A mechanical simulator method is proposed as a speed-sensorless vector control in an ultra-low speed region. In this method, error between the estimated and the actual rotor frequencies occurs when the set value of disturbance torque is different from its actual value. This error causes the slip frequency to increase, which reduces both the rotor flux and the motor torque. To cope with this problem, the torque current error is compensated by a PI controller, which compensates the disturbance torque in the mechanical simulator. The proposed method is verified by both numerical simulations and a scaled-down experimental system tests.
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