Characterization of a Variable Flux Machine for Transportation Using a Vector-Controlled Drive

Variable flux machines (VFMs) have one more dimension for the control and performance improvement of the drive. The magnet flux in the VFM can be controlled to optimize motor performance. Software packages used in the design and performance evaluation of variable flux permanent magnet (PM) machine use a single demagnetization curve and recoil the operating point based on a linear recoil line parallel to the original demagnetization curve. Since the magnets like AlNiCo that is used in VFM have a nonlinear demagnetization curve, performance prediction of a VFM designed using finite-element software needs experimental verification. This paper presents a method based on vector control for the characterization of a VFM. An existing drive is used to measure the dq inductances of the machine at several magnetization levels, including the cross-magnetization effects. The same technique is extended to measure the torque-ripple and the torque-angle characteristics of the machine at different magnetization levels. Experimental results are provided for a 5-hp variable flux PM machine. The proposed method uses an existing drive to perform the tests, requiring no additional test setup.