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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...
The application of predictive current control to a multilevel converter is explored for application in an aerospace starter-generator system to investigate how such as system may be used to limit the harmonic distortion in the starter-generator's stator current waveform and also at the point of common connection with the aircraft supply system. The proposed system is analyzed, and a prototype converter...
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 use of silicon carbide (SiC) semiconductor power devices has been studied and evaluated in a wide variety of converters. The work presented in this paper shows the performance of C2M SiC MOSFETs compared to Si devices operating as switching elements in a 5-level, single phase, multilevel converter. The paper describes the multilevel converter platform used to undertake the evaluation study and...
Grid-connected battery energy storage systems with fast acting control are a key technology for improving power network stability and increasing the penetration of renewable generation. This paper describes two battery energy storage research facilities connected to the UK electricity grid. Their performance is detailed, along with hardware results, and a number of grid support services are demonstrated,...
ICT equipment is usually replaced at regular intervals, usually before the equipment has failed, opening up the opportunity of providing a second-life through repurposing. In this paper we investigate the technical feasibility of repurposing the standard ATX power supply found in many desktop computers into a 12V battery charger. We provide an overview of the ATX power supply before describing how...
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...
This paper presents a technique for predicting the temperature response of a system to arbitrary power dissipation in its constituent elements under variable air-cooling. The thermal impedance is first characterised under the available range of cooling levels. This data is used to predict the thermal response directly. Practical results show good agreement with predicted temperature waveforms. The...
In this paper, epoxy/aluminium oxide powder composites designed for use as encapsulants are produced and thermally characterised. Experimental results obtained for a variety of filler concentrations, sample thicknesses and manufacturing methods are presented and compared to analytical and empirical models from literature. Further to this the effects of modifying analytical models using experimental...
Maximum power point tracking (MPPT) converters are often used to continuously track the optimum operating point of a solar panel. Due to their low-cost and ease of implementation, hill climbing (HC) MPPT methods based on the perturbation principles are most commonly used to extract the maximum power (MP). However, the efficiency of these methods are highly influenced by the continued oscillation around...
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