Bearing-less motor control device, motor system, and bearing-less motor control method

Abstract

This bearing-less motor control device controls a bearing-less motor which comprises a rotor and a stator having electric motor winding that generates torque and in which the rotor and the stator are disposed with a specific gap therebetween, and is provided with an observer and a speed estimator. The observer receives a voltage command value to the electric motor winding or a voltage detection value applied to the electric motor winding and a current detection value of the electric motor winding to calculate an estimated rotor magnetic flux which is an estimated value of the rotor magnetic flux generated in the electric motor winding by the rotor. The speed estimator receives a value output from the observer to calculate and output an estimated axial speed, which is an estimated value of the axial speed of the rotor. The observer has a voltage error calculator that calculates an induced voltage error that is the difference between a first induced voltage, which is calculated from the voltage command value or the voltage detection value and the current detection value, and a second induced voltage, which is calculated from the estimated rotor magnetic flux. The speed estimator receives the induced voltage error to calculate and output the estimated axial speed.

Description

Bearingless motor control device, motor system, and bearingless motor control method

[0001] The present disclosure relates to a control device for a bearingless motor in which a rotor is supported without contact with a stator by magnetic levitation and rotates, a motor system, and a control method for a bearingless motor.

[0002] A bearingless motor combines the functions of an electric motor (which generates torque) and a magnetic bearing (which generates a supporting force to levitate the rotor without contact with the stator) on the same magnetic circuit. To levitate the rotor, it is necessary to actively control all five degrees of freedom except for the rotation axis, or to create a passively stable structure where some of the degrees of freedom are not actively controlled.

[0003] In a two-axis control type bearingless motor, the position is detected by sensors only in the radial direction, specifically in two directions of the X-axis and Y-axis which are orthogonal to each other, and the supporting force is adjusted so that the detected position matches the target position, thereby actively controlling the two axial directions. The rotor is generally arranged in the radial direction with a gap separated from the stator. The Z-axis, which is the axial direction of the two-axis control type bearingless motor and is perpendicular to both the X-axis and Y-axis, and the Z-axis, which is the tilt direction (θ x , θ y ) is generally not actively controlled, but has a passively stable structure. Hereinafter, the controlled direction will be referred to as the control direction. On the other hand, the direction that is passively stable without control will be referred to as the passively stable direction. To achieve passive stability, the attractive force between the rotor's permanent magnet and the stator's iron core is utilized. In one example, when the rotor is displaced in the axial direction, magnetic flux flows between the rotor's permanent magnet and the stator's iron core, which are separated by a radial gap, generating an attractive force between them, which acts to return the axial displacement of the rotor. As a result, a restoring force is generated in the opposite direction to the axial displacement without being controlled. The attractive force acting between the permanent magnet and the iron core is proportional to the distance, so it can be considered as a spring force. Hereinafter, the ratio of the restoring force [N] to the axial displacement [m] is referred to as the restoring force coefficient k z It is called [N / m].

[0004] In the axial direction of a two-axis control bearingless motor, stability is ensured solely by utilizing the restoring force generated in the radial gap, resulting in poorer stability compared to the control direction. Furthermore, the restoring force does not function to damp vibrations. Damping forces, which are proportional to speed and have the effect of damping vibrations, do not, in principle, occur in the passively stable direction. This can result in vibrations in the passively stable direction continuing or diverging, leading to instability.

[0005] Patent Document 1 proposes a method for controlling the axial position of a rotor by passing a field current through the windings of the teeth of a stator that faces the rotor across a radial gap. In the technology described in Patent Document 1, the rotor and stator have surface portions that do not face each other in the axial direction, a displacement sensor detects the axial position of the rotor, and a control device generates a field current command for controlling the axial position of the rotor based on the position information detected by the displacement sensor. In the technology described in Patent Document 1, an axial force is generated in the rotor by magnetic flux generated by passing a field current through the windings arranged between the stator teeth that protrude toward the rotor and magnetic flux generated by the permanent magnets.

[0006] Japanese Patent Application Laid-Open No. 2015-171165

[0007] Controlling the rotor's axial position required an axial displacement sensor or a sensor measuring speed or acceleration, from which displacement can be calculated. Integrating acceleration yields speed, and integrating speed yields displacement. Furthermore, differentiating displacement yields speed, and differentiating speed yields acceleration. By detecting at least one of displacement, speed, and acceleration, the remaining physical quantities can be calculated. In the technology described in Patent Document 1, a sensor for detecting position using the rotor shaft as the sensor target is located at the shaft end. However, the structure elongates axially by the sensor, resulting in increased volume. Furthermore, the shaft's extension along the two directions, where the sensor is located, presents a problem: physical interference with the sensor makes it difficult to connect the shaft to a load such as a fan. Furthermore, the technology described in Patent Document 1, which uses sensors as described above, can lead to problems such as increased costs due to the use of sensors, sensor failure, disconnection of signal lines connected to the sensor, and fluctuations in sensor characteristics or increased errors due to temperature changes.

[0008] The present disclosure has been made in consideration of the above, and aims to provide a control device for a bearingless motor that can estimate the axial displacement, speed, or acceleration of the rotor while simplifying the structure compared to conventional devices.

[0009] In order to solve the above-mentioned problems and achieve the object, a control device for a bearingless motor according to the present disclosure is a device for controlling a bearingless motor including a rotor and a stator having a motor winding that generates torque, the rotor and stator being disposed with a predetermined gap therebetween, and the control device includes an observer and a speed estimator. The observer receives as input a voltage command value for the motor winding or a detected voltage value that is a detected value of the voltage applied to the motor winding, and a detected current value that is a value of the current through the motor winding, and calculates an estimated rotor magnetic flux that is an estimate of the rotor magnetic flux generated in the motor winding by the rotor. The speed estimator receives as input a value output from the observer, and calculates and outputs an estimated axial speed that is an estimate of the axial speed of the rotor. The observer includes a voltage error calculator that calculates an induced voltage error that is the difference between a first induced voltage calculated from the voltage command value or the detected voltage value and the detected current value, and a second induced voltage calculated from the estimated rotor magnetic flux. The speed estimator receives the induced voltage error as an input, calculates an estimated axial speed, and outputs it.

[0010] The control device for a bearingless motor according to the present disclosure has an advantageous effect of being able to estimate the axial displacement, speed, or acceleration of the rotor while having a simpler structure than conventional devices.

