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

Online battery state of power prediction using PRBS and extended Kalman filter

This paper presents a hybrid battery parametrisation technique for the purpose of battery state-of-charge (SOC) and state-of-power (SOP) monitoring in real time. The proposed technique is centred around an opportunistic initialisation of a dual Extended Kalman Filter (DEKF) algorithm using Pseudo Random Binary Sequence (PRBS) battery excitation. A Second-order electrical equivalent-circuit battery model is used whose parameters are identified using a carefully designed 10-bit 10-Hz PRBS signal while the battery is in a zero- or low-current quiescent mode. The PRBS-identified resistive elements of the battery model are then utilised to provide an initial estimate for the battery's SOP. Once in load conditions, the DEKF algorithm is implemented recursively to provide an accurate estimate of the battery's parameters, SOC and subsequently its SOP in real time. The experimental results obtained form an electrochemical impedance spectroscopy (EIS) method give confidence to the performance of the proposed hybrid battery parametrisation technique

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

A hybrid battery parameter identification concept for lithium-ion energy storage applications

© 2016 IEEE.Persistent of excitation of the input/output signals is a necessity for any online parameter identification technique. In most real battery systems, the drive signals may not fully satisfy this condition at all times, which can lead to divergence and failure of the incorporated battery management system. Therefore, in this paper, a hybrid battery parameter identification concept is proposed whereby the parameters are initially identified using a special random signal called the pseudo random binary sequences. Thereafter, the Kalman filter algorithm is implemented online to estimate and track any 'disturbances' caused by varying operating conditions. A dynamic European drive cycle is used to experimentally verify the excellent performance of the proposed technique against a more precise electrochemical impedance spectroscopy method

Experimental analysis of dynamic charge acceptance test conditions for lead-acid cells

© 2016 IEEE.This paper presents the results of a series of tests to determine the Dynamic Charge Acceptance (DCA) performance of small form-factor 2 V, 6 Ah, carbon-enhanced VRLA cells designed for Hybrid Electric Vehicle (HEV) applications. A test procedure has been written for a battery test system, based on a modified DCA Short Test profile. Results have been obtained for a batch of cells, tested at various temperatures, rest periods and states of charge. These conditions have been chosen to mimic a range of real-life scenarios which could potentially be encountered during HEV operation. The resulting analysis demonstrates clear variations and trends in DCA performance which may be used to inform conditions for future testing regimes. The same test procedure is then applied to standard lead-acid cells and the results compared

On-chip implementation of Extended Kalman Filter for adaptive battery states monitoring

This paper reports the development and implementation of an adaptive lithium-ion battery monitoring system. The monitoring algorithm is based on the nonlinear Dual Extended Kalman Filter (DEKF), which allows for simultaneous states and parameters estimation. The hardware platform consists of an ARM cortex-M0 processor with six embedded analogue-to-digital converters (ADCs) for data acquisition. Two definitions for online state-of-health (SOH) characterisation are presented; one energy-based and one power-based. Moreover, a method for online estimation of battery's capacity, which is used in SOH characterisation is proposed. Two definitions for state-of-power (SOP) are adopted. Despite the presence of large sensor noise and incorrect filter initialisation, the DEKF algorithm poses excellent SOC and SOP tracking capabilities during a dynamic discharge test. The SOH prediction results are also in good agreement with actual measurements

Phase shift control based Maximum Efficiency Point Tracking in resonant wireless power system and its realization

A modern Wireless Power Transfer (WPT) system is commonly realized by Strongly Coupled Magnetic Resonances (SCMR), which transfer energy by using the mutual inductance between coils. The application of wireless power transfer is critically limited by its energy transfer efficiency. SCMR systems are designed to transmit at a frequency that is equal to the self-resonant frequency of its power receiver, in applications where the self-resonant frequency varies during operation the measurement of the frequency is typically not possible. In this paper, a phase shift control based Maximum Efficiency Point Tracking (MEPT) approach is proposed along with implementation methodologies to enable real-world application. A prototype wireless power system with MEPT featured is built which verifies that the new MEPT method could effectively track the optimized frequencies continuously on the fly and maximise the efficiency of the WPT

Vehicle-to-vehicle charging system fundamental and design comparison

The popularisation of the Electric Vehicle (EV) is restrained by the stagnation of energy storage technology and inadequate plug-in charging stations. This paper proposes a new vehicle-to-vehicle (V2V) charging technology platform, that can achieve wireless charging working in harmony with plug-in charging technology, or operate independently. V2V charging technology can effectively solve the problem of the limited number of plug-in stations. Moreover, it can charge the car any-time, anywhere, like a power bank. V2V charging system design requires a number of technical challenges to be overcome including the power balancing between vehicles and charging circuit design to maximizing the power transfer efficiency. In this paper, the schematic of V2V charging system is proposed, and we also propose the fundamentals of calculating the power capacity and the cost of EV energy when an EV is a power source in a V2V charging system. The hardware circuit design is presented and a detailed comparison of different coil shapes/ combinations and compensation circuit topologies is provided using the simulation tool ANSYS

An analysis of the influence of high-frequency ripple currents on dynamic charge acceptance in lead-acid batteries

This paper presents the results of an experimental analysis of the influence of high-frequency injected ripple currents on the Dynamic Charge Acceptance (DCA) performance of lead-acid batteries. A wide-bandwidth battery model, derived from real-world data is described, this being a hybrid of the standard Randles model and a high-frequency model previously presented in literature. A bespoke test procedure is introduced, based on the existing DCA Short Test profile (EN50342-6). The results demonstrate that the injection of ripple currents can significantly improve charge acceptance, whilst having no appreciable effect on the State of Charge (SoC) of the battery. This study further demonstrates the importance of knowledge of the impedance spectrum of the battery if the improvements in DCA performance are to be achieved with maximum efficiency and effectiveness