Dynamic DC-link voltage adaptation for thermal management of traction drives

Power density and reliability specifications for motor drives in traction applications are getting increasingly stringent. The main challenge in meeting these conflicting requirements, is managing heat dissipation. A drive´s peak torque rating is limited by switching device temperatures which must be kept below critical values at all times for the sake of reliability, preferably without major hardware adaptations. In this challenge lies a large potential for advanced control algorithms. This paper proposes a PMSM drive control strategy which combines active thermal management with dynamic DC-link voltage adaptation. The bus voltage level is adjusted to the required PMSM terminal voltage in each operating point. Doing so, switching losses can be reduced at low speed by lowering the bus voltage. At high speed, the voltage level is boosted and field-weakening operation and the associated additional losses are avoided. An 11 kW PMSM drive, with an active front-end controlling the bus voltage, is used as a test setup to mimic a series-hybrid drivetrain. Compared to a fixed DC-link voltage, efficiency maps show a significant inverter loss reduction at low speed. This results in lower switching device temperatures which in turn allows a higher peak torque rating.