Due to the star connection of the windings, the impact of the third harmonic which does not exist in three-phase permanent magnet synchronous motor (PMSM) cannot be ignored in five-phase PMSM. So the conventional sensorless control methods for three-phase PMSM cannot be applied for five-phase PMSM directly. To achieve the sensorless control for five-phase PMSM, an iterative sliding mode observer (ISMO) is proposed with the consideration of the third harmonic impact. First, a sliding mode observer (SMO) is designed based on the fivephase PMSM model with the third harmonic to reduce the chattering and obtain the equivalent signal of the back electromotive force (EMF). Then, an adaptive back EMF observer is built to estimate the motor speed and rotor position, which eliminates the low-pass filter and phase compensation module and improves the estimation accuracy. Meanwhile, by iteratively using the SMO in one current sampling period to adjust the sliding mode gains, the sliding mode chattering and estimation errors of motor speed and rotor position are further reduced. Besides, the stability of the SMO and the adaptive back EMF observer are demonstrated in detail by Lyapunov stability criteria. Experiment results verify the effectiveness of the proposed observer for sensorless control of five-phase PMSM.
 A. Mohammadpour, and L. Parsa, “Global fault-tolerant control technique for multiphase permanent-magnet machines”, IEEE Trans. Ind. Appl. 51 (1), 178‒186 (2015).
 M. Janaszek, “Structures of vector control of n-phase motor drives based on generalized Clarke transformation”, Bull. Pol. Ac.: Tech. 64 (4), 865‒872 (2016).
 N.K. Nguyen, F. Meinguet, E. Semail, and X. Kestelyn, “Fault-tolerant operation of an open-end winding five-phase PMSM drive with short-circuit inverter fault”, IEEE Trans. Ind. Electron. 63 (1), 595‒605 (2016).
 A. Mohammadpour, S. Sadeghi, and L. Parsa, “A generalized fault-tolerant control strategy for five-phase PM motor drives considering star, pentagon, and pentacle connections of stator windings”, IEEE Trans. Ind. Electron. 61 (1), 63‒75 (2014).
 A. Mohammadpour and L. Parsa, “A unified fault-tolerant current control approach for five-phase PM motors with trapezoidal back EMF under different stator winding connections”, IEEE Trans. Power Electron. 28 (7), 3517‒3527 (2013).
 S. Sadeghi, L. Guo, H.A. Toliyat, and L. Parsa, “Wide operational speed range of five-phase permanent magnet machines by using different stator winding configurations”, IEEE Trans. Power Electron. 59 (6), 2621‒2631 (2012).
 L. Guo and L. Parsa, “Model reference adaptive control of fivephase IPM motors based on neural network”, IEEE Trans. Ind. Electron. 59 (3), 1500‒1508 (2012).
 N. Leboeuf, T. Boileau, B. Nahid-Mobarakeh, N. Takorabet, F. Meibody-Tabar, and G. Clerc, “Effects of imperfect manufacturing process on electromagnetic performance and online interturn fault detection in pmsms”, IEEE Trans. Ind. Electron. 62 (6), 3388‒3398 (2015).
 M. Trabelsi, N.K. Nguyen, and E. Semail, “Real-time switches fault diagnosis based on typical operating characteristics of five-Phase permanent-magnetic synchronous machines”, IEEE Trans. Ind. Electron. 63 (8), 4683‒4694 (2016).
 F. Betin, G.A. Capolino, D. Casadei, B. Kawkabani, R.I. Bojoi, L. Harnefors, E. Levi, L. Parsa, and B. Fahimi “Trends in electrical machines control: samples for classical, sensorless, and fault-tolerant Techniques”, IEEE Trans. Ind. Electron. 8 (2), 43‒55 (2014).
 B. Alecsa, M.N. Cirstea, and A. Onea, “Simulink modeling and design of an efficient hardware-constrained FPGA-based PMSM speed controller”, IEEE Trans. Ind. Informat. 8 (3), 554‒562 (2012).
 Q. Tang, A. Shen, X. Luo, and J. Xu, “PMSM sensorless control by injecting HF pulsating carrier signal into ABC frame”, IEEE Trans. Power Electron. 32 (5), 3767‒3776 (2017).
 X. Song, J. Fang, B. Han, and S. Zheng, “Adaptive compensation method for high-speed surface PMSM sensorless drives of EMF-based position estimation error”, IEEE Trans. Power Electron. 31 (2), 1438‒1449 (2016).
 T. Atalik, M. Deniz, E. Koc, C. Gercek, B. Gultekin, M. Ermis, and I. Cadirci, “Multi-DSP and FPGA based fully-digital control system for cascaded multilevel converters used in FACTS applications”, IEEE Trans. Ind. Informat. 8 (3), 511–527 (2012).
 A. Al Nabulsi and R. Dhaouadi, “Efficiency optimization of a DSP-based standalone PV system using fuzzy logic and dual-MPPT control”, IEEE Trans. Ind. Informat. 8 (3), 573–584 (2012).
