Method for estimating motor parameter in a load commutated inverter arrangement, and a load commutated inverter arrangement therefor

1. A method for estimating a motor parameter in a load commutated inverter arrangement, comprising the steps of:

measuring, with a sensor, a motor side ac-voltage;

detecting, with a controller, commutation interval information of the measured motor side ac-voltage;

estimating, with the controller, a motor parameter, comprising:

converting the measured motor side ac-voltage to an internal motor voltage based on the detected commutation interval information,

estimating a firing angle based on the converted internal motor voltage, and

estimating a motor commutation inductance based on the estimated firing angle and the converted internal motor voltage; and

indicating, with the controller, when the estimated motor parameter deviates from a monitoring parameter thereof,

wherein the step of indicating comprises indicating a faulty condition of a motor.

2. The method according to claim 1 , comprising the further steps of:

measuring or estimating a dc-link current; and

wherein said step of estimating a motor parameter comprises:

converting the measured motor side ac-voltage to a dc-link voltage, or converting the measured or estimated dc-link current to an ac-current, based on said detected commutation interval information; and

estimating a motor power based on the measured or estimated dc-link current and the converted dc-link voltage, or estimating a motor power based on the measured motor side ac-voltage and the converted ac-current.

3. The method according to claim 2 , wherein said step of measuring or estimating a dc-link current is performed by estimating the dc-link current through a grid side ac-current transformer.

4. The method according to claim 2 , comprising a further step of estimating a shaft power for said motor power.

5. The method according to claim 2 , comprising the further steps of:

estimating a process power for a compressor driven by said motor power; and

indicating when the estimated motor power deviates from the estimated process power outside a set boundary thereof.

6. The method according to claim 1 , wherein said step of detecting commutation interval information is performed by utilization of known jumps in a motor voltage space vector angle.

7. The method according to claim 1 , wherein said step of detecting commutation interval information is performed by utilization of known voltage jumps during commutation in motor voltages.

8. The method according to claim 1 , wherein said commutation interval information comprises commutation interval length, commutation interval starting angle, and/or commutating phases.

9. The method according to claim 1 , wherein said estimated motor commutation inductance is used to detect a motor faulty condition.

10. The method according to claim 1 , wherein the sensor comprises a transformer.

11. The method according to claim 1 , wherein estimation of the motor parameter is achieved with utilization of motor side ac-voltage sensors only.

12. A load commutated inverter arrangement for estimation of a motor parameter, comprising:

a grid side ac-current sensor;

a motor side ac-voltage sensor; and

a controller arrangement connected to said grid side ac-current sensor, said motor side ac-voltage sensor, and to a motor, wherein

said controller arrangement is configured to detect commutation interval information based on data from said motor side ac-voltage sensor;

said controller arrangement is configured to estimate a motor parameter, configured to convert the measured motor side ac-voltage to an internal motor voltage based on the detected commutation interval information, configured to estimate a firing angle based on the converted internal motor voltage, and configured to estimate a motor commutation inductance based on the estimated firing angle and the converted internal motor voltage; and

said controller arrangement is configured to generate an indication when the estimated motor parameter deviates from a monitoring parameter thereof,

wherein the indication comprises a faulty condition of the motor.

13. A rotary machine arranged in a load commutated inverter arrangement according to claim 12 .