0278-0046 (c) 2016 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. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIE.2016.2561261, IEEE Transactions on Industrial Electronics IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS Abstract— In this paper, the rotor position estimation accuracy of rotating carrier signal injection utilizing zero sequence carrier voltage method for dual three-phase (DTP) permanent magnet synchronous machines (PMSMs) is investigated. When utilizing the zero-sequence carrier voltage, the system bandwidth and rotor position estimation accuracy can be significantly enhanced. However, undesirable 6 th harmonic estimation error occurs for single three-phase PMSM with rotating signal injection due to multiple saliency components in the zero-sequence carrier voltage. To solve such a problem, the existing methods require time-consuming offline measurements and complex structures. Fortunately, for the case of DTP- PMSM drives, thanks to the existence of additional degrees of freedom, two high frequency signals can be injected independently for two winding sets. Therefore, by applying the optimum phase shift angle between the injected signals, a modified rotating carrier signal injection using zero-sequence voltage based sensorless control strategy is proposed to suppress the 6 th harmonic position errors. In addition, a new simple measurement method of zero- sequence carrier voltage is proposed where one voltage sensor is placed between the two isolated neutral points. The proposed method can achieve improved rotor position estimation accuracy with low computational burden. The experimental results verify the effectiveness of the proposed strategy. Index Terms—Carrier signal injection, dual three-phase (DTP), permanent magnet synchronous machine (PMSM), rotor position estimation, zero-sequence voltage. I. INTRODUCTION ULTIPHASE AC machine drives are nowadays considered for many applications, especially for high-power and/or high-current applications including ship propulsion, aerospace applications, renewable energy generation, and electric/hybrid vehicles [1]. This is due to the excellent features such as reduced torque ripples, reduced DC-link current harmonics, improved efficiency, and increased reliability of the system compared to their three-phase machine drives counterparts [2]-[6]. Manuscript received October 12, 2015; revised January 28, 2016 and March 17, 2016; accepted March 25, 2016. Z. Q. Zhu, Ali H. Almarhoon, and P. L. Xu are with the Department of Electronic and Electrical Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, U.K. (e-mail: z.q.zhu@sheffield.ac.uk; elp12aha@sheffield.ac.uk; pxu5@sheffield.ac.uk). Recently, the dual three-phase (DTP) machine is the frequently discussed and most common type among different types of multiphase machines. The DTP machine has two stator winding sets spatially shifted by 30 electrical degrees with isolated neutral points, and it is supplied by six-phase inverter, Fig.1. Multiphase machines are mainly aimed for fault-tolerant application. Thus, in case of post-fault condition such as one three-phase stator winding is completely disconnected from corresponding source, the redundant three-phase stator winding can be put into operation to maintain the continuity of machine drives operation including sensorless control [7] and [8]. High performance control of permanent magnet synchronous machines (PMSMs) requires an accurate rotor position information. Generally, High-resolution sensors, e.g. encoders and resolvers, are often used to obtain the information of the rotor position. However, the use of such sensors not only increases the system cost and size but also reduces the reliability and robustness of the system. Therefore, various techniques have been developed to achieve high sensorless control performance which can be classified into methods based on the fundamental model [9]-[12] and methods based on machine saliency sensing [13]-[35]. Fig. 1. Voltage source inverter (VSI) fed dual three-phase PMSM. For zero- and low-speed operating region, the methods based on fundamental model cannot be employed due to the lack of back-EMF. In contrast, the machine-saliency-based sensorless control methods can handle such limitation, including discrete voltage pulses injection [13], PWM signal injection [14], and continuous carrier-voltage signal injection [15]-[35], etc. Improved Rotor Position Estimation Accuracy by Rotating Carrier Signal Injection Utilizing Zero-Sequence Carrier Voltage for Dual Three-Phase PMSM Z. Q. Zhu, Fellow, IEEE, Ali H. Almarhoon, and P. L. Xu, Student Member, IEEE M