05. - 07.06.2018
PCIM Europe 2018
Power Electronics | Intelligent Motion | Renewable Energy | Energy Management


Seminar 2

Diagnosing and Locating Sources of EMI in Switchmode Power Converters


Sunday, 03.06.2018, 14:00 - 17:30 hrs


Arvena Park Hotel Nuremberg, Görlitzer Str. 51, 90473 Nuremberg


14:00 Diagnosing and Locating Sources of EMI in Switchmode Power Converters
B.Sc. Bruce Carsten, Bruce Carsten Associates, Corvallis, USA
The instructor advocates that a power converter be designed for low EMI from the beginning, but he realizes that it can take many years of experience to "get it right the first time", or even come close. A central problem is that EMI is a very "low energy" phenomena, with only 8 to 80 nW of conducted EMI allowed below 30 MHz at any given frequency (depending on the applicable standards), with similar constraints on radiated EMI above 30 MHz. These limits generally apply regardless of converter power level, so a 10 kW converter has 1.000 times tighter limits than a 10 W converter, with 0.8 to 8 pW per watt output allowed. Consequently, the sources of EMI are easily overlooked as trivial by the less experienced engineer.

Failure to meet EMI standards can be found "the hard way", by paying for an EMI lab to find out for you (and they will not be able to advise you how to fix it). Alternatively, with a relatively modest investment in equipment, your can first get a reasonable estimate of the conducted and radiated emissions level, and then, with very little more equipment, begin to track down the origins.

Conducted EMI is measured with a LISN (Line Impedance Stabilization Network) on each power input, and with these can be measured yourself with a spectrum analyzer, a tunable voltmeter, or even an oscilloscope with an FFT (fast Fourier transform) capability. However, this measurement is the vector sum of common (longitudinal) and differential (transverse) mode currents, which are generated by completely different phenomena. A transformer circuit will be presented which can simultaneously separate the LISN outputs into mutually isolated common and normal mode currents, allowing their sources to be tracked down individually. Typical sources of both will be described, and methods to minimize each presented.

The instructor has found that radiated noise is almost invariably generated by common mode currents in the input (and/or output) power lines, using these lines as a radiating antenna. "Exceptions" can occur with: common mode currents on other lines, such as control or communication lines; normal mode currents on widely separated input or output power lines; or (rarely) direct radiation form an unenclosed power converter.

The sources of these currents are largely the same as for conducted EMI and, to some extent, can be found from the separated LISN outputs, but HF current transformers are better suited to this task due to the high frequencies which may be involved. Suitable constructions of current transformers for common and normal mode currents will be described.

Who should attend?
This seminar is directed towards the engineer, technologist or technician who needs to locate sources of EMI in a switching power converter so that, once found, they can be remedied.


Speaker detail

Mr. Bruce Carsten
B.Sc. Bruce Carsten
Bruce Carsten Associates, Corvallis, USA
Bruce Carsten has 48 years of design and development experience in switchmode power converters at frequencies from 20 kHz to 1 MHz. In 1982 he designed a 48 Vdc, 200 A, 50 kHz natural convection cooled switchmode telecom rectifier which met the FCC Class A requirements for conducted and radiated emissions. His seminars target the practicing design engineer, and emphasize an intuitive understanding of phenomena involved.