Man Hay Pong

Status of electromagnetic compatibility research in power electronics

Recent development and research trends related to the EMC/EMI issues in power electronics system are reviewed. Research activities on EMI characterization of power converters, the EMI power filter design, EMI suppression techniques for drive system and switching power supply, PCB layout, EMI modeling and simulation for power electronics systems are discussed separately in different sections.

Electro-magnetic interference (EMI) due to non-conducted coupling paths in switching mode converter

A simplified model which takes into account minimum coupling paths (MCP) for a switching mode power converter is presented. A minimum number of coupling capacitors are found which connect between all three terminals of a LISN and nodes of a converter circuit. Simulation that shows both inductive and capacitive coupling mechanisms may contribute substantial noise at the input.

A model to analyze and improve dynamic response of high light load efficiency multi-mode converters

Reduced switching frequency peak current mode is a popular method to boost up light load efficiency of isolated power converters. However, transient response decreases dramatically when low switching frequency is adopted. This paper covers small signal analysis of control scheme that peak current and switching frequency both modulated by the control signal. An interesting result is found that the control scheme can be decomposed into two parts: peak current mode part and frequency modulation mode part. At low switching frequency light load conditions the bandwidth from control to output is low. According to the proposed model, special design on voltage control oscillator is desirable to boost up the bandwidth at light load conditions. By the time domain concept the switching frequency should be designed to rise quickly during step up transient in order to overcome the drawbacks caused by low switching frequency and prevent transformer saturation. Experimental prototype Two-FET-Forward converter is build to verify the proposed idea.

Design and analysis on reduced switching frequency current mode control isolated power converters for light load efficiency

This paper focus on improving light load efficiency of isolated DC/DC converters. A mixed signal control platform is proposed to implement multiple-mode variable frequency control. An 8-bit Micro Controller Unit MCU is used in the platform to provide adaptive control schemes and cost effectiveness digital solutions. Small signal analysis is covered to explain frequency modulation effects. Control of isolation transformer flux swing to avoid saturation is also implemented, to provide safe operation both in steady and transient states. A 300 Watt prototype Two-FET forward converter is built up to verify the proposed mixed signal control platform.