Direct Coupling Method for Coupled Field-Circuit Thermal Model of Electrical Machines

A direct coupling method for coupled field-circuit thermal model of electrical machines is proposed, by which the temperature distributions in the lumped-parameter thermal network and finite-element region are solved simultaneously without iterative calculation procedure. Each thermal resistance in the lumped-parameter thermal network is seen as a one-dimensional finite element. The lumped-parameter thermal network and the finite-element region are linked with the two kinds of boundaries, namely: equivalent convective and equivalent temperature. The users can take advantage of both methods together for more accurate and efficient thermal modeling of the electrical machines using the direct coupling method. An outer-rotor permanent magnet machine with an uneven distribution of ac copper loss in the winding region is used to highlight the benefits of the proposed method. The proposed method is verified by comparing with the indirect method and experiments as well.