A drive system (60, 62) for driving an AC electric machine, the drive system (60, 62) comprising: an electric machine power converter configured to provide a primary current excitation to drive the AC electric machine, the primary current excitation comprising a current vector having a magnitude and angle; and a control system configured to: inject a carrier signal to the AC electric machine that is superimposed onto the current vector, with the carrier signal being selected by the control system to generate a carrier response signal that has sensitivity to magnetic alignment information of the AC electric machine at its operating point; characterized in that the control system is configured to measure at least one magnetic alignment signature chosen by the control system from among a plurality of magnetic alignment signatures of the AC electric machine from the generated carrier response signal, the plurality of magnetic alignment signatures including at least one magnetic alignment signature derived from saturation behavior of the AC electric machine and at least one magnetic alignment signature derived from saliency of the AC electric machine; and control an orientation of the current vector using the measured magnetic alignment signature, so as to achieve a desired magnetic operation of the AC electric machine, wherein the injected carrier signal and the measured magnetic alignment signature are chosen by the control system based upon the operating point of the AC electric machine and a dynamic state of the AC electric machine so that the magnetic alignment signature can be measured with a desired sensitivity. an electric machine power converter configured to provide a primary current excitation to drive the AC electric machine, the primary current excitation comprising a current vector having a magnitude and angle; and a control system configured to: inject a carrier signal to the AC electric machine that is superimposed onto the current vector, with the carrier signal being selected by the control system to generate a carrier response signal that has sensitivity to magnetic alignment information of the AC electric machine at its operating point; characterized in that the control system is configured to measure at least one magnetic alignment signature chosen by the control system from among a plurality of magnetic alignment signatures of the AC electric machine from the generated carrier response signal, the plurality of magnetic alignment signatures including at least one magnetic alignment signature derived from saturation behavior of the AC electric machine and at least one magnetic alignment signature derived from saliency of the AC electric machine; and control an orientation of the current vector using the measured magnetic alignment signature, so as to achieve a desired magnetic operation of the AC electric machine, wherein the injected carrier signal and the measured magnetic alignment signature are chosen by the control system based upon the operating point of the AC electric machine and a dynamic state of the AC electric machine so that the magnetic alignment signature can be measured with a desired sensitivity. inject a carrier signal to the AC electric machine that is superimposed onto the current vector, with the carrier signal being selected by the control system to generate a carrier response signal that has sensitivity to magnetic alignment information of the AC electric machine at its operating point; characterized in that the control system is configured to measure at least one magnetic alignment signature chosen by the control system from among a plurality of magnetic alignment signatures of the AC electric machine from the generated carrier response signal, the plurality of magnetic alignment signatures including at least one magnetic alignment signature derived from saturation behavior of the AC electric machine and at least one magnetic alignment signature derived from saliency of the AC electric machine; and control an orientation of the current vector using the measured magnetic alignment signature, so as to achieve a desired magnetic operation of the AC electric machine, wherein the injected carrier signal and the measured magnetic alignment signature are chosen by the control system based upon the operating point of the AC electric machine and a dynamic state of the AC electric machine so that the magnetic alignment signature can be measured with a desired sensitivity.