Device for detecting the direction of rotation of a rotor, associated control and drive systems, and method

Abstract

The device (17) for detecting the direction of rotation of a rotor for a magnetic bearing comprises: - comparison means (100) configured to compare the rotation speed of the rotor with a predefined speed threshold (Se), - first determination means (105) configured to determine the rotation speed gradient of the rotor, and - second determination means (107) configured to determine the direction of rotation of the rotor from the result of the comparison of the rotation speed of the rotor with the predefined speed threshold (Se) and the value of the parameter representative of the kinetics of the rotor determined. Figure for the abstract: Fig 5

Description

Title of the invention: Device for detecting the direction of rotation of a rotor, associated control and drive systems, and method Technical field of the invention

[0001] The present invention relates to the control of magnetic bearings.

[0002] The present invention relates more particularly to a device for detecting the direction of rotation of a rotor of a magnetic bearing, a system for controlling a magnetic bearing comprising such a device, a drive system comprising such a system and a magnetic bearing, and a method for detecting the change in direction of rotation of the rotor. State of the prior art

[0003] Conventionally, magnetic bearings are implemented in systems comprising a rotor operating at high rotational speed.

[0004] A magnetic bearing supports the rotor by magnetic levitation in a stator of the system.

[0005] The magnetic bearings are controlled by a control system generally comprising a synchronous filter implementing magnetic bearing control algorithms.

[0006] The synchronous filter comprises a modulation module performing a change of reference from a stator reference frame to a rotor reference frame, a magnetic bearing control algorithm performing operations in the rotor reference frame in order to simplify said operations, and a demodulation module performing a change of reference frame from the rotor reference frame to the stator reference frame.

[0007] The reference change operations implement trigonometric functions dependent on the direction of rotation of the rotor.

[0008] When developing the control system, the direction of rotation of the rotor is defined and entered into the modulation and demodulation modules manually by an operator.

[0009] If the direction of rotation entered is not representative of the direction of rotation of the rotor, the modulation module delivers, after filtering, a zero value.

[0010] The operator may make an error in the direction of rotation which could damage the system in which the bearing is implemented.

[0011] In addition, when the direction of rotation needs to be changed, it is necessary for an operator to intervene to manually change the direction of rotation of the rotor.

[0012] It is therefore proposed to overcome all or part of these drawbacks. Summary of the invention

[0013] In view of the above, the invention provides a method for detecting a change in the direction of rotation of a magnetic bearing rotor, comprising:

[0014] - a determination of the rotational speed gradient of the rotor,

[0015] - a comparison of the rotational speed of the rotor with a predefined speed threshold, and

[0016] - detecting a change in the direction of rotation of the rotor from the result of the comparison of the rotor rotation speed with the predefined speed threshold and the determined rotor rotation speed gradient.

[0017] The change in the direction of rotation of the rotor is detected from the rotational speed of the rotor and the gradient of the rotational speed of the rotor to adapt the control algorithms of the magnetic bearing autonomously and automatically, without the manual intervention of an operator.

[0018] Advantageously, when the rotor rotates in a first direction of rotation, the method comprises:

[0019] - the detection of a first inversion of the direction of rotation of the rotor according to a second direction of rotation opposite to the first direction of rotation when the absolute value of the rotor rotation speed is less than the speed threshold and when the speed gradient is negative, and

[0020] - the detection of a second inversion of the direction of rotation of the rotor according to the first direction of rotation following the first inversion when the speed gradient is greater than or equal to zero, and when the absolute value of the rotor rotation speed is less than the speed threshold.

[0021] There is also provided a device for detecting a change in the direction of rotation of a rotor for a magnetic bearing, comprising:

[0022] - comparison means configured to compare the rotation speed of the rotor at a predefined speed threshold,

[0023] - first determination means configured to determine the gradient of rotor rotation speed, and

[0024] - second determination means configured to detect the change of direction of rotation of the rotor from the result of the comparison of the rotor rotation speed with the predefined speed threshold and the determined rotor rotation speed gradient.

