Bearingless motor system, compressor and refrigeration device

Abstract

A bearingless motor (110) includes a rotor (111) disposed on a rotating shaft (101), and a stator (112) having a shaft support winding (113) and a motor winding (115). The first inverter (114) supplies power to the shaft support winding (113) and generates a shaft support force that supports the rotating shaft (101) in a non-contact manner. The second inverter (116) supplies power to the motor winding (115), thereby generating a rotational torque on the rotating shaft (101). The control unit (200) causes one or both of the first inverter (114) and the second inverter (116) to output a voltage or a current in which a harmonic wave obtained by multiplying the rotational frequency of the bearingless motor (110) by a natural number of 2 or more is superimposed so as to reduce fluctuations in the shaft supporting force.

Description

Technical Field

[0001] This disclosure relates to a bearingless motor system, a compressor, and a refrigeration device. Background Technology

[0002] Previously, bearingless motors were known that integrated the motor and the magnetic circuit of the magnetic bearing (Patent Document 1). Bearingless motors have motor windings and shaft support windings housed in slots in the stator. Thus, a set of rotor and stator can generate both a motor torque that rotates the motor's rotating shaft and a shaft support force that supports the rotating shaft in a non-contact manner. The shaft support force is a force acting radially along the rotating shaft and suspending the rotating shaft at the center of the stator.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2004-120886 Summary of the Invention

[0006] -The technical problem the invention aims to solve-

[0007] In existing bearingless motors, the shaft support current is controlled to obtain the required shaft support force, based on the premise that the relationship between shaft support force and shaft support current does not depend on the electric rotation angle of the motor rotor (electric angle: the angle obtained by multiplying the mechanical rotation angle of the rotor by the number of pole pairs of the motor).

[0008] However, in reality, due to the influence of spatial high-order harmonics determined by the shape of the motor's magnetic circuit, the relationship between the shaft support force and the shaft support current will change depending on the rotor's rotation angle (electric angle). This will lead to the following problem: the rotating shaft will generate radial vibration, and in the worst case, it will touchdown.

[0009] The purpose of this disclosure is to provide a bearingless motor capable of generating the required shaft support force independently of the rotor's rotation angle (electric angle).

[0010] - Technical solutions used to solve technical problems -

[0011] A first aspect of this disclosure relates to a bearingless motor system 100, comprising a rotating shaft 101, a bearingless motor 110, a first inverter 114, a second inverter 116, and a control unit 200. The bearingless motor 110 includes a rotor 111 disposed on the rotating shaft 101 and a stator 112 disposed radially outward of the rotor 111 and having a shaft support winding 113 and a motor winding 115. The first inverter 114 supplies power to the shaft support winding 113, thereby generating a shaft support force that supports the rotating shaft 101 in a non-contact manner. The second inverter 116 supplies power to the motor winding 115, thereby generating a rotational torque on the rotating shaft 101. The control unit 200 controls the first inverter 114 and the second inverter 116. The control unit 200 causes one or both of the first inverter 114 and the second inverter 116 to output a voltage or current superimposed with high-order harmonics in order to reduce the fluctuation of the shaft support force. The high-order harmonics are obtained by multiplying the rotation frequency of the bearingless motor 110 by a natural number greater than 2.

[0012] In the first aspect, a voltage or current superimposed with higher harmonics is supplied to the shaft support winding 113 or the motor winding 115, wherein the higher harmonics are obtained by multiplying the rotational frequency of the bearingless motor 110 by a natural number greater than 2. Therefore, the required shaft support force can be generated independently of the rotational angle (electrical angle) of the rotor 111, thereby enabling the rotating shaft 101 to rotate smoothly.

[0013] The second aspect of this disclosure, based on the first aspect, involves the shaft support winding 113 and the motor winding 115 arranged in a plurality of first slots 121, which are circumferentially arranged on the stator 112. The order of the higher harmonics is determined by a value obtained by dividing the number of the first slots 121 by the number of pole pairs of the bearingless motor 110, and one or more factors selected from the number of pole pairs.

[0014] In the second aspect, it is possible to suppress fluctuations in the mutual inductance between the shaft support winding 113 and the motor winding 115, which are determined by the spatial higher harmonics due to the magnetic circuit characteristics of the bearingless motor 110, and which are dependent on the rotation angle (electric angle) of the rotor 111 of the bearingless motor 110.

[0015] The third aspect of this disclosure, based on the first or second aspect, involves a rotor 111 having a plurality of permanent magnets 123A and 123B arranged in a plurality of second slots 122 circumferentially on the rotor 111. The order of the higher harmonics is determined by one or more factors selected from the number of the second slots 122 divided by the number of pole pairs of the bearingless motor 110, and the number of the permanent magnets 123A and 123B constituting one pole of the rotor 111.

[0016] In the third aspect, it is possible to suppress the fluctuation of the mutual inductance between the shaft support winding 113 and the motor winding 115 due to the spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor 110, which depends on the rotation angle (electric angle) of the rotor 111.

[0017] Based on any one of the first to third aspects, the fourth aspect of this disclosure states that the control unit 200 adds a correction signal to the control signal of one or both of the first inverter 114 and the second inverter 116, thereby causing one or both of the first inverter 114 and the second inverter 116 to output a voltage or current superimposed with the higher harmonics.

[0018] In the fourth aspect, high-order harmonics can be superimposed on the control signal of the first inverter 114 for shaft support or the control signal of the second inverter 116 for motor drive, which cancels the influence of spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor 110.

[0019] The fifth aspect of this disclosure, based on the fourth aspect, states that the correction signal is determined according to the electrical angle of the rotor 111, the current value of the shaft support winding 113, and the current value of the motor winding 115.

[0020] In the fifth aspect, by adding a correction signal to the control signal of one or both of the first inverter 114 and the second inverter 116, it is possible to cancel the influence of spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor 110.

[0021] The sixth aspect of this disclosure relates to a compressor 10 comprising a bearingless motor system 100 as described in any one of the first to fifth aspects, and compression mechanisms 102, 103, said compression mechanisms 102, 103 being driven by said bearingless motor system 100 to compress fluid.

[0022] In the sixth aspect, in the bearingless motor system 100 constituting the compressor 10, the required shaft support force can be generated without relying on the rotation angle (electric angle) of the rotor 111, so the operation of the compressor 10 is stable and the reliability is improved.

[0023] The seventh aspect of this disclosure relates to a refrigeration apparatus 1, which includes the compressor 10 of the sixth aspect.

[0024] In the seventh aspect, in the bearingless motor system 100 constituting the compressor 10 for the refrigeration device 1, the required shaft support force can be generated without relying on the rotation angle (electric angle) of the rotor 111, thus the operation of the refrigeration device 1 is stable and the reliability is improved. Attached Figure Description

[0025] Figure 1 This is a schematic diagram showing a simplified structure of a compressor including the bearingless motor system of the first embodiment.

[0026] Figure 2 This is a diagram showing the circuit structure of the bearingless motor system according to the first embodiment.

[0027] Figure 3 This is a diagram showing the circuit structure of the bearingless motor system according to the first embodiment.

[0028] Figure 4 This is a diagram showing an example of the cross-sectional structure of a bearingless motor in the direction perpendicular to the axis of rotation.

[0029] Figure 5 This is another example of a cross-sectional structure of a bearingless motor in a direction perpendicular to the axis of rotation.

[0030] Figure 6 This diagram illustrates how the shaft support force of a bearingless motor fluctuates depending on the electrical angle.

[0031] Figure 7 This is a diagram showing the structure of the control unit of the bearingless motor system according to the first embodiment.

[0032] Figure 8 It means in Figure 7 The diagram shows an example of a structure in the control unit that applies a correction signal to the control signal of the inverter for shaft support.

[0033] Figure 9 This is a diagram illustrating one example of the calculation of correction amount in the control unit of the bearingless motor system of the first embodiment.

[0034] Figure 10 This is a diagram illustrating one example of the calculation of correction amount in the control unit of the bearingless motor system of the first embodiment.

