A Transient-State Lumped Parameter Thermal Model for Brushless Wound Field Switched Flux Machines

In this article, the transient-state lumped parameter thermal model (LPTM) of the wound field switched flux (WFSF) machine is characterized for the first time. The modeling methodology for the LPTM is given in detail, including the process of determining the parameters of the LPTM, based on which two LPTMs are compared with the experiments, i.e., the LPTM-I and LPTM-II without and with consideration of the practical winding position in the stator slot. It is found that the practical positions of the dc and ac coils in the slots are important to improve the accuracy of the LPTM, due to the existence of slot empty space caused by overlapped dc and ac windings. By considering the practical positions of the dc and ac coils in the slots, the maximum value of the absolute error between the LPTM model predicted temperature and the measured values of the ac winding are 3.4 degrees C, 5.23 degrees C, 3.18 degrees C, and 5.22 degrees C under dc test, steady-state test, cycling test-I, and cycling test-II, respectively, while they are 3.95 degrees C, 2.00 degrees C, 2.28 degrees C, and 4.89 degrees C for the dc winding temperature error. The average value of the absolute error between the LPTM model predicted temperature and the measured values of the ac winding are 0.88 degrees C, 1.25 degrees C, 0.85 degrees C, and 1.87 degrees C under dc test, steady-state test, cycling test-I, and cycling test-II, respectively, while they are 1.08 degrees C, 1.47 degrees C, 1.06 degrees C, and 2.73 degrees C for the dc winding temperature. The temperature of the WFSF machine during a 9-h experiment can be predicted in 27.8 s by the LPTM, which has a more than 1100 times faster calculation speed.