0093-9994 (c) 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. 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/TIA.2018.2789858, IEEE Transactions on Industry Applications 1 Simplified Implementation of Synthetic Vectors for DTC of Asymmetric Six-Phase Induction Motor Drives Jay K. Pandit, Mohan V. Aware, Senior Member, Ronak Nemade, Yogesh Tatte Abstract—This paper presents simplified implementation tech- nique for Direct Torque Control (DTC) of asymmetric six-phase induction motor drive. Current harmonics of order 5 th and 7 th are observed in the phase currents if conventional DTC scheme is extended for the asymmetric six-phase machine. These harmonic components are not responsible for torque production, thus cause losses in the motor winding. Synthetic vectors are generally used for reduction of current harmonics. Average voltage in xy subspace is maintained to zero by synthetic vectors leading to reduction of currents in xy subspace. A simplified method of implementation of synthetic vectors is proposed in this paper which eliminates the need of designing of switching sequence and requirement of Field Programmable Gate Array (FPGA). Also, number of synthetic vectors that can be possibly produced is increased compared to the ones developed by techniques available in the literature. Experimentation is carried out on laboratory developed prototype and experimental results are presented in paper to verify the proposed scheme. Index Terms—Induction Motor Drives, Harmonic Reduction, Synthetic Vectors, Direct Torque Control, PWM Module NOMENCLATURE L ls ,L lr Leakage inductances. L s ,L r Stator and rotor self inductances. L ms Mutual inductance. r s ,r r Stator and rotor resistances. v ds ,v qs dq subspace voltages. v xs ,v ys xy subspace voltages. i ds ,i qs Stator currents in dq subspace. i xs ,i ys Stator currents in xy subspace. ψ s ,ψ r Stator and rotor flux. P Number of pole pairs. T e Electromagnetic torque. ω r Rotor speed. I. I NTRODUCTION M ULTI-PHASE machines are becoming popular due to additional degree of freedom available for control. Con- verter driven machines have no restriction on the number of phases as it can be easily changed by changing number of legs in converter. Multi-phase machines have number of advantages like fault tolerance, absence of low-frequency torque ripple, reduction in power rating of semiconductor devices [1]–[5]. These merits make them suitable for application such as ship propulsion, electric vehicles, and more electric aircrafts. Asymmetric six-phase induction motor consist of two three- phase windings which are phase shifted from each other by 30 0 (electrical) in space. Asymmetric six-phase induction motor is preferred because such spatial displacement allows easy construction of asymmetrical six phase machine from existing three-phase designs [6]. Direct Torque Control (DTC) is a popular technique used for speed and torque control because of its simple structure and fast transient response [7] [8]. Six-phase variables are transformed into dq, xy and 0 1 0 2 subspaces based on the Vector Space Decomposition (VSD) technique presented in [9]. It is stated in [9] that only the components in dq subspace are responsible for torque production and components in auxiliary subspaces (xy and 0 1 0 2 ) cause losses in the motor. Hence, reduction of currents in auxiliary subspace is the major problem to be addressed while using DTC technique with the multi-phase machines. Individual flux control method is proposed in [10] for reduction of current harmonics. In paper [11], xy subspace currents are reduced by modifying lookup table depending on position of flux in the xy subspace. Modified lookup table based DTC is used in [12] for creating two groups of virtual vectors which are used for reduction of torque ripple along with current harmonics reduction. In paper [13], modified lookup table based technique is suggested for the reduction of current harmonics as well as torque ripple, however for torque ripple reduction seven-level torque comparator is used. Synthetic vectors are proposed in [14]–[16] for reduction of current harmonics and are also used in [17] for reduction of torque ripple. Synthetic vectors are also proposed in [18] for reduction of current harmonics in case of five-phase induction motor. Synthetic vectors are also used in open-end winding operation of six-phase induction motor in [19] for reduction of current harmonics. In paper [20], generation of synthetic vectors with the help of FPGA is presented. By using synthetic vectors position estimation of flux in xy subspace is not required. Problems related to implementation of synthetic vectors using Pulse Width Modulation (PWM) modules are discussed in [14]. Switching sequence is designed in [14], which enables the use of PWM modules for implementation of synthetic vectors. A total of 24 synthetic vectors can be developed by method proposed in literature which allows use of five- level torque comparator for torque ripple reduction [17]. In this paper, a simplified method is proposed for implemen- tation of synthetic vectors using PWM module. Proposed implementation method eliminates requirement of switching sequence design. Also, every active vector in dq subspace can be replaced by corresponding synthetic vector. A total