A hybrid dual-phase step-up power conversion system includes a step-up converter apparatus comprising a first leg, a second leg, a first capacitor and a second capacitor, wherein the first capacitor and the second capacitor are cross-coupled between the first leg and the second leg, and a plurality of expansion circuits coupled to the step-up converter apparatus, wherein the plurality of expansion circuits is configured to increase a power conversion ratio of the hybrid dual-phase step-up power conversion system.