A method of detecting a permanent magnet rotor of a synchronous machine, includes: injecting a voltage waveform to the stator windings of the synchronous machine, measuring two phase currents in the stator winding, transforming the two phase currents to a rotor reference frame to obtain a current waveform, sampling the current waveform to obtain positive and negative portion values, constructing first and second periodic waveforms by using the sampled positive and negative portion values, performing a frequency analysis of a first and second spectrums of the periodic waveforms, and determining whether a permanent magnet is present in the synchronous machine based on the spectrums.