Abstract
One of the largest sources of power loss within a direct drive wind turbine generator is the copper loss due to ohmic heating in the stator coils. This paper presents a thermal analysis of additively manufactured conformal cooling channels in the stator back iron as a means of cooling the stator. Cooling through the stator body as opposed to direct liquid cooling of the coils in slots allows for easier generator assembly and isolation of magneto-electric components. Temperatures can be reduced leading to the ability to increase the current density or lower the copper loss. Conformal cooling channels provide an effective cooling solution that can be optimized and incorporated within standard industry cooling solutions. This paper compares cooling channel performance in several different configurations using design of experiments (DoE) and computational fluid dynamic (CFD) software. Three different cooling channel layouts were considered: parallel, series and honeycomb. The parallel and series layouts use parallel and series fluid flow respectively. The honeycomb layout incorporates a hexagonal pattern to uniformly distribute fluid. The series layout maintained a surface temperature of 31 °C while at the same flow rate the parallel and honeycomb layouts maintained temperatures of 160 °C and 155 °C respectively. At the selected flow rate of 168 L/min, the pressure drop for the series, parallel, and honeycomb configurations was 5239 kPa, 45 kPa, 414 kPa respectively. An analytical model was also created to compare the configurations within two leading industry cooling systems. The work suggests that additively manufactured conformal cooling channels incorporated into the stator of direct drive generators allows a reduction in winding temperature advantageous to direct drive electric machines.
