Adaptive Operating Strategy for Induction Motors Under Changing Electrical-Thermal Conditions

Besides precise motor control, a suitable operating strategy is required for a highly efficient operation of an induction motor. Especially due to the present extensive use of these motors in torque-controlled applications, e.g., electric vehicles, efficiency improvements by optimizing the operating strategy are of prime interest. Most model-based operating strategies in the literature use simplified motor models or offline optimized look up tables, so that they are generally not able to adequately consider all loss effects in the entire operating range of the drive. In contrast, this paper presents an adaptive operating strategy that takes into account all relevant losses and changing system conditions (e.g., temperature, DC-link voltage) at runtime. Using a precise electrical-thermal motor model identified offline, the changing system states are adapted online and the resulting nonlinear optimization problem for loss minimization is solved iteratively. Experimental validation demonstrates the efficiency improvement of the adaptive operating strategy – Over the entire constant torque range, the efficiency of an industrial motor can be increased by an average of 0.7 percentage points compared to a standard operating strategy.