FPGA-based 2nd-order sigma-delta A/D converter for current measurement for resonant power converters

This paper presents a second-order sigma-delta (ΣΔ) analog-to-digital converter for measuring magnitudes of interest in power converters. The ΣΔ modulator has been implemented using discrete components and the digital system is embedded in an FPGA. The desired signal is extracted from the bit-stream output of the ΣΔ modulator by a digital low-pass filter structure. An optimized structure is proposed for this filter to improve the accuracy while having low hardware resources consumption. The analytical and simulation results have been tested through a resonant power converter applied to domestic induction heating whose switching frequency varies from 40 kHz to 75 kHz. The experimental results of current measurements show a good accuracy in the whole operating range.