Abstract: 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.

Abstract: 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.

Abstract: The invention relates to a method in connection with an inverter, the inverter comprising a direct voltage intermediate circuit, an optimum switching table and output power switches. The method comprises steps where phase currents (iA, iC) of the inverter are converted to a synchronous dq coordinate system in order to achieve vector components (id, iq), the synchronous current vector components (id, iq) are low pass filtered in order to achieve current vector components (id,jpf, iq,jpf), a current reference (iq,ref) is generated in the direction of the q axis, a current reference (id,ref) is generated, a torque reference (te,ref) is generated, an absolute value reference (|?|ref) of a flux linkage is generated from the currents and switching commands are formed on the basis of the torque reference (te,ref) and the flux reference (|?|ref) using the optimum switching table (5).

Abstract: A method in connection with converter bridges connected in parallel, whereby the converter bridges are directly connected in parallel and the converter bridges are controlled independently on the basis of control variables, the method comprising the steps of controlling the converter bridges to produce an output switching vector on the basis of the control variables, determining the magnitude of a common-mode current component of the converter bridges, and selecting a zero vector to be used during control as a switching vector on the basis of the sign of the common-mode current component to minimize common-mode current of the converter bridges.