fuel cells and managing the building loads, the buildings can achieve more efficient operation. In this paper, we develop an optimal energy dispatch controller to operate a fuel cell-integrated building. The controller leverages the inherent thermal storage and the dispatchable fuel cell to reduce its operating cost and to allow the building to participate in grid services. The proposed controller is implemented on two types of commercial buildings, a large office building and a large hotel, and the effectiveness of the controller is demonstrated through simulations. The results also indicate that the potential saving varies significantly with different system parameters, including season, fuel prices, and equipment sizing, which provide helpful insights for building operators and other stake holders.

Simulating dispatchable grid services provided by flexible building loads: State of the art and needed building energy modeling improvements

End-use electrical loads in residential and commercial buildings are evolving into flexible and cost-effective resources to improve electric grid reliability, reduce costs, and support increased hosting of distributed renewable generation. This article reviews the simulation of utility services delivered by buildings for the purpose of electric grid operational modeling. We consider services delivered to (1) the high-voltage bulk power system through the coordinated action of many, distributed building loads working together, and (2) targeted support provided to the operation of low-voltage electric distribution grids. Although an exhaustive exploration is not possible, we emphasize the ancillary services and voltage management buildings can provide and summarize the gaps in our ability to simulate them with traditional building energy modeling (BEM) tools, suggesting pathways for future research and development.

A Critical Exploration of the Efficiency Impacts of Demand Response From HVAC in Commercial Buildings

Increasing quantities of renewable energy generation has yielded a need for greater energy storage capacity in power systems. Thermal storage in variable air volume (VAV) heating, ventilation, and air conditioning (HVAC) in commercial buildings has been identified as an inexpensive source of grid storage, but the true costs are not known. Recent literature explores the inefficiency associated with providing grid services from these HVAC-based demand response (DR) resources by employing a battery analogy to calculate round-trip efficiency (RTE). Results vary significantly across studies and in some cases reported efficiencies are strikingly low. This article has three objectives to address these prior results. First, we synthesize and expand on insights into existing literature by systematically exploring the potential causes for the discrepancies in results. We reinforce previous work indicating baseline modeling may drive differences across studies and deduce that control accuracy plays a role in the major differences between experiments and simulation. Second, we discuss why the RTE metric is problematic for DR applications, discuss another proposed metric, additional energy consumption (AEC), and propose an extension, which we call uninstructed energy consumption (UEC), to evaluate DR performance. Finally, we explore the merits of different metrics using experimental data and highlight UEC’s reduced sensitivity to the characteristics of the DR signal than previously proposed metrics.

Wake redirection for active power control: a realistic case study

This paper presents a realistic case study of how wake redirection can be used to provide ancillary grid service. Wake redirection is a wind farm control approach in which the wake of a wind turbine is redirected by imposing a yaw misalignment to minimise the flow interactions with downwind wind turbines. The increase in power is controlled in our approach to meet a requested power increase. The methodology is implemented in FAST.Farm, a mid-fidelity wind farm simulation tool. In a case study with 12 wind turbines the applicability of the methodology is analysed. Hereby, provision of active power control was achieved in some cases. Structural loads were investigated at tower base, blade root and drivetrain of the turbines, indicating that the concept tends to increase the fatigue damage compared to a baseline case where all turbines are operated with zero yaw misalignment.

Time and voltage domain load models for appliance-level grid edge simulation and control

Developments in simulation and distributed control of distributed energy resources require increasingly granular characterization and modeling of load behavior. Previous work has demonstrated the viability of voltage-based power control of residential appliances to enable load flexibility without service interruption. However, conventional static and dynamic load models fail to capture the coupled voltage and state dynamics relevant for this type of control.We develop a new class of dynamic load models for residential appliances. The input-output dynamics are learned by varying input voltage, which is enabled by custom hardware capable of controlling single-phase AC voltage and collecting high-resolution measurements. We estimate model parameters using nonlinear least squares regression and particle swarm optimization. The RMSE of power predictions is significantly reduced for loads with coupled time and voltage dynamics relative to traditional models. Using these models for voltage-based power control can help improve the ability of DERs to provide grid services.