The operation of the input IGBT input bridge rectifier significantly reduces lower order harmonics compared to conventional AC PWM drives with 6-pulse diode bridges (<50th harmonic). However, as an inherent nature it introduces significant higher order harmonics, above the 50th. In addition, the action of IGBT switching introduces a pronounced “ripple” at carrier frequencies (~2-3 kHz) into the voltage waveform which must be attenuated by a combination of AC line reactors (which also serve as an energy store that allows the input IGBT rectifier to act as a boost regulator for the DC bus) and capacitors to form a passive (also known as clean power) filter. As compared to conventional 6-pulse AC PWM drives of same rating, AFE drives have significantly higher conducted and radiated EMI emissions, and therefore, special precautions and installation techniques may be necessary when applying them. AFE drives are inherently “four quadrant” (i.e. they can drive and brake in both directions of rotation with any excess kinetic energy during braking regenerated to the supply), offer high dynamic response and are relatively immune to voltage dips.