EMI emissions up to 1 GHz from adjustable speed drives

Electromagnetic interference (EMI) has always been a problem with motors and motor controllers. Older drives based on analog circuit technology generated EMI primarily at harmonic frequencies well below 1 MHz. However, within the last decade or so, the popularity of solid-state adjustable speed drives (ASD) has increased greatly, and such systems are being widely deployed. The new systems use pulse-width modulation (PWM) techniques and high-speed switching circuits to achieve better control and higher efficiency. Unfortunately, they also tend to generate EMI at much higher frequencies than older systems. As a consequence, EMI problems are beginning to appear in unexpected locations where new drives have replaced older technology (e.g., elevators and HVAC installations). This paper studies ASD-generated EMI at frequency ranges up to 1 GHz. It describes measurements made on inverters and ASDs that determine EMI frequency and time-domain characteristics. Tests include spectrum analyzer measurements as well as time domain power analysis using zero-span techniques. Tests are made at different lateral ranges within a building and in an open field, as well as within a building on different floors