STABLE AND PASSIVE OBSERVER-BASED V/HZ CONTROL FOR SYNCHRONOUS MOTORS

According to an aspect, there is provided an apparatus for a drive for driving a synchronous motor. The apparatus comprises means for performing the following. The apparatus obtains a stator current vector and estimates, using a state observer, a stator flux linkage vector based on the stator current vector, a voltage reference vector, a stator angular frequency reference and a control-rotor rotation angle estimated by the state observer and being defined as an angle between control and rotor coordinates. The state observer is a speed-sensorless back-electromotive-force-based state observer defined in the control coordinates and based on a mathematical model for the synchronous motor. The apparatus performs speed-sensorless state-feedback control based on the estimated stator flux linkage vector, the stator current vector, a stator flux linkage reference vector and the stator angular frequency reference for calculating the stator voltage reference vector. Finally, the apparatus applies the stator voltage reference vector to an inverter of the drive.