Parallel-Cascaded Narrow-Band Adaptive Digital Active EMI Filters for Broadband CM-Noise Reduction in Motor Inverters

Motor inverters with periodically operated fast-switching semiconductor devices can cause high electromagnetic interferences (EMI) in a large frequency range. Conventionally, EMI is reduced using passive filters. High weight and large volume of such filters complicate the application in aerospace or automotive. Analog or digital active EMI filters (AEF/DAEF) can be promising alternatives. In periodically operated systems, much higher frequencies could be reached with digital compared to analog active EMI filters. Several approaches therefore have been proposed. One promising suppression method for periodic noise synthesizes an appropriate compensation signal from a set of continuously adapted sine waves. This narrow-band adaptive DAEF (NADAEF) is limited in its bandwidth, even with fast digital signal processing units only some kHz could be reached. Parallel operation of a set of NADAEFs with different center frequencies can enlarge the bandwidth. Since the needed adaption algorithm results in additional harmonics, this approach has so far been limited to special applications with larger noise-free frequency ranges. The broadband noise of motor inverters could only be compensated in some selected cases. In this article, for the first time, a large set of NADAEFs is combined in a newly developed parallel-cascaded structure to reach broadband CM-noise reduction on the supply lines of two different motor inverter systems. This new filter system is discussed and analyzed regarding the suppression performance and its capability to react to motor speed changes. The system shows reliable suppression performance over a larger bandwidth of more than 500 kHz. Changes in the inverter operation mode could be compensated within a very short time. Noise reductions of up to 37 dB at 2 MHz could be reached.