Generation, control and regulation of EMI from AC drives

Adjustable speed AC drive (ASD) manufacturers recently migrated from bipolar junction transistor (BJT) semiconductors to insulated gate bipolar transistors (IGBTs) as the preferred output switching device. The advantage of IGBTs is that device rise/fall time switching capability is 5-10 times faster, resulting in lower device switching losses and a more efficient and smaller drive package. However, faster output dv/dt transitions and higher drive carrier frequencies increase the magnitude of common mode (CM) electrical noise and electromagnetic interference (EMI) problems. Experience suggests all PWM drives with steep fronted output voltage waveforms have these problems. This paper provides a basic understanding of EMI generated by these drives solutions to control EMI, as well as regulation standards on allowable conducted and radiated emissions to insure a successful drive system installation.