Impeller position compensation using field oriented control
A centrifugal pump system having an impeller rotating with first and second magnetic structures on opposite surfaces. A levitation magnetic structure is disposed at a first end of a pump housing having a levitating magnetic field for axially attracting the first magnetic structure. A multiphase magnetic stator at a second end of the pump housing generates a rotating magnetic field for axially and rotationally attracting the second magnetic structure. A commutator circuit provides a plurality of phase voltages to the stator. A sensing circuit determines respective phase currents. A controller calculates successive commanded values for the phase voltages in response to the determined phase currents and a variable commutation angle. The angle is selected to correspond to an axial attractive force of the stator that maintains a levitation of the impeller at a centered position within the pumping chamber.
1. A centrifugal pump system comprising:
a disc-shaped impeller rotating about an axis and having a first magnetic structure disposed at a first surface and a second magnetic structure disposed at a second surface;
a pump housing defining a pumping chamber which receives the impeller;
a levitation magnetic structure disposed at a first end of the pump housing having a levitating magnetic field for axially attracting the first magnetic structure;
a multiphase magnetic stator disposed at a second end of the pump housing for generating a rotating magnetic field for axially and rotationally attracting the second magnetic structure;
a commutator circuit for providing a plurality of phase voltages to the stator;
a sensing circuit determining respective phase currents flowing in response to the phase voltages; and
a controller configured to:
calculate successive commanded values for the phase voltages in response to the determined phase currents; and
select a variable commutation angle, wherein the angle is selected to correspond to an axial attractive force of the stator that maintains a levitation of the impeller at a centered position within the pumping chamber.
2. The system of claim 1 wherein the levitating magnetic field is substantially constant.
3. The system of claim 2 wherein the levitation magnetic structure is comprised of a permanent magnet material.
4. The system of claim 1 wherein the angle for calculating the commanded values is determined in response to a phase current characteristic and a rotational speed of the impeller.
5. The system of claim 4 wherein the phase current characteristic is comprised of a peak current flowing in the stator during a predetermined sampling interval.
6. The system of claim 4 wherein the controller includes a lookup table storing predetermined values for the commutation angle corresponding to respective ranges of the phase current characteristic and the rotational speed.