[0035] Figure 11 This is another example of calculating the correction amount in the control unit of the bearingless motor system of the first embodiment.

[0036] Figure 12 This is another example of calculating the correction amount in the control unit of the bearingless motor system of the first embodiment.

[0037] Figure 13 It is a diagram showing the waveform of the current output from the inverter for shaft support in the bearingless motor system of the first embodiment.

[0038] Figure 14 This is a simplified structural diagram of an air conditioning unit (an example of a refrigeration unit) according to the second embodiment.

[0039] Figure 15 This is a schematic diagram illustrating a structural modification of the compressor that can be applied to the air conditioning device of the second embodiment.

[0040] Figure 16 This is a schematic diagram illustrating a structural modification of the compressor that can be applied to the air conditioning device of the second embodiment.

[0041] Figure 17 This is a schematic diagram illustrating a structural modification of the compressor that can be applied to the air conditioning device of the second embodiment.

[0042] Figure 18 This is a schematic diagram illustrating a structural modification of the compressor that can be applied to the air conditioning device of the second embodiment.

[0043] Figure 19 This is a schematic diagram illustrating a structural modification of the compressor that can be applied to the air conditioning device of the second embodiment. Detailed Implementation

[0044] The embodiments of this disclosure are described below with reference to the accompanying drawings. It should be noted that the following embodiments are essentially preferred examples and are not intended to limit the invention, its application, or its scope of use. Furthermore, in the drawings, the same symbols denote the same constituent elements; however, to make the drawings clear and concise, dimensions such as length, width, thickness, and depth have been appropriately modified according to actual proportions, and there may be discrepancies between the actual relative dimensions and the actual dimensions.

[0045] (First Implementation)

[0046] <Structure of a Bearingless Motor System>

[0047] Hereinafter, an example is given of a case in which the bearingless motor system 100 of the first embodiment is installed inside the pressure vessel 150 to form a compressor 10, but the application of the bearingless motor system 100 is not particularly limited.

[0048] like Figure 1 As shown, the bearingless motor system 100 mainly includes a rotating shaft 101, thrust magnetic bearings 105 and 107, a bearingless motor 110, and a radial magnetic bearing 130. In the following description, the direction extending along the axis of the rotating shaft 101 is referred to as the axial direction, the direction extending along the circle centered on the rotating shaft 101 is referred to as the circumferential direction, and the direction perpendicular to the axis of the rotating shaft 101 is referred to as the radial direction.

[0049] At one axial end of the rotating shaft 101, a first impeller 102 and a second impeller 103 constituting the compression mechanism of the compressor 10 are provided. It should be noted that... Figure 1 The diagrams of components such as pipes, control units, and power supply units that make up the compression mechanism are omitted.

[0050] Thrust magnetic bearings 105 and 107 are arranged at the other end of the rotating shaft 101 along the axial direction, so that electromagnetic force acts on the rotating shaft 101 in two directions along the axial direction. Specifically, a radially extending disk portion 104 is provided on the rotating shaft 101, and a first thrust magnetic bearing 105 is arranged so that electromagnetic force acts on the disk portion 104 in the axial direction, and a second thrust magnetic bearing 107 so that electromagnetic force acts on the disk portion 104 in the opposite axial direction. Thus, the thrust magnetic bearings 105 and 107 can support the disk portion 104 in a non-contact manner by electromagnetic force.

[0051] The first thrust magnetic bearing 105 has a first electromagnet coil 106. The second thrust magnetic bearing 107 has a second electromagnet coil 108. The thrust magnetic bearings 105 and 107 can control the position of the disk portion 104, i.e., the axial position of the rotating shaft 101, by controlling the current flowing in the first electromagnet coil 106 and the second electromagnet coil 108.

[0052] The bearingless motor 110 is configured to drive the rotating shaft 101 to rotate via electromagnetic force and to support the radial load of the rotating shaft 101 in a non-contact manner. The radial magnetic bearing 130 is configured to support the radial load of the rotating shaft 101 in a non-contact manner. The bearingless motor 110 and the radial magnetic bearing 130 are arranged axially along the rotating shaft 101. In this example, the bearingless motor 110 is located near the thrust magnetic bearings 105 and 107, and the radial magnetic bearing 130 is located near the impellers 102 and 103. The radial position of the rotating shaft 101 is controlled by the bearingless motor 110 and the radial magnetic bearing 130.

[0053] The bearingless motor 110 has a rotor 111 and a stator 112. The rotor 111 is fixed to a rotating shaft 101. The stator 112 is disposed radially outside the rotor 111 and is fixed to the inner peripheral wall of the pressure vessel 150. Multiple permanent magnets 123A and 123B (see reference) are embedded in the core portion of the rotor 111. Figure 4 , Figure 5 The stator 112 has multiple teeth 112b (see reference). Figure 4 , Figure 5 The shaft 101 is supported by a shaft support winding 113 and a motor winding 115 wound on each tooth 112b. The shaft support force that supports the rotating shaft 101 in a non-contact manner is generated by supplying power to the shaft support winding 113. The rotational torque that causes the rotating shaft 101 to rotate is generated by supplying power to the motor winding 115. The shaft support winding 113 and the motor winding 115 are multiphase windings with three or more phases (in this example, three-phase windings: U-phase, V-phase, and W-phase).

[0054] The radial magnetic bearing 130 is fixed to the inner peripheral wall of the pressure vessel 150. The diameter of the magnetic body 131 arranged on the rotating shaft 101 opposite to the radial magnetic bearing 130 may be larger than the diameter of the other parts. The radial magnetic bearing 130 includes a stator 132 having a plurality of teeth (not shown) and an electromagnetic coil 135 wound on each tooth.

[0055] <Circuit diagram of a bearingless motor system>

[0056] like Figure 2 As shown, power is supplied from the first inverter 114 to the shaft support winding 113 of the bearingless motor 110. For example... Figure 3 As shown, power is supplied from the second inverter 116 to the motor windings 115 of the bearingless motor 110. Inverters 114 and 116 can be, for example, PWM (Pulse Width Modulation) inverters using switching elements. Inverters 114 and 116 are located outside the pressure vessel 150 and connected to the windings 113 and 115 via dedicated hermetically sealed terminals that electrically connect the interior and exterior of the pressure vessel 150. Inverters 114 and 116 convert the input DC current to generate three-phase AC current for supplying to the windings 113 and 115.

[0057] In the bearingless motor system 100 of this embodiment, inverters 114 and 116 are controlled by the control unit 200 (see reference 100). Figure 7 Control unit 200 causes one or both of the first inverter 114 and the second inverter 116 to output a voltage or current superimposed with high-order harmonics, in order to reduce the shaft support force fluctuation of the bearingless motor 110 (see reference). Figure 2 , Figure 3The higher harmonics are obtained by multiplying the rotational frequency of the bearingless motor 110 by a natural number greater than 2. The specific details of how the control unit 200 controls the inverter will be described below.

[0058] It should be noted that the rotational frequency f of the bearingless motor 110 and the electrical angle φ of the rotor 111 (i.e., the mechanical angle multiplied by the number of pole pairs of the motor) satisfy the following relationship: φ=∫ωdt=∫2πfdt. The electrical angle φ is the angle obtained by multiplying the mechanical rotation angle of the rotor 111 by the number of pole pairs of the bearingless motor 110, ω is the angular rotational speed (electrical angle) (=number of pole pairs of the motor × angular rotational speed (mechanical angle)), ∫dt is the time integral, and π is pi.

[0059] <Construction of a Bearingless Motor>

[0060] There are no particular restrictions on the type of bearingless motor 110. For example, it can be an SPM (Surface Permanent Magnet) type bearingless motor, an Inset type bearingless motor, an IPM (Interior Permanent Magnet) type bearingless motor, a BPM (Buried Permanent Magnet) type bearingless motor, a Consequent Pole type bearingless motor, etc. Alternatively, it can be a synchronous reluctance type bearingless motor whose rotor does not contain magnets.

