A direct torque and stator flux vector control system is presented. The principle of this method was proposed by Takahashi and Noguchi in 1985. In contrast to the field oriented control, no coordinate transformation and current control loop is required. In practical application, however, problems occur with start and operation at zero speed region. This paper shows how by introducing an additional carrier signal to the torque controller input, the robust start and improved operation at low speed region can be achieved. The simulation and experimental results which illustrate the performances of the system are presented. Also, the nomogram for controller design and comparison with most popular current type of indirect field oriented control are presented.
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