[0011] 6 is a cross-sectional view showing a schematic example of the configuration of a bearingless motor according to embodiment 1; FIG. 7 is a block diagram showing an example of the configuration of a control device for a bearingless motor according to embodiment 1; FIG. 8 is a block diagram showing another example of the configuration of a control device for a bearingless motor according to embodiment 1; FIG. 9 is a block diagram showing an example of the configuration of a speed estimator; FIG. 10 is a block diagram showing an example of the configuration of a d-axis current command value generator in a control device for a bearingless motor according to embodiment 2;

[0012] A control device for a bearingless motor, a motor system, and a control method for a bearingless motor according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0013] In the following embodiments, when a character indicates a vector, it is written as "character (vector)", and when a character indicates a matrix, it is written as "character (matrix)". Furthermore, when a character is represented by a symbol above it in a mathematical formula, it is written as "character (symbol above it)" in the text. For example, when a character is represented by a "^" above it in a mathematical formula, it is written as "character ^" in the text.

[0014] Embodiment 1. Figure 1 is a cross-sectional view showing a schematic example of the configuration of a bearingless motor according to embodiment 1. Here, the axial direction of rotor 20 is defined as the z-axis, and two axes perpendicular to each other on a plane perpendicular to the z-axis are defined as the x-axis and y-axis. Figure 1 shows a zx cross-section of bearingless motor 1. Bearingless motor 1 includes a stator 10 and a rotor 20.

[0015] The stator 10 has a stator core 11, a motor winding 12, and a support winding 13. The stator core 11 is substantially cylindrical and surrounds a central axis CA of the bearingless motor 1. The central axis CA is the center of rotation of the rotor 20 in the bearingless motor 1, and in one example is an imaginary line passing through the center of the rotor 20. The central axis CA is an example of a rotation axis. Hereinafter, the extension direction of the central axis CA will also be referred to as the axial direction. Also, FIG. 1 shows a case where the central axis CA faces vertically. The motor winding 12 is a rotation winding provided in a slot of the stator core 11 and rotates the rotor 20, i.e., generates torque. The support winding 13 is a magnetic levitation winding provided in a slot of the stator core 11.

[0016] The rotor 20 includes a shaft 21 and permanent magnets 22. The shaft 21 is, for example, a cylindrical member made of a magnetic material. The shaft 21 has a rotation axis along the z-axis. The diameter of the shaft 21 in a direction perpendicular to the z-axis is smaller than the inner diameter of the stator core 11. The permanent magnets 22 are disposed on the outer periphery of the shaft 21. The permanent magnets 22 may be fixed to the shaft 21 by magnetic force or by a fixing member such as an adhesive. While FIG. 1 shows a surface permanent magnet (SPM) bearingless motor 1 in which the permanent magnets 22 are embedded on the surface of the shaft 21, the motor may also be an interior permanent magnet (IPM) bearingless motor 1 in which the permanent magnets 22 are embedded inside the core of the shaft 21. The stator 10 and the rotor 20 are disposed with a predetermined gap between them. In this example, the rotor 20 is provided inside the cylindrical stator 10 with a predetermined gap from the inner periphery of the stator 10 .

[0017] Passing a current through the motor winding 12 of the stator 10 generates a magnetic flux with pole number p, generating torque. Passing a current through the support winding 13 of the stator 10 generates a magnetic flux with pole number p±2 or 2, generating a radial support force. In a typical bearingless motor 1, including a surface permanent magnet type bearingless motor, the support force is generated by the magnetic field with pole number p±2 due to the support winding 13, and in a consequent pole type bearingless motor or homopolar type bearingless motor, the support force is generated by the magnetic field with pole number p±2 due to the support winding 13.

[0018] At least a portion of the magnetic circuit for the magnetic flux of pole number p for generating torque and the magnetic circuit for the magnetic flux of pole number p±2 or 2 for generating support force are shared. By sharing at least a portion of the magnetic circuit and superimposing the magnetic flux of pole number p±2 or 2 on the magnetic flux of pole number p, variations in magnetic flux density are generated. Therefore, by adjusting the magnitude and phase of the support current, the magnitude and direction of the radial support force can be controlled.

[0019] If the gravitational acceleration is g and the mass of the rotor 20 is m, the rotor 20 is constantly subjected to its own weight mg acting downward. When the rotor 20 is located on the lower side of the axial direction, i.e., on the negative side of the z-axis, the stator 10 exerts an axial restoring force F z Then, the weight mg and the restoring force F z Therefore, as shown in FIG. 1, when the rotor 20 is positioned so that the z-axis is oriented vertically, the rotor 20 is balanced at a position displaced downward from the magnetic center in the axial direction, i.e., the position z = 0. On the other hand, when the rotor 20 is displaced upward in the axial direction, i.e., toward the positive side of the z-axis, the restoring force F z will be in the same downward direction as its own weight.

[0020] Although not shown, a fan or the like may be attached to the rotor 20. In this case, a reaction force generated when the fan circulates air or the like acts in the axial direction of the rotor 20. This also changes the position of balance in the axial direction of the rotor 20. This reaction force occurs even if the axial direction of the rotor 20 is horizontal. In other words, even if the central axis CA of the rotor 20 is aligned horizontally, the position of balance may shift from the magnetic center in the axial direction.

[0021] FIG. 1 shows an inner rotor type bearingless motor 1 in which the rotor 20 is located inside the stator 10, but the same phenomenon occurs in an outer rotor type bearingless motor in which the rotor 20 is located outside the stator 10, and the technology of the embodiments described below can be applied to an outer rotor type bearingless motor 1.

[0022] The bearingless motor 1 configured as described above is controlled by a control device for the bearingless motor 1, which will be described later. A system including the bearingless motor 1 and the control device for the bearingless motor 1 corresponds to a motor system.

[0023] 2 is a block diagram showing an example of the configuration of a control device for a bearingless motor according to embodiment 1. Here, the control device 30 shows a plant 40, which is the control target, a bearingless motor 1, an observer 32 that receives voltage as an input, and a speed estimator 33 that receives a voltage error, which is a value output from the observer 32, and outputs an estimated axial speed, which is an estimate of the axial speed of the rotor 20. In other words, in this example, the control device 30 includes a current controller 31, the observer 32, and the speed estimator 33. Thin lines in the diagram represent scalars, and thick lines represent vectors, and this also applies to the following block diagrams. The equations of motion in the axial direction of the rotor 20 are expressed as the following equations (1) and (2).

[0024] F z = -mg-(k z0 +k zi i d ) z ... (2)

[0025] The ratio of the restoring force to the displacement is the stiffness. When the current is not controlled, the stiffness is a constant value k z0 However, the d-axis current i d By passing k, the rigidity can be increased or decreased. In other words, the attractive force generated between the stator core 11 and the permanent magnet 22 of the rotor 20 can be increased or decreased. zi is the d-axis current i d is the rate at which the stiffness changes depending on the current, and the stiffness when energized is k z0 +k zi i d This is shown by the axial motion model 41 in FIG.