[0025] Preferably, the second determining means are configured to:

[0026] - detect a first inversion of the direction of rotation of the rotor in a second direction of rotation opposite to the first direction of rotation when the absolute value of the rotor rotation speed is less than the speed threshold and when the speed gradient is negative, and

[0027] - detect a second reversal of the direction of rotation of the rotor according to the first direction of rotation following the first inversion when the speed gradient is greater than or equal to zero, and when the absolute value of the rotor rotation speed is less than the speed threshold.

[0028] A control system for a magnetic bearing is also proposed comprising a device as defined previously, and a synchronous filter comprising at least one algorithm for controlling the magnetic bearing, the algorithm comprising a variable gain controlled by said device according to the direction of rotation of the rotor.

[0029] Preferably, the synchronous filter comprises a modulation module and a demodulation module, the modulation module comprising a first algorithm comprising at least one variable gain controlled by said device according to the direction of rotation of the rotor, and the demodulation module comprising a second algorithm comprising at least one variable gain controlled by said device according to the direction of rotation of the rotor.

[0030] Advantageously, the synchronous filter further comprises a control module connected on the one hand to the modulation module and on the other hand to the demodulation module, the control module implementing an algorithm for correcting the rotor unbalance.

[0031] A drive system is also proposed comprising a magnetic bearing comprising a rotor and a stator comprising coils distributed uniformly in the stator forming at least one servo axis, a power converter supplying the servo axis, and a control system as defined previously controlling the power converter. Brief description of the figures

[0032] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0033] [Fig.l]

[0034] illustrates an example of a drive system according to the invention;

[0035] [Fig.2]

[0036] schematically illustrates an exemplary embodiment of a magnetic bearing control system according to the invention;

[0037] [Fig.3]

[0038] schematically illustrates an embodiment of a modulation module according to the invention,

[0039] [Fig.4]

[0040] schematically illustrates an exemplary embodiment of a control module according to the invention,

[0041] [Fig.5]

[0042] schematically illustrates an exemplary embodiment of the detection device according to the invention,

[0043] [Fig.6]

[0044] illustrates an example of implementation of the example embodiment of the detection device according to the invention, Detailed description of the invention

[0045] Reference is made to [Fig.l] which illustrates an example of a drive system comprising a magnetic bearing 1, a power converter 2, and a control system 3.

[0046] In a manner known per se, the magnetic bearing 1 comprises a stator 4 and a rotor 5 placed in the stator 4, and a direct orthogonal reference frame R(O, V, W) comprising two axes V, W and an origin O centered on the axis of rotation of the rotor 5.

[0047] The stator 4 comprises coils 6 distributed uniformly in the circumferential direction on the internal side of the stator 4, two diametrically opposed coils being connected to each other so as to be powered simultaneously by the power converter 2.

[0048] Two diametrically opposed stator coils define a control axis of the magnetic bearing and allow this axis to be controlled.

[0049] The stator 4 comprises for example four coils 6a, 6b, 6c, 6d forming four pairs of poles PI, P2, P3, P4 connected to the power converter 2.

[0050] The stator 4 further comprises two position sensors 7, 8 of the rotor 5 measuring the position of the rotor 5.

[0051] A first position sensor 7 is arranged on a first axis V of the reference frame R(O, V, W) and a second position sensor 8 is arranged on the second axis W of the reference frame R(O, V, W).

[0052] The stator 4 further comprises a speed sensor 9 measuring the rotational speed of the rotor 5.

[0053] The measurements generated by the position sensors 7, 8 are transmitted to inputs 10, 11 of the control system 3, and the measurements generated by the speed sensor are transmitted to a third input 12 of the control system 3.

[0054] The control system 3 further comprises two outputs 14, 15 connected to the power converter 2.

[0055] [Fig.2] schematically illustrates an exemplary embodiment of the control system 3.

