IEEE SENSORS JOURNAL, VOL. 17, NO. 23, DECEMBER 1, 2017 7877 Performance Analysis of Concentrated Wound- Rotor Resolver for Its Applications in High Pole Number Permanent Magnet Motors Ramin Alipour-Sarabi , Student Member, IEEE, Zahra Nasiri-Gheidari, Member, IEEE, Farid Tootoonchian, Member, IEEE, and Hashem Oraee, Senior Member, IEEE, Abstract— High pole number permanent magnet (PM) motors, due to their high torque density, have been receiving considerable attentions in recent years. To achieve an accurate position control in PM machines, resolvers are suggested for industrial applications. Mechanical and electromagnetic considerations in the case of high pole number resolvers lead the machine designers to choose small cores with low slot numbers. This paper proposes two different on-tooth winding configurations to achieve high pole number without increasing the slot numbers, while the accuracy of the detected position is intended to be the maximum value. Variable turn on tooth winding (VTTW) is compared with fractional slot concentrated winding (FSCW) for two-phase machines. By the aid of winding function’s harmonic contents and winding factors, the accuracy of different configurations is analyzed and confirmed by the 3-D time stepping finite-element method. Results show that the wound field resolver equipped with FSCW has higher accuracy than the VTTW. Moreover, it is shown that concentrated winding suffers from sub-harmonics. In this regard, a modification on the rotor winding is performed to decrease the total harmonic distortion of output signals and decrease the estimated position error. In addition, the role of winding layers and displacement angle between them is further investigated in this paper. Finally, a prototype with 20-pole 6-layer FSCW resolver has been constructed. Practical results are in good agreement with the analytical predictions. Index Terms—Axial flux resolver, magnetic position sensor, variable turn on-tooth winding (VTTW), fractional slot concen- trated winding (FSCW), permanent magnet (PM), total harmonic distortion (THD), finite-element analysis (FEA). I. I NTRODUCTION A NGULAR position sensors are essential parts of any motion control system. Various position sensors namely; optical encoders, potentiometers, resolvers and Hall-effect sen- sors have been developed and commercially available [1]–[3]. Among them, resolvers are less susceptible to vibrations, dust and temperature variations [4] and consequently more reliable Manuscript received September 8, 2017; accepted October 1, 2017. Date of publication October 10, 2017; date of current version November 10, 2017. This work was supported by the research office of the Sharif University of Technology. The associate editor coordinating the review of this paper and approving it for publication was Prof. Vedran Bilas. (Corresponding author: Zahra Nasiri-Gheidari.) R. Alipour-Sarabi, Z. Nasiri-Gheidari, and H. Oraee are with the Center of Excellence in Power System Management & Control, Electrical Engineer- ing Department, Sharif University of Technology, Tehran 1458889694, Iran (e-mail: r_alipour@ee.sharif.edu; znasiri@sharif.edu; oraee@sharif.edu). F. Tootoonchian is with the Electrical Engineering Department, Iran University of Science and Technology, Tehran 1684613114, Iran (e-mail: tootoonchian@iust.ac.ir). Digital Object Identifier 10.1109/JSEN.2017.2761796 Fig. 1. Scheme of WF resolver. for industrial applications and harsh environment, such as oil exploration, aerospace, motor drive control and robot arms [5]. A typical resolver system consists of a machinery structure (resolver) and an electronic part (R/D) as shown in Fig. 1. When a high frequency voltage is applied to the moving coil through a rotary transformer (RT) [6], [7] or brushes [8], volt- ages are inducted in the output coils. Those voltages are func- tions of relative position of moving and stationary parts. R/D is responsible to find the envelope of output analog signals and calculate the position of moving part. Therefore, the accuracy of estimated position is highly dependent on the resolver and the R/D converter performance [9]. Some of errors caused by the machinery part can be compensated by software-based and hardware-based solutions in R/D [10], [11]. These solutions can be categorized in two groups. The first group uses open- loop techniques such as linearization, arctangent, ac signal and time measurement, and the second group utilizes phase- lock loop (PLL), vector tracking conversion and angle tracking observer (ATO) techniques as a close-loop method [12], [13]. Noting that these solutions are costly and complicated, and since an ounce of prevention is worth a pound of cure, it is more rational to prevent these errors at origin in the machinery part. Rotational resolvers, like other electrical machines can be classified into two categories: Variable Reluctance (VR) resolvers [4]–[7], [14]–[18] and Wound Field (WF) ones [19]–[22]. While the rotor of VR resolvers has no windings, WF resolvers have at least one winding on the rotor, at least. VR resolvers have some advantages with respect to WF resolvers. They have a simple structure with no need to RT. They have short length and frameless structure that makes them suitable to be integrated with motors. However, commercial VR resolvers operate on sinusoidal variation of air-gap length and have higher accuracy [19]. The accuracy of VR resolvers is strongly affected by eccentricity fault 1558-1748 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.