 C. Buccella, C. Cecati, and H. Latafat, “Digital control of power converters-A survey”, IEEE Trans. Ind. Informat. 8 (3), 437–447 (2012).
 X. Luo, Q.P. Tang, A.W. Shen, and Q. Zhang, “PMSM Sensorless control by injecting HF pulsating carrier signal into estimated fixed-frequency rotating reference frame”, IEEE Trans. Ind. Electron. 63 (4), 2294‒2303 (2016).
 M. Ramezani and O. Ojo, “The modeling and position-sensorless estimation technique for A nine-phase interior permanent-magnet machine using high-frequency injections”, IEEE Trans. Ind. Appl. 52 (2), 1555‒1565 (2016).
 A. Accetta, M. Cirrincione, M. Pucci, and G. Vitale, “Sensorless control of PMSM fractional horsepower drives by signal injection and neural adaptive-band filtering”, IEEE Trans. Ind. Electron. 59 (3), 1355–1366 (2012).
 G. Wang, L. Ding, Z.M. Li, J. Xu, G.Q. Zhang, H.L. Zhan, R.G. Ni, and D.G. Xu, “Enhanced position observer using second-order generalized integrator for sensorless interior permanent magnet synchronous motor drives”, IEEE Trans. Ener. Conv. 29 (2), 486‒495 (2014).
 F.J. Lin, Y.C. Hung, J.M. Chen, and C.M. Yeh, “Sensorless IPMSM drive system using saliency back-EMF-based intelligent torque observer with MTPA control”, IEEE Trans. Ind. Informat. 10 (2), 1226–1241 (2014).
 G.L. Wang, H.L. Zhan, G.Q. Zhang, X.G. Gui, and D.G. Xu, “Adaptive compensation method of position estimation harmonic error for EMF-based observer in sensorless IPMSM drives”, IEEE Trans. Power Electron. 26 (6), 3055‒3064 (2014).
 H.X. Liu and S.H. Li, “Speed control for PMSM servo system using predictive functional control and extended state observer”, IEEE Trans. Ind. Electron. 59 (2), 1171‒1183 (2012).
 R. Errouissi, M. Ouhrouche, W.-H. Chen, and A.M. Trzynadlowski, “Robust nonlinear predictive controller for a PMSM with optimized cost function”, IEEE Trans. Ind. Electron. 59 (7), 2849‒2858 (2012).
 N.K. Quang, N.T. Hieu, and Q.P. Ha, “FPGA-based sensorless PMSM speed control using reduced-order extended Kalman filters”, IEEE Trans. Ind. Electron. 61 (12), 6574‒6582 (2014).
 K. Zawirski, D. Janiszewski, and R. Muszynski, “Unscented and extended Kalman filters study for sensorless control of PM synchronous motors with load torque estimation”, Bull. Pol. Ac.: Tech. 61 (4), 793–801 (2013).
 H. Lee and J. Lee, “Design of iterative sliding mode observer for sensorless PMSM control”, IEEE Trans. on Control Syst. Technol. 21 (4), 1394‒1399 (2013).
 Z.W. Qiao, T.N. Shi, Y.D. Wang, Y.Yan, C.L. Xia, and X.N. He “New sliding-mode observer for position sensorless control of permanent-magnet synchronous Motor”, IEEE Trans. Ind. Electron. 60 (2), 710‒719 (2013).
 S.H. Li, M.M. Zhou, and X.H. Yu, “Design and implementation of terminal sliding mode control method for PMSM speed regulation system”, IEEE Trans. Ind. Inf. 9 (4), 1879‒1891 (2012).
 G.L. Wang, T.L. Li, G.Q. Zhang, X.G. Gui, and D.G. Xu, “Position estimation error reduction using recursive-least-square adaptive filter for model-based sensorless interior permanent-magnet synchronous motor drives”, IEEE Trans. Ind. Electron. 61 (9), 5115‒5125 (2014).
 Y. Gao, W.G Liu, and Q. Yang, “Study of position sensorless control based on sliding mode observer”, in proc. International conference on electrical machines and systems (ICEMS), 1‒3 (2011).
 J.W. Yang, M.F. Dou, Z.Y. Dai, D.D. Zhao, and Z. Zhang, “Modeling and fault diagnosis of inter-turn short circuit for five-phase PMSM based on particle swarm optimization”, in Proc. IEEE Appl. Power Electron. Conf. Expo. 3134‒3139 (2016).
 W.C. Chi and M.Y. Cheng, “Implementation of a sliding-mode-based position sensorless drive for high-speed micro permanent-magnet synchronous motors”, ISA Trans. 53 (2), 444‒453 (2014).
 D. Xu, S.G. Zhang, and J.M. Liu, “Very-low speed control of PMSM based on EKF estimation with closed loop optimized parameters”, ISA Trans. 52 (6), 835‒843 (2013).