[0061] Figure 4 The cross-sectional structure of the bearingless motor 110 when configured as a 4-pole, 36-slot BPM type bearingless motor is shown as an example. Figure 4 In the structure shown, the stator 112 has an annular back yoke 112a and 36 teeth 112b arranged circumferentially along the back yoke 112a. Each tooth 112b extends radially inward to form 36 first slots 121, which are surrounded by adjacent teeth 112b and the back yoke 112a. Shaft support windings 113 and motor windings 115 are arranged in each first slot 121. On the rotor 111, 24 second slots 122 are arranged circumferentially. A permanent magnet 123A with a north pole or a permanent magnet 123B with a south pole is arranged in each second slot 122. The permanent magnets 123A with a north pole and the permanent magnets 123B with a south pole are respectively arranged in 6 adjacent second slots 122 in the circumferential direction. In other words, two sets of permanent magnets 123A with N poles arranged in six adjacent second slots 122 and two sets of permanent magnets 123B with S poles arranged in six adjacent second slots 122 are alternately arranged in the circumferential direction. Therefore, in Figure 4 In the case of the bearingless motor 110 shown, the number of pole pairs is 2.

[0062] Figure 5 The cross-sectional structure of the bearingless motor 110, configured as a 6-pole, 9-slot IPM type bearingless motor, is shown as an example. Figure 5 In the structure shown, the stator 112 has an annular back yoke 112a and nine teeth 112b arranged circumferentially along the back yoke 112a. Each tooth 112b extends radially inward, forming nine first slots 121, which are surrounded by adjacent teeth 112b and the back yoke 112a. Shaft support windings 113 and motor windings 115 are arranged in each first slot 121. On the rotor 111, six second slots 122 are arranged circumferentially. In each second slot 122, two permanent magnets 123A (N pole) or two permanent magnets 123B (S pole) are spaced apart. That is, three sets of two adjacent N-pole permanent magnets 123A and three sets of two adjacent S-pole permanent magnets 123B are alternately arranged circumferentially. Therefore, in Figure 5 In the case of the bearingless motor 110 shown, the number of pole pairs is 3.

[0063] <Inverter Control>

[0064] In a bearingless motor, the relationship between the shaft support force and the shaft support current can be expressed using a rotating coordinate system as shown in the following equation.

[0065] [Formula 1]

[0066]

[0067] [Equation 2]

[0068]

[0069] Here, F x F y It is the shaft support force in the rotating coordinate system, i sd i sq M is the shaft support current, and M is the correlation coefficient matrix between the shaft support force and the shaft support current. md M mq It is the mutual inductance between the shaft support winding and the motor winding, i md i mq It is the motor current.

[0070] To support the rotating shaft in a non-contact manner, the shaft support force needs to be directly controlled in the stator coordinate system. Therefore, as shown in the following equation, the shaft support force F in the rotating coordinate system is... x F y Rotational conversion to shaft support force F in the stator coordinate system x，φ F y，φ .

[0071] [Formula 3]

[0072]

[0073] Here, φ is the electrical angle of the rotor (the angle obtained by multiplying the mechanical rotation angle of the rotor by the number of pole pairs of the motor).

[0074] Previously, the shaft support force F in the rotating coordinate system was used as a reference. x F y With shaft support current i sd i sq The relationship between them is independent of the rotor's rotation angle (electric angle φ), and inverter control is performed to obtain the required shaft support force F. x，φ F y，φ However, it cannot adequately suppress radial vibrations on the rotating shaft.

[0075] The inventors of this application investigated the cause and discovered that: due to the spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor, the mutual inductance between the shaft support winding and the motor winding fluctuates depending on the rotor's rotation angle (electrical angle φ). The result is as follows: Figure 6 As shown, the shaft support force will fluctuate unexpectedly depending on the rotor's rotation angle (electric angle φ).

[0076] The causes of spatial higher harmonics, determined by the magnetic circuit characteristics of bearingless motors, can be listed in the following aspects.

[0077] (1) Stator slot shape, rotor slot shape

[0078] Because the slots are composed of air, copper wire, and magnets, they have low permeability and high magnetic reluctance, making it difficult for magnetic flux to pass through. Therefore, high-order harmonic components corresponding to the number of slots in the stator or rotor are generated.

[0079] (2) Magnet shape of bearingless motor

[0080] When a rotor's magnetic pole is composed of multiple magnets, the magnetic force (magnetic flux potential) weakens in the regions that separate the magnets, thus generating higher harmonic components in each magnetic pole corresponding to the number of magnets (number of divisions).

[0081] (3) Number of pole pairs of a bearingless motor

[0082] The number of electrical cycles a rotor completes in one mechanical rotation determines the generation of corresponding higher harmonic components. For example, in a bearingless motor with two pole pairs, the rotor completes two electrical cycles in one mechanical rotation.

[0083] Based on the above insights, the inventors of this application propose the following invention: In order to reduce the fluctuation of shaft support force, in other words, to suppress the influence of spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor 110, a voltage or current superimposed with high-order harmonics is output from one or both of the first inverter 114 supplying power to the shaft support winding 113 and the second inverter 116 supplying power to the motor winding 115, wherein the high-order harmonics are obtained by multiplying the rotational frequency of the bearingless motor 110 by a natural number greater than 2. Therefore, the required shaft support force can be generated independently of electrical angles, thereby suppressing radial vibrations on the rotating shaft 101 and allowing the rotating shaft 101 to rotate smoothly.

[0084] The higher harmonic components (orders) of the frequency that are natural multiples of the rotational frequency of the bearingless motor 110 are determined by a combination of one or more of the following factors based on the magnetic circuit characteristics of the bearingless motor 110.

[0085] (1) The number of higher harmonic components that the bearingless motor 110 passes through during one electrical cycle, which is several times the number of stator slots (first slot 121).

[0086] (2) The number of higher harmonic components that the bearingless motor 110 passes through during one electrical cycle, which is several times the number of rotor slots (second slot 122).

[0087] (3) The number of higher harmonic components that constitute one pole of the rotor 111, which is several times the number of permanent magnets (permanent magnet 123A with magnetic pole N and permanent magnet 123B with magnetic pole S).

[0088] (4) The higher harmonic components of the pole pairs of the bearingless motor 110

[0089] It should be noted that the number of stator slots (first slot 121) traversed by the bearingless motor 110 during one electrical cycle is equal to the number of first slots 121 divided by the number of pole pairs of the bearingless motor 110. Similarly, the number of rotor slots (second slot 122) traversed by the bearingless motor 110 during one electrical cycle is equal to the number of second slots 122 divided by the number of pole pairs of the bearingless motor 110.

[0090] For example, for such Figure 4 For the 4-pole 36-slot bearingless motor (BPM type) shown, the higher harmonic components (orders) superimposed on the voltage or current output by the inverter for shaft support or motor drive are determined as follows.

[0091] (1) Considering that the bearingless motor has 4 poles, the rotor passes through 18 stator slots when it rotates 180 degrees mechanically. Therefore, the higher harmonic component that the bearingless motor passes through in one electrical cycle is 18 times the number of stator slots. This number is equal to the number of stator slots (36) divided by the number of pole pairs of the bearingless motor, which is 2.

[0092] (2) Considering that the bearingless motor has 4 poles, the rotor passes through 12 rotor slots when it rotates 180 degrees mechanically. Therefore, the higher harmonic component that the bearingless motor passes through in one electrical cycle is 12 times the number of rotor slots. This number is equal to the number of rotor slots (24) divided by the number of pole pairs of the bearingless motor, which is 2.

[0093] (3) Since each of the N and S poles is composed of 6 magnets, the number of high-order harmonic components of the permanent magnets that make up one pole of the rotor (the permanent magnets with the N pole and the permanent magnets with the S pole) is 6 times.

[0094] (4) Since the bearingless motor has two pole pairs, the higher harmonic components of the pole pairs of the bearingless motor are the second order.

[0095] In summary, for such Figure 4 For the 4-pole 36-slot bearingless motor (BPM type) shown, in order to reduce the fluctuation of shaft support force, it is only necessary to add the 2nd, 6th, 12th and 18th harmonic components of the rotation frequency of the bearingless motor to the voltage or current output by the inverter for shaft support or motor drive.

