Induction motor control based on approximate stator flux

In this study, a novel sensorless method for the induction motor control is proposed. In this method, magnitude and rotational speed of approximate stator flux vector are controlled. In the proposed approximate stator flux control (ASFC) method, utilisation of the mechanical sensors and current transducers is not required. Therefore implementation cost of ASFC is comparable with that of conventional v/f control method. In ASFC, in linear modulation range, to control rotating field speed and stator flux modulus, desired voltage vector components in line with and perpendicular to the stator flux vector are calculated. Based on these two components, three-phase voltages are applied to three-phase inverter using pulse-width modulation strategy. In addition, in overmodulation range, a switching-table-based approach is presented to control the rotating field speed by adjusting the stator flux modulus. The relationship between the stator flux modulus and rotating field speed is derived and it is shown that average switching frequency is calculable and under control. Through simulations and experiments, ASFC method is compared with v/f method in terms of motor behaviour in starting and steady-state operation. Also, correctness of presented formulas is validated by simulations and experimental results.