Multiphase Buck converter (MBC) is widely used in many dc-dc applications due to its low output ripple and highpower capability. However, the advantage of ripple cancellation is limited by the asymmetry in each phase, mainly the tolerance of inductors and drivers. This nonidealities will cause a significant switching frequency component (fsw component) in the spectrum of MBC's output current ripple. A novel threepoint perturbation-observation (3p-PO) algorithm is introduced to cancel the fsw component. Additionally, to eliminate the need for high-resolution and high-speed ADCs, a fsw component extraction circuit is designed to obtain a high-sensitivity DC signal for the fsw component. A 4-phase MBC prototype is developed to validate the effectiveness, demonstrating significant ripple suppression in the output ripple with only 8 adjustment intervals.