Device and method for determining rotation of an induction machine

1. A device, wherein the device comprises a processing system implemented with one or more processor circuits configured 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.

2. The device according to claim 1 , wherein the processing system is configured to detect a direction of change of the q-component of the current space-vector at a beginning of fulfillment of the condition related to the stator currents, and to determine the direction of rotation based on the detected direction of change.

3. The device according to claim 1 , wherein the processing system is configured to detect a polarity of a first local extreme of the waveform of the q-component of the current space-vector occurring after a beginning of fulfillment of the condition related to the stator currents, and to determine the direction of rotation based on the detected polarity.

4. The device according to claim 1 , wherein the processing system is configured to measure a first time-value indicative of time elapsed from a beginning of fulfillment of the condition related to the stator currents to a moment when the waveform of the q-component of the current space-vector reaches a first local extreme value after the beginning of fulfillment of the condition related to the stator currents, and to estimate the rotation speed based on the measured first time-value.

5. The device according to claim 1 , wherein the processing system is configured to measure at least one second time-value indicative of time elapsed between two local maximum values or between two local minimum values of the waveform of the q-component of the current space-vector, and to estimate the rotation speed based on the measured at least one second time-value.

6. The device according to claim 1 , wherein the processing system is configured to estimate the rotation speed based on the waveform of the q-component of the current space-vector, and subsequently to control the stator voltages to rotate the current space-vector at the estimated rotation speed.

7. The device according to claim 6 , wherein the processing system is configured to estimate a flowing direction of air-gap power of the induction machine based on the stator voltages, the stator currents, and stator resistance when the current space-vector is rotated, to decrease the rotation speed of the current space-vector when the estimated flowing direction is towards the rotor of the induction machine, and to increase the rotation speed of the current space-vector when the estimated flowing direction is out from the rotor of the induction machine.

8. The device according to claim 1 , wherein the processing system is configured to:

monitor whether the waveform of the q-component of the current space-vector reaches a local extreme value within a predetermined time period after a beginning of fulfillment of the condition related to the stator currents, and

estimate, in response to a situation in which the q-component of the current space-vector reaches no local extreme value within the predetermined time period, at least one of the following based on behavior of the induction machine having a magnetic flux generated during the predetermined time period: the rotation speed, the direction of rotation.

9. The device according to claim 1 , wherein the condition related to the stator currents is that the current space-vector has the pre-determined length, and the pre-determined length is within a range from 30% to 100% of a peak-value of a nominal current of the induction machine.

10. The device according to claim 1 , wherein the condition related to the stator currents is that the current space-vector has the predetermined d-component, and the pre-determined d-component is within a range from 20% to 70% of a peak-value of a nominal current of the induction machine.

11. A power electronic converter comprising:

a converter stage for forming stator voltages for an induction machine,

a controller for controlling the stator voltages at least partly based on stator currents of the induction machine, and

a device according to claim 1 for estimating at least one of the following: a rotation speed of a rotor of the induction machine, a direction of rotation of the rotor.

12. 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.

13. 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.

14. A non-volatile computer readable medium encoded with a computer program according to claim 13 .