Method for determining the movement of a synchronous machine, in which method: - a frequency converter is fitted to supply power between the synchronous machine and an electricity network, the frequency converter comprises a load bridge which is connected to the stator winding of the synchronous machine, a control of the frequency converter is fitted to control the solid state switches of the load bridge, for forming a variable amplitude and variable frequency control voltage to the phases of the stator winding of the synchronous machine, - an encoder is fitted via a friction wheel to the rim of the rotor of the synchronous machine, in which case when the rotor rotates the rotating shaft on the encoder fixed to the friction wheel rotates via the friction wheel, wherein the encoder comprises an output for the movement signal expressing the movement of the rotor of the synchronous machine, the control comprises an input for the movement signal of the encoder, - the movement signal of the encoder is read, - the control measures a current of the stator winding of the synchronous machine, - the position error of the rotor of the synchronous machine is determined on the basis of the measured current of the stator winding as well as on the basis of the stator voltage determined from the switching reference of the solid-state switches of the load bridge, - the read movement signal of the encoder is corrected by the control on the basis of the aforementioned determination of the position error of the rotor of the synchronous machine, characterized in that: - a correcting circuit of an encoder signal, wherein the encoder signal is the read movement signal of the encoder scaled by a transmission ratio between the friction wheel of the encoder and the rim of the rotor of the synchronous machine, functions in the following manner: - the position error is filtered with a low-pass filter, - on the basis of the filtered position error the encoder signal is corrected by repetitively summing a correction term, which is proportional to the magnitude of the position error, into the encoder signal, wherein the correcting circuit of the encoder signal comprises a scaling factor, the value of which is determined as a function of the velocity of the rotor, and - the value of the scaling factor is determined as zero in the environment of zero speed of the rotor, wherein, when the value of the scaling factor is zero, the aforementioned encoder signal is not corrected with the correcting circuit such that the correcting circuit of the encoder signal is fitted to correct the encoder signal only when the velocity of the rotor differs from zero by more than a set limit value. - a frequency converter is fitted to supply power between the synchronous machine and an electricity network, the frequency converter comprises a load bridge which is connected to the stator winding of the synchronous machine, a control of the frequency converter is fitted to control the solid state switches of the load bridge, for forming a variable amplitude and variable frequency control voltage to the phases of the stator winding of the synchronous machine, - an encoder is fitted via a friction wheel to the rim of the rotor of the synchronous machine, in which case when the rotor rotates the rotating shaft on the encoder fixed to the friction wheel rotates via the friction wheel, wherein the encoder comprises an output for the movement signal expressing the movement of the rotor of the synchronous machine, the control comprises an input for the movement signal of the encoder, - the movement signal of the encoder is read, - the control measures a current of the stator winding of the synchronous machine, - the position error of the rotor of the synchronous machine is determined on the basis of the measured current of the stator winding as well as on the basis of the stator voltage determined from the switching reference of the solid-state switches of the load bridge, - the read movement signal of the encoder is corrected by the control on the basis of the aforementioned determination of the position error of the rotor of the synchronous machine, - a correcting circuit of an encoder signal, wherein the encoder signal is the read movement signal of the encoder scaled by a transmission ratio between the friction wheel of the encoder and the rim of the rotor of the synchronous machine, functions in the following manner: - the position error is filtered with a low-pass filter, - on the basis of the filtered position error the encoder signal is corrected by repetitively summing a correction term, which is proportional to the magnitude of the position error, into the encoder signal, wherein the correcting circuit of the encoder signal comprises a scaling factor, the value of which is determined as a function of the velocity of the rotor, and - the value of the scaling factor is determined as zero in the environment of zero speed of the rotor, wherein, when the value of the scaling factor is zero, the aforementioned encoder signal is not corrected with the correcting circuit such that the correcting circuit of the encoder signal is fitted to correct the encoder signal only when the velocity of the rotor differs from zero by more than a set limit value.