Abstract: A carrier synchronization method based on phase-locked loop (PLL) is proposed to address the issue of uncontrollable carrier phase in multi-module parallel operation of hydrogen production power supplies. This method employs a variable-period digital PLL with a segmented counter architecture to simultaneously regulate the AC/DC carriers' increase/decrease states and correct the DC/DC carriers' phases. Simulation results demonstrate that under conditions of asynchronous startup of power modules, inconsistent FPGA sampling cycles, power grid frequency fluctuations, and asynchronous DSP sampling and communication, the proposed method reliably achieve carrier synchronization and uniform phase-shifting. Specifically, the AC/DC carrier phase error is eliminated within at most half a carrier cycle, while the DC/DC carrier phase error is corrected within the least common multiple of two carrier cycles.