[0026] The plant 40 to be controlled is a bearingless motor 1, and the input is a voltage v s (vector) = [v d v q ] T and the output is current i s (vector) = [i d i q ] THere, the subscript s means the stator 10, d means the d-axis, q means the q-axis, and the superscript T means transpose. Also, variables that are located between the input and output of the plant 40 and represent the state are called state variables. The state variables include the rotor magnetic flux Φ r (vector) = [Φ dr Φ qr ] T Here, r denotes the rotor 20. The rotor magnetic flux Φ r Since (vector) has two components, there are two state variables.

[0027] As shown in the following equation (3), the armature reaction flux Φ s (vector), and the current i observed in the motor winding 12 of the stator 10. s (vector) and are proportional to each other. Here, the current i s (vector) and armature reaction flux Φ s By not using (vector) as a state variable, the number of state variables is reduced from four to two, thereby reducing the amount of calculation.

[0028]

[0029] The current i observed in the motor winding 12 of the stator 10 s The (vector) has three phases, U, V, and W, but can be converted into a current on the dq axis, which is a two-axis rotation coordinate system, by performing a uvw-dq transformation. The dq axis will be referred to as the rotation dq axis below. The current detection values ​​i of the U, V, and W phases u , i v , i w The d-axis current i d and the q-axis current i q The equation for converting into is the following equation (4): where θ is the angle of the rotating dq axis with respect to the stationary coordinate system, that is, the rotation angle.

[0030]

[0031] When the true rotation angle θ is unknown, the conversion can be performed using the estimated rotation angle θ̂, which is an estimated value of the rotation angle θ. u , i v , i wThe d-axis current i d and q-axis current i q When the equation is converted into the above equation, the following equation (5) is obtained: In this case, the values ​​on the left side are the current values ​​on the estimated d-axis and the estimated q-axis.

[0032]

[0033] In FIG. 2, the current i output from the plant 40 s (vector) is converted into a current on the dq axis, i.e., i s (vector) = [i d i q ] T That is, in FIG. 2, the block for converting three-phase currents into d- and q-axes is omitted.

[0034] The current i, which is the output of the plant 40 s (vector) = [i d i q ] T are fed back to obtain the d-axis current command value i d * and the q-axis current command value i q * The deviation between and is calculated and input to the current controller 31. Here, the superscript * indicates a command value. The d-axis current i d and the d-axis current command value i d * The deviation between the q-axis current i q and the q-axis current command value i q * The deviation between the voltage command value v and the reference voltage v is calculated by the current value deviation calculation unit 34q. The current controller 31 receives these deviations and calculates the voltage command value v so as to make the deviation zero. s * (vector) = [v d * v q * ] T Output.

[0035] The inverter operates based on the voltage command value v s *A voltage is applied to the plant 40 according to (vector). In reality, voltages are applied to the windings of the U, V, and W phases, respectively, but in Figure 2, the uvw-dq transformation block is omitted and the values ​​are shown as they are on the dq coordinates. Also, in Figure 2, the inverter is omitted from illustration.

[0036] The observer 32 calculates the voltage v applied to the stator 10. s (vector) is used as input, and the state variables of the plant 40 are calculated and output. As described above, in this example, the state variables of the plant 40 are the rotor magnetic flux Φ r (vector), and the observer 32 calculates the rotor magnetic flux Φ r (vector) is estimated as the rotor flux Φ r It is constructed to output and reproduce the estimated rotor flux Φ r ^ (vector) = [Φ dr ^ Φ qr ^] T is the estimated rotor flux Φ r (vector) and is marked with a hat "^".

[0037] In the example of FIG. 2, the observer 32 calculates the voltage command value v s * (vector) or the detected voltage value v s (vector), and the current detection value i, which is the value of the current in the motor winding 12. s (vector) and are input, the rotor magnetic flux Φ generated in the motor winding 12 by the rotor 20 is r (vector) and the estimated rotor flux Φ, which is also a state variable r ^ (vector) is calculated. Current detection value i s (vector) is the current i s corresponds to (vector).

[0038] 2, the observer 32 includes a voltage error calculator 321. The voltage error calculator 321 calculates the voltage v applied to the stator 10. s (vector), and the current i flowing through the motor winding 12 s(vector), and the estimated rotor magnetic flux Φ calculated by the observer 32. r ^ (vector) and calculates the voltage error e (vector). The voltage error e (vector) is calculated from the voltage command value v s * (vector) or voltage detection value v s (vector) and the detected current value i s (vector), the first induced voltage calculated from r The voltage error e (vector) corresponds to the induced voltage error.

[0039] The speed estimator 33 receives the voltage error e (vector) as input and estimates an estimated axial speed d|z^| / dt, which is an estimate of the axial speed d|z| / dt of the rotor 20. In the example of FIG. 2 , the speed estimator 33 receives the voltage error e (vector) and the estimated rotor magnetic flux Φ r ^ (vector) is used as input, and the estimated axial velocity d|z^| / dt is calculated and output.

[0040] The voltage input to the observer 32 is the voltage command value v s * (vector), the voltage detection value v s (vector) may also be used. s * When a vector is input, a voltage sensor is not required, and the structure can be simplified. s When inputting a vector, the voltage command value v s * (vector) and voltage detection value v s (vector) can be eliminated. In this way, the estimated axial speed d|z^| / dt of the rotor 20 can be estimated without providing a displacement sensor, a speed sensor, or an acceleration sensor to detect the axial position of the rotor 20. From the estimated speed, the remaining physical quantity, displacement, can be calculated and estimated by integration, and acceleration can also be calculated and estimated by differentiation. In addition, the voltage command value v s *By configuring the observer 32 to input the vectors (vectors), it is possible to eliminate the need for a voltage sensor. In this case, the only sensor required is a current sensor. In other words, there is no need to provide new hardware such as sensors required for estimating axial displacement, velocity, or acceleration.

[0041] The relational expression that holds for the plant 40, which is the controlled object, is expressed as the following equation (6), where the first induced voltage, which includes the influence of the axial speed d|z| / dt of the rotor 20, is the left side. r (vector) = [Φ dr Φ qr ] T This is the voltage detection value v s (vector) and current i s (vector).

[0042]

[0043] Here, the matrices in equation (6) are defined as B2 (matrix) and K2 (matrix) as shown in the following equations (7) and (8).