[0096] For example, for such Figure 5 For the 6-pole, 9-slot bearingless motor (IPM type) shown, the higher harmonic components (orders) superimposed on the voltage or current output by the inverter for shaft support or motor drive are determined as follows.

[0097] (1) Considering that the bearingless motor has 6 poles, the rotor passes through 3 stator slots when it rotates 120 degrees mechanically. Therefore, the higher harmonic component that the bearingless motor passes through in one electrical cycle is the 3rd harmonic. This number is equal to the number of stator slots (9) divided by the number of pole pairs of the bearingless motor, which is 3.

[0098] (2) Considering that the bearingless motor has 6 poles, when the rotor rotates 120 degrees, it passes through 2 rotor slots. Therefore, the higher harmonic component that the bearingless motor passes through in one electrical cycle is the number of rotor slots, which is 2nd. This number is equal to the number of rotor slots (6) divided by the number of pole pairs of the bearingless motor, which is 3.

[0099] (3) Since each of the N and S poles is composed of two magnets, the number of higher harmonic components that constitute one pole of the rotor (the permanent magnet with the N pole and the permanent magnet with the S pole) is multiple of the number of the two magnets.

[0100] (4) Since the bearingless motor has 3 pole pairs, the higher harmonic components of the pole pairs of the bearingless motor are 3rd.

[0101] In summary, for such Figure 5 For the 6-pole 9-slot bearingless motor (IPM type) shown, in order to reduce the fluctuation of shaft support force, it is only necessary to add the second and third harmonic components of the rotation frequency of the bearingless motor to the voltage or current output by the inverter for shaft support or motor drive.

[0102] The following is a detailed explanation using the following example: In order to output a voltage or current with a high-order harmonic superimposed on a natural number multiplied by the rotational frequency of the bearingless motor 110 by 2 or more from one or both of the first inverter 114 for shaft support and the second inverter 116 for motor drive, the control unit 200 applies a correction signal to the control signal of one or both of the first inverter 114 and the second inverter 116. However, the technology disclosed herein is not limited to this. For example, by changing the structure of the control unit 200 itself, specifically by using a machine learning model in the control unit 200, or by changing the control gain in the control unit 200 according to the electrical angle of the rotor 111, the voltage or current with a high-order harmonic superimposed on a natural number multiplied by 2 or more from one or both of the first inverter 114 and the second inverter 116 can be output.

[0103] <Correction of Inverter Control Signals>

[0104] like Figure 7 As shown, the control unit 200 of the bearingless motor system 100 in this embodiment mainly includes a shaft support control unit 210 and a motor control unit 220. The control unit 200 is composed, for example, a processor and a memory, wherein the memory stores programs and information for making the processor work.

[0105] The shaft support control unit 210 controls the first inverter 114 for the shaft support. Thus, the first inverter 114 supplies the three-phase voltages vsu, vsv, vsw of the shaft support winding and the three-phase currents isu, isv, isw of the shaft support winding to the shaft support winding 113, and the shaft support force f... x f y The force generated by the shaft support winding 113 acts on the rotating shaft 101. At this time, the radial positions x and y of the rotating shaft 101 are measured by the gap sensor 118. It should be noted that the shaft support force f generated by the shaft support winding 113...x f y It is affected by magnetic permeability fluctuations (L fluctuations), excitation magnetic field fluctuations, and motor current fluctuations flowing in motor winding 115.

[0106] The motor control unit 220 controls the second inverter 116 for driving the motor. The second inverter 116 then supplies the three-phase voltages vmu, vmv, vmw and the three-phase currents imu, imv, imw of the motor windings to the motor windings 115, and the rotational torque T is applied from the motor windings 115 to the rotor 111. At this time, the mechanical rotation angle θ of the rotor 111 is measured by the encoder 117.

[0107] In this example, the shaft support control unit 210 and the motor control unit 220 use PWM (Pulse Width Modulation) to control the first inverter 114 and the second inverter 116. Specifically, the inverters 114 and 116 are configured to output pulses that change the ratio (duty cycle) of the period for H-level output to the period for L-level output within a certain period. The shaft support control unit 210 and the motor control unit 220 control the voltage and current output by the inverters 114 and 116 by changing the duty cycle setting.

[0108] In this example, the shaft support control unit 210 consists of a position controller 211, a shaft support winding current command calculation unit 212, a current controller 213, an inverse dq coordinate conversion unit 214, and a PWM modulation unit 215.

[0109] Position controller 211 responds to a pre-set radial position command value x ＊ y ＊ The position deviation value obtained by subtracting the measured values ​​x and y of the radial position is used to calculate the shaft support force command value f for stably suspending the rotating shaft 101 using PID calculation. x ＊ f y ＊ .

[0110] The shaft support winding current command calculation unit 212 calculates the shaft support force command value f. x ＊ f y ＊ Calculate the command value of the shaft support winding current isd ＊ isq ＊ At this point, as mentioned above, since the relationship between the shaft support force and the shaft support winding current changes due to the motor winding current, the shaft support winding current command value isd is calculated while taking into account the motor winding current detection values ​​imd and imq. ＊ isq＊ The motor winding current detection values ​​imd and imq are input from the dq coordinate conversion unit 202 to the shaft support winding current command calculation unit 212. The dq coordinate conversion unit 202 converts the three-phase motor winding current detection values ​​imu, imv, and imw into the motor winding current detection values ​​imd and imq in the rotating coordinate system based on the electrical angle φ of the rotor 111. The electrical angle φ of the rotor 111 is input from the electrical angle calculation unit 201 to the dq coordinate conversion unit 202. The electrical angle calculation unit 201 calculates the electrical angle φ of the rotor 111 by multiplying the measured value of the mechanical rotation angle θ of the rotor 111 by the number of pole pairs of the bearingless motor 110.

[0111] The current controller 213 controls the current command value isd of the shaft support winding. ＊ isq ＊ The current deviation value obtained by subtracting the detected current values ​​isd and isq of the shaft support winding is calculated using PI calculation to determine the value isd used to adjust the shaft support winding current to the command value of the shaft support winding current. ＊ isq ＊ The shaft support winding voltage command value vsd superimposed on the shaft support winding 113 ＊ vsq ＊ The shaft support winding current detection values ​​isd and isq are input from the dq coordinate conversion unit 202 to the current controller 213. The dq coordinate conversion unit 202 converts the three-phase current detection values ​​isu, isv, and isw of the shaft support winding into shaft support winding current detection values ​​isd and isq in the rotating coordinate system based on the electrical angle φ of the rotor 111. The electrical angle φ of the rotor 111 is input from the electrical angle calculation unit 201 to the dq coordinate conversion unit 202. The electrical angle calculation unit 201 calculates the electrical angle φ of the rotor 111 by multiplying the measured value of the mechanical rotation angle θ of the rotor 111 by the number of pole pairs of the bearingless motor 110.

[0112] The inverse dq coordinate transformation unit 214 converts the shaft support winding voltage command value vsd in the rotating coordinate system based on the electrical angle φ of the rotor 111. ＊ vsq ＊ Convert to shaft support winding three-phase voltage command value vsu ＊ vsv ＊ vsw ＊ The electrical angle φ of rotor 111 is input from electrical angle calculation unit 203 to inverse dq coordinate conversion unit 214. Electrical angle calculation unit 203 calculates the electrical angle φ of rotor 111 by multiplying the measured value of mechanical rotation angle θ of rotor 111 by the number of pole pairs of bearingless motor 110.

[0113] The PWM modulation unit 215 modulates the three-phase voltage command value vsu of the shaft support winding. ＊ vsv＊ vsw ＊ The ratio of the detected voltage value Vdc of the main circuit (power supply) is used to calculate the comparison value (duty cycle) for PWM, so that the average value of the three-phase voltages (inter-winding voltages) Vsu, vsv, and vsw of the shaft support winding is equal to the command value Vsu of the three-phase voltage of the shaft support winding. ＊ vsv ＊ vsw ＊ The values ​​are equal, and the output (control signal) of the PWM timer for the shaft support is input to the first inverter 114 for the shaft support.

