High Sensitivity Current Transformer with low Settling Time, for Magnified AC Current Measurements in Pulsed Applications

Abstract

In solid-state pulsed power systems based on switching converters often a low amplitude, high frequency ripple current is superimposed on the high flat-top pulse current. Despite its low amplitude (usually measured in ppm) the ripple current could have a major impact on the performance of the system and therefore needs to be quantified/reduced. However, measuring such currents is challenging, due to the limited resolution of the current probe, especially when the DC offset current of the pulse is in the kA range. Therefore a suitable AC current probe able to perform magnified ripple current measurements with high fidelity is proposed in this paper. The probe is based on the principle of current transformers and filters the DC offset of the pulsed current, enabling to measure the ripple with a very high resolution. The design trade-offs of the conventional CT for such an application are explained, and an adaptive burden resistance topology is proposed in order to achieve simultaneously a low settling time, which is essential for measuring short pulses, and the needed high sensitivity, while maintaining a relatively high bandwidth.