Active Control of Variable DC-Link for Maximum Efficiency of Traction Motor Drives

Modern electric vehicles often interpose a DC/DC converter between traction battery and inverter, boosting the supply voltage of the drive. The power losses in the two converters and in the electric motor significantly vary with the DC-link voltage amplitude. In this work, a novel control algorithm is proposed to adapt online the DC-link voltage during vehicle operation, pursuing the maximum efficiency of the DC/DC converter and traction inverter without affecting the motor control dynamic. The key principle of the proposal, suitable for 3-phase and multi-three-phase drives, relies on the DC-link voltage minimization on varying the drive operating conditions. Among its advantages, the proposed variable DC-link control is independent of the motor parameters, the adopted torque/speed control strategy and the number of 3-phase sets of the drive. Although originally developed for electric vehicles, it can be adopted in a wide number of applications. Straightforward calibration roles are also provided. The proposed algorithm is deeply validated in simulation and experiments using a full-scale 135 kW 6-phase traction motor drive at TRL6.