Cycle-Skipping Technique based on Sigma-Delta Modulation for Power Regulation in Modular SRC-DCX

This manuscript investigates a sigma-delta–based cycle-skipping modulation strategy for power regulation and current sharing in modular series resonant DC transformers. The method enables continuous power control without changing the switching frequency, duty cycle, or phase shift, making it suitable for DC transformer architectures that normally operate in a load-independent manner. A modified cycle-skipping approach is introduced to maintain magnetizing current during idle intervals, thereby preserving soft switching across the full operating range. The sigma-delta modulator replaces the fixed burst patterns of traditional cycle skipping with a noise-shaped pulse distribution that improves control resolution and mitigates low-frequency ripple. A practical implementation on an STM32 microcontroller is presented, including a lookup-table-based mapping of the sigma-delta bitstream to hardware burst-mode registers. Experimental validation on a 1-kW SRC-DCX prototype confirms accurate power regulation. Later demonstrated that, when extended to a dual-module IPOP configuration, the method achieves effective current balancing, with a peak efficiency of nearly 98%.