Grid disturbance rejection via improved DC-Link voltage feedforward control for L-Bend power supplies in the APS upgrade

As part of the Advanced Photon Source Upgrade (APS-U), two high-power DC supplies for the L-Bend M1 and M2 magnets were installed. During the APS-U commissioning, a 1 Hz ripple was detected in the output currents of the M1/M2 and slow corrector supplies, leading to 1 Hz beam motion. This low-frequency harmonic originated from the booster ramping supply operating at 1 Hz, causing periodic grid voltage sags. This paper proposes an improved DC-Link voltage feedforward control for the M1/M2 supplies to reject grid disturbances, significantly attenuating the 1 Hz and other low-frequency ripples in the output currents. Combined with regulation circuit modification of the slow corrector power supplies, the 1 Hz harmonic was successfully eliminated from the beam motion.