William Gerard Hurley

State-of-Charge Determination From EMF Voltage Estimation: Using Impedance, Terminal Voltage, and Current for Lead-Acid and Lithium-Ion Batteries

State-of-charge (SOC) determination is an increasingly important issue in battery technology. In addition to the immediate display of the remaining battery capacity to the user, precise knowledge of SOC exerts additional control over the charging/discharging process, which can be employed to increase battery life. This reduces the risk of overvoltage and gassing, which degrade the chemical composition of the electrolyte and plates. The proposed model in this paper determines the SOC by incorporating the changes occurring due to terminal voltage, current load, and internal resistance, which mitigate the disadvantages of using impedance only. Electromotive force (EMF) voltage is predicted while the battery is under load conditions; from the estimated EMF voltage, the SOC is then determined. The method divides the battery voltage curve into two regions: 1) the linear region for full to partial SOC and 2) the hyperbolic region from partial to low SOC. Algorithms are developed to correspond to the different characteristic changes occurring within each region. In the hyperbolic region, the rate of change in impedance and terminal voltage is greater than that in the linear region. The magnitude of current discharge causes varying rates of change to the terminal voltage and impedance. Experimental tests and results are presented to validate the new models.

Optimized transformer design: inclusive of high-frequency effects

Switching circuits, operating at high frequencies, have led to considerable reductions in the size of magnetic components and power supplies. Nonsinusoidal voltage and current waveforms and high-frequency skin and proximity effects contribute to power transformer losses. Traditionally, power transformer design has been based on sinusoidal voltage and current waveforms operating at low frequencies. The physical and electrical properties of the transformer form the basis of a new design methodology while taking full account of the current and voltage waveforms and high-frequency effects. Core selection is based on the optimum throughput of energy with minimum losses. The optimum core is found directly from the following transformer specifications: frequency; power output; and temperature rise. The design methodology is illustrated with a detailed design of a push-pull power converter.

Calculation of self and mutual impedances in planar magnetic structures

The high frequency operation of magnetic components, in applications such as filters, makes them ideal candidates for thick film technology along with resistors and capacitors. This in turn leads to distinct advantages over labor intensive wire wound components: improved reliability, repeatability, accuracy and consequential cost reductions. This paper establishes a new set of formulas for the self and mutual impedances of planar coils on ferromagnetic substrates. A planar coil in air is a special case of the generalized formulas. The formulas are derived directly from Maxwells equations and therefore serve as a useful yardstick for simpler approximations. The formulas take full account of the current density distribution in the coil cross-section and the eddy current losses in the substrate. Experimental and calculated impedances up to 100 MHz are presented for a four layer device with three turns per layer which is 150 /spl mu/m thick and 40 mm/sup 2/ in area. >

A stand-alone photovoltaic supercapacitor battery hybrid energy storage system

Most of the stand-alone photovoltaic (PV) systems require an energy storage buffer to supply continuous energy to the load when there is inadequate solar irradiation. Typically, Valve Regulated Lead Acid (VRLA) batteries are utilized for this application. However, supplying a large burst of current, such as motor startup, from the battery degrades battery plates, resulting in destruction of the battery. An alterative way of supplying large bursts of current is to combine VRLA batteries and supercapacitors to form a hybrid storage system, where the battery can supply continuous energy and the supercapacitor can supply the instant power to the load. In this paper, the role of the supercapacitor in a PV energy control unit (ECU) is investigated by using Matlab/Simulink models. The ECU monitors and optimizes the power flow from the PV to the battery-supercapacitor hybrid and the load. Three different load conditions are studied, including a peak current load, pulsating current load and a constant current load. The simulation results show that the hybrid storage system can achieve higher specific power than the battery storage system.

