Direct Stator Field Oriented Control of Speed Sensorless Induction Motor

Field oriented control (FOC), published by BLASHKE in his pioneering work in 1972, allows high performance speed and torque response to be achieved from an induction motor. The instantaneous magnitude and position of the stator flux space vector must continuously be known with precision in order to achieve and maintain perfect filed orientation. When driven by a filed oriented controller, an induction motor behaves like a separately excited DC machine where the torque and the flux are controlled independently. In this paper, based on the model of the stator flux and rotor speed of this machine are estimated simultaneously using Luenberger observer for flux and PI observer for rotor speed. With the help of the observed (d, q) axis of the stator flux, the direct stator field orientation vector control is implemented. The salient advantage of the proposed method is the accuracy of the observed flux and rotor speed in low range and in the filed weakening region. The validity of the proposed method is verified by the simulation results.