Magnetic bearing arrangement and method of operating a magnetic bearing arrangement

1. An electromagnetic bearing arrangement for a rotating equipment, the electromagnetic bearing arrangement comprising an electromagnet; an amplifier arrangement based on IGBT switches; a power supply for powering the amplifier arrangement; a controller for controlling the amplifier arrangement to operate the electromagnet; and a position sensor for measuring the position of the rotating equipment in relation to the electromagnet, characterized in that the controller comprises a position control module and a direct force control module, wherein the

the position sensor is operatively connected to the position control module to forward the measured position (S) of the rotating equipment in relation to the electromagnet;

the position control module is configured to calculate a force reference (F ref ) based on the measured position of the rotating equipment in relation to the electromagnet;

the position sensor is operatively connected to the direct force control module to forward the measured position of the rotating equipment in relation to the electromagnet to the direct force control module; and

the electromagnetic bearing arrangement comprises a sensor arrangement for measuring at least one parameter (i u , i d ) indicative of a force exerted by the electromagnet and is operatively connected to the direct force control module to forward the measured parameter indicative of the force exerted by the electromagnet to the direct force control module; and

the direct force control module is configured to calculate an estimated force (F cal ) exerted by the electromagnet based on the measured position of the rotating equipment in relation to the electromagnet and the measured parameter indicative of the force exerted by the electromagnet, to compare the force reference with the estimated force exerted by the electromagnet, and to control the amplifier arrangement to operate the electromagnet by a switch command determined based on said comparison.

2. The arrangement of claim 1 wherein the sensor arrangement for measuring at least one parameter indicative of a force exerted by the electromagnet comprises one or more current sensors and the at least one parameter indicative of a force exerted by the electromagnet comprises one or more currents of the amplifier arrangement.

3. The arrangement of claim 1 wherein the sensor arrangement for measuring a parameter indicative of a force exerted by the electromagnet comprises one or more voltage sensors and the at least one parameter indicative of a force exerted by the electromagnet comprises one or more voltages of the amplifier arrangement.

4. The arrangement of claim 1 wherein the direct force control module comprises

a flux observer submodule configured to calculate a flux (Ψ u , Ψ i ) of the electromagnet based on the measured parameter indicative of the force exerted by the electromagnet; and

a force calculator submodule configured to calculate the estimated force (F cal ) exerted by the electromagnet based on the flux of the electromagnet.

5. The arrangement of claim 1 wherein the direct force control module comprises a force comparator submodule configured to compare the force reference with the estimated force exerted by the electromagnet, to provide a force status based on the comparison, and to determine the a switch command based on the force status.

6. The arrangement of claim 5 wherein the direct force control module comprises a gate selection table submodule configured to provide the switch command for the amplifier arrangement based on the force status.

7. The arrangement of claim 6 wherein the gate selection table submodule holds a table comprising force statuses, and, for each force status, a switch command to be used, and wherein the gate selection table submodule is configured to provide the switch command for the amplifier arrangement by referring to the table.

8. The arrangement of claim 1 comprising a second electromagnet, wherein the direct force control module of the controller is configured to control the amplifier arrangement to operate the second electromagnet by a switch command determined based on said comparison.

9. The arrangement of claim 8 comprising a third and a fourth electromagnet; a second position sensor for measuring the position of the rotating equipment in relation to the third and fourth electromagnets; and a second sensor arrangement for measuring at least one parameter indicative of a force exerted by the third and fourth electromagnets, wherein the

the second position sensor is operatively connected to the position control module of the controller to forward the measured position of the rotating equipment in relation to the third and fourth electromagnets to the position control module;

the second position control module is configured to calculate a second force reference based on the measured position of the rotating equipment in relation to the third and fourth electromagnets;

the position sensor is operatively connected to the direct force control module to forward the measured position of the rotating equipment in relation to the third and fourth electromagnets to the direct force control module;

the second sensor arrangement is operatively connected to the direct force control module of the controller to forward the measured parameter indicative of the force exerted by the third and fourth electromagnets to the direct force control module; and

the direct force control module of the controller is configured to calculate an estimated force exerted by the third and fourth electromagnets based on the measured position of the rotating equipment in relation to the third and fourth electromagnets and the measured parameter indicative of the force exerted by the third and fourth electromagnets, to compare the second force reference with the estimated force exerted by the third and fourth electromagnets, and to control the amplifier arrangement to operate the third and fourth electromagnets by a switch command determined based on the comparison of the second force reference with the estimated force exerted by the third and fourth electromagnets.

10. The arrangement of claim 1 wherein the amplifier arrangement comprises, for each electromagnet to be operated, two switching legs, each switching leg having one IGBT switch and one diode in series, and opposite ends of each switching leg being electrically connected to the power supply, wherein the coil of the electromagnet is electrically connected to the junction between the IGBT switch and the diode of each switching leg.

11. The arrangement of claim 1 wherein the amplifier arrangement comprises, for at least one electromagnet to be operated, two switching legs, each switching leg having two IGBT switches in series, each of the IGBT switches comprising an IGBT and a diode connected in parallel, and opposite ends of each switching leg being electrically connected to the power supply, wherein the coil of the electromagnet is electrically connected to the junction between the IGBT switches of each switching leg.

12. A method of operating an electromagnetic bearing arrangement for a rotating equipment, the electromagnetic bearing arrangement comprising an electromagnet; an amplifier arrangement based on IGBT switches; a power supply for powering the amplifier arrangement; and a position sensor for measuring the position of the rotating equipment in relation to the electromagnet, characterized by the steps of:

measuring the position (S) of the rotating equipment in relation to the electromagnet by the position sensor;

calculating a force reference (F ref ) based on the measured position of the rotating equipment in relation to the electromagnet;

measuring at least one parameter (i u , i d ) indicative of a force exerted by the electromagnet;

calculating an estimated force (F cal l) exerted by the electromagnet based on the measured position of the rotating equipment in relation to the electromagnet and the measured parameter indicative of the force exerted by the electromagnet;

compare the force reference with the estimated force exerted by the electromagnet; and

controlling the amplifier arrangement to operate the electromagnet by a switch command determined based on said comparison.

13. The method of claim 12 comprising:

calculating a flux (Ψ u , Ψ i ) of the electromagnet based on the measured parameter indicative of the force exerted by the electromagnet;

calculating the estimated force (F cal ) exerted by the electromagnet based on the flux of the electromagnet.

14. The method of claim 12 comprising

providing a force status based on the comparison of the force reference with the estimated force exerted by the electromagnet; and

providing the switch command for the amplifier arrangement based on the force status.

15. The method of claim 14 wherein the switch command for the amplifier arrangement is provided by means of referring to a table comprising force statuses, and for each force status a switch command to be used.