Improved torque regulator to reduce steady-state error of torque response for direct torque control of permanent magnet synchronous machine drives

This study presents an improved switching-table-based direct torque control method for three-phase permanent magnet synchronous machine drives. The instantaneous variation rates of stator flux and torque of each converter output voltage vector are analysed. It is found that large steady-state error of torque response exists because of the difference in the decreasing and increasing variation rates. A novel and simple on-line band-shifted torque regulator is proposed to reduce this steady-state error of torque response. The experimental results verify that the proposed method can significantly reduce the steady-state error of torque response with the extra bonus of slight reduction of both the torque ripple and average commutation frequency, while preserve the merits of the conventional direct torque control, that is, simple structure, good robustness and excellent transient response.