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A charge equalization method for a series of string of battery cells has been proposed. This technique uses a simple isolated dc-to-dc converter that has a capacitive output filter and a multiwinding transformer. Its use during charge equalization of an electric vehicle battery system reveals that it improves the uniformity of the battery cells, and thus, prolong battery life. Furthermore, the cost of its application was found to be reasonable.

This paper presents a simple technique for evaluating the ac losses of magnetic windings including two-dimensional (2-D) edge effects. Although one-dimensional (1-D) analysis tools have been developed to evaluate winding losses in conductor windings, the additional ac losses due to 2-D edge effects are quite significant and cannot be predicted by the developed 1-D solutions. The proposed approach is based on introducing a set of correction factors for the 1-D analysis results to account for the 2-D edge effects. Finite-element analyses (FEA's) will be utilized to validate the obtained results. Index Terms - Edge effects, foil windings, high-frequency ac losses, two-dimensional analysis.

High-frequency ac losses are normally induced in transformer and inductor windings due to skin, proximity, fringing, and other ac effects. In addition, the winding structure greatly affects the distribution of losses within the windings. Air gaps are usually placed in the core of magnetic devices to support the high magnetic motive force (mmf). Fringing fields can cause additional ac winding losses, and care must be taken to minimize the additional losses. In this paper, the effect of air-gap design on the induced losses will be investigated. In particular, three air-gap designs - lumped, discretely distributed, and uniformly distributed - will be investigated and evaluated. Both one-dimensional (1-D) and finite-element analyses (FEA's) are used to investigate the different design structures. Index Terms - Air-gap design, foil windings, high-frequency ac losses, skin and proximity effects.

Charge equalization for series connected battery strings has important ramifications on battery life. It enhances the uniformity of the battery cells and hence improves the life of the battery as a whole. A new charge equalization technique for a series string of battery cells has been recently proposed by the authors. The basic technique utilizes a simple isolated dc-to-dc converter with a capacitive output filter along with a multiwinding transformer. The possibility of integrating the trickle charge function with the charge equalization function is potentially very attractive, as it can lead to an efficient and low cost implementation.

The design of high-power inductors for applications with broad current spectrum excitation is a challenging task. The resonant inductor of a resonant dc-link inverter (RDCLI) is one such example. The inductor current consists of a resonant current component, a dc component, which supplies the active power to the load and a modulation component, which depends on the modulation strategy. In addition, the frequency and amplitude of the dominant current components change with operating point. Conventional inductor designs for single-frequency excitation do not perform well in broad-spectrum applications. In order to improve these designs, the impact of broad current spectrums on winding design, core selection, power density, and thermal-handling capability must be investigated. In this paper, alternate inductor topologies, which better address the above issues, are proposed and investigated. Index Terms - High-frequency magnetics, inductor design, resonant dc-link inverter, strip windings.

Fast charging of electric vehicles (EV's) is a very desirable feature, especially for long-distance travel. For an EV with a battery capacity of 30 kWh, a 15-min charge requires 120-kW charging power. Inductive charging offers a safe and convenient means to accomplish this task. This paper investigates the design criteria of the high-power converter for a 120-kW inductive battery charger. Since insulated gate bipolar transistors (IGBT's) are the devices of choice at this power level, the impact of IGBT losses on the converter design and topology selection is investigated. A comparison between a zero-voltage-switching (ZVS) and zero-current-switching (ZCS) series-resonant converter (SRC) is presented. Based on the comparison results, a ZCS SRC topology is selected for this application, and an experimental 120-kW/75-kHz unit was built and tested in the laboratory to verify the results. Index Terms - Electric vehicle charging, series-resonant converters, zero-current switching, zero-voltage switching.

This paper presents a generalized computer program that can be used to derive the control characteristics of resonant converters from their state-plane trajectories. It has been shown that the geometrical properties of the state-plane trajectory can be used to derive the control characteristics of a given resonant converter topology. These characteristics are essential in determining the design parameters such as the converter gain, component stresses, and required feedback controller. The main program consists of several subroutines, each of which is associated with a segment of the state-plane trajectory. Such a program will make it faster and easier for a design engineer to obtain the design parameters of any given resonant topology. Index Terms - Frequency control of resonant converters, resonant converters, state-plane analysis.

A simple technique that provides charge equalization for a series string of battery cells is presented. The advantages of accurate charge equalization are very substantial and include reduced damage to battery cells in the stack, and a dramatic increase in battery life. The basic technique utilizes a simple isolated dc/dc converter with a capacitive output filter along with a multi-winding coaxial winding transformer (CWT). The coaxial winding transformer is known for its low and controlled leakage inductance. The transformer leakage inductance is used as the main driving impedance to control the total charging current for the individual cells. The use of one low-power converter to obtain charge equalization for the entire battery string is very attractive and leads to a low cost implementation.

An improved full-bridge ZVS PWM using a two-inductor rectifier dc/dc converter is presented in this paper. For this improved topology, the main devices are switched on under zero-voltage (ZVS) conditions using the energy stored in the secondary filter inductors. In addition, it utilizes the low leakage inductance of a coaxial winding transformer to reset the currents in the rectifier diodes and eliminate the secondary voltage spike. The two-inductor rectifier has only one diode conduction drop in addition to frequency doubling in the output capacitor. The secondary filter size in the proposed topology is rather small. The advantages of the new topology include a wide load range with ZVS, no lost duty cycle due to diode recovery, no secondary voltage spikes, in addition to high power density and high efficiency.