[0044]

[0045]

[0046] The variables used in equations (6) to (8) are as follows: r (vector) = [Φ dr Φ qr ] T : Rotor magnetic flux R: Stator resistance L: Inductance v s (vector) = [v d v q ] T : Voltage input to the plant 40 i s (vector) = [i d i q ] T : Current output from plant 40 ω1: Power supply angular frequency ω r : rotational angular velocity (electrical angle) of rotor 20

[0047] However, the inductance L is the d-axis inductance L dand q-axis inductance L q When distinguishing between the two, the first column of K2 (matrix) in equation (8) is replaced with L. d Then, change L in the second column to L q In addition, when the rotor 20 is displaced in the axial direction, the rotor magnetic flux Φ r (vector) is considered to change, and k is the rotor flux Φ with respect to the axial displacement. r Furthermore, the axial speed d|z| / dt corresponds to the time-differentiated value of the absolute value of the axial position, with the center of coordinates of the axial position of the rotor 20, i.e., z=0, being the central position magnetically opposed to the stator 10.

[0048] Next, the estimated rotor flux Φ r ^ (vector) = [Φ dr ^ Φ qr ^] T The observer 32 with state variables is constructed as shown in the following equation (9).

[0049]

[0050] Here, the matrix and vector in equation (9) are defined as A' (matrix), e (vector), and H (matrix) as shown in the following equations (10) to (12). Note that e (vector) is a vector indicating the voltage error, and H (matrix) is a matrix indicating the feedback gain.

[0051]

[0052]

[0053]

[0054] Also, the matrix in equation (11) is defined as C2 (matrix) as in the following equation (13).

[0055]

[0056] Furthermore, the variables used in equations (9) to (13) are as follows: r ^ (vector) = [Φ dr ^ Φ qr ^]T : Estimated rotor flux ω r ^: Estimated rotational angular velocity

[0057] Estimated rotor flux Φ r ^ (vector) = [Φ dr ^ Φ qr ^] T The right side of equation (9) showing the observer 32 with the state variables is the rotor magnetic flux Φ r (vector) is not included and can be calculated from the voltage and current. In other words, all values ​​included in equation (9) are known values ​​or values ​​calculated during operation. Therefore, by using this equation, the estimated rotor magnetic flux Φ r ^ (vector) = [Φ dr ^ Φ qr ^] T can be calculated.

[0058] Note that the first row, first column and the second row, second column of A' (matrix) shown in equation (10) are set to 0. This is because, unlike the plant 40, the observer 32 estimates that the rotor 20 of the bearingless motor 1 does not move in the axial direction.

[0059] In addition, in A2' (matrix) shown in equation (10) and C2 (matrix) shown in equation (13), the rotational angular velocity ω r Assuming that it is not possible to detect the estimated rotational angular velocity ω r The rotational angular velocity ω is expressed using ^. r can be detected, the rotational angular velocity ω can be calculated using A2' (matrix) and C2 (matrix) as shown in the following equations (14) and (15). r may also be used.

[0060]

[0061]

[0062] The voltage error e (vector) calculated by the voltage error calculator 321 of the observer 32 is expressed as B2 (matrix) [v ds v qs ] T -K2 (matrix) [i d i q ]T The first induced voltage represented by C2 (matrix) [Φ dr ^ Φ qr ^] T and the estimated rotation angular velocity ω r If there is an error in ^ or if the rotor 20 is vibrating in the axial direction, the voltage error e will be a value other than 0, as will be described later. Utilizing this principle, the state of the rotor 20 is estimated without using a sensor. Note that in this example, the number of state variables of the observer 32 is two, but it may be less than two. In other words, the number of state variables of the observer 32, or the number of state variables calculated by the observer 32 in this example, may be two or less. Reducing the number of state variables of the observer 32 can reduce the calculation load.

[0063] In Fig. 2, the observer 32 includes a voltage error calculator 321. The observer 32 and the voltage error calculator 321 are configured on the same circuit board. The first induced voltage and the second induced voltage are input to the voltage error calculator 321, which outputs a voltage error e (vector). At the same time, the observer 32 calculates an estimated rotor magnetic flux Φ r The voltage error e (vector) calculated by the voltage error calculator 321 is input to the speed estimator 33, which will be described later.

[0064] The configuration in Figure 2 is one example, and other configurations may be used. Figure 3 is a block diagram showing another example of the configuration of the control device for a bearingless motor according to embodiment 1. Note that the same components as those described in Figure 2 are given the same reference numerals, and their description will be omitted. As shown in Figure 3, the control device 30A for the bearingless motor 1 further includes a voltage error calculator 37, and the observer 32A has a configuration in which the voltage error calculator 321 is omitted from the configuration of the observer 32 in Figure 2. The configuration of the voltage error calculator 37 is the same as the configuration of the voltage error calculator 321 described in Figure 2.

[0065] However, the observer 32 receives the voltage error e (vector) output from the voltage error calculator 37 as an input and calculates the estimated rotor magnetic flux Φ r ^ (vector). The voltage error calculator 37 calculates the voltage command value vs * (vector) or voltage detection value v s (vector) and the detected current value i s (vector), and the estimated rotor flux Φ which is the output of the observer 32. r ^ (vector) and is input, and a voltage error e (vector) which is the difference between the first induced voltage and the second induced voltage is output.

[0066] As shown in Fig. 3, the voltage error calculator 37 and the observer 32A may be considered to be separate areas. That is, the calculations in the voltage error calculator 37 and the calculations in the observers 32, 32A may be performed on the same circuit board as shown in Fig. 2, or may be performed on separate circuit boards as shown in Fig. 3. Furthermore, if the voltage error calculator 37 and the observer 32A are not separated into separate areas and, for example, the observer 32A includes the voltage error calculator 37, the configuration will be the same as that shown in Fig. 2. Furthermore, although not shown in the figure, the observer 32A may include the speed estimator 33. The configuration shown in Fig. 3 is an example and is not limited to this configuration.

[0067] 4 is a block diagram showing an example of the configuration of the speed estimator 33. The speed estimator 33 includes a calculation unit 331a and a P (Proportional) controller 332a. That is, the calculation unit 331a calculates a voltage error e in the d-axis direction. d The estimated rotor flux Φ in the d-axis direction dr ^, and the P controller 332a adds a P gain coefficient K P1 When the d-axis of the controlled dq-axes is approximately aligned with the north pole of the permanent magnet 22 of the rotor 20, the rotor magnetic flux Φ qr and estimated rotor flux Φ qr The value of ^ can be approximated to 0. Also, the estimated rotor flux Φ dr ^ and rotor flux Φ dr Between dr ^≒Φ dr If it is assumed that the above holds, the voltage error e (vector) is expressed by the following equation (16).