[0114] In this example, the motor control unit 220 consists of a speed calculation unit 221, a speed controller 222, a current controller 223, an inverse dq coordinate conversion unit 224, and a PWM modulation unit 225.

[0115] The speed calculation unit 221 detects the angular rotation speed ω of the bearingless motor 110 (rotor 111) based on the time change of the measured value of the mechanical rotation angle θ of the rotor 111.

[0116] The speed controller 222 responds to the preset angular rotational speed command value ω. ＊ The angular rotational speed deviation value obtained by subtracting the detected angular rotational speed ω from the angular rotational speed is used to calculate the motor winding current command value imd to achieve the required angular rotational speed using PID calculation. ＊ ,imq ＊ .

[0117] The current controller 223 controls the current command value imd for the motor winding. ＊ ,imq ＊ The current deviation value obtained by subtracting the detected motor winding current values ​​imd and imq from the input current is used to calculate the value imd used to adjust the motor winding current to the command value imd. ＊ ,imq ＊ The motor winding voltage command value vmd superimposed on the motor winding 115 ＊ vmq ＊ The motor winding current detection values ​​imd and imq are input from the dq coordinate conversion unit 202 to the current controller 223. The dq coordinate conversion unit 202 converts the three-phase current detection values ​​imu, imv, and imw of the motor windings into the motor winding current detection values ​​imd and imq in the rotating coordinate system based on the electrical angle φ of the rotor 111. The electrical angle φ of the rotor 111 is input from the electrical angle calculation unit 201 to the dq coordinate conversion unit 202. The electrical angle calculation unit 201 calculates the electrical angle φ of the rotor 111 by multiplying the measured value of the mechanical rotation angle θ of the rotor 111 by the number of pole pairs of the bearingless motor 110.

[0118] The inverse dq coordinate transformation unit 224 converts the motor winding voltage command value vmd in the rotating coordinate system according to the electrical angle φ of the rotor 111. ＊ vmq ＊ Convert to motor winding three-phase voltage command value vmu ＊ vmv ＊ vmw ＊ The electrical angle φ of rotor 111 is input from electrical angle calculation unit 203 to inverse dq coordinate conversion unit 224. Electrical angle calculation unit 203 calculates the electrical angle φ of rotor 111 by multiplying the measured value of mechanical rotation angle θ of rotor 111 by the number of pole pairs of bearingless motor 110.

[0119] The PWM modulation unit 225 modulates the motor winding three-phase voltage command value vmu. ＊ vmv ＊ vmw ＊ The ratio of the detected voltage value Vdc of the main circuit (power supply) is used to calculate the comparison value (duty cycle) for PWM, so that the average value of the three-phase voltages (inter-winding voltages) Vmu, Vmv, and Vmw of the motor windings is equal to the command value Vmu of the three-phase voltages of the motor windings. ＊ vmv ＊ vmw ＊ The values ​​are equal, and this is used as the output (control signal) of the PWM timer for the motor, which is then input to the second inverter 116 for the motor drive.

[0120] In this example, in order to output a voltage or current from the first inverter 114 for shaft support that is superimposed with a higher harmonic obtained by multiplying the rotational frequency of the bearingless motor 110 by a natural number greater than 2, such as Figure 8 As shown, a correction calculation unit 216 is provided in the shaft support control unit 210.

[0121] The correction calculation unit 216 adds the correction signal to the control signal, i.e., the shaft support force command value f, which is input from the position controller 211 to the shaft support winding current command calculation unit 212. x ＊ f y ＊ Above, to suppress the influence of spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor 110. The correction calculation unit 216 calculates the correction amount based on the electrical angle φ of the rotor 111, the shaft support winding current detection values ​​isd and isq in the rotating coordinate system, and the motor winding current detection values ​​imd and imq in the rotating coordinate system, and uses the calculated correction amount as a correction signal, which is then fed forward to the shaft support force command value f, which is a control signal. x ＊ f y ＊ superior.

[0122] In the correction calculation of the correction calculation unit 216, the shaft support winding voltage detection values ​​vsd and vsq detected by the voltage sensor, and the shaft support force detection value f detected by the force sensor can be used. x f y Alternatively, the radial position detection value of the rotating shaft 101 detected by the gap sensor can be used instead of the shaft support winding current detection values ​​isd and isq detected by the current sensor. The motor winding voltage detection values ​​vmd and vmq detected by the voltage sensor, or the rotational torque detection value T of the rotor 111 detected by the torque meter, can also be used instead of the motor winding current detection values ​​imd and imq. Details of the correction calculation will be described later.

[0123] exist Figure 8 In the example shown, the correction signal is added to the control signal (shaft support force command value f) input from the position controller 211 to the shaft support winding current command calculation unit 212. x ＊ f y ＊ However, instead, the correction signal can be added to the control signal (shaft support winding current command value isd) input from the shaft support winding current command calculation unit 212 to the current controller 213. ＊ isq ＊ The control signal (shaft support winding voltage command value vsd) input from the current controller 213 to the inverse dq coordinate transformation unit 214 ＊ vsq ＊ (Before inverse dq coordinate transformation)), the control signal (shaft support winding three-phase voltage command value vsu) input from the inverse dq coordinate transformation unit 214 to the PWM modulation unit 215. ＊ vsv ＊ vsw ＊ (After inverse dq coordinate transformation) or the control signal input to the position controller 211 (radial position command value x) ＊ y ＊ )superior.

[0124] Alternatively, the correction signal can be applied to the control signal of the second inverter 116 used for motor drive, instead of applying the correction signal to the control signal of the first inverter 114 used for shaft support. Specifically, the correction signal can be applied to the control signal (motor winding current command value imd) input from the speed controller 222 to the current controller 223. ＊ ,imq ＊ The control signal (motor winding voltage command value vmd) input from the current controller 223 to the inverse dq coordinate transformation unit 224 ＊ vmq ＊(Before inverse dq coordinate transformation), or the control signal (motor winding three-phase voltage command value vmu) input from the inverse dq coordinate transformation unit 224 to the PWM modulation unit 225. ＊ vmv ＊ vmw ＊ (After inverse dq coordinate transformation) on.

[0125] In a bearingless motor, the magnetic circuit that generates motor torque and the magnetic circuit that generates shaft support force are shared. Therefore, the current value of both the shaft support winding and the motor winding will affect the shaft support force. Therefore, the correction signal used to suppress shaft support force fluctuations can be applied only to the control signal of the motor drive inverter. In other words, whether the control signal of the shaft support inverter or the control signal of the motor drive inverter is corrected, the magnitude of the output shaft support force can be corrected. Therefore, in order to reduce the fluctuation of shaft support force, any of the following methods can be used depending on the situation: (1) correcting only the control signal of the shaft support inverter, (2) correcting only the control signal of the motor drive inverter, (3) correcting the control signals of both the shaft support inverter and the motor drive inverter.

[0126] <Correction Calculation>

[0127] In the correction calculation unit 216, the correction amount can be prepared in advance as tabular data for the electrical angle φ of the rotor 111, the shaft support winding currents isd and isq in the rotating coordinate system, and the motor winding currents imd and imq in the rotating coordinate system. Using this tabular data, the correction amount is calculated based on the detected values ​​of the electrical angle φ of the rotor 111, the shaft support winding currents isd and isq in the rotating coordinate system, and the motor winding currents imd and imq in the rotating coordinate system. The tabular data can be stored in the memory of the control unit 200.

[0128] For example, magnetic field analysis can be performed in advance based on the design information of a bearingless motor to generate tabular data. In this method, an analytical model for magnetic field analysis is created based on the attached diagram of the bearingless motor. Magnetic field analysis is performed under various conditions while varying the shaft support winding current and the motor winding current to obtain the waveform of the radial shaft support force. Based on this waveform, correction amounts for reducing shaft support force fluctuations are calculated for each value of the rotor rotation angle (electric angle), motor winding current, and shaft support winding current, and these are summarized into tabular data.

