Reduction of variable speed drive IGBT switching loss, utilising the IGBT gate drive, without increasing radio frequency radiated emissions

Abstract

Radio frequency radiated emission from a variable speed drive must be limited below defined limits to avoid interference with electronic equipment. It is possible to comply with the international standards however, the current state of the art methods such as large gate drive resistance and output filters significantly reduce the efficiency or increase the cost of the products. It is known that the main source of emissions emanate from the switching transients associated with the output power semiconductors, however the exact mechanisms and specific sources are unknown. This thesis examines the interaction of power devices during the switching transient identifying features which can be controlled by a sophisticated gate drive design. Analysis of the frequency content of the signals is presented together with methods to minimise power losses while maintaining compliance with radiated emission standards. A research program has been undertaken to identify the sources responsible for radiated emissions and predict a figure of merit as an indication of compliance. Measuring radio frequency content on high voltage and current signals is difficult and several techniques to accurately achieve this are presented. Simple passive gate drive solutions which can be easily implemented are examined along with a discussion on more complicated optimised solutions.