Experimental verification of optimal flux weakening in surface PM machines using concentrated windings

Previous analytical work has shown that it is possible to design surface PM (SPM) machines using fractional-slot concentrated windings to achieve wide speed ranges of constant power operation by satisfying the optimal flux-weakening condition. This paper presents a 6 kW 36-slot/30-pole concentrated winding prototype SPM machine that has been designed using a closed-form analytical technique developed specifically for this class of machines. Experimental testing of this machine has been carried out to determine its performance capabilities, including flux-weakening operation. Detailed comparisons between analytical, finite element analysis (FEA), and experimental results are presented that confirm the ability of fractional-slot concentrated winding SPM machines to achieve their high-speed operating objectives. Important issues including the machine's back-emf voltage at top speed, eddy current losses in the magnets, and inverter performance are analyzed and discussed in detail.