[0129] Specifically, arbitrary motor winding currents imd1 and imq1, and arbitrary shaft support winding currents isd1 and isq1 are used as input currents for magnetic field analysis to obtain the radial shaft support force of the rotor at each electrical angle φ (refer to...). Figure 9(A)). Next, the obtained radial shaft support force waveform is divided into a DC component (refer to...). Figure 9 (B)) and fluctuation components (refer to) Figure 9 (C)). Next, by reversing the waveform of the undulating component of the radial shaft support force waveform (multiplying by -1), the correction amount for each electrical angle φ of the rotor is calculated (refer to...). Figure 9 (D) Based on the waveform of this correction amount, create Figure 10 The table data is shown schematically. Similarly, magnetic field analysis is performed using various motor winding currents (imd2, imq2, imd3, imq3, etc.) and shaft support winding currents (isd2, isq2, isd3, isq3, etc.) as input currents, and the table data is created following the steps described above. It should be noted that... Figure 10 (A) represents the correction amount for each electrical angle φ of the rotor when the motor winding currents are imd1 and imq1, and the shaft support winding currents are isd1 and isq1. Figure 10 (B) represents the correction amount for each electrical angle φ of the rotor when the motor winding currents are imd2 and imq2, and the shaft support winding currents are isd2 and isq2. Figure 10 The table data shown illustrates the correction values ​​in words, but in practical applications, it includes calculated values ​​as described above.

[0130] according to Figure 10 For example, when the motor winding current detection values ​​are imd1[A] and imq1[A], the shaft support winding current detection values ​​ared1[A] and isq1[A], and the rotor electrical angle detection value is 4[deg], the correction signal (correction amount) applied to the control signal, i.e., the shaft support force command value, input from the position controller 211 to the shaft support winding current command calculation unit 212 is FX4[N]. In this case, the radial shaft support force correction amount is decomposed into the x-direction and y-direction, and applied to the shaft support force command value f respectively. x ＊ f y ＊ The correction amount Δf x ＊ , Δf y ＊ Represented as: Δf x ＊ =FX4cosφ, Δf y ＊ =FX4sinφ. It should be noted that in... Figure 10 The table data shown records the correction amount up to 14 degrees, but the actual table data records the correction amount up to 360 degrees.

[0131] Alternatively, as another method, a mathematical formula for calculating the correction signal based on the magnetic circuit characteristics of a bearingless motor can be constructed, and tabular data of the gain and phase of the higher harmonic components in this formula can be created based on the actual machine's operating information (calibration). In this method, firstly, the order of the higher harmonic components of the correction signal applied to the inverter's control signal is determined based on the magnetic circuit characteristics of the bearingless motor. Next, the amplitude and phase of the predetermined higher harmonic components for each order are determined using the actual machine's operating information (calibration). Specifically, while the actual machine is operated by varying the rotor's rotation angle (electric angle), the shaft support winding current, and the motor winding current, the amplitude and phase of the higher harmonic components superimposed on the control signal are determined under each operating condition to reduce the fluctuation of the shaft support force. Then, the amplitude and phase of the higher harmonic components determined for each value of the rotor's rotation angle (electric angle), the motor winding current, and the shaft support winding current are summarized into tabular data.

[0132] Depending on the number of superimposed higher harmonic components due to the magnetic circuit characteristics of the bearingless motor, for example, when a single higher harmonic component is superimposed, the correction signal X(φ) as a function of the electrical angle φ is as follows.

[0133] [Formula 4]

[0134]

[0135] It should be noted that k represents the order of the higher harmonic components, and X k γ k These represent the amplitude and phase of the higher harmonic components, respectively. As mentioned above, X k γ k It is determined through calibration. Furthermore, i md i mq i represents the motor winding current in the rotating coordinate system. sd i sq This represents the current in the shaft support winding in a rotating coordinate system.

[0136] For example, in Figure 4 In the case of the 4-pole, 36-slot bearingless motor (BPM type) shown, based on the magnetic circuit characteristics, the 2nd, 6th, 12th, and 18th harmonic components can also be used as correction signals X(φ) expressed by the following mathematical formula, and added to the control signal input to the shaft support winding current command calculation unit 212, i.e., the shaft support force command value f. x ＊ f y ＊ superior.

[0137] [Formula 5]

[0138]

[0139] Here, X2(i md i mq i sd i sq ), X6(i md i mq i sd i sq) X 12 (i md i mq i sd i sq ), X 18 (i md i mq i sd i sq ) represents the amplitude of each higher harmonic component, which varies with the motor winding current and the shaft support winding current. Furthermore, γ2(i md i mq i sd i sq ), γ6(i md i mq i sd i sq ), γ 12 (i md i mq i sd i sq ), γ 18 (i md i mq i sd i sq The phase of each higher harmonic component varies with the motor winding current and the shaft support winding current.

[0140] Specifically, the amplitude and phase of each higher harmonic component can be determined as follows: First, the variables in the program (microcomputer software) in the control unit 200 are output via DA conversion, and the shaft support force command value f is set... x ＊ f y ＊The control signal and the gap sensor detection signal of the rotating shaft 101 at the radial position (suspended position) x, y are in an output state. Next, while changing the motor winding current and the shaft support winding current, the actual machine operation begins. For any motor winding current imd1, imq1 and any shaft support winding current isd1, isq1, the amplitude and phase of the higher harmonic components of the correction signal are changed. At this time, the suspended position detection waveform is confirmed, and the amplitude and phase of the higher harmonic components of the correction signal are determined to reduce the fluctuation of the suspended position detection waveform. Figure 11 The diagram schematically illustrates the levitation position waveform when the amplitude and phase of the higher harmonic components of the correction signal applied to the control signal are changed. Figure 11 In the examples shown, among the solid line case 1, the dotted line case 2, and the dashed line case 3, the floating position waveform of case 3 has the smallest fluctuation. Therefore, the amplitude and phase of the higher harmonic components of case 3 are recorded in the table data. Figure 12 The amplitude and phase of the higher harmonic components for each order in cases 1 to 3 are shown, i.e.: X2(i md i mq i sd i sq ), γ2(i md i mq i sd i sq ), X6(i md i mq i sd i sq ), γ6(i md i mq i sd i sq ), X 12 (i md i mq i sd i sq ), γ 12 (i md i mq i sd i sq ), X 18 (i md i mq i sd i sq ), γ 18 (i md i mq i sd i sq ).exist Figure 12The diagram illustrates each amplitude and phase in words, but in actual applications, these are the values ​​set as correction signals during actual machine operation.

[0141] Similarly, for various motor winding currents (imd2, imq2), (imd3, imq3), etc., and shaft support winding currents (isd2, isq2), (isd3, isq3), etc., the amplitude and phase of the higher harmonic components of the correction signal used to reduce fluctuations in the floating position waveform are also determined. In this way, for each value of the motor winding current and shaft support winding current, the amplitude and phase of the higher harmonic components of the correction signal used to reduce fluctuations in the floating position waveform are summarized in tabular data.

[0142] <Voltage Calculation Example>

[0143] When the control unit 200 does not add a correction signal to the inverter control signal, the control signal is only the fundamental frequency (a frequency that is only one times the angular rotation speed), such as the three-phase voltage V. u v v v w As shown below, where the power supply voltage is V. m The electrical angle is φ. It should be noted that the following instructions apply to the shaft support winding 113 and the motor winding 115, and also to three-phase current.

[0144] [Formula 6]

[0145]

[0146] The dq-axis transformation matrix Z for converting the three-phase voltage into the dq-axis voltage of the rotating coordinate system is shown below.

[0147] [Formula 7]

[0148]

[0149] Using the dq-axis transformation matrix Z, the three-phase (UVW phase) voltage v u v v v w It is converted into dq axis voltage v as described below. d v q .

[0150] [Formula 8]

[0151]

[0152] Therefore, the d-axis voltage v d Calculate as follows.

[0153] [Formula 9]

[0154]

[0155] q-axis voltage v q Calculate as follows.

[0156] [Formula 10]

[0157]

[0158] In summary, when the inverter control signal is only the fundamental (first order) without applying a correction signal, multiplying it by a rotation matrix for dq coordinate transformation will result in a DC voltage. It should be noted that the above calculations are performed with the U-phase phase set to 0 [deg].

