Device and method for determining rotation of an induction machine

A method, wherein the method comprises:

• controlling stator voltages of an induction machine to constitute a voltage space-vector having a fixed direction with respect to a stator of the induction machine,
• controlling a length of the voltage space-vector to regulate stator currents of the induction machine to fulfill a condition that a current space-vector constituted by the stator currents has a pre-determined length, and
• estimating at least one of the following based on a waveform of a q-component of the current space-vector:
• rotation speed of a rotor of the induction machine, a direction of rotation of the rotor,
• wherein a d-component of the current space-vector is parallel with the voltage space-vector and the q-component of the current space-vector is perpendicular to the voltage space-vector.

A computer program, wherein the computer program comprises computer executable instructions for controlling a programmable processor to:

• control stator voltages of an induction machine to constitute a voltage space-vector having a fixed direction with respect to a stator of the induction machine,
• control a length of the voltage space-vector to regulate stator currents of the induction machine to fulfill a condition that a current space-vector constituted by the stator currents has a pre-determined length, and
• estimate at least one of the following based on a waveform of a q-component of the current space-vector:
• rotation speed of a rotor of the induction machine, a direction of rotation of the rotor,
• wherein a d-component of the current space-vector is parallel with the voltage space-vector and the q-component of the current space-vector is perpendicular to the voltage space-vector.