Frequency converter, comprising a load bridge and also a control of the load bridge, supplying electricity between the load bridge and an electric machine connected to the load bridge; and which frequency converter comprises a determination for the current and/or voltage of the aforementioned electric machine, and which frequency converter comprises a determination for the position of the rotor of the electric machine; wherein a load bridge is fitted to supply a first alternating voltage or current excitation signal to the aforementioned electric machine, which first alternating voltage or current excitation signal is formed in relation to the electrical angle of the electric machine, and in that the frequency converter is fitted to determine a first alternating current or voltage response signal (9,16) corresponding to the aforementioned first alternating voltage or current excitation signal, and in that the position of the rotor is determined on the basis of the first alternating current or voltage response signal (9,16), characterized in that the load bridge is fitted to supply a first and a second alternating voltage or current excitation signal to the aforementioned electric machine, which first and second alternating voltage or current excitation signals are formed in relation to the electrical angle of the electric machine, and which first and second alternating voltage or current excitation signals are fitted to be of opposite directions in their rotation direction, and in that the position of the rotor is determined on the basis of the first (9,16) and the second (10,17) alternating current or voltage response signals corresponding to the aforementioned first and second alternating voltage or current excitation signals, whereby, since the phase shift between the first alternating voltage or current excitation signal and the first alternating current or voltage response signal is in the opposite direction with regard to the phase difference between the second alternating voltage or current excitation signal and the second alternating current or voltage response signal, the phase difference between the first and the second alternating current or voltage response signal is compensated, wherein the position of the rotor of the electric machine is determined from the first and the second alternating current or voltage response signal as follows: the first and the second alternating current or voltage response signals are measured, and on the basis of the measured signals the amplitudes of the alternating current or voltage response signals are determined as a function Î(θ) of an electrical angle reference; the determined amplitudes of the alternating current or voltage response signals are recorded, in which case the graphs (16, 17) of the amplitudes of the alternating current or voltage response signals are formed as a function of the electrical angle reference; the value of the electrical angle corresponding to the greatest value of the amplitude is determined from the graphs of the amplitude of the first and the second alternating current or voltage response signals such that the value of the amplitude of the greatest measured alternating current or voltage response signal is identified, and a curve fit is formed by means of the measuring points of the environment of the greatest value, where after the value of the electrical angle corresponding to the maximum value of the curve fit is resolved; the value (25, 26) of the electrical angle being resolved separately for the first and the second graph of the amplitude of the alternating current or voltage response signals and the value of the electrical angle comprising the position information of the rotor is determined as an average value of the value of the electrical angle corresponding to the maximum value of the graph of the amplitude of the first alternating current or voltage response signal and the value of the electrical angle corresponding to the maximum value of the graph of the amplitude of the second alternating current or voltage response signal.