[0159] In contrast, when the 6th harmonic component is applied as a correction signal to the inverter control signal in the control unit 200, the three-phase voltage v u v v v w For example, as shown below, where V m V is the power supply voltage, φ is the electrical angle, and V6 is the amplitude of the 6th harmonic.

[0160] [Equation 11]

[0161]

[0162] Using the aforementioned dq-axis transformation matrix Z, the three-phase (UVW phase) voltage v u v v v w It is converted into dq axis voltage v as described below. d v q .

[0163] [Equation 12]

[0164]

[0165] Therefore, the d-axis voltage v d Calculate as follows.

[0166] [Equation 13]

[0167]

[0168] It should be noted that the calculation of the d-axis voltage v d When, let V m ×√2 / 3=V m '、V6×√2 / 3=V6'. The second expression on the right contains V. mThe sum of the first, third, and fifth terms is 0. When transforming the fourth equation from the right to the fifth equation, use the following relation.

[0169] [Formula 14]

[0170]

[0171] On the other hand, the q-axis voltage v q Calculate as follows.

[0172] [Formula 15]

[0173]

[0174] It should be noted that the calculation of the q-axis voltage v q When, let V m ×√2 / 3=V m '、V6×√2 / 3=V6'. The second expression on the right contains V. m The sum of the first, third, and fifth terms is √3 / 2 × V m When transforming from the fourth equation on the right to the fifth equation, use the following relation.

[0175] [Formula 16]

[0176]

[0177] In summary, if the 6th harmonic component is applied as a correction signal to the inverter control signal, and the composite wave (three-phase voltage in this example) with the 6th harmonic component superimposed is transformed using dq coordinates, it will become a waveform with the 5th harmonic component superimposed on the DC voltage component. Therefore, it can be concluded that if the composite wave with N harmonic components superimposed is transformed using dq coordinates, it will become a waveform with (N-1) harmonic components superimposed on the DC component.

[0178] For example, in Figure 4 In the case of the 4-pole 36-slot bearingless motor (BPM type) shown, it is necessary to add the correction signals of the 2nd, 6th, 12th and 18th harmonic components of the rotational frequency (angular rotational speed) to the control signal. In this case, if dq conversion is performed, it will become a waveform with 1, 5, 11 and 17 times the frequency of the angular rotational speed superimposed on the DC component.

[0179] In this way, when performing dq coordinate transformation on motor current and shaft support current, which are, for example, three-phase AC current, the order of higher harmonics decreases by one order. Therefore, the order of the correction signal for the control signal after dq coordinate transformation also decreases by one order. For example, if it is desired to superimpose the 6th harmonic on the voltage or current, the correction signal of the 5th harmonic component is added to the control signal after dq coordinate transformation. Specifically, the shaft support winding current command value isd, which is the control signal after dq coordinate transformation, is... ＊ isq ＊ ( Figure 7 (Control signal sent to current controller 213), shaft support winding voltage command value vsd ＊ vsq ＊ (before inverse dq coordinate transformation) Figure 7 The higher harmonic components of the correction signal (such as the control signal sent to the inverse dq coordinate transformation unit 214) are reduced by one order from the spatial higher harmonic order of the correction object, which is determined by the magnetic circuit shape characteristics of the bearingless motor. In other words, the higher harmonic components of the correction signal used to correct the control signal in the dq coordinate axis differ by one order from the higher harmonic components of the correction signal used to correct the control signal in the uvw or xy coordinate axes.

[0180] <Features of the Implementation Method>

[0181] In summary, in the bearingless motor system 100 of this embodiment, the control unit 200 causes one or both of the first inverter 114 for shaft support and the second inverter 116 for motor drive to output a voltage or current superimposed with high-order harmonics, thereby reducing fluctuations in the shaft support force. These high-order harmonics are obtained by multiplying the rotational frequency of the bearingless motor 110 by a natural number greater than 2. Therefore, fluctuations in the mutual inductance between the shaft support winding 113 and the motor winding 115, which are determined by the spatial high-order harmonics due to the magnetic circuit characteristics of the bearingless motor 110, can be suppressed, as the mutual inductance depends on the rotor's rotational angle (electrical angle). Thus, the required shaft support force can be generated independently of the rotor's rotational angle (electrical angle), thereby suppressing radial vibration on the rotating shaft 101 and allowing the rotating shaft 101 to rotate smoothly.

[0182] In the past, with various rotor configurations such as SPM, Inset, IPM, BPM, and Consequent Pole, changes in the rotor's rotation angle (electrical angle) cause fluctuations in the mutual inductance due to spatial harmonics determined by the magnetic circuit characteristics of bearingless motors. This fluctuation in mutual inductance is dependent on the electrical angle. In contrast, the inverter control of this embodiment is applicable even with changes in the rotor structure and can suppress shaft support force fluctuations.

[0183] Figure 13 The waveform of the current output from the first inverter 114 for the shaft support in the bearingless motor system 100 of this embodiment is schematically shown. If the bearingless motor system 100 is an SPM type, Inset type, IPM type, BPM type, etc., that drives the shaft support winding 113 with AC power, the output current waveform is as follows: Figure 13 As shown in (A), if it is a Consequent Pole type or the like that that uses DC electric drive to propel the shaft support winding 113, the output current waveform is as follows: Figure 13 As shown in (B). It should be noted that, in Figure 13 (A) Figure 13 In (B), the dashed line represents the output current waveform in the prior art where the correction signal for higher harmonic components is not added to the inverter control signal.

[0184] In the bearingless motor system 100 of this embodiment, the order of higher harmonics obtained by multiplying the rotational frequency of the bearingless motor 110 by a natural number greater than 2 can be determined based on one or more factors selected from the following: the number of first slots 121 where the shaft support winding 113 and the motor winding 115 are arranged divided by the number of pole pairs of the bearingless motor 110; the number of second slots 122 where permanent magnets 123A and 123B are arranged divided by the number of pole pairs of the bearingless motor 110; the number of permanent magnets 123A and 123B constituting one pole of the rotor 111; and the number of pole pairs of the bearingless motor 110. Therefore, it is possible to suppress fluctuations in the mutual inductance between the shaft support winding 113 and the motor winding 115 due to spatial higher harmonics determined by the magnetic circuit characteristics of the bearingless motor 110, which depend on the rotational angle (electrical angle) of the rotor 111.

[0185] In the bearingless motor system 100 of this embodiment, the control unit 200 can apply a correction signal to the control signal of one or both of the first inverter 114 for shaft support and the second inverter 116 for motor drive, thereby superimposing a voltage or current output with a high-order harmonic obtained by multiplying the rotational frequency of the bearingless motor 110 by a natural number of 2 or more. This allows the high-order harmonic to be superimposed on the control signal of the first inverter 114 or the control signal of the second inverter 116, and this high-order harmonic cancels out the influence of spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor 110. In this case, if the correction signal is determined based on the rotational angle (electrical angle) of the rotor 111, the current value of the shaft support winding 113, and the current value of the motor winding 115, then by applying the correction signal to the control signal of one or both of the first inverter 114 and the second inverter 116, the influence of spatial high-order harmonics determined by the magnetic circuit characteristics of the bearingless motor 110 can be canceled.

[0186] Regarding the compressor 10, which includes the bearingless motor system 100 of this embodiment, the bearingless motor system 100 can generate the required shaft support force without relying on the rotation angle (electric angle) of the rotor 111, thus the compressor 10 operates stably and its reliability is improved.

[0187] (Second Implementation)

[0188] The following is an example of a refrigeration device that includes a compressor 10 equipped with a bearingless motor system 100 according to the first embodiment (including variations, the same applies below). Figure 14 The air conditioning unit 1 shown is used as an example for explanation.

[0189] Air conditioning unit 1 is a device that regulates the air in a target space through a vapor compression refrigeration cycle. Air conditioning unit 1 is capable of performing refrigeration operation and mainly includes a compressor 10, a heat source-side heat exchanger 3, an expansion mechanism 4, and a utilization-side heat exchanger 5.

