This paper proposes an improved control strategy for a quasi-Z-source inverter (QZSI)-fed permanent-magnet synchronous machine (PMSM)-based electric vehicle. The proposed strategy aims to improve efficiency of the powertrain with this particular dc/ac converter. For this purpose, it is proposed to adapt in real time the dc-bus voltage to the mechanical speed of the machine. The strategy is realized by implementing a control method based on the flatness properties of the system. These particular properties allow mastering all the state variable or input variable trajectories, which is interesting in the present case where the dc-bus voltage trajectory has to be well known. In order to increase the control dynamic, a one-loop flatness-based control is implemented. The structure thus allows increasing the controller bandwidth that helps in reducing the size of the dc-bus capacitors. Simulations and experiments on a 500-W powertrain are carried out to show that the proposed control strategy is effective and provides an efficiency improvement.