Abstract-This paper deals with sensorless vector control of PWM-inverter-fed induction motor drives equipped with a threephase diode rectifier. An electronically controlled braking resistor across the dc link is not used. Instead, the power regenerated during braking is dissipated in the motor while a dc-link overvoltage controller limits the braking torque. Losses in the motor are increased by an optimum flux-braking controller, maximizing either the stator voltage or the stator current depending on the speed. Below the rated speed, the braking times are comparable to those achieved using a braking resistor. The proposed braking scheme is very simple and causes no additional torque ripple. Experimental results obtained using a 2.2-kW induction motor drive show that the proposed scheme works well.

Abstract-This paper deals with flux estimation for induction motor drives. The equations of the parameter sensitivity of both the rotor flux estimation and the torque production are derived for a full-order flux observer. Based on the parameter sensitivity analysis, practical methods of designing robust observer gains combining the current model and the voltage model are proposed. The proposed gains are easy to tune and lead to a simple observer structure. Experimental results show that for inaccurate parameter estimates, both the steady-state and dynamic errors in the produced torque are small as compared to the current model. Furthermore, high-speed operation is possible without modelling the magnetic saturation even if motor parameters are highly erroneous.