Nasser H. Kutkut

Design considerations for charge equalization of an electric vehicle battery system

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 power 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.

Charge equalization for an electric vehicle battery system

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.

Design considerations and topology selection for a 120 kW IGBT converter for EV fast charging

Fast charging of electric vehicles (EVs) 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 (IGBTs) 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.

Nondissipative current diverter using a centralized multi-winding transformer

Series connected battery strings are prone to dramatic reduction in life if individual cells are not maintained at the same charge level. This can be achieved by diverting the excess energy around fully charged cells while continuing to charge undercharged ones. Nondissipative current diverters provide a means to divert the charging current away from a fully charged cell to the weak cells in the stack in a nondissipative manner. This allows the rest of the stack to be fully charged while avoiding overcharging healthy cells. This paper presents a new technique for equalizing a series battery stack using a nondissipative current diverter.

Optimal air-gap design in high-frequency foil windings

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 magnetomotive force (MMF). Fringing fields can cause additional AC winding losses, and care must be taken to minimize these losses. In this paper, the effect of air-gap design on the induced losses is investigated. In particular, three air-gap designs-lumped, discretely distributed and uniformly distributed-are investigated and evaluated. Both one-dimensional (1-D) and finite-element analyses (FEAs) are used to investigate the different design structures.

An improved full bridge zero-voltage switching PWM DC-DC converter using a two inductor rectifier

An improved full bridge ZVS (zero-voltage switching) PWM (pulse-width-modulated) converter using a two inductor rectifier DC/DC power converter is presented. For this improved topology the main devices are switched on under ZVS conditions using the energy stored in the secondary filter inductors. 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 range with ZVS, no lost duty cycle due to diode recovery, no secondary voltage spikes, and to high power density and high efficiency.<<ETX>>

Current mode control of a full bridge DC-to-DC converter with a two inductor rectifier

In this paper, both peak current mode and average current mode control schemes are investigated as applied to a full bridge PWM converter with a two inductor rectifier. The two inductor rectifier circuit offers reduced secondary side current rating and is most suitable for high current applications. With current mode control, the two inductor rectifier is modeled as two parallel connected buck converters.

A generalized program for extracting the control characteristics of resonant converters via the state-plane diagram

This paper presents a generalized computer program that can be used to derive the control characteristics of resonant power 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 power converter topology. These characteristics are essential in determining the design parameters such as the power converter gain, component stresses and the 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. >

Analysis of winding losses in high frequency foil wound inductors

The design of high power and high frequency foil wound inductors is not a straightforward task. At high frequencies, additional losses occur within the foil windings due to the eddy currents induced by skin, proximity, fringing and other AC effects. In addition, the winding structure greatly affects the distribution of losses within the windings. In this paper, the various loss mechanisms of a foil winding are analyzed and quantified. Both analytical and finite element analysis tools are utilized to investigate and understand the different loss mechanisms. The results show a strong correlation between the current and field distributions within the windings where the current is always attracted to the high field regions. By shaping and controlling the field distribution in a given design, the current distribution can be improved which results in an improvement in the winding losses.

Optimal air gap design in high frequency foil windings

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 magneto motive force. 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 is investigated. In particular, three air gap designs: the lumped, the discretely distributed, and the uniformly distributed air gap designs are investigated and evaluated. Both one-dimensional and finite element analyses are used to investigate the different design structures.