Beyond 50 MHz Bandwidth Extension of Commercial DC-Current Measurement Sensors With Ultra-Compact PCB-Integrated Pickup Coils

The control of very high switching frequency power electronic converter systems featuring latest generation wide bandgap devices requires current measurements with a very high bandwidth (BW) to achieve high closed-loop control dynamics. One example is an ultrahigh BW
$\mathbf {4.8}$
MHz parallel-interleaved multilevel GaN inverter ac power source with a target large-signal output BW of
$\mathbf {100}$
kHz. This work investigates the combination of commercially available low-frequency (LF) Hall-effect current sensors (BW
$\mathbf {\approx 1}$
MHz) with suitable high-frequency (HF) sensors to extend the BW above
$\mathbf {10}$
MHz, i.e., enough to measure the HF inductor current. Based on a conventional PCB-integrated Rogowski coil, for the HF sensor, three improved pickup coil (PUC) geometries based on proposals in the literature are investigated. The LF and HF sensor signals are combined with a precision fully differential combiner circuit. Design guidelines for the HF sensors as well as the combiner circuit are presented and thereby the influence of mismatches and tolerances is examined. The performance of the proposed HF sensors is experimentally verified and compared with previous solutions based on galvanically isolated inductor voltage sensing and a current transformer. The PUCs reach a BW
$\mathbf {>50}$
MHz, which is an improvement by more than a factor of
$\mathbf {50}$
compared to the fastest available Hall sensor. Furthermore, it is proven that all investigated sensors are capable to accurately measure the triangular inductor current ripple in a hardware prototype of the aforementioned ac power source. In a final step, the influence of common-mode (CM) disturbances originating from fast
$\mathbf {{d}v/{d}t}$
switching transients on the sensor performance is analyzed. The presented current sensors achieve a CM rejection ratio of almost
$\mathbf {100}$
dB.