Design of an Integrated Air Coil for Current Sensing

This article proposes a design procedure of an integrated air coil in a laminated bus bar for current sensing. The concept is based on an air coil inserted into the insulators inside the laminated bus bar, avoiding the use of intrusive current sensors with an additional stray inductance. First, the basic principle of the integrated current sensor is described, and the relationship between the mutual inductance and the structure of the air coil is discussed. Next, the frequency characteristic of the current sensor obtained based on an equivalent circuit is detailed, the parameters of which are derived from the sensor structure. A postprocessing method is proposed to achieve a 100-MHz frequency bandwidth. A prototype of the current sensor is designed based on the proposed design procedure, and the frequency characteristic is evaluated. The validations of the design procedure and the postprocessing method are confirmed experimentally.

I. Introduction

With the practical use of Silicon Carbide and Gallium Nitride, the recent power devices have improved dramatically. Such devices make the circuit possible to operate at a higher switching frequency compared with the use of conventional devices. This allows an increase of power density, by reducing the size of the passive elements [1], [2].