A method for estimating a magnet temperature of a rotor magnet within a rotary electric machine includes, while a rotor of the electric machine is stationary, injecting a high-frequency voltage component onto a control voltage of the electric machine, via a controller, to generate an adjusted voltage command, and extracting a high-frequency component of a resulting current as an extracted high-frequency component. The method also includes calculating an inductance value of the electric machine using the extracted high-frequency component of the resulting current. The magnet temperature is estimated using the calculated inductance value and an angular position of the rotor. The method includes controlling an operation of the electric machine using the estimated magnet temperature. An electric powertrain uses the electric machine and controller noted above.