Abstract: A method of controlling an inverter to provide protection for an AC traction motor includes starting the inverter and estimating a rotor cage resistance. A slip limit command is calculated from the estimated rotor cage resistance and used to control the inverter. Calculating the slip limit command can include determining a first slip limit using the rotor cage resistance, a stator leakage inductance, a rotor leakage inductance, a magnetizing leakage inductance, a number of motor poles, and a fundamental frequency of a voltage applied to the motor; determining a second slip limit using a predetermined maximum slip limit, a predetermined minimum slip limit, and a switch dependent on initial flux build up conditions; and calculating the slip limit command as the lower of the first and second slip limits.