[0068]

[0069] The estimated rotational angular velocity ω of the rotor 20 r ^ and rotational angular velocity ω r The difference between r ^-ω r is the rotational angular velocity error Δω r is.

[0070] From equation (16), the voltage error e = [e d e q ] T Among them, the voltage error e in the d-axis direction in the first row d is a value proportional to the axial velocity d|z| / dt as shown in the following equation (17).

[0071]

[0072] As a result, the estimated axial velocity d|z^| / dt, which is the estimated value of the axial velocity d|z| / dt, is expressed as e d / Φ dr That is, the speed estimator 33 shown in FIG. 4 can estimate the input voltage error e d The input estimated rotor flux Φ dr The value e divided by ^ d / Φ dr ^ is calculated, and the estimated axial velocity d|z^| / dt is calculated by this e d / Φ dr Assuming that it is proportional to ^, e d / Φ dr ^ as a constant P gain K P1 In this way, the speed estimator 33 outputs an estimated axial speed d|z^| / dt corresponding to the value obtained by differentiating the absolute value of the axial position with respect to time, with the coordinate center of the axial position of the rotor 20 being the central position magnetically opposed to the stator 10.

[0073] As described above, when the observer 32 estimates that the rotor 20 of the bearingless motor 1 does not move in the axial direction, the speed estimator 33 calculates the estimated rotor magnetic flux Φ rThe estimated axial speed d|z^| / dt can be obtained from the relational expression between the voltage error e (vector), which is the difference between the second induced voltage generated by ^ (vector) and the first induced voltage including the influence of the axial speed d|z| / dt of the rotor 20, and the axial speed d|z| / dt.

[0074] In addition, the voltage command value v s * (vector) or voltage detection value v s (vector) and estimated rotor flux Φ r ^ (vector) and the detected current value i s The voltage error e (vector) and the voltage error e (vector) are converted into the rotational dq axes, and the speed estimator 33 calculates the value of the d-axis component of the voltage error e (vector), i.e., the d-axis voltage error e d Based on this, the estimated axial velocity d|z^| / dt is output.

[0075] In the calculation by the speed estimator 33 shown in FIG. 4, the voltage error e d and estimated rotor flux Φ dr ^ and both are input, but the input is the voltage error e d This can be simplified to only the estimated rotor flux Φ dr This can suppress the divergence of the calculated value when ^ unexpectedly becomes close to 0.

[0076] Typically, to estimate velocity from displacement information, a derivative (D) controller is required to perform a differential operation. However, when a differential operation is performed, high frequencies are amplified, which poses a problem of amplifying noise containing frequencies higher than the frequency components of the required signal. However, in the first embodiment, a P controller is used instead of a D controller, which makes it possible to suppress the amplification of noise containing frequencies higher than the frequency components of the required signal.

[0077] Rotation angular velocity error Δω r is the voltage error e = [e d e q ] T The second line of q It is included only in eq does not include the axial velocity d|z| / dt. Therefore, the influence of the axial velocity d|z| / dt and the rotational angular velocity error Δω r That is, in one example, when feeding back the influence of the axial velocity d|z| / dt, the influence of the rotational angular velocity error Δω r This has the effect of facilitating control design. Furthermore, since unintended components are not fed back, when the estimated axial velocity d|z^| / dt, which is an estimate of the axial velocity d|z| / dt, is used for control, the effect of stabilizing operation can be obtained.

[0078] A control method for controlling a bearingless motor 1 including such a rotor 20 and a stator 10 having a motor winding 12 that generates torque includes an observer step and a speed estimation step. In the observer step, an observer 32 estimates a voltage command value v d * , v q * or a voltage detection value v which is a detection value of the voltage applied to the motor winding 12 d , v q and the current detection value i, which is the value of the current in the motor winding 12. d , i q and the rotor magnetic flux Φ generated in the motor winding 12 by the rotor 20 is r (vector) and the estimated rotor flux Φ, which is a state variable r In the speed estimation step, the value calculated in the observer step is used as an input to calculate and output an estimated axial speed d|z^| / dt, which is an estimate of the axial speed d|z| / dt of the rotor 20. Here, in the observer step, the voltage command value v d * , v q * or voltage detection value v d , v q and the detected current value i d , i q and the first induced voltage calculated from the estimated rotor magnetic flux Φ rA voltage error e (vector) is calculated, which is the difference between the second induced voltage calculated from ^ (vector) and . In the velocity estimation step, the voltage error e (vector) is used as an input to calculate and output an estimated axial velocity d|z^| / dt.

[0079] As described above, the control device 30 for the bearingless motor 1 according to the first embodiment controls the bearingless motor 1, which includes the rotor 20 and the stator 10 having the motor windings 12 that generate torque. The control device 30 for the bearingless motor 1 includes an observer 32, voltage error calculators 321 and 37, and a speed estimator 33. The observer 32 calculates the voltage command value v s * (vector) or the detected voltage value v s (vector), and the current detection value i, which is the value of the current in the motor winding 12. s (vector) and are input, the rotor magnetic flux Φ generated in the motor winding 12 by the rotor 20 is r (vector) and the estimated rotor flux Φ, which is a state variable r The voltage error calculators 321 and 37 calculate the voltage command value v s * (vector) or voltage detection value v s (vector) and the detected current value i s (vector), the first induced voltage calculated from r The speed estimator 33 calculates a voltage error e (vector) which is the difference between the second induced voltage calculated from the second induced voltage d|z| / dt and the second induced voltage calculated from the voltage error e (vector). The speed estimator 33 receives the voltage error e (vector) as an input, calculates an estimated axial speed d|z^| / dt which is an estimate of the axial speed d|z| / dt of the rotor 20, and outputs the estimated axial speed d|z^| / dt. Using this estimated axial speed d|z^| / dt, it is possible to obtain the axial position of the rotor 20, and therefore a sensor for detecting the axial displacement, speed, or acceleration of the rotor 20 is not required. In other words, compared to conventional bearingless motors which have sensors for detecting the axial displacement, speed, or acceleration of the rotor 20, it has the advantage of being able to estimate the axial displacement, speed, or acceleration of the rotor 20 while simplifying the structure.

[0080] In the second embodiment, the control device 30 of the bearingless motor 1 calculates the d-axis current command value i d * The d-axis current command value generator uses the estimated axial speed d|z^| / dt output from the speed estimator 33 to generate the d-axis current command value i d * and outputs it to the current controller 31. The d-axis current command value generator corresponds to the current command value generator.

