6624 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 61, NO. 12, DECEMBER 2014 Sensorless Control for SPMSM With Concentrated Windings Using Multisignal Injection Method Zhe Chen, Jianbo Gao, Fengxiang Wang, Zhixun Ma, Zhenbin Zhang, and Ralph Kennel, Senior Member, IEEE Abstract—Surface-mounted permanent magnet synchronous machine with concentrated windings (cwSPMSM) is a high- performance drive machine and has been adopted in many appli- cations. The difficulty of implementing its sensorless control at low and zero speeds is its multiple saliencies, which is much more sig- nificant than most other ac machines. The traditional decoupling methods provide successful results only under the condition that high-order saliencies are not stronger than half of the primary saliency. Furthermore, the behavior of the multiple saliencies is principally frequency dependent. Based on the characteristics of such machines, this paper proposes a multisignal injection method for realizing sensorless control. This method injects multiple high- frequency signals with different frequencies and magnitudes into the machine. Different frequency components in the response current signals are demodulated and then combined together to get the clear primary saliency signal, which is used to identify the rotor position. This new method was validated using a cwSPMSM at low speed. The experimental results proved the effectiveness and accuracy of the new method. Index Terms—Multisignal injection, sensorless control, surface- mounted permanent magnet synchronous machine with concen- trated windings (cwSPMSM). I. I NTRODUCTION C ONCENTRATED-WINDING surface-mounted perma- nent magnet synchronous machine (cwSPMSM) has been receiving increasing attention over the past decade because it has lower production costs, higher feasibility, and more compact designs than the machines with distributed windings [1]. In the applications of electric and hybrid vehicles, these type of machines are adopted to realize shorter motor length and higher efficiency [2]. The cwSPMSM has a drawback: con- siderable torque ripple. Fortunately, the development of magnet materials and machine design technologies can relieve this problem [3], [4]. It is therefore foreseen that cwSPMSM will find more applications in wind energy generators [5], [6] and the automotive industry [7]. Sensorless control for cwSPMSM can make this type of drive even more competitive. In particular, at low and zero speeds, saliency-based sensorless methods, e.g., Manuscript received October 24, 2013; revised January 14, 2014; accepted March 11, 2014. Date of publication April 9, 2014; date of current version September 12, 2014. This work was supported by Deutsche Forschungsge- meinschaft under Grant KE 817/28-1 and the Chinese Scholarship Council. (Corresponding author: F. Wang.) The authors are with the Institute for Electrical Drive Systems and Power Electronics, Technische Universität München, 80333 Munich, Germany (e-mail: zhe.chen@tum.de; micheal.gao@tum.de; fengxiang.wang1982@gmail.com; mzhixun@gmail.com; james.cheung@tum.de; ralph.kennel@tum.de). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2014.2316257 switching transient or carrier signal injection [8], have been widely adopted in electrical drives. However, for this machine type, sensorless control still faces some challenges [9]. Experiment results of a cwSPMSM, us- ing the high-frequency (HF) injection method, illustrate two significant characteristics that bring great challenges to the researchers for sensorless control. First, because of the smooth rotor structure as normal SPMSM, the machines have very weak inductive saliencies [10], on which many sensorless con- trol technologies are based. Second, evoked by their special winding structures, the machines show strong multiple salien- cies [11], which cause strong torque ripples if traditional sen- sorless control technologies are applied. Due to these problems, particularly the latter one, no sensorless control methods have been realized yet in practical applications for a commercial cwSPMSM. The characteristic of multiple saliencies is common in all ac machines, either in induction machines [12], [13] or in PMSMs [14]. A very interesting work was published in 2011 to study the principle of multiple saliencies phenomena in PMSM [15]. This work confirmed that the higher order saliencies were evoked by the zigzag leakage [16] of the rotor flux in the stator teeth. This effect is more significant in machines with concentrated windings than those with distributed windings. This is a structure-induced effect and has no relationship to load conditions. Fortunately, some remarkable work has been done during recent years concerning multiple saliencies for different ma- chine types. This provides important supports for cwSPMSM to be applied in practice. In 1998, the characteristics of multiple saliencies in induction machines were reported in [17]. In this study, sensorless control was realized for an induction ma- chine using the decoupling method, where higher orders of the saliencies were decoupled from the fundamental saliency to ob- serve the rotor position. Another attempt using the decoupling method was done in 2008 with an interior PMSM [18], where the higher order saliencies were emerging only under load conditions. Other work has been also investigated to deal with multiple saliencies for sensorless control, not only for synchro- nous machines [19] but also for induction machines [20], [21]. Summarizing the available literature, it is seen that all of these studies were focused on the decoupling idea, where the higher order saliencies were compensated, i.e., removed from the estimation loop. This concept is effective if the higher order saliencies are weaker compared with the fundamental saliency [17], [21]. However, if their magnitudes are larger than half of the primary saliency, these methods fail to decouple [11]. 0278-0046 © 2014 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.