Generalized two-vector-based direct torque control of permanent-magnet synchronous machine drives

Conventional single-vector-based direct torque control (SVB-DTC) has been widely researched owing to its simple control structure, parameter robustness and fast response. However, the SVB-DTC often features large torque and flux ripple. To suppress the large ripple in torque and stator flux, recently, a duty-cycle-based DTC (DCB-DTC) scheme applying a zero vector and a nonzero vector to the drive during every control period has been presented. However, the torque and flux ripple fail to be reduced to a minimal value owing to the fixed vector combination of a zero and a nonzero vector. A generalized two-vector-based DTC (GTV-DTC) for permanent-magnet synchronous machine (PMSM) drives which relaxes the vector combination to two arbitrary voltage vectors is proposed. In contrast to the DCB-DTC, two nonzero vectors might be chosen in the proposed method. Then the torque ripple can be reduced by the broad possible vector combination. In addition, a simple analytical and graphical method is proposed to select two voltage vectors and to determine their optimal durations based on the principle of stator flux vector error minimization. The simulation results are provided to verify the outstanding performance of the proposed method that, compared to prior SVB-DTC and DCB-DTC, the proposed GTV-DTC achieves much better steady-state performance and similar transient-state performance without significantly increasing computational burden.