Sensorless 3-level inverter-fed induction motor drive based on indirect torque control

A sensorless induction motor drive fed by 3-level inverter is presented, which combines the principle of indirect torque control, space vector modulation (SVM), speed adaptive flux observer and fuzzy logic controller (FLC). By using SVM, the switching frequency is kept constant and it is easy to solve the problems such as neutral point balance, voltage jump, etc, and more accurate results are obtained. A novel speed adaptive flux observer is proposed in this paper, which can observe flux and rotor speed accurately over a wide speed range. FLC is employed in the outer speed loop to provide excellent dynamic performance and steady state accuracy, especially for variable load changes. Large starting current is one of the problems in application for indirect torque control. By using pre-excitation technique and a ramp function, the stator flux is firstly established smoothly before motor starts, thus starting current is decreased while maintaining enough starting torque. Both simulation and experimental results are presented to validate the effectiveness of the techniques proposed in this paper.