Patent ID: 8410742

Claim:
A method of operating a synchronous motor having a stator comprising a set of electromagnets and having a permanent magnet rotor, the method comprising: calculating in a flux controller a measure of a flux magnitude, which is a magnitude of a stator flux of the motor; calculating in a load angle controller a measure of a load angle, which is an angle between the stator flux and a rotor flux referred to as an axis of rotation of the rotor, wherein information about at least one of a desired motor torque and a reduced motor torque, which is smaller than the desired motor torque, is input to the load angle controller and the load angle controller calculates the measure of the load angle depending on an input motor torque; combining the measure of the flux magnitude and the measure of the load angle to obtain a signal which is to be used to obtain commands for controlling electric currents of the electromagnets of the stator, thereby directly controlling the stator flux, repeatedly calculating a flux limit value which depends on a predetermined maximum value of the stator flux allowed for the motor, which depends on a maximum value of an electric voltage used to drive the currents through the stator electromagnets, and on an actual rotor speed, during acceleration of the rotor while the stator flux is smaller than a maximum flux allowed for the motor; calculating the measure of the flux magnitude depending on the output of a predetermined function, wherein an output of the predetermined function depends on the desired motor torque and corresponds to the magnitude of the stator flux, which results in the desired motor torque using a minimum possible stator current; and calculating the measure of the load angle depending on the desired motor torque.