Method and arrangement for operating pump system

A computer program product comprising program instructions stored in a non-transitory computer readable medium, which program instructions, when run by a computing apparatus controlling an AC drive which is operably coupled to a three-phase induction motor operably coupled to a rotary pump cause the computing apparatus to carry out the following:

• estimate a rotational velocity of the motor, the estimating including:
• supplying, by the AC drive, the induction motor with a three-phase AC voltage at multiple different angular velocities;
• monitoring an output current of the AC drive generated in response to the supplied voltage at the multiple different angular velocities;
• determining an angular velocity of the supplied voltage at which at least one predetermined characteristic in the monitored output current is detected;
• and
• determining a rotational velocity corresponding to the determined angular velocity as an estimate of the rotational velocity of the motor,
• and operate the pump system on the basis of the determined estimate of the rotational velocity of the motor.

An apparatus for operating a pump system, the pump system comprising a rotary pump, a three-phase induction motor operably coupled to the rotary pump to rotate the pump, and an AC drive operably coupled to the induction motor to control the motor, the apparatus having at least one processor and at least one memory storing computer program code which, when executed with the at least one processor, cause the apparatus to:

• estimate a rotational velocity of the motor, the estimating including
• supplying, by the AC drive, the induction motor with a three-phase AC voltage at multiple different angular velocities;
• monitoring an output current of the AC drive generated in response to the supplied voltage at the multiple different angular velocities;
• determining an angular velocity of the supplied voltage at which at least one predetermined characteristic in the monitored output current is detected;
• and
• determining a rotational velocity corresponding to the determined angular velocity as an estimate of the rotational velocity of the motor,
• and operate the pump system on the basis of the determined estimate of the rotational velocity of the motor.

An electric drive comprising an electric power converter configured to be operably coupled to an induction motor coupled to a rotary pump to rotate the pump, wherein the electric drive is configured to:

• estimate a rotational velocity of the motor by:
• supplying the induction motor with a three-phase AC voltage at multiple different angular velocities;
• monitoring an output current of the electric drive generated in response to the supplied voltage at the multiple different angular velocities;
• determining an angular velocity of the supplied voltage at which at least one predetermined characteristic in the monitored output current is detected;
• and
• determining a rotational velocity corresponding to the determined angular velocity as an estimate of the rotational velocity of the motor,
• and operate the pump on the basis of the determined estimate of the rotational velocity of the motor.