A Battery Energy Management Strategy for UK Enhanced Frequency Response

Balancing the grid at 50 Hz requires managing many distributed generation sources against a varying load, which is becoming an increasingly challenging task due to the increased penetration of renewable energy sources such as wind and solar and loss of traditional generation which provide inertia to the system. In the UK, various frequency support services are available, which are developed to provide a real-time response to changes in the grid frequency. The National Grid (NG) – the main distribution network operator in the UK – have introduced a new and fast service called the Enhanced Frequency Response (EFR), which requires a response time of under one second. A battery energy storage system (BESS) is a suitable candidate for delivering such service. Therefore, in this paper a control algorithm is developed to provide a charge/discharge power output with respect to deviations in the grid frequency and the ramp-rate limits imposed by the NG, whilst managing the state-of-charge (SOC) of the BESS for an optimised utilisation of the available stored energy. Simulation results on a 2 MW/1 MWh lithiumtitanate BESS are provided to verify the proposed algorithm based on the control of an experimentally validated battery model

A Battery Energy Management Strategy for UK Enhanced Frequency Response and Triad Avoidance

This paper describes a control algorithm for a battery energy storage system (BESS) to deliver a charge/discharge power output in response to changes in the grid frequency constrained by the National Grid Electricity Transmission (NGET) - the primary electricity transmission network operator in the UK - whilst managing the state-of-charge (SOC) of the BESS to optimise the availability of the system. Furthermore, this paper investigates using the BESS in order to maximise Triad avoidance benefit revenues whilst layering other services. Simulation using a 2 MW/1 MWh lithium-titanate BESS validated model are carried out to explore possible scenarios using the proposed algorithms. Finally, experimental results of the 2MW/1MWh Willenhall Energy Storage System (WESS) verify the performance of the proposed algorithms

Bi-directional power control of grid-tied battery energy storage system operating in frequency regulation

This paper presents a design of an average value PWM voltage source converter (VSC) along with bi-directional active and reactive power flow control in a grid-tied battery energy storage system. A vector control strategy with PI controllers is proposed. In this paper, a grid frequency regulation control design is also implemented in the BESS in order to meet the frequency response requirement by the National Grid Electricity Transmission, the primary distribution network operator in the UK. Simulation results on a 2MW/968kWh lithium-ion BESS are provided to verify the proposed control design based on the control of an experimentally validated battery model

A fast battery cycle counting method for grid-tied battery energy storage system subjected to microcycles

In this paper, a fast battery cycle counting method for grid-connected Battery Energy Storage System (BESS) operating in frequency regulation is presented. The methodology provides an approximation for the number of battery full charge-discharge cycles based on historical microcycling state-of-charge (SOC) data typical of BESS frequency regulation operation. An enhanced frequency response (EFR) algorithm, a new and fast frequency response service in the UK, that provides a charge/discharge response with respect to the deviations in the grid frequency, is used for analysis. The obtained historical SOC data from the EFR analysis is then considered as an input for evaluating the proposed battery cycle counting estimation method

A study of different loss of life based calculations on batteries operating in enhanced frequency response

© 2018 IEEE. National Grid are investigating battery energy storage as a solution to help with energy balancing for frequency control. They are currently looking at Enhanced Frequency Response (EFR) as a solution, but, are unlikely to adapt this directly as they investigate new, more open, market strategies. Battery Energy Storage is still an expensive asset and the opportunity to use a hybrid scheme (with new and second life batteries) offers a potential lower cost solution. Determining the life cycle of a battery energy storage system is complex, as this is a combination of several processes including cyclic and calendric aging. Determining life cycles of a hybrid system is even more complex. This paper discusses different ways of determining life span published in literature and uses a model based case study approach using National Grid published data on frequency and EFR envelopes to investigate the different range of theoretical loss of life within different battery system

Battery SOC management strategy for enhanced frequency response and day-ahead energy scheduling of BESS for energy arbitrage

The electricity system has to balance demand and supply every second, a task that is becoming evermore challenging due to the increased penetration of renewable energy sources and subsequent inertial levels. In the UK, a number of grid frequency support services are available, which are developed to provide a real-time response to changes in the grid frequency. The National Grid Electricity Transmission (NGET) - the primary electricity transmission network operator in the UK - has introduced a new faster frequency response service, called the Enhanced Frequency Response (EFR), which requires a response time of under one second. Battery energy storage systems (BESSs) are ideal choice for delivering such a service. In this paper a control algorithm is presented which supplies a charge/discharge power output with respect to deviations in the grid frequency and the ramp-rate limits imposed by NGET, whilst managing the state-of-charge (SOC) of the BESS to maximise the utilisation of the available energy capacity. Using the real UK market clearing prices, a forecasted battery state of charge (SOC) management strategy has been also developed to deliver EFR service whilst scheduling throughout the day for energy arbitrage. Simulation results demonstrate that the proposed algorithm delivers an EFR service within the specification whilst generating arbitrage revenue. A comparative study is also presented to compare the yearly arbitrage revenue obtained from the model of the Willenhall and an experimental Leighton Buzzard battery storage system. Simulation results on a 2MW/1MWh lithium-titanate BESS are provided to verify the proposed algorithm based on the control of an experimentally validated battery model

Energy-constrained model for scheduling of battery storage systems in joint energy and ancillary service markets based on the energy throughput concept

Among different local renewable resources, using battery energy storage (BES) has grown more than other technologies. The main reasons for this growth are flexibility and schedulability of BES. The fast ramp-rate of BES systems provides the opportunity of effective participation of these resources in the regulation ancillary service. However, continuous charging and discharging cycles of BES could decrease its lifetime and the expected profit, consequently. Therefore, the lifespan is a crucial parameter that shall be considered in the scheduling of BES. In this paper, an energy-constrained model is proposed for the scheduling of BES in joint energy and ancillary service markets. Moreover, the Energy Throughput (ET) concept is proposed for modeling the lifetime in the short-term scheduling strategy. In the proposed strategy, the uncertainties of energy prices in energy and regulation markets are modeled by Robust Optimization (RO) methodology. The scheduling problem is linearized and formulated based on the mixed-integer linear programming (MILP) method. The proposed model determines the optimal scheduling of BES based on the profit maximization, operational constraints, lifespan, and the defined risk level. Finally, the performance of model is evaluated vie case study results.This work has received funding from the EU Horizon 2020 research and innovation program under project TradeRES (grant agreement No 864276) and from FEDER Funds through COMPETE program and from National Funds through FCT under the projects UIDB/00760/2020 and CEECIND/02887/2017 CIND.info:eu-repo/semantics/publishedVersio

Controller to enable the enhanced frequency response services from a multi-electrical energy storage system

The increased adoption of renewable energy generation is reducing the inertial response of the Great Britain (GB) power system, which translates into larger frequency variations in both transient and pseudo-steady-state operation. To help mitigate this, National Grid (NG), the transmission system operator in GB, has designed a control scheme called Enhanced Frequency Response (EFR) specifically aimed at energy storage systems (ESSs). This paper proposes a control system that enables the provision of EFR services from a multi-electrical energy storage system (M-EESS) and at the same time allows the management of the state of charge (SOC) of each ESS. The proposed control system uses a Fuzzy Logic Controller (FLC) to maintain the SOC as near as possible to the desired SOC of each ESS while providing EFR. The performance of the proposed controller is validated in transient and steady-state domains. Simulation results highlight the benefits of managing the SOC of the energy storage assets with the proposed controller. These benefits include a reduced rate of change of frequency (ROCOF) and frequency nadir following a loss of generation as well as an increase in the service performance measure (SPM) which renders into increased economic benefits for the service provider