Abstract: In order to meet the refrigeration demand of space high-power Stirling refrigeration system under complex working conditions in orbit, it is necessary to solve the problem of real-time conversion of driving voltage frequency of refrigeration controller in orbit. In this paper, a frequency conversion strategy based on natural sampling method was proposed. An unsigned sinusoidal modulation wave was generated by looking up table method and multiplexing quarter-cycle sinusoidal wave. An unsigned triangular carrier was created synchronously by parallel process. And the duty cycle changing according to sinusoidal law was generated through cross comparison. Based on impulse equivalence principle, SPWM wave was obtained by filtering. The frequency conversion designs in command mode and in automatic mode were realized by means of iterative division and state machine alternating transfer respectively. The frequency conversion accuracy of both modes reaches 0.1 Hz. The feasibility of this scheme has been verified by simulation and system experiments, as well as on-orbit verification of the refrigeration controller of infrared optical camera.