Paul Imbertson

Asymmetrical duty cycle permits zero switching loss in PWM circuits with no conduction loss penalty

Operating a bridge-type PWM (pulse width modulation) switch mode power converter with asymmetrical duty ratios can eliminate switching losses with no increase in conduction loss. This circuit topology combines the best features of resonant (zero switching loss) and switch mode (low conclusion loss) circuits. Design equations are presented for just such a circuit.<<ETX>>

Restructuring of first courses in power electronics and electric drives that integrates digital control

Since 1994, the University of Minnesota has been undertaking a long overdue restructuring of power electronics and electric machines/drives courses. This restructuring allows digital control to be integrated into first courses, thereby teaching students what they need to learn, making these courses appealing, and providing a seamless continuity to advanced courses. By a concise presentation in just two undergraduate courses, this restructuring motivates students to take related courses in programmable logic controllers, microcontrollers and digital signal processor applications. This ensures a first-rate education that is meaningful in the workplace as well as in graduate education leading to a research and development oriented career. This restructuring has several components to it. Outdated topics that waste time and mislead students are deleted. To integrate control in the first courses, unique approaches are developed to convey information more effectively. In the first course in power electronics, a building block is identified in commonly used power converter topologies in order to unify their analysis. In the field of electric drives, the use of space vectors is introduced on a physical basis to describe operation of ac machines in steady state in the first course, and to discuss their optimum control under dynamic conditions in the advanced course. Appropriate simulation software and software-reconfigurable hardware laboratories using a DSP-based rapid prototyping tool are used to support the analytical discussion.

New directions in DC-DC power conversion based on idealized concepts leading ultimately to the asymmetrical duty-cycle power converter

Following the precepts of an ideal DC-DC power converter, the asymmetrical duty-cycle power converter, a zero-switching loss converter, is, in a demonstrable way, a new direction in DC power conversion. Its benefits include low conduction loss, low EMI generation, and lossless switching. This paper includes conceptual discourse on the nature of the asymmetrical converter, as well as experimental results.

New PWM converter circuits combining zero switching loss with low conduction loss

A new PWM (pulse width modulation) technique is presented and applied to two DC-DC power converters. The new converter topologies completely eliminate switching losses while retaining the low conduction losses typical of PWM circuits. The switches are operated for differing lengths of time, i.e., with unbalanced or asymmetrical duty cycles (for example, one switch at 40% and the other at 60%). The deadtime between switch conduction intervals is made long enough to insure that the switch voltages have commutated naturally from rail to rail, but not so long that the switch voltages have begun their return trip along their oscillatory path between the input rails. Thus, the best features of resonant (zero switching loss) and PWM (low conduction loss) circuits are combined. Design equations and notes are included for a buck type (step-down) and a boost type (step-up) converter.<<ETX>>

An efficient, low cost DC-AC inverter for photovoltaic systems with increased reliability

This paper presents a topology for photovoltaic inverters to convert the DC voltage to single phase or split-single-phase AC. The proposed modular approach helps to increase the reliability of the system by introducing redundancy while lowering cost by having identical modules in parallel to achieve different output power levels.

A novel asymmetrical duty-cycle soft-switching DC-DC converter with lower conduction losses than in hard-switched PWM converters

An asymmetrical duty-cycle DC-DC power converter was proposed recently, which allows zero-voltage switching while keeping the switch conduction losses as low as in standard hard switched PWM power converters. Further developments now allow the asymmetrical circuit to exhibit lower conduction losses than standard PWM circuits.

A method for estimating switch-mode power supply size

A method of estimating the physical size and layout of switch-mode power supplies is presented. This method includes analytical expressions for determining the physical size of inductors, capacitors, and transformers. The calculations are based on the black box input-output requirements of the power supply, and can be used to evaluate and compare competing design approaches or topologies. The technique is based on fundamental power supply parameters-power, energy, and electric charge-and avoids needless calculations during the initial estimation stage of a power supply design. Calculations using this estimation technique are presented for buck, forward flyback, and boost regulators.<<ETX>>