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This paper presents a simplified implementation technique for direct torque control (DTC) of asymmetric six-phase induction motor drive. Current harmonics of fifth and seventh order 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 causing 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 for designing of switching sequence and requirement of field-programmable gate array. Also, the number of synthetic vectors that can be possibly produced is increased compared with the ones developed by techniques available in the literature. The experimentation is carried out on a laboratory-developed prototype and the experimental results are presented in this paper to verify the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper presents an improved direct torque control (DTC) method for an asymmetrical six-phase induction motor using a two-level six-phase inverter. As is well known, a simple extension of three-phase DTC technique to an asymmetrical six-phase motor, using large vectors only, introduces significant current harmonics of the order 6 n±1 (n = 1, 3, 5,…), which are mapped into the nonflux/torque producing (xy) plane. These harmonics cause only losses in the motor winding as they do not take part in torque production. Hence, a number of different improved DTC techniques have been developed in the past for multiphase motor drives. The paper takes one such DTC method as the starting point and improves it further by using the concept of virtual voltage vectors. Developed vector selection algorithm, based on two virtual voltage vectors, requires the information on position of the flux in the auxiliary (xy) subspace and provides stator current quality commensurate with the currently available best DTC algorithm for six-phase drives. However, use of two virtual voltage vectors enables a substantial reduction of the torque ripple, which is achieved by means of a five-level torque comparator. Extensive experimentation is performed and it is shown that the reduction of the current harmonics is in essence almost the same as in another recently developed DTC scheme, based on the use of a single virtual voltage vector. However, the achieved torque ripple reduction, which is verified experimentally, makes the scheme superior when compared to the existing approaches. At the same time, developed scheme retains qualities of conventional DTC schemes, such as simple structure and fast response. Its additional beneficial feature is the easiness of implementation. [ABSTRACT FROM PUBLISHER]