In traditional direct torque control (DTC), it often has the shortcoming of large
flux linkage ripple, large torque ripple, and poor performance in low-speed
range. A modified DTC suitable for the full-speed range of electric motor
asynchronous motor is proposed from three aspects, which are motor speed range,
stator flux linkage observation, and control mode. The super-twisting (ST)
sliding mode algorithm is introduced into the traditional DTC. In the low-speed
range of motors, it adopts the circular flux control strategy and stator flux
linkage observation based on current model. In the middle or high speed range of
motors, the regular hexagonal flux linkage control strategy is adopted, which
reduces the switching loss of the inverter, and stator flux linkage observation
using voltage model. The simulation results show that the ST sliding mode
algorithm not only eliminates the chattering problem of the first-order sliding
mode, but also significantly reducing the stator flux linkage and torque ripple,
overcome the influence of stator resistance change on stator flux linkage
observation at low speed of motor and improved motor low-speed control
performance. The system has stronger dynamic and static performance, and has
stronger robustness performance against system parameter changes.