High Performance Field-Weakening Control Algorithm of Sensorless Induction Motor Using Speed Adaptive Full-Order Observer

In this paper, a novel voltage control scheme with a speed adaptive full-order observer is presented to improve the performance of sensorless induction motor control in the field-weakening region. The difference between the switching period time and the valid switching time of SVPWM (Space Vector Pulse Width Modulation) is introduced to regulate the field current, which maximizes the utilization of the dc-link voltage and extends the output torque. So when the motor speed exceeds the base speed, the corresponding magnetizing current would decrease with the increase of the motor speed. Meanwhile, a speed adaptive full-order observer is designed to obtain accurate rotor speed of the motor. The experiment results based on a 7.5 KW induction motor drive system show the validity of the proposed field-weakening method.