A conversion device comprises: an inductor electrically connected to the AC power grid; a first-stage converter configured to output a bus voltage according to the AC power grid, wherein the first-stage converter comprises an N-level alternating current-direct current (AC-DC) converter, and the N-level AC-DC converter comprises a plurality of switch bridge arms, wherein both an upper bridge arm and a lower bridge arm of each of the plurality of switch bridge arms of the N-level AC-DC converter include a plurality of semiconductor devices connected in series, and a rated withstand voltage Vsemi of each of the semiconductor devices is greater than or equal to (Vbus*δ)/((N−1)*Nseries*λ); and a second-stage converter configured to convert the bus voltage into an output voltage to supply energy to the load.