Sensorless Field Oriented Control for an Induction Motor Drive Using an Ideal Voltage Integration Scheme with a Dynamic Stabilising Feedback

The paper proposes a simple technique for implementing a stator voltage integration-based speed sensorless vector control scheme for an induction motor. The challenges associated with offset and drift in an ideal implementation of the integrator for stator flux estimation are well known. To overcome these, the conventional stator voltage integration scheme employs a low pass filter with a low cutoff frequency to approximate the integrator action. However, this approximation is associated with magnitude and phase errors, especially at low speeds. Though good performance can be achieved by using closed-loop flux observers, their structure and implementation are usually complex. A simpler method is proposed in this paper, wherein the dynamic equations of the machine are used to obtain additional information about the stator flux magnitude at steady state. This information is then used to correct the integrator drift. This results in zero steady-state phase and magnitude errors in the flux vector estimation. The proposed scheme is validated using simulations on a 5.5 kW, 415 V squirrel cage induction motor drive.