Motor Thermal Model for Aging Control Applications

Abstract

Deeper integration of renewable energy sources on the electric grid has increased flexibility requirements across power systems, from generation to transmission/distribution and consumer equipment. On the consumer end, the use of variable-speed electric motors in commercial and residential heating, ventilation, and air-conditioning (HVAC) applications is becoming widespread due to their energy and cost-saving benefits compared to single-speed motors. However, the enhanced features and operational flexibility of these modern motors may come at the cost of increased thermal stress on the motor components, particularly the stator winding insulation. To address this challenge, this thesis presents the development of a generic Lumped Parameter Thermal Network (LPTN) model that can accurately capture the thermal behavior of induction motors under dynamic and varying speed and load conditions. The LPTN model parameters are systematically tuned and calibrated using test data from laboratory tests covering different speed and load settings, achieving a maximum error of 4.8°C between the model predictions and experimental measurements for a 3 HP test motor. The dynamic, modulating control of the motor leads to winding temperatures 7.3°C higher than that under constant-speed control, showing significant aging effect of dynamic operation of motors due to flexibility provision. The calibrated thermal model and the physical 3 HP motor are tested under constant and modulation speed control cases. The thermal model is able to predict the hot spot temperature difference between these two test cases for the test motor with an accuracy of 0.2°C, validating the model’s capability to accurately replicate the change in the thermal behavior of the case study motor. This generic, calibrated LPTN model can serve as a powerful tool to facilitate faster and more cost-effective development of control strategies and maintenance plans for variable-speed electric motors, ultimately improving their reliability and energy efficiency in a wide range of commercial and residential applications.