Techno-economic assessment of energy storage technologies for inertia response and frequency support from wind farms

This paper provides the result of a techno-economic study of potential energy storage technologies deployable at wind farms to provide short-term ancillary services such as inertia response and frequency support. Two different scenarios are considered including a single energy storage system for the whole wind farm and individual energy storage for each wind turbine (located at either the dc or the ac side of its grid-side converter). Simulations are introduced to check the technical viability of the proposal with different control strategies. Power and energy capability requirements demanded by both specific services are defined for each studied case based on present and future grid code needs. Based on these requirements, the study compares a wide range of energy storage technologies in terms of present-day technical readiness and properties and identifies potential candidate solutions. These are flywheels, supercapacitors, and three chemistries out of the Li-ion battery family. Finally, the results of a techno-economic assessment (mainly based on weight, volume, lifetime, and industry-confirmed costings) detail the advantages and disadvantages of the proposed solutions for the different scenarios under consideration. The main conclusion is that none of the candidates are found to be clearly superior to the others over the whole range of scenarios. Commercially available solutions have to be tailored to the different requirements depending on the amount of inertia, maximum Rate of Change of Frequency and maximum frequency deviation to be allowed

Extraction of Inertial and Droop Response from Utility Scale Battery Pack at the State of Charging.

M.S. Thesis. University of Hawaiʻi at Mānoa 2018

Battery Energy Storage Systems in the United Kingdom: A Review of Current State-of-the-Art and Future Applications

The number of battery energy storage systems (BESSs) installed in the United Kingdom and worldwide is growing rapidly due to a variety of factors, including technological improvements, reduced costs and the ability to provide various ancillary services. The aim of this paper is to carry out a comprehensive literature review on this technology, its applications in power systems and to identify potential future developments. At first, the main BESSs projects in the UK are presented and classified. The parameters provided for each project include rated power, battery technology and ancillary services provided, if any. In the next section, the most commonly deployed ancillary services are classified and described. At the same time, the nomenclature found in the literature is explained and harmonised. The second part of the paper focuses on future developments and research gaps: ancillary services that currently are not common but that are likely to be deployed more widely in the future will be described, and more general research topics related to the development of BESSs for power system applications will be outlined

Delta STATCOM with partially rated energy storage for intended provision of ancillary services

This thesis presents research on two distinct areas, where the work carried out in the first half highlights the challenges posed by the declining system inertia in the future power systems and the potential capability of the energy storage systems in bridging the gap, supporting a safe and reliable operation. A comparison of various energy storage technologies based on their specific energy, specific power, response time, life-cycle, efficiency, cost and further correlating these characteristics to the timescale requirements of frequency and RoCoF services showed that supercapacitors (SC) and Li-ion batteries present the most suitable candidates. Results of a network stability study showed that for a power system rated at 2940 MVA with a high RES contribution of 1688 MVA, equating to 57% of the energy mix, during a power imbalance of 200 MW, an ESS designed to provide emulated inertia response (EIR) in isolation required a power and energy rating of 39.54 MW and 0.0365 MWh respectively. Similarly, providing primary frequency response (PFR) on its own required a power and energy rating of 114.52 MW and 2.14 MWh respectively. ESS providing these services in isolation was not able to maintain all the frequency operating limits and similar results were also seen in the case of the recently introduced Dynamic Containment service. However, with the introduction of a combined response capability, a significantly improved performance, comparable to that of the synchronous generators was observed. In order to maintain the RoCoF and the statutory frequency limit of 0.5 Hz/s and ±0.5 Hz respectively, an ESS must be able to respond with a delay time of no more than 0.2 seconds and be able to ramp up to full response within 0.3 seconds (0.5 seconds from the start of contingency) for a frequency deviation of ±0.5 Hz. The second half of the thesis focused on investigating the current state-of-the-art power conversion system topologies, with the objective of identifying a suitable topology for interfacing ESSs to the grid at MV level. A delta-connected Modular Multilevel STATCOM with partially rated storage (PRS-STATCOM) is proposed, capable of providing both reactive and active power support. The purpose is to provide short-term energy storage enabled grid support services such as inertial and frequency response, either alongside or temporarily instead of standard STATCOM voltage support. The topology proposed here contains two types of sub-modules (SM) in each phase-leg: standard sub-modules (STD-SMs) and energy storage element sub-modules (ESE-SMs) with a DC-DC interface converter between the SM capacitor and the ESE. A control structure has been developed that allows energy transfer between the SM capacitor and the ESE, resulting in an active power exchange between the converter and the grid. A 3rd harmonic current injection into the converter waveforms was used to increase the amount of power that can be extracted from the ESE-SMs and so reduce the required ESE-SMs fraction in each phase-leg. Simulation results demonstrate that for three selected active power ratings, 1 pu, 2/3 pu, & 1/3 pu, the fraction of SMs that need to be converted to ESE-SMs are only 69%, 59% & 38%. Thus, the proposed topology is effective in adding real power capability to a STATCOM without a large increase in equipment cost. Furthermore, modifying the initially proposed topology with the use of Silicon Carbide (SiC) switching devices and interleaved DC-DC interface converter with inverse coupled inductors resulted in similar efficiencies when operated in STATCOM mode.Open Acces

