Abstract: A compressor unit is disclosed comprising at least a first motor driving in rotation at least one impeller of a compression stage, having at the outlet of the impeller a diffuser designed to centrifugally channel the gases coming from the impeller, and having a centripetal return channel downstream of the diffuser. The return channel includes at least one movable blade portion that, when moved, can vary a tangential component of the speed of the gases coming from the return channel.