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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...
Multilevel converters are an emerging industrial technology and are the subject of a substantial amount of research. However, they are yet to find their way into many mainstream engineering applications. This paper presents a method of quantifying the benefits and disadvantages of multilevel converters of increasing order. The analysis focuses on the cascaded H-bride topology for grid-tie battery...
In 2013, the University of Sheffield commissioned a 1 MWh lithium-titanate (LTO) battery energy storage system (BESS), directly connected to the grid through an 11 kV feed. With a view to later on develop a comprehensive model structure for the whole battery pack — key to many online battery management system (BMS) operations — in this paper, an in-depth frequency-domain analysis is performed on one...
This paper presents the results of a series of tests to determine the influence of high-frequency injected ripple currents on the Dynamic Charge Acceptance (DCA) performance of lead-acid batteries. A wide-bandwidth battery model is described, this being a hybrid of the standard Randles model and a high-frequency model previously described in literature. A bespoke test procedure is described, based...
There is an increasing prevalence of energy storage systems on the electricity grid network. However, as of yet, there is no overriding standard on how to deal with DC arc-flash calculations and subsequent determination of the PPE requirements for a DC system within the UK. This paper compares various published DC arc-flash calculations using a case study based approach. The paper uses data available...
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...
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...
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...
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...
The use of wireless technologies to power devices has many practical benefits however it is commonly disregarded due to losses in transferring power in this way. The most common method for wireless power transfer is via Strongly Coupled Magnetic Resonances (SCMR), which transfers energy by using the mutual inductance between coils. Generally, to achieve a high efficiency wireless power transfer the...
The open-circuit voltage (OCV) forms the basis for many real-time state-of-charge (SOC) estimation algorithms. The OCV-SOC relationship for most battery chemistries often provides a good estimate for SOC. However, for the lithium-ion iron phosphate (LiFePO4) variation of the lithium-ion cell chemistry, the OCV curve is fairly flat over the operational SOC range. Thus, even the smallest error in the...
The high cost of batteries has led to investigations in using second-life ex-transportation batteries for grid support applications. Vehicle manufacturers currently all have different specifications for battery chemistry, arrangement of cells, capacity and voltage. With anticipated new developments in battery chemistry which could also affect these parameters, there are, as yet, no standards defining...
A sensitivity analysis for a two time-constant Randies' circuit model to its forming resistor-capacitor elements is presented. The model parameters are identified for a cylindrical lithium-ion iron phosphate cell using the electrochemical impedance spectroscopy technique and a nonlinear least squares approach. Initially, it is shown that the model parameters vary as a function of the battery's state-of-charge...
Despite the many advantages of rechargeable batteries, their capacity degradation and state-of-health (SoH - ability of a battery to provide its nameplate discharge capacity over its lifetime) remains an issue in most power applications. The SoH is a qualitative measure of the battery's charge storage capability, which is a key factor in determining the battery's end-of-service-life, thus preventing...
In order for successful second-life implementation of Electric Vehicle (EV) battery packs, the viability of the intended second-life use must be ascertained based on a cost-benefit analysis and technical appraisal of the estimated condition of the available battery packs. This paper discusses the issues in measuring State-of-Health (SoH) and other battery condition metrics of a battery pack. Measurements...
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