Provision of Frequency Response from Wind Farms: A Review

Renewable sources of energy play a key role in the process of decarbonizing modern electric power systems. However, some renewable sources of energy operate in an intermittent, non-dispatchable way, which may affect the balance of the electrical grid. In this scenario, wind turbine generators must participate in the system frequency control to avoid jeopardizing the transmission and distribution systems. For that reason, additional control strategies are needed to ensure the frequency response of variable-speed wind turbines. This review article analyzes diverse control strategies at different levels which are aimed at contributing to power balancing and system frequency control, including energy storage systems.This research was funded by the Basque Government, through the project EKOHEGAZ (ELKARTEK KK-2021/00092), Diputación Foral de Álava (DFA) through the project CONAVANTER, and UPV/EHU through the project GIU20/063

A closed-loop analysis of grid scale battery systems providing frequency response and reserve services in a variable inertia grid

With increasing penetration of wind and solar generation the deployment of fast response plant, principally batteries, is currently considered necessary to mitigate reduced system inertia and the possibility of demand-supply imbalances. In this work the impact of these factors on battery cycling rates, taking into account the input from the batteries themselves, are analysed by applying the swing equation to a future inertia based on forecast generation mix. The operational capacity of batteries is a determining factor in their cycling rate, though the depth of discharge appears to be less well correlated. It is found that reducing system inertia does not, of itself, significantly impact on frequency volatility where the volatility of the generation to load imbalance is unchanged. However, the potential for a reduction in the damping of frequency deviations as a result of an increase in inverter connected motor drives may have a large impact on battery cycling characteristics. Provision of reserve services from battery systems requires a more complex operational strategy to ensure services are always deliverable and results in a significantly different cycling profile that may lead to greater battery degradation and consequently higher operational costs

Design of control tools for use in microgrid simulations

2018 Summer.Includes bibliographical references.New technologies are transforming the way electricity is delivered and consumed. In the past two decades, a large amount of research has been done on smart grids and microgrids. This can be attributed to two factors. First is the poliferation of internet. Internet today is as ubiquitous as electricity. This has spawned a new area of technology called the internet of things (IoT). It gives us the ability to connect almost any device to the internet and harness the data. IoT finds use in smart grids that allow utiliy companies to deliver electricity efficiently. The other factor is the advancement in renewable sources of electricty and high power semiconductors coupled with their decreasing cost. These new sources disrupt the traditional way of electicity production and delivery, putting an increased focus on distributed power generation and microgrids. A microgrid is different from a utility grid. The difference is in the size of the grid, power level, a variety of possible sources and the way these are tied together. These characteristics lead to some unique control challenges. Today's appliances and consumer goods are powered using a standardized AC power. Thus a microrid must deliver uninterrupted and high quality power while at the same time taking into account the vastly different nature of the microsurces that produce the power. This work describes control system tools for different power converters that will be used in simulating microgrids.\ Simulations are important tool for any researcher. It allows researchers to test their research and theories at a greatly reduced cost. The process of design, testing and verification is an iterative process. Simulations allow a cost effective method of doing research, substituting the actual process of building experimental systems. This greatly reduces the amount of manpower and capital investment. A microgrid consists of several building blocks. These building blocks can be categorized into microsources, energy stores, converters and the loads. Microsources are devices that produce electric power. For example, a photovoltaic panel is a mirosource that produces DC power. Converters act as an interface between microsources and the grid. The constituent chapters in the document describe microsources and converters. The chapters describe the underlying control system and the simulation model of the system designed in Simulink. Some of the tools described are derived from the MATLAB/Simulink Examples library. Original authors of the simulation models and systems have been duly credited. Colorado State University has a vibrant research community. The tools described in this thesis are geared to be used for research into microgrids. The tools are developed in a simulation software called Simulink. The tools would allow future researchers to rapidly build microgrid simulations and test new control system implementations etc. The research described in the thesis builds upon the research by Han on natural gas engine based microgrid. The control tools described here are used to construct a microgrid simulation. The microgrid is built around a natural gas engine. Due to the transport lag in delivering fuel, a natural gas engine exhibits significant deviation in the AC grid frequency when subjected to step load. The microgrid setup along with the control system described here, minimizes the frequency deviation, thus stabilizing the microgrid. Simulation results verify the working of the tools

Battery Energy Storage Emulation for Power System Applications

The concept of energy storage for power systems has received increasingly more attention in recent decades, and the growing penetration of renewable energy sources has only escalated demand for it. Energy storage systems are excellent for balancing generation and load, for suppressing power fluctuations, and for providing other ancillary services to the grid. The Hardware Testbed (HTB) is a novel converter-based grid emulator created for studying the needs associated with high renewable penetration, but the system currently lacks a battery storage emulator. Thus, this work documents the development of a battery energy storage system (BESS) emulator for the HTB. The BESS emulator includes internal battery models for Lithium Ion, Lead Acid, and Vanadium redox flow battery technologies. The emulated BESS contains a two-stage power electronics interface using a DC-DC converter and a boost rectifier separated by a DC link. Controllers for active power output, reactive power output, and DC link voltage are designed for the power electronics interface, and application-specific control loops for primary frequency regulation, inertia emulation, and voltage support are also added. The models and control for this emulated BESS are implemented on a digital signal processor that controls one voltage source inverter on the HTB as if it were the BESS’s boost rectifier. Consequently, the voltage source inverter mimics the behavior of a BESS at its point of common coupling with the HTB’s power system. The BESS emulator is simulated and then tested experimentally on the HTB, and all of its control functions demonstrate correct operation. The BESS emulator’s primary frequency regulation and inertia emulation functions nearly eliminate the system frequency swing following a step change in load, and the voltage support keeps the BESS terminal voltage at a safer level following the disturbances. These three support functions are concluded to be capable of simultaneous operation, which allows the BESS emulator to support the HTB’s power system in multiple ways at the same time. In the future, the BESS emulator can be used on the HTB to study how battery storage can be used to support renewables and other dynamic power system needs