An LC-RC Filter for Multi-Phase Interleaved Buck Converter to Generate High Stability Magnetic Field

Nuclear magnetic resonance (NMR) and specific heat measurements demand a high-stability flat-top pulsed magnetic field (FTPMF). The multi-phase Interleaved Buck Converter (IBC), with its high power density and swift transient response, emerges as a promising solution for a compact FTPMF system. Yet, the PWM usage in IBC introduces output current ripple, limiting FTPMF's stability. This research introduces an LC-RC filter for ripple cancellation in IBC under magnetic loads. The proposed filter ensures cost-effective ripple cancellation in IBC with fewer passive components and reduces load oscillation risks. We present a frequency-domain model for IBC with an LC-RC filter, analyze its transient response, and deploy an optimization algorithm for LC-RC parameters selection. We take the variation of the passive components into account and propose a frequency correction method to further reduce the ripple. Simulations and experiments highlight the benefits of the filter as well as the feasibility of the frequency correction scheme.

I. Introduction

High stability flat-top pulsed magnetic field (FTPMF) is one of the essential experiment conditions in modern scientific research [1]. Flat-top stability is a key metric for FTPMF [2], [3], [4]. Due to supply voltage fluctuations and magnetic coil temperature increases [5], [6], FTPMFs produced by open-loop discharges from capacitors or batteries require closed-loop controlled active compensation networks for enhanced stability. However, these networks, with their significant power consumption or limited capacitor storage [7], [8], [9], are not only voluminous but also constrain the range of magnetic field adjustments.