1637 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 36, NO. 6, NOVEMBER/DECEMBER 2000 Experimental and Finite-Element Analysis of an Electronic Pole-Change Drive Mohamed Osama, Member, IEEE, and Thomas A. Lipo, Fellow, IEEE Abstract—The theory and modeling of an electronic pole-change drive for the purpose of extending the constant power speed range of a four-pole induction machine have been previously reported. This paper presents verification of the power capability charac- teristics of the proposed drive through experimental implemen- tation. An indirect field-oriented controller is developed for the pole-change drive with the estimated rotor open-circuit time con- stant and d-axis current commands dependent on the mode of oper- ation. It is demonstrated that, for a constant power load, the drive can operate at 6340 r/min in two-pole mode without exceeding ei- ther the voltage or current limits at 3600 r/min in four-pole mode. A finite-element method is also utilized to examine the influence of magnetic saturation on the pole-change drive performance. The nature of the magnetic flux distribution and saturation progression is investigated in both four-pole and two-pole modes. The satura- tion-induced inductance variation is also studied and its influence on the inductance matrix is quantified. Index Terms—Electronic pole changing, induction machine, magnetic flux distribution, power capability. I. INTRODUCTION H IGH-INERTIA traction loads (among other applications) require an electric drive capable of high torque at low speeds in addition to a constant output power wide speed range above rated speed. The traditional approaches to meet these re- quirements involved either oversizing of the machine and/or in- verter, or modifying the machine magnetic structure design to decrease its leakage inductance [1]. Space constraints in certain drives make oversizing the machine infeasible, while oversizing the inverter is uneconomical. Modifying the machine magnetic structure to decrease the leakage results in higher motor torque ripple and copper losses due to the increase in motor harmonic current components. The induction machine equivalent per phase impedance (at a given speed) can be reduced by various stator winding change techniques, including Y– changeover, winding tapping, series-to-parallel reconnection, and reducing the pole number of a pole-change winding. Recently, several of these methods have been reintroduced in adjustable-speed drives for the pur- Paper IPCSD 99–91, presented at the 1999 Industry Applications Society Annual Meeting, Phoenix, AZ, October 3–7, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Industrial Drives Committee of the IEEE Industry Applications Society. Manuscript submitted for review July 1, 1999 and released for publication May 31, 2000. This work was supported by the Electric Power Research Institute and the National Sci- ence Foundation. M. Osama is with the Corporate Research and Development Center, General Electric Company, Niskayuna, NY 12309 USA (e-mail: osama@crd.ge.com). T. Lipo is with the Department of Electrical and Computer Engi- neering, University of Wisconsin, Madison, WI 53706-1691 USA (e-mail: lipo@engr.wisc.edu). Publisher Item Identifier S 0093-9994(00)09251-3. pose of extending the constant power speed range during field weakening for a field-oriented drive [2], [3]. This is achieved by operating at a large motor impedance until the maximum speed for constant power operation (about twice base speed). Switching to a lower motor impedance (using contactors) facil- itates extending the constant power range without increasing the required motor voltage by readjusting the flux level. In [4], the authors proposed a four–/two-pole induction machine drive that achieves the desired torque–speed capability based on elec- tronic pole changing [5], [6]. In electronic pole changing, the desired MMF distribution is attained by reversing the necessary coil groups currents instead of reversing their connections. Based on the same principle, an eight-/four-pole induction motor drive is currently being developed for an electric vehicle application by Meidensha Corporation, Nishikasugai-gun, Japan [7]. An electronic pole-changing drive avoids using any winding connection switching devices such as contactors. The total inverter rating is not increased while the motor is marginally oversized [8]. No change in the motor magnetic structure is required. On the other hand, the main limitations of such a drive are the need to access the individual machine coil groups, the additional control complexity, and doubling of the number of inverter switches. This paper presents verification of the power capability characteristics of the four-/two-pole drive through experimental implementation. An indirect field-ori- ented controller is also developed based on a six-dimensional reference frame model. In addition, the influence of magnetic saturation on the pole-change drive performance is investigated via finite-element analysis (FEA). II. INDIRECT FIELD-ORIENTATION CONTROL FOR POLE-CHANGE DRIVE Fig. 1(a) shows the four-/two-pole drive stator winding dis- tribution which is a full-pitch double-layer 120 phase belt. The two coil groups per phase are connected separately, resulting in a six-terminal stator (1–6). As illustrated by Fig. 1(b), a six-leg inverter is needed to supply this machine. The proposed drive operates as a four-pole machine from zero speed until the end of its constant power range (3600 r/min for 2-p.u. overload torque capability). The constant power speed range is extended by em- ploying “electronic” pole changing to obtain two-pole opera- tion. In order to compare the capability characteristics of the pro- posed drive in four-pole and two-pole operation, an indirect field-orientation controller with an outside speed loop is imple- mented. As is illustrated in Fig. 2, several features distinguish this controller from those used in conventional three-phase in- duction motor drives. The rotor open-circuit time constant and 0093–9994/00$10.00 © 2000 IEEE