SOFTWARE WAITING LOOP LENGTH CONTROL - TECHNIQUE FOR REDUCTION OF RADIATED EMI FROM MICROPROCESSOR-BASED PWM DRIVE SYSTEM

A novel technique, referred to as software waiting loop length control (SWLLC), for reducing the radiated EMI from microprocessor-based PWM drive systems is presented. By randomly changing the length of the sof tware waiting loops, the energy concentrated into discrete bands by th e action of periodic signals on the external and internal buses of the microprocessor system can be spread across a larger frequency range. Using this technique, significant reduction of radiated interference l evels has been observed in a typical PWM drive system.