1. Introduction The electrification of a vehicle has been gaining momentum recently, and more and more vehicles are being equipped with many electric motors and their inverters. In particular, a series–parallel hybrid electric vehicle and coaxial helicopter have two motors in its drive train [1-2]. In order to reduce the space of the motors, we proposed a two-controllable-rotor motor [3]. The proposed motor has two axially-arranged rotors and a common stator. The two rotors can be independently controlled using 3- and 6-phase superimposed currents created by a 6-phase inverter. One rotor is driven by a 3-phase current and the other is driven by a 6-phase current. In the transportation applications, it is important to continue the drive operation under fault conditions. Therefore, a fault tolerant control for multiphase motors have been studied [4-5]. In this paper, we propose a fault-tolerant control for a two-controllable-rotor motor using a 6-phase inverter, and its effectiveness is verified using finite element analysis. 2. Structure and Operational Principle Fig. 1 shows general and sectional views of our proposed motor with two axially-arranged rotors. The proposed motor has a common stator and two rotors: 6- and 12-pole rotors. The common stator has 36 slots and 6-phase distributed winding from A-phase to F-phase, and the in-phase coils are connected in series. This motor has a high heat dissipation because the stator is located outside. The two rotors can be easily supported because the two rotors are axially located with each other, and the 6-pole rotor shaft is mounted in the 12-pole rotor shaft through bearings. The 6- and 12-pole rotors are driven as 3- and 6-phase permanent magnet synchronous motors, respectively, by using superimposed currents created by a 6-phase inverter. Furthermore, it is known that the 3- and 6-phase currents do not mathematically interfere with each other [6]. In the proposed motor shown in Fig. 1, the stator and rotors diameters are Φ110 mm and Φ64 mm, respectively, the radial air gap length is 1 mm, and the rotor, stator thickness, and axial air gap length are 30 mm, 62 mm, and 2 mm, respectively. The winding factors of the 6- and 12-pole rotors are 0.7 and 1.0, respectively. The Maximum current density is 10Arms/mm2. 3. Fault-Tolerant Control A multiphase motor can be used for a fault-tolerant operation due to its additional degrees of freedom. This is because, under fault conditions, the remaining healthy phases in a multiphase machine can be used to compensate the faults and to continue the drive operation [4-5]. A two-controllable-rotor motor needs at least 5 phases to independently control the both rotors [7]. Therefore, a two-controllable-rotor motor using a 6-phase inverter can be driven although one phase is in a fault condition. In this paper, we propose a fault-tolerant control for a two-controllable-rotor motor when one phase is in an open circuit. In order to investigate the torque ripple due to a superimposed current when one phase is in an open circuit, an electromagnetic field analysis using finite element method is conducted. Figs. 2 (a) and (b) show the drive current waveforms for the 6- and 12- pole rotors under normal condition, respectively. Figs. 2 (c) and (d) show the drive current waveforms for the 6- and 12- pole rotors in A-phase open condition, respectively. Figs. 2 (e) and (f) show the torque waveforms of the 6- and 12- pole rotors, respectively under the normal and fault conditions. From Figs. 2 (e) and (f), the torque ripple rate of both rotor torque under the fault condition due to the superimposed current hardly changes. Therefore, the both rotors can be independently controlled under the fault condition. 4. Conclusion In this paper, we propose a fault-tolerant control for a two-controllable-rotor motor using a 6-phase inverter. The torque ripple rate of both rotor torque due to a superimposed current when one phase in an open circuit hardly changes compared with a normal condition. Therefore, the both rotors can be independently controlled under the fault condition. In the final paper, a mathematical model of the fault-tolerant control is described in detail. Furthermore, the torque ripple and N-T characteristics in normal and fault conditions are compared using a prototype.

**References:**

[1]H. A. Borhan, A. Vahidi, A. M. Phillips, American Control Conference, pp. 3970-3976 (2009) [2]J. Paulos, B. Caraher, M. Yim, IEEE ICRA, pp. 7011-7016 (2018) [3]H. Suzuki, K. Hirata, N. Niguchi, IEEE INTERMAG (2018) [4]S. Dwari, L. Parsa, IEEE Trans. Industrial Electronics, vol. 58, no. 2, pp. 476-485 (2011) [5]W. Zhang , X. Liang, F. Yu, IEEE Trans. Magnetics, vol. 54, no. 11 (2018) [6]N. Tan, M. Arimitsu, Y. Naruse, The International Power Electronics Conference, pp 1482-1488 (2005) [7]H. Suzuki, K. Hirata, N. Niguchi, IEEE ICEM, pp. 5-11 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/9522b5cce994fe503fc306c95d036b41.jpg)
Fig. 1 Our proposed two-controllable-rotor motor.

![](https://assets.underline.io/uploads/markdown_image/1/image/5de7dc7b5fcf2c594b799e8516a4529e.jpg)
Fig. 2 Current and torque waveforms.

 Fault-Tolerant Control for a Six-Phase Two-Controllable-Rotor Motor

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Fault-Tolerant Control for a Six-Phase Two-Controllable-Rotor Motor

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