An apparatus comprises a processing system (201) configured to produce voltage control signals for controlling an electrical machine (202) comprising two or more multiphase stator windings. The processing system is configured to produce the voltage control signals on the basis of rotation-converted stator currents expressed in a coordinate system bound to a rotor of the electrical machine and on the basis of a model of the electrical machine modeling at least inductances of the multiphase stator windings and mutual inductances between the multiphase stator windings. The processing system is configured to convert phase currents of the multiphase stator windings into the rotation-converted stator currents with a conversion rule corresponding to a form of the model of the electrical machine where each of the stator flux-linkages of the model is dependent on only one of the rotation-converted stator currents in spite of the mutual inductances between the multiphase stator windings.