Duty-ratio-based Direct Torque Control for Dual Three-phase Permanent Magnet Synchronous Machine Drives

This paper investigates the duty-ratio-based direct torque control strategies for dual three-phase permanent magnet synchronous machine (PMSM) drives. The classical switching-table-based direct torque control (ST-DTC) scheme for dual three-phase drives usually suffers from significant harmonic currents and large torque ripple. To reduce the harmonic currents, 12 combined voltage vectors are generated and employed as active vectors. Then, considering that the typical duty-ratio-based ST-DTC exhibits the drawbacks of machine parameter dependent and having failure odds of the duty-ratio regulatory, a simple and effective method taking into account the effect of machine speed is employed to obtain the duty-ratio. With the proposed method, not only the harmonic currents have been suppressed, but also the torque ripple can be considerably reduced, while the merits of classical ST-DTC such as simple structure and excellent dynamic performance are preserved. The experimental results validate the effectiveness of the proposed strategy.