Design of a High-Bandwidth Compact DC-Bus Embedded Planar Rogowski Coil for SiC MOSFET Current Sensing

This article quantitatively investigates the design considerations for a planar Rogowski coil. Within one printed circuit board (PCB), the Rogowski coil is placed between the overlapping dc-bus traces, the dc-link capacitor, and the half-bridge. This integration allows for measuring both dc-bus currents with one Rogowski coil, hence enabling the Silicon Carbide (SiC) mosfet switch transient current measurement of both half-bridge mosfets with one coil. A parametric mutual inductance equation and the Rogowski coil transfer function are proposed to simplify the design process of a planar Rogowski coil. Design considerations are evaluated. In additionally, the induced measurement error due to current crowding within the dc bus is investigated, and the impact of Rogowski coil windings exceeding the dc-bus trace width as a measure to reduce the mutual inductance error is explored and experimentally validated. A 106 mm(2) small planar Rogowski coil current sensor with a maximum bandwidth of 185 MHz is built. The prototype is evaluated for its parasitic parameters. Its current measurement performance is compared to that of a commercial Rogowski coil. Measurement results compare well between the planar Rogowski coil and the commercial Rogowski coil. In addition, measurements show that the mutual inductance of the proposed Rogowski coil is insusceptible to current crowding within the dc bus.