[0190] The compressor 10 draws in low-pressure refrigerant flowing in the suction pipe 6 through the suction port 11, compresses the refrigerant drawn in through the suction port 11 to make it a high-pressure refrigerant, and then sprays the high-pressure refrigerant into the discharge pipe 7 through the discharge port 12. It should be noted that the suction pipe 6 is a refrigerant pipe that guides the refrigerant flowing out of the utilization side heat exchanger 5 to the suction side (suction port 11) of the compressor 10, and the discharge pipe 7 is a refrigerant pipe that guides the refrigerant sprayed from the compressor 10 through the discharge port 12 to the inlet of the heat source side heat exchanger 3.

[0191] For example, as described in the first embodiment, the compressor 10 mainly includes a rotating shaft 101, impellers 102 and 103, and a bearingless motor 110. The driving force of the bearingless motor 110 is transmitted from the rotating shaft 101 to the impellers 102 and 103, which rotate about the rotating shaft 101. As a result, the compressor 10 compresses the refrigerant that flows in through the suction port 11.

[0192] The heat exchanger 3 on the heat source side acts as a radiator for the refrigerant, releasing heat from the refrigerant ejected from the compressor 10 by exchanging heat between the refrigerant and water or air, which serve as a cooling source. One end of the heat exchanger 3 is connected to the outlet 12 of the compressor 10 via the ejector pipe 7. The other end of the heat exchanger 3 is connected to the expansion mechanism 4.

[0193] The expansion mechanism 4 is a mechanism for reducing the pressure of the refrigerant after it has released heat in the heat exchanger 3 on the heat source side. The expansion mechanism 4 is, for example, composed of an electric expansion valve. One end of the expansion mechanism 4 is connected to the heat exchanger 3 on the heat source side. The other end of the expansion mechanism 4 is connected to the heat exchanger 5 on the utilization side.

[0194] The side heat exchanger 5 acts as a heater for the refrigerant, heating it after it has been depressurized in the expansion mechanism 4 by exchanging heat between the refrigerant and water or air, which serves as a heat source. One end of the side heat exchanger 5 is connected to the expansion mechanism 4. The other end of the side heat exchanger 5 is connected to the suction port 11 of the compressor 10 via the suction pipe 6.

[0195] In summary, in the air conditioning unit 1, the compressor 10, the heat source side heat exchanger 3, the expansion mechanism 4, and the utilization side heat exchanger 5 are connected in sequence by refrigerant pipes including the suction pipe 6 and the discharge pipe 7, thereby forming a path 8 for refrigerant circulation.

[0196] According to the refrigeration device (air conditioning device 1) of this embodiment, since the compressor 10 driven by the bearingless motor system 100 of the first embodiment is used, the bearingless motor system 100 can generate the required shaft support force without relying on the rotation angle (electric angle) of the rotor 111, so the operation of the refrigeration device is stable and the reliability is improved.

[0197] It should be noted that the structure of the compressor 10, which is applicable to the refrigeration device (air conditioning device 1) of this embodiment, is not limited to... Figure 1 The example shown. In Figure 1 In the example shown, two impellers 102 and 103 are provided at one end of the axial direction of the rotating shaft 101, but they can be replaced by something else, such as... Figure 15 As shown, only a single impeller 102 is set, or as... Figure 16 As shown, the second impeller 103 can also be positioned at the other end of the axial direction of the rotating shaft 101. Figure 1 In the example shown, the rotating shaft 101 is radially supported by a bearingless motor 110 and a radial magnetic bearing 130, but this can be replaced by other methods, such as... Figure 17 As shown, instead of using radial magnetic bearings 130, two bearingless motors 110 provide radial axial support for the rotating shaft 101. Figure 1 In the example shown, the thrust magnetic bearings 105 and 107 are arranged at the end of the rotating shaft 101 on the side opposite to the impellers 102 and 103, but they can be replaced, as shown in the example below. Figure 18 As shown, the thrust magnetic bearings 105 and 107 are arranged near the impellers 102 and 103, or as... Figure 19 As shown, it is arranged between the bearingless motor 110 and the radial magnetic bearing 130.

[0198] (Other implementation methods)

[0199] In the embodiments described above (including variations, the same applies below), the case of applying the bearingless motor system 100 to the compressor 10 is illustrated. However, the application of the bearingless motor system 100 is not particularly limited, and it can be applied to rotating motors such as generators or various devices including such rotating motors.

[0200] The embodiments have been described above, but it should be understood that various changes can be made to the methods and specific circumstances without departing from the spirit and scope of the claims. Furthermore, the above embodiments and variations can be appropriately combined or substituted.

[0201] -Industry Applicability-

[0202] In summary, this disclosure is useful for bearingless motor systems, compressors, and refrigeration devices.

[0203] - Symbol Explanation -

[0204] 1. Air conditioning unit (refrigeration unit)

[0205] 10 Compressors

[0206] 100 Bearingless Motor System

[0207] 101 Rotating Axis

[0208] 102 First impeller (compression mechanism)

[0209] 103 Second impeller (compression mechanism)

[0210] 110 Bearingless Motor

[0211] 111 Rotor

[0212] 112 Stator

[0213] 113 shaft support winding

[0214] 114 First Inverter

[0215] 115 motor winding

[0216] 116 Second Inverter

[0217] 121 First slot

[0218] 122 Second slot

[0219] 123A and 123B permanent magnets

Claims

1. A bearingless motor system, characterized in that: The bearingless motor system includes a rotating shaft (101), a bearingless motor (110), a first inverter (114), a second inverter (116), and a control unit (200). The bearingless motor (110) includes a rotor (111) and a stator (112). The rotor (111) is mounted on the rotating shaft (101), and the stator (112) is located radially outside the rotor (111) and has a shaft-supported winding (113) and a motor winding (115). The first inverter (114) supplies power to the shaft support winding (113) to generate a shaft support force that supports the rotating shaft (101) in a non-contact manner. The second inverter (116) supplies power to the motor windings (115), thereby generating rotational torque on the rotating shaft (101). The control unit (200) controls the first inverter (114) and the second inverter (116). The control unit (200) causes one or both of the first inverter (114) and the second inverter (116) to output a voltage or current superimposed with higher harmonics in order to reduce the fluctuation of the shaft support force. The higher harmonics are obtained by multiplying the rotation frequency of the bearingless motor (110) by a natural number greater than 2.

2. The bearingless motor system according to claim 1, characterized in that: The shaft support winding (113) and the motor winding (115) are arranged in a plurality of first slots (121), which are arranged circumferentially on the stator (112). The order of the higher harmonics is determined by the value obtained by dividing the number of the first slots (121) by the number of pole pairs of the bearingless motor (110), and one or more factors selected from the number of pole pairs.

3. The bearingless motor system according to claim 1 or 2, characterized in that: The rotor (111) has multiple permanent magnets (123A, 123B). The permanent magnets (123A, 123B) are arranged in a plurality of second slots (122), which are arranged circumferentially on the rotor (111). The order of the higher harmonics is determined by one or more factors selected from the number of the second slots (122) divided by the number of pole pairs of the bearingless motor (110) and the number of permanent magnets (123A, 123B) constituting one pole of the rotor (111).

4. The bearingless motor system according to any one of claims 1 to 3, characterized in that: The control unit (200) applies a correction signal to the control signal of one or both of the first inverter (114) and the second inverter (116), thereby causing one or both of the first inverter (114) and the second inverter (116) to output a voltage or current superimposed with the higher harmonics.

5. The bearingless motor system according to claim 4, characterized in that: The correction signal is determined based on the electrical angle of the rotor (111), the current value of the shaft support winding (113), and the current value of the motor winding (115).

6. A compressor, characterized in that: The compressor includes a bearingless motor system (100) as described in any one of claims 1 to 5, and a compression mechanism (102, 103) driven by the bearingless motor system (100) to compress the fluid.

7. A refrigeration device, characterized in that: The refrigeration device includes the compressor (10) as described in claim 6.

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