Comparative Study of Stator-Mounted PM Machine With Forced Liquid Cooling

This paper investigates the thermal performance of some stator-mounted permanent magnet (PM) machines under forced liquid cooling. For reference, a conventional surface-mounted PM (SPM) machine is also analyzed. Three typical stator-mounted topologies are considered: the doubly salient PM (DSPM), flux reversal PM (FRPM), and flux switching PM (FSPM) machines. Initial evaluation with a water-jacket system demonstrates that stator-mounted machines achieve lower magnet temperatures than the rotor-mounted SPM machine. The extended modular FSPM machine further benefits from the flux gaps between the stator segments, which enhance heat dissipation and make it especially effective for liquid cooling. Several advanced cooling strategies are then proposed, showing improved performance compared with the standard water-jacket due to increased contact area. Moreover, the modular FSPM design enables semi-flooded cooling by utilizing the flux gaps between stator segments as cooling channels. Under this approach, water is shown to be significantly more effective than oil as a coolant. The results also indicate that the optimal flux gap width for maximum cooling performance depends on both coolant properties and inlet conditions.