Chi Kwan Lee

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.

General Analysis on the Use of Tesla's Resonators in Domino Forms for Wireless Power Transfer

In this paper, we present a brief overview of historical developments of wireless power and an analysis on the use of Teslas resonators in domino forms for wireless power transfer. Relay resonators are spaced between the transmitter and receiver coils with the objectives of maximizing energy efficiency and increasing the overall transmission distance between the power source and the load. Analytical expressions for the optimal load and maximum efficiency at resonance frequency are derived. These equations are verified with practical measurements obtained from both coaxial and noncoaxial domino resonator systems. To avoid the use of high operating frequency for wireless power transfer in previous related research, the technique presented here can be used at submegahertz operation so as to minimize the power loss in both the power supply and the output stage. We demonstrated both theoretically and practically that unequal spacing for the coaxial straight domino systems has better efficiency performance than the equal-spacing method. Also, the flexibility of using resonators in various domino forms is demonstrated.

Circuit-level comparison of STATCOM technologies

This paper performs a comprehensive circuit-level evaluation of four modern STATCOM systems, namely true-48-pulse and quasi-48-pulse STATCOMs, cascade multilevel and binary multilevel inverters. The comparison is based on a number of factors including circuit topology, harmonic distortion, system losses, GTO quantities, their specific applications, and other considerations. The theoretical results are verified by simulation with the use of MATLAB-Simulink Power System Blockset.

A 31-level cascade inverter for power applications

Power inverter modules fed with separate DC voltage sources of voltage ratio 1:2:4:8 are connected to form a cascade multilevel inverter. This new proposal combines the advantages of the static phase-shifter and chain-cell converter concept. Using the same number of power devices as a standard nine-level inverter, the proposed converter operates as a high-power digital-to-analog converter with 31-level resolution. Electrolytic capacitors used in the proposed inverter for providing the DC voltage sources will never be connected in opposite polarity in all cases, thus ensuring high reliability. The proposal has the potential for uninterruptible power supply and flexible AC transmission applications.

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.

Optimal operation of contactless transformers with resonance in secondary circuits

Contactless transformer is an essential element in inductive power transfer systems. To improve its efficiency performance, a resonant tank is normally formed at the secondary side by adding an external capacitor in series (SS) or in parallel (SP) with the secondary winding. In this paper, a mathematical analysis based on simplified circuit model is presented. It leads to the theory of the boundary frequency which can be used to determine the optimal operating range for SS and SP mode, respectively, from the efficiency point of view. Calculated and measured results have been given to verify the theory in a case study.

A randomized voltage vector switching scheme for three-level power inverters

In this paper, a feasibility study of a randomized space vector switching scheme for three-level inverters is reported. Based on the traditional space vector concept for pulse width modulation (PWM) inverters, the sequence of the space vector is randomized in this scheme. The overall vector, resulting from the randomization, is mathematically identical to that of the traditional space vector. It has been found that the randomized scheme can effectively spread the switching noise over a wide frequency range and at the same time keep the steady-state link capacitor voltage balanced. The proposed scheme has been implemented in real time in a digital controller and its features have been experimentally confirmed.

Investigation of the harmonic response of a photovoltaic system with a solar emulator

This paper proposes a solar emulator to imitate the output of a solar panel and introduces a novel approach to maximum power point tracking (MPPT). It is difficult to analyse the performance of a photovoltaic system, therefore, an emulator circuit which models the solar array under controlled conditions is required. A DC halogen lamp, where the brightness can be adjusted as required, will illuminate a single solar cell. The output of the solar cell is amplified to produce the characteristics of a large solar panel. A new methodology, the harmonic detection method (HDM) is investigated which aims to locate the maximum power point by examining the harmonics produced at different locations on the current-voltage characteristic curve

Printed Spiral Winding Inductor With Wide Frequency Bandwidth

Winding parasitic capacitance is a major factor limiting the bandwidth of an inductor. In this paper, 1) the traditional, 2) the alternating, and 3) the partial alternating winding methods are evaluated for the multilayer printed spiral winding inductors for megahertz operations. The self-capacitances of various winding structures are estimated by the summation of parasitic capacitance among the turns of a winding. The electric field energy distributions in the inductors are derived from the voltage profiles to illustrate the relative magnitudes of winding parasitic capacitances. The results show that parasitic capacitance reduction can be achieved by reducing stored electric field energy. The partial alternating winding method is found to have the widest frequency bandwidth with reduced number of through-hole vias for multilayer printed spiral winding design. The theoretical analysis has been confirmed with practical measurements. The results provide useful information for the optimal design of coreless or core-based high-frequency planar magnetics.

State of Health Determination: Two Pulse Load Test for a VRLA Battery

State of Health (SOH) is an important characteristic in determining the overall profile of a battery. SOH is a measure of the remaining full charge capacity of a battery with respect to its nominal or rated capacity. As a battery ages and is continuously charged and discharged, the chemical composition starts to degrade. Sulphation of the plates starts to occur and the condition of the battery deteriorates which leads to a decrease in capacity. SOH determination can aid in the optimisation of the battery and prevent the battery being over charged and over discharged. This paper describes a novel two-pulse load test to determine the SOH of a Valve Regulated Lead Acid (VRLA) battery. The measurement of the change in battery terminal voltage (ΔV) in the second pulse will alter as the battery ages in relation with the change in the maximum available capacity and this in turn allows the determination of SOH. Experimental validation of this new methodology is described in detail in the paper.