Turbo compressor

1. A turbo compressor for compressing refrigerant, the turbo compressor being disposed in a refrigerant circuit that performs a refrigeration cycle, comprising:

an impeller;

a drive shaft;

a drive support unit through which currents in a predetermined current range flow to generate electromagnetic forces, the drive support unit being configured to rotationally drive the drive shaft by using one of the electromagnetic forces and to support a radial load of the drive shaft in a contactless manner by using another one of the electromagnetic forces,

the drive support unit including one bearingless motor and one radial magnetic bearing;

a power source that allows the currents to flow through the drive support unit; and

a controller that controls the power source,

wherein the bearingless motor includes a rotor-stator pair constituted by a rotor and a stator, and is configured to rotationally drive the drive shaft and to support the radial load of the drive shaft in the contactless manner,

wherein the bearingless motor, the radial magnetic bearing, and a pair of touch-down bearings are housed within a compartment formed within a casing, with the bearingless motor being arranged side-by-side with the radial magnetic bearing in the casing,

wherein the bearingless motor and the radial magnetic bearing are arranged in the compartment between the pair of touch-down bearings,

wherein the radial magnetic bearing includes a plurality of electromagnets and is configured to support the radial load of the drive shaft in the contactless manner, and

wherein the one radial magnetic bearing is the only radial magnetic bearing in the turbo compressor, and is arranged on only one side of the drive shaft in its axial direction as viewed from the bearingless motor,

wherein a magnetic flux generated in the drive support unit to rotationally drive the impeller and the drive shaft is represented by a driving magnetic flux BM,

wherein a magnetic flux generated in the drive support unit to support the radial load of the drive shaft is represented by a supporting magnetic flux BS,

wherein respective sizes of the rotor and the stator of the bearingless motor impose an upper limit of Bmax on a magnetic flux generated in the drive support unit by a total current flowing through the drive support unit,

wherein the controller issues motor power commands to the power source that limit a maximum value of a sum of the driving magnetic flux BM and the supporting magnetic flux BS in a predetermined operating region of the turbo compressor to (BM+BS)max,

wherein the controller issues, as one of the motor power commands, a command causing a magnetic flux represented by BMmax to be generated in the drive support unit to generate a driving torque corresponding to a maximum torque load in the predetermined operating region,

wherein the controller issues, as another one of the motor power commands, a command causing a magnetic flux represented by BSmax to be generated in the drive support unit to support a maximum radial load of the drive shaft in the predetermined operating region, and

wherein the controller issues the respective motor power commands to control the power source such that a relationship given by (BM+BS)max≤Bmax<BMmax+BSmax is satisfied in the predetermined operating region of the turbo compressor.

2. The turbo compressor according to claim 1 ,

wherein the controller controls the power source by issuing a motor power command, in response to the turbo compressor operating in a rotating-stall generation region and a surging region, that causes a ratio of current IS for generating the supporting magnetic flux BS to current IM for generating the driving magnetic flux BM to be increased, compared to during normal operation at a same rotational speed.

3. The turbo compressor according to claim 1 ,

wherein the controller controls the power source by issuing a motor power command, in response to the turbo compressor operating in a rotating-stall generation region and a surging region, that causes a ratio of current IS for generating the supporting magnetic flux BS to current IM for generating the driving magnetic flux BM to be increased as a refrigerant volumetric flow rate decreases, when compared at a same rotational speed during normal operation.

4. The turbo compressor according to claim 1 ,

wherein the drive support unit includes first and second coils through which respective first and second coil currents in the predetermined current range flow, and

wherein

the driving magnetic flux BM is generated in the drive support unit as a result of the flow of the first coil current through the first coil, the supporting magnetic flux BS is generated in the drive support unit as a result of the flow of the second coil current through the second coil,

a value of the first coil current flowing through the first coil when the driving torque corresponding to the maximum torque load is generated is represented by a maximum torque current IBMmax,

a value of the second coil current flowing through the second coil when the maximum radial load of the drive shaft is supported is represented by a maximum support force current IBSmax, and

a combined magnetic flux generated in the drive support unit by causing a current obtained by adding together the maximum torque current IBMmax and the maximum support force current IBSmax to flow through the first and second coils, respectively, is represented by BMSmax,

the drive support unit is configured such that a relationship given by BMSmax<BMmax+BSmax is satisfied.

5. The turbo compressor according to claim 1 ,

wherein the controller controls the power source by issuing a motor power command, in response to the turbo compressor operating in a surging region or the rotation of the drive shaft being stopped under normal operation, that causes only a current for supporting the radial load of the drive shaft in the contactless manner flows through the drive support unit by stopping a current that contributes to a driving torque from flowing through the drive support unit.

6. The turbo compressor according to claim 1 ,

wherein the radial magnetic bearing is arranged at a position on the drive shaft at which a larger radial load than the radial load supported by the bearingless motor is exerted.

7. The turbo compressor according to claim 6 ,

wherein the impeller is connected to one end of the drive shaft, and

wherein the radial magnetic bearing is arranged at a position on the drive shaft that is closer to the impeller than the bearingless motor in the axial direction of the drive shaft.

8. The turbo compressor according to claim 6 ,

wherein the bearingless motor is configured as a surface permanent magnet bearingless motor.

9. The turbo compressor according to claim 1 ,

wherein the bearingless motor is arranged at a position on the drive shaft at which a larger radial load than the radial load supported by the radial magnetic bearing is exerted.

10. The turbo compressor according to claim 9 ,

wherein the impeller is connected to one end of the drive shaft, and

wherein the bearingless motor is arranged at a position on the drive shaft that is closer to the impeller than the radial magnetic bearing in the axial direction of the drive shaft.

11. The turbo compressor according to claim 9 ,

wherein the bearingless motor is configured as a consequent-pole bearingless motor or an interior permanent magnet bearingless motor.

12. A refrigeration apparatus comprising:

a heat source unit including the turbo compressor according to claim 1 ; and

at least one utilization unit.

13. The refrigeration apparatus according to claim 12 ,

wherein the at least one utilization unit comprises a plurality of utilization units, and

wherein the plurality of utilization units perform air-conditioning of a plurality of air-conditioning-target spaces.

14. The turbo compressor according to claim 1 ,

wherein the controller issues, as respective ones of the motor power commands,

a command controlling the power source to generate a voltage that increases the driving magnetic flux BM in the drive support unit to the magnetic flux represented by BMmax to generate the driving torque corresponding to the maximum torque load in the predetermined operating region and simultaneously decreasing the supporting magnetic flux BS in the drive support unit, and

a command issued in response to the turbo compressor operating in a surging region of the predetermined operating region that controls the power source to generate a voltage that increases the supporting magnetic flux BS in the drive support unit to the magnetic flux represented by BSmax to support the maximum radial load of the drive shaft in the predetermined operating region.