Optimizing variable DC link voltage for an induction motor drive under dynamic conditions

Induction motor drives are conventionally operated with a fixed inverter dc-link bus voltage. However, low drive speeds will result in low modulation index and poor dc bus utilization of the inverter. Aperiodic current controllers, such as hysteresis controllers, exhibit increased switching frequencies and losses for higher dc-link voltages. These high switching frequencies can be avoided by dynamically varying the dc-link voltage according to drive operating conditions. In addition to reducing inverter switching losses, varying the dc-link voltage also reduces the switched voltage magnitude across inverter semiconductor switches, potentially increasing inverter reliability. In the proposed work, the link voltage is varied by using a front-end dc-dc buck converter. The link voltage command is derived using a loss minimization technique that uses flux and rotor speed commands to the drive. The effect of additional loss from the front-end converter on the total loss is also investigated. Simulation and experimental results indicate that a variable dc-link voltage supports substantial power electronics loss reduction in applications with highly varying speed conditions.