Calculation of self- and mutual impedances in planar sandwich inductors

High-frequency planar magnetic components, employing thin film and thick film technology, have become important components in applications, such as filters and switching converters, due to their ease of manufacture and reliability. In a previous paper, the authors established a frequency dependent impedance formula for planar coils on a magnetic substrate that is infinitely thick. In this paper, two new impedance models are described: the first is for planar coils on a magnetic substrate of finite thickness, and the second represents a planar coil sandwiched between two substrates. The models include the electrical conductivity of the magnetic material so that the effects of eddy currents, particularly at high frequencies, are taken into account. The eddy currents reduce the inductance and increase the losses associated with the device. The new impedance formulas are derived from Maxwells equations. Simulations were carried out on a typical device, using finite element analysis, and the results validate the new formulas. This paper establishes the frequency limitations of lossy magnetic substrates.

Development, implementation, and assessment of a web-based power electronics laboratory

A Web-based laboratory exercise with remote access is presented, through which a student of Electrical/Electronic Engineering is introduced in both a theoretical and practical way, to many fundamental aspects of power electronics. The system is flexible and can expand the range of laboratory exercises where full-scale laboratories are not feasible. In the electrical environment, limits can be placed on voltages and currents for safety reasons. Prelaboratory investigations allow students to take an active involvement in the learning process by addressing some challenging and critical aspects of the design before approaching the physical system. Further understanding is gained by studying the circuit in a Web-based, interactive power electronics seminar (iPES) by simulating the circuit using PSpice and then analyzing the control and feedback issues with MATLAB. In the final stage, a real power converter is tested remotely over the Web, and the cycle of design, simulation, and test is completed using Web-based tools.

An Improved Battery Characterization Method Using a Two-Pulse Load Test

It is very important to have the ability to determine the available capacity, the state of charge (SoC), and the state of health (SoH) of a battery; this ensures that the battery has the available power for the system requirements. A battery is aged by charging and discharging cycles; this process degrades the chemical composition of the battery. An undercharged battery has sulphation and stratification effects that shorten the lifetime of the battery. Overcharging causes gassing and water loss. This paper describes a novel two-pulse test to determine the AHC, SoC, and SoH of a valve regulated lead acid (VRLA) and a lithium ion battery. These parameters are related to the voltage drop after each pulse of current discharge. The first pulse stabilizes the battery relative to its previous history, and the second pulse establishes the parameters. The new approach is fully validated by experiment.

Calculation of leakage inductance in transformer windings

A formula is presented to calculate mutual impedance between transformer windings on ferromagnetic cores. The formula is based on the solution of Maxwells equations for coils on ferromagnetic cores and as such offers the ultimate in accuracy. The formula is frequency dependent, taking into account the effect of eddy currents in the core on the flux distribution as well as representing the eddy current core loss as an equivalent resistance. Experimental results are presented for leakage inductance and an illustrative example is presented showing how leakage inductance affects the operation of a typical switching mode power supply. Approximations for the formula are also presented to simplify the calculations under certain operating conditions. >

Electromagnetic design of a magnetic suspension system

Magnetic levitation of a metallic sphere provides a high-impact visual demonstration of many principles in undergraduate educational programs in electrical engineering, e.g., electromagnetic design, compensation of a unstable control system and power amplifier design. This paper deals with the electromagnetic and dynamic analysis of the levitation system and it has design formulae which are derived from first principles. This analysis leads to a plant transfer function which is used to implement a proportional plus derivative (PD) compensation strategy. Issues covered include coil and wire sizing for a given temperature rise. The paper shows that the electromagnet can be optimized for a given sphere. An experimental system is described which levitates a 6 cm, 0.8 kg sphere.

Optimizing the AC resistance of multilayer transformer windings with arbitrary current waveforms

AC losses due to nonsinusoidal current waveforms have been found by calculating the losses at harmonic frequencies when the Fourier coefficients are known. An optimized foil or layer thickness in a winding may be found by applying the Fourier analysis over a range of thickness values. This paper presents a new formula for the optimum foil or layer thickness, without the need for Fourier coefficients and calculations at harmonic frequencies. The new formula requires the RMS value of the current waveform and the RMS value of its derivative. It is simple, straightforward and applies to any periodic waveshape.