[0081] 5 is a block diagram showing an example of the configuration of a d-axis current command value generator in the control device for a bearingless motor according to embodiment 2. The d-axis current command value generator 35 receives the estimated axial speed d|z^| / dt from the speed estimator 33 as an input and calculates the d-axis current command value i d * The d-axis current command value generator 35 includes an axial position controller 351, a zero value output unit 352, and a switch 353. The axial position controller 351 calculates and outputs the d-axis current command value i from the estimated axial speed d|z^| / dt. d * The zero value output unit 352 calculates and outputs the d-axis current command value i d * The switch 353 selects either the output of the axial position controller 351 or the output from the zero value output unit 352, and outputs 0 as the d-axis current command value i d * The zero value output unit 352 outputs the d-axis current command value i d * In FIG. 5, the estimated axial speed d|z^| / dt is input and the axial position controller 351 calculates the d-axis current command value i d * and outputs the d-axis current i d That is, the d-axis current command value i d * In FIG. 5, the estimated axial speed d|z^| / dt is input and the axial position controller 351 calculates the d-axis current command value i d * and outputs the d-axis current i dThis makes it possible to switch to a control state in which the above can be adjusted.

[0082] Furthermore, the d-axis current command value generator 35 generates a positive d-axis current i when the estimated axial speed d|z^| / dt is a positive value. d If the value is negative, the negative d-axis current i d A P controller is a typical controller that outputs such a command. FIG. 5 shows a case where a P controller is used for the axial position controller 351. The P gain of the P controller is set to K P3 Let's say. P3 By making is a positive value, the signs of the input and output can be made to match.

[0083] Furthermore, the axial position controller 351 is not limited to a P controller that simply makes the output proportional to the input, but may use an sgn (signum) function that outputs 1 if the input value is positive and -1 if the input value is negative, or may use the sgn function in combination with a P controller. Furthermore, a limiter may be applied to the input value. Furthermore, the cube of the input value may be used.

[0084] A P controller is applied to the axial position controller 351, and the d-axis current i d is the estimated axial velocity d |z^| / dt K P3 x times and the estimated axial velocity d|z^| / dt is equal to the axial velocity d|z| / dt. In this case, the equation of motion in the axial direction, i.e., the Z-axis direction, is given by the following equation (18).

[0085]

[0086] Here, when z≧0, the following equation (19) is obtained, and k zi K P3 z>0 holds. When z<0, the following equation (20) holds, and k zi K P3 (-z)>0 holds.

[0087]

[0088]

[0089] Therefore, a force proportional to the axial velocity d|z| / dt and directed in the opposite direction to the velocity can be generated. This corresponds to a damping force that attenuates vibration. In other words, the d-axis current command value i is calculated from the estimated axial velocity d|z^| / dt output from the velocity estimator 33. d * By generating the above, when the rotor 20 vibrates in the axial direction, a damping force that attenuates the vibration can be generated.

[0090] As described above, the control device 30 of the bearingless motor 1 according to the second embodiment receives the estimated axial speed d|z^| / dt as an input and calculates the d-axis current command value i d * As a result, the d-axis current i d can be increased or decreased in accordance with the axial vibration of the rotor 20. As a result, an axial attractive force can be generated between the stator 10 and the rotor 20 so as to attenuate the axial vibration of the rotor 20.

[0091] 6 is a block diagram showing an example of the configuration of a speed estimator of a control device for a bearingless motor according to embodiment 3. In embodiment 3, a speed estimator 33B calculates a voltage error e (vector) and an estimated rotor magnetic flux Φ r ^ (vector) is input, and the estimated axial velocity d|z^| / dt is output, and at the same time, the estimated rotational angular velocity ω r Outputs ^.

[0092] Fig. 7 is a block diagram showing an example of the detailed configuration of the speed estimator shown in Fig. 6. The speed estimator 33B receives the voltage error e (vector) as an input, calculates and outputs an estimated axial speed d|z^| / dt, and also receives the voltage error e (vector) as an input, and calculates and outputs the rotational angular speed ω of the rotor 20. r The estimated rotational angular velocity ω r Specifically, the speed estimator 33B includes an estimated axial speed calculator 337 that calculates an estimated axial speed d|z^| / dt and an estimated rotational angular speed ω rThe estimated shaft speed calculator 337 includes a calculator 331a and a P controller 332a. The estimated shaft speed calculator 338 includes a calculator 333b, a sign inverter 334b, and a PI (Proportional-Integral) controller 335b. The configuration of the estimated shaft speed calculator 337 and the processing performed by the estimated shaft speed calculator 337 are the same as those described for the speed estimator 33 in FIG. 4 , and therefore description thereof will be omitted.

[0093] Estimated rotational angular velocity ω r The output of ^ contains the voltage error e (vector) = [e d e q ] T Among them, the voltage error e in the q-axis direction in the second row q The voltage error in the q-axis direction e q is the estimated rotor flux Φ dr ^ is the rotor flux Φ dr When the condition that they are approximately equal is satisfied, it is expressed by the following equation (21).

[0094]

[0095] Therefore, e q / Φ dr If you calculate ^, the rotational angular velocity error Δω r =ω r ^-ω r The rotational angular velocity error Δω r is input to a P controller, a PI controller, etc., to obtain the estimated rotational angular velocity ω r 7 shows the case where the PI controller 335b is used, and the P gain is set to K P2 and the I gain is K I2 Then, the estimated rotational angular velocity ω is calculated according to the following equation (22): r ^ is being calculated.

[0096]

[0097] That is, in the estimated rotational angular velocity calculation unit 338, the calculation unit 333b calculates the voltage error e in the q-axis direction. q The estimated rotor flux Φ in the d-axis direction drThe sign inverter 334b ​​inverts the sign of the calculation result in the calculator 333b, and the PI controller 335b applies a PI gain coefficient K P2 +K I2 / s to obtain the estimated rotational angular velocity ω r Outputs ^.

[0098] In one example, the rotational angular velocity error Δω r =ω r ^-ω r is a negative value, i.e., the estimated rotational angular velocity ω r ^ is the rotational angular velocity ω r When the value is smaller than q becomes a negative value, but is multiplied by -1 in the sign inverting unit 334b ​​and then calculated by the PI controller 335b. P2 +K I2 / s, the estimated rotation angular velocity ω r The value of ^ increases, and the true value of the rotational angular velocity ω r approaching.

