Method for determining a rotor angle of a rotor of an electric machine, having the following steps: generating a torque-dependent test signal that depends on the torque of the electric machine and has a higher frequency than a supply signal for the electric machine, driving the electric machine with the supply signal, which corresponds to a manipulated variable generated by a current controller in a dq coordinate system, and with the test signal which is superimposed on the supply signal, capturing phase currents (13, 14, 15) of the electric machine, and determining the rotor angle of the rotor of the electric machine on the basis of the effects of the test signal on the phase currents (13, 14, 15), characterized in that the method comprises the following further steps: transforming the captured phase currents (13, 14, 15) of the electric machine into a motor-current vector in a stator-fixed coordinate system by means of a first transformation module; transforming the motor-current vector from the stator-fixed coordinate system into the rotor-fixed coordinate system on the basis of the determined rotor angle by means of a second transformation module; generating a test-voltage vector in a voltage-vector coordinate system with a first axis (k), which corresponds to the direction of injection of the test signal, and a second axis, which is perpendicular to the first axis (k), in such a manner that said vector has only one component in the first axis (k), by means of a voltage function generator; transforming the test-voltage vector into the rotor-fixed coordinate system on the basis of a transformation angle determined on the basis of the set currents in the rotor-fixed coordinate system, and outputting the transformed test-voltage vector as a test signal, by means of a third transformation module; wherein the test signal is superimposed on the supply signal by adding the supply signal and the test signal. generating a torque-dependent test signal that depends on the torque of the electric machine and has a higher frequency than a supply signal for the electric machine, driving the electric machine with the supply signal, which corresponds to a manipulated variable generated by a current controller in a dq coordinate system, and with the test signal which is superimposed on the supply signal, capturing phase currents (13, 14, 15) of the electric machine, and determining the rotor angle of the rotor of the electric machine on the basis of the effects of the test signal on the phase currents (13, 14, 15), characterized in that the method comprises the following further steps: transforming the captured phase currents (13, 14, 15) of the electric machine into a motor-current vector in a stator-fixed coordinate system by means of a first transformation module; transforming the motor-current vector from the stator-fixed coordinate system into the rotor-fixed coordinate system on the basis of the determined rotor angle by means of a second transformation module; generating a test-voltage vector in a voltage-vector coordinate system with a first axis (k), which corresponds to the direction of injection of the test signal, and a second axis, which is perpendicular to the first axis (k), in such a manner that said vector has only one component in the first axis (k), by means of a voltage function generator; transforming the test-voltage vector into the rotor-fixed coordinate system on the basis of a transformation angle determined on the basis of the set currents in the rotor-fixed coordinate system, and outputting the transformed test-voltage vector as a test signal, by means of a third transformation module; wherein the test signal is superimposed on the supply signal by adding the supply signal and the test signal. transforming the captured phase currents (13, 14, 15) of the electric machine into a motor-current vector in a stator-fixed coordinate system by means of a first transformation module; transforming the motor-current vector from the stator-fixed coordinate system into the rotor-fixed coordinate system on the basis of the determined rotor angle by means of a second transformation module; generating a test-voltage vector in a voltage-vector coordinate system with a first axis (k), which corresponds to the direction of injection of the test signal, and a second axis, which is perpendicular to the first axis (k), in such a manner that said vector has only one component in the first axis (k), by means of a voltage function generator; transforming the test-voltage vector into the rotor-fixed coordinate system on the basis of a transformation angle determined on the basis of the set currents in the rotor-fixed coordinate system, and outputting the transformed test-voltage vector as a test signal, by means of a third transformation module; wherein the test signal is superimposed on the supply signal by adding the supply signal and the test signal.