Error Analysis for Near-Field EMC Problems Based on Multipolar Expansion Approach

Devices using power electronics are ubiquitous today and they are unfortunately intrinsic sources of electromagnetic interference. To address these electromagnetic compatibility problems at the initial design phase, a predictive method based on multipole expansion in spherical harmonics of the near field around each device was developed. To determine the basic expansions of a given source, a dedicated measurement bench has been designed. In this paper, some important issues of this approach and the measurement bench are studied, especially the error analysis on the measurements and the inverse problems. Some experimental results are also shown in the end.

I. Introduction

With the advance of technology, electronic devices are moving in the direction of smaller size and increased power, which results in an increase of the electromagnetic interference (EMI) between two power electronic systems. These EMI may even cause malfunctions of the equipment. Hence, the issue of electromagnetic compatibility (EMC) becomes an essential activity in the conception of a new device. Conventionally, for the sake of the verification of the EMC norms, a large quantity of experimental tests is necessary after the production of a prototype. It causes additional costs and significant delays if the required standards are not reached. The origin of the problems is usually the magnetic near-field coupling. This coupling can be between components (intrasystem coupling) and also between systems (intersystem coupling). In order to solve this problem, a predictive method has been developed at Ampère Laboratory [1]. This method is based on the multipole expansion of the magnetic field around the device under test (DUT). The DUT can then be represented by an equivalent punctual source, which allows calculating the near-field coupling with other components.