[0099] Fig. 8 is a block diagram showing an example of the configuration of a control device for a bearingless motor according to embodiment 3. Note that the same components as those explained in Fig. 2 are given the same reference numerals, and their explanation will be omitted. The control device 30B in Fig. 8 includes the speed estimator 33B shown in Fig. 6 or 7. That is, the estimated rotational angular velocity ω estimated by the speed estimator 33B r ^ is used in the observer 32. The observer 32 does not use the signal of the rotational angular velocity sensor, which is the angle sensor around the Z axis of the rotor 20, but uses the estimated rotational angular velocity ω output from the speed estimator 33B. r The value of ^ is the rotational angular velocity ω r is used as a substitute.

[0100] Although Figure 8 shows a case where the control device 30B includes a speed estimator 33B instead of the speed estimator 33 in Figure 2, the control device 30B may also be configured to include a speed estimator 33B instead of the speed estimator 33 in Figure 3.

[0101] As described above, the bearingless motor 1 according to the third embodiment uses the control device 30B shown in FIG.d and the estimated rotor flux Φ in the d-axis direction dr ^ and an estimated axial speed calculation unit 337 that calculates an estimated axial speed d|z^| / dt from q and the estimated rotor flux Φ in the d-axis direction dr ^ and the estimated rotational angular velocity ω r The speed estimator 33B includes an estimated rotational angular velocity calculation unit 338 that calculates the estimated rotational angular velocity ω r ^ is output to the observer 32. With this configuration, not only can the axial displacement sensor be eliminated, but also the angle sensor of the rotor 20. This solves the problems of increased volume and cost due to the use of an angle sensor, sensor failure, disconnection of the signal line connected to the sensor, fluctuations in sensor characteristics or increased errors due to temperature changes, etc.

[0102] Embodiment 4 In the first to third embodiments, the control devices 30, 30A, 30B of the bearingless motor 1 are provided with a speed estimator 33 that receives the voltage error e (vector) as input, calculates the estimated axial speed d|z^| / dt, which is an estimate of the axial speed d|z| / dt of the rotor 20, and outputs the estimated axial speed d|z^| / dt. In this case, as shown in the second embodiment, the speed estimator 33 estimates the estimated axial speed d|z^| / dt, and then the d-axis current command value generator 35 receives the estimated axial speed d|z^| / dt as input and calculates the d-axis current command value i d * In this way, the estimated axial speed d|z^| / dt is calculated as an intermediate variable, and then the d-axis current command value i d * Instead of calculating the voltage error e (vector), the d-axis current command value i d * The following may be calculated.

[0103] Figure 9 is a block diagram showing an example of the configuration of a control device for a bearingless motor according to embodiment 4. Note that the same components as those explained in Figure 2 are given the same reference numerals, and their explanation will be omitted. The control device 30C for the bearingless motor 1 in Figure 9 includes an axial position controller 38 instead of the speed estimator 33 of embodiment 1. The axial position controller 38 calculates the voltage error e (vector) and the estimated rotor magnetic flux Φ r ^ (vector) to calculate the d-axis current command value i d * The axial position controller 38 calculates the calculated d-axis current command value i d * to the current value deviation calculation unit 34d. As a result, while a plurality of controllers were used in the second embodiment, which outputs the estimated axial velocity d|z^| / dt as an intermediate variable, only one controller is required in the fourth embodiment, thereby reducing the number of controllers. As a result, not only can the amount of calculation be reduced, but also the load of adjusting the controllers due to parameter changes can be reduced.

[0104] Although FIG. 9 shows a case where the control device 30C includes the axial position controller 38 instead of the speed estimator 33 of FIG. 2, the control device 30C may also be configured to include the axial position controller 38 instead of the speed estimator 33 of FIG. 3.

[0105] The control device 30C of the bearingless motor 1 of the fourth embodiment calculates the voltage error e (vector) and the estimated rotor magnetic flux Φ r ^ (vector) to calculate the d-axis current command value i d * This allows the d-axis current command value i corresponding to the axial displacement, speed, or acceleration of the rotor 20 to be calculated. d *can be directly calculated. Furthermore, as shown in the first to third embodiments, there is no need to calculate the estimated axial velocity d|z^| / dt as an intermediate variable, so the controller that calculates the estimated axial velocity d|z^| / dt can be omitted. In other words, there is an effect that the number of controllers can be reduced compared to the case of the second embodiment. Furthermore, there is an effect that not only the amount of calculation can be reduced, but also the load of adjusting the controller due to parameter changes can be reduced.

[0106] Fig. 10 is a diagram showing an example of a hardware configuration for realizing the control devices for bearingless motors according to embodiments 1 to 4. Fig. 10 shows an example of a configuration in which the main parts of the control devices 30, 30A, 30B, 30C for the bearingless motor 1, namely the current controller 31, the observers 32, 32A, the speed estimators 33, 33B, the d-axis current command value generator 35, the voltage error calculators 37, 321, and the axial position controller 38, are realized by a processing circuit 61 having a processor 63 and a memory 64.

[0107] The processor 63 is a CPU (Central Processing Unit) that executes a control program. The control program describes processes for causing the processing circuit 61 to operate as the current controller 31, the observers 32 and 32A, the speed estimators 33 and 33B, the d-axis current command value generator 35, the voltage error calculators 37 and 321, and the axial position controller 38, which are essential parts of the control devices 30, 30A, 30B, and 30C of the bearingless motor 1.

[0108] The memory 64 is, for example, a non-volatile or volatile memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM). The memory 64 stores control programs. The memory 64 is also used as a temporary memory when the processor 63 executes various processes.

[0109] The input unit 62 is a circuit that receives input signals for the control devices 30, 30A, 30B, and 30C from the outside. The output unit 65 is a circuit that outputs signals generated by the control devices 30, 30A, 30B, and 30C to the outside of the control devices 30, 30A, 30B, and 30C.

[0110] The functions of the processing circuit 61 may be realized by a processing circuit that is dedicated hardware. The processing circuit that is dedicated hardware is, for example, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a circuit that combines these. Some of the main parts of the control devices 30, 30A, 30B, and 30C of the bearingless motor 1 may be realized by the processor 63 and memory 64, and the rest may be realized by dedicated hardware.

[0111] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0112] 1 Bearingless motor, 10 Stator, 11 Stator core, 12 Motor winding, 13 Support winding, 20 Rotor, 21 Shaft, 22 Permanent magnet, 30, 30A, 30B, 30C Control device, 31 Current controller, 32, 32A Observer, 33, 33B Speed ​​estimator, 34d, 34q Current value deviation calculation unit, 35 d-axis current command value generator, 37, 321 Voltage error calculator, 38 Axial position controller, 40 Plant, 41 Axial motion model, 61 Processing circuit, 62 Input unit, 63 Processor, 64 Memory, 65 Output unit, 331a, 333b Calculation unit, 332a P controller, 334b ​​Sign inversion unit, 335b PI controller, 337 Estimated axial speed calculation unit, 338 Estimated rotational angular velocity calculation unit, 351 axial position controller, 352 zero value output device, 353 switch, CA central axis.

