Design and Experimental Verification of a Direct-Drive Interior PM Synchronous Machine Using a Saturable Lumped-Parameter Model . . The research is supported by the MIT Consortium on Advanced Automotive Electrical/Electronic Components and Systems, http://auto.mit.edu/consortium . The experimental IPM machines were built by McCleer Power Inc., Jackson MI, with the financial support of Ford Motor Company. Additional support from the Wisconsin Electric Machines and Power Electronics Consortium (WEMPEC) is also acknowledged. Edward C. Lovelace SatCon Technology Corporation Cambridge, MA, USA ed.lovelace@satcon.com Thomas Keim, Jeffrey H. Lang, David D. Wentzloff Massachusetts Institute of Technology Cambridge, MA, USA tkeim@mit.edu , lang@mit.edu , ddw@mit.edu Thomas M. Jahns, Jackson Wai University of Wisconsin-Madison Madison, WI, USA jahns@engr.wisc.edu , waij@cae.wisc.edu Franco Leonardi, John M. Miller Ford Motor Company Dearborn, MI, USA fleonar2@ford.com , jmille24@ford.com Patrick J. McCleer McCleer Power Inc. Jackson, MI, USA pat@mccleerpower.com Abstract— This paper presents the design and experimental verification of a 6kW interior permanent magnet (IPM) synchronous machine intended for an automotive direct-drive starter/alternator application. The machine was designed using a saturable lumped-parameter magnetic circuit model in combination with a Monte Carlo optimization process that minimized the machine-plus-converter cost. An experimental IPM machine has been constructed based on the resulting design specifications. Laboratory tests have confirmed the accuracy of the analytical models for predicting the q-axis inductance L q (including saturation effects) and the torque production characteristics, but discrepancies between the predicted and measured d-axis inductance L d were revealed. The impact of these differences on machine performance is discussed, as well as potential adjustments in the IPM analytical model to improve the performance of future machines. Keywords—alternator; generator; interior permanent magnet synchronous machine; lumped parameter model; magnetic saturation; starter. I. INTRODUCTION Interior permanent magnet synchronous (IPM) machines are presently being used in a wide variety of commercial, industrial, and transportation applications. However, the nonlinear electromagnetic characteristics of this machine have posed special challenges to designers and discouraged the selection of the IPM machine in some new applications. Previous lumped-parameter models of IPM machines that have been developed to calculate the d- and q-axis inductances of the IPM salient rotor structure have typically adopted linear models for the magnetic materials without directly including magnetic saturation effects [1-3]. More complex nonlinear models have been used to predict the performance of IPM machines under the assumption of radial flux distribution in the airgap. In [4] the authors recognize that L q becomes progressively more saturated with loading resulting in a 50 percent reduction at high currents. This paper is based on recent work that has developed a nonlinear lumped-parameter model (LPM) for the IPM machine that explicitly incorporates the effects of magnetic core saturation along the axis orthogonal to the rotor magnet flux, defined as the q-axis [13]. This lumped-parameter model is flexible enough to accommodate many important structural design variations while remaining sufficiently tractable for rapid, repetitive design optimizations. It has been successfully used to evaluate IPM machine designs of various pole numbers and stator slotting distributions. While the analysis focuses on machines with two layers of buried magnets, it can be extended to higher numbers of magnet layers. One of the prime applications of this saturable LPM approach to date has been the design of an automotive direct- drive starter/alternator (S/A) machine. Fig. 1 shows the cross- section of a single pole in a 12-pole IPM machine designed for this application. Each rotor pole contains two layers of buried magnets that are magnetized across their shorter dimensions along the d-axis. The stator of the IPM machine is excited with polyphase balanced sinusoidal currents to produce the characteristic synchronously-rotating mmf wave. Control of 2486 0-7803-7420-7/02/$17.00 © 2002 IEEE