Claims

1. A control device for a bearingless motor that includes a rotor and a stator having motor windings that generate torque, the rotor and the stator being arranged with a defined gap therebetween, the control device comprising: an observer that calculates an estimated rotor flux, which is an estimated value of the rotor flux generated in the motor windings by the rotor, using as inputs a voltage command value of the motor windings or a voltage detection value, which is a detected value of the voltage applied to the motor windings, and a current detection value, which is a value of the current in the motor windings; and a speed estimator that calculates and outputs an estimated axial speed, which is an estimated value of the axial speed of the rotor, using as an input a value output from the observer. The observer has a voltage error calculator that calculates an induced voltage error, which is a difference between a first induced voltage calculated from the voltage command value or the voltage detection value and the current detection value, and a second induced voltage calculated from the estimated rotor flux. The speed estimator is characterized by calculating and outputting the estimated axial speed using the induced voltage error as an input.

2. A control device for a bearingless motor that includes a rotor and a stator having motor windings that generate torque, the rotor and the stator being arranged with a defined gap therebetween, the control device comprising: a voltage error calculator that calculates an induced voltage error, which is a difference between a first induced voltage calculated from a voltage command value of the motor windings or a voltage detection value, which is a detected value of the voltage applied to the motor windings, and a current detection value, and a second induced voltage calculated from an estimated rotor flux, which is an estimated value of the rotor flux generated in the motor windings by the rotor; an observer that calculates the estimated rotor flux using as an input the induced voltage error, which is an output of the voltage error calculator; and a speed estimator that calculates and outputs an estimated axial speed, which is an estimated value of the axial speed of the rotor, using as an input the induced voltage error. The voltage error calculator is characterized by outputting the induced voltage error using as inputs the voltage command value or the voltage detection value, the current detection value, and the estimated rotor flux, which is an output of the observer.

3. The voltage command value or the voltage detection value, the estimated rotor magnetic flux, the current detection value, and the induced voltage error are converted into the d-q axes which are the rotating two-axis coordinates. The speed estimator outputs the estimated axial direction speed based on the induced voltage error of the d-axis. The control device for a bearingless motor according to claim 1 or 2, characterized in that.

4. The number of state variables of the observer is two or less. The control device for a bearingless motor according to claim 1 or 2, characterized in that.

5. The speed estimator outputs the estimated axial direction speed corresponding to the value obtained by time-differentiating the absolute value of the axial direction position, with the coordinate center of the axial direction position of the rotor as the central position magnetically opposed to the stator. The control device for a bearingless motor according to claim 1 or 2, characterized in that.

6. The control device for a bearingless motor according to claim 3, further comprising a current command value generator that calculates and outputs a command value of the current in the d-axis using the estimated axial direction speed as an input.

7. The observer estimates that the rotor of the bearingless motor does not move in the axial direction. The speed estimator obtains the estimated axial direction speed from the relational expression between the induced voltage error, which is the difference between the first induced voltage including the influence of the axial direction speed of the rotor and the second induced voltage generated by the estimated rotor magnetic flux calculated by the observer, and the axial direction speed. The control device for a bearingless motor according to claim 1 or 2, characterized in that.

8. The speed estimator calculates and outputs the estimated axial direction speed with the induced voltage error as an input, and at the same time, calculates and outputs the estimated rotational angular velocity, which is an estimated value of the rotational angular velocity of the rotor, with the induced voltage error as an input. The control device for a bearingless motor according to claim 1 or 2, characterized in that.

9. A control device for a bearingless motor that includes a rotor and a stator having motor windings that generate torque, the rotor and the stator being arranged with a defined gap therebetween, the control device comprising: an observer that calculates an estimated rotor flux, which is an estimated value of the rotor flux generated in the motor windings by the rotor, using as inputs a voltage command value of the motor windings or a voltage detection value, which is a detected value of the voltage applied to the motor windings, and a current detection value, which is a value of the current in the motor windings; and an axial position controller that calculates and outputs a d-axis current command value for controlling the axial position of the rotor, using as an input a value output from the observer. The observer has a voltage error calculator that calculates an induced voltage error, which is a difference between a first induced voltage calculated from the voltage command value or the voltage detection value and the current detection value, and a second induced voltage calculated from the estimated rotor flux. The axial position controller is characterized by calculating and outputting the d-axis current command value using the induced voltage error as an input.

10. A motor system comprising: a bearingless motor that includes a rotor and a stator having motor windings that generate torque, the rotor and the stator being arranged with a defined gap therebetween; and a control device for the bearingless motor. The control device for the bearingless motor comprises: an observer that calculates an estimated rotor flux, which is an estimated value of the rotor flux generated in the motor windings by the rotor, using as inputs a voltage command value of the motor windings or a voltage detection value, which is a detected value of the voltage applied to the motor windings, and a current detection value, which is a value of the current in the motor windings; and a speed estimator that calculates and outputs an estimated axial speed, which is an estimated value of the axial speed of the rotor, using as an input a value output from the observer. The observer has a voltage error calculator that calculates an induced voltage error, which is a difference between a first induced voltage calculated from the voltage command value or the voltage detection value and the current detection value, and a second induced voltage calculated from the estimated rotor flux. The speed estimator is characterized by calculating and outputting the estimated axial speed using the induced voltage error as an input.

11. A method for controlling a bearingless motor including a rotor and a stator having motor windings that generate torque, the rotor and the stator being disposed with a defined gap therebetween, the method comprising: an observer step of calculating an estimated rotor magnetic flux, which is an estimated value of the rotor magnetic flux generated in the motor windings by the rotor, using as inputs a voltage command value of the motor windings or a voltage detection value, which is a detected value of the voltage applied to the motor windings, and a current detection value, which is a value of the current in the motor windings; and a speed estimation step of calculating and outputting an estimated axial speed, which is an estimated value of the axial speed of the rotor, using as an input the value calculated in the observer step. In the observer step, an induced voltage error, which is a difference between a first induced voltage calculated from the voltage command value or the voltage detection value and the current detection value and a second induced voltage calculated from the estimated rotor magnetic flux, is calculated. In the speed estimation step, the estimated axial speed is calculated and output using the induced voltage error as an input. A method for controlling a bearingless motor characterized by the above.

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