[0056] The control system 3 comprises a synchronous filter 16, a device 17 for detecting the change in direction of rotation of the rotor 5, means of determination of the angular position 18 of the rotor 5 from the measurements delivered by the speed sensor 9.

[0057] The control system 3 further comprises a processing unit 19 implementing the synchronous filter 16, the detection device 17, and the means for determining the angular position 18 connected to the third input 12.

[0058] The means for determining the angular position 18 determine in a known manner the angular position of the rotor 5 from the data generated by the speed sensor 9 by estimating the time required for the rotor 5 to complete one revolution over a first period of rotation of the rotor 5, then performs a linear interpolation on the estimated time to estimate the position of the rotor 5 over a second period subsequent to the first period of rotation.

[0059] The synchronous filter 16 comprises a modulation module 20, a control module 21, and a demodulation module 22.

[0060] The modulation module 20 comprises a first input 23 connected to a first input 10 of the control system 3, a second input 24 connected to the second input 11 of the control system 3, a first output 25 connected to a first input 26 of the control module 21, and a second output 27 connected to a second input 28 of the control module 2.

[0061] The modulation module 21 further comprises a third input 29 connected to the means for determining the angular position 18, and a control input 30 connected to an output 31 of the detection device 17.

[0062] The detection device 17 comprises an input 170 connected to the third input 12 of the control system 3.

[0063] The control module 21 comprises a first output 32 connected to a first input 33 of the demodulation module 22, a second output 34 connected to a second input 35 of the demodulation module 22.

[0064] The demodulation module 22 further comprises a first output 36 connected to a first output 14 of the control module 3, a second output 37 connected to a second output 15 of the control module 3.

[0065] The demodulation module 22 further comprises a third input 38 connected to the means for determining the angular position 18, and a control input 39 connected to an output 31 of the detection device 17.

[0066] In a known manner, the modulation module 20 filters the sinusoidal signals delivered by the position sensors 7, 8 so that the first output 25 delivers a first continuous value indicative of the amplitude of the sinusoidal signal delivered by the first position sensor 7, and so that the second output 27 delivers a second continuous value indicative of the amplitude of the sinusoidal signal delivered by the second position sensor 8.

[0067] The modulation module 20 implements a low-frequency filtering algorithm allowing frequencies equal to the rotation frequency of the rotor 5 to pass within a threshold so as to also allow a change of base from the reference frame R(0, V, W) to be made to a direct orthogonal reference frame RI of the rotor 5 having as its origin a point on the axis of rotation of the rotor 5.

[0068] The threshold is for example equal to 10Hz.

[0069] The control module 21 implements an unbalance correction algorithm determined by the modulation module 20, and the demodulation module 22 performs the change of reference from the RI reference linked to the rotor 5 to the R reference linked to the stator 4.

[0070] Since the modulation 20 and demodulation 22 modules are of similar structure, only one example of embodiment of the modulation module 20 and one example of embodiment of the processing module 21 are presented in the following.

[0071] [Fig.3] schematically illustrates an embodiment of the modulation module 20.

[0072] The modulation module 20 comprises four multipliers 40, 44, 52, 48 each comprising a first input 41, 45, 49, 53, a second input 42, 47, 50, 52, and an output 43, 46, 51, 55.

[0073] The modulation module 20 comprises a sine operator 56 comprising an input 57 connected to the third input 29 of the modulation module 21, and an output 58 connected to the second input 47, 50 of a second and third multiplier 44, 48.

[0074] The modulation module 20 further comprises a cosine operator 59 comprising an input 60 connected to the third input 29 of the modulation module 21, and an output 61 connected to the second input 42, 54 of a first and fourth multiplier 44, 52.

[0075] The first input 41, 54 of the first and second multipliers 40, 44 is connected to the first input 23 of the modulation module 20, and the first input 49, 53 of the third and fourth multipliers 48, 52 is connected to the second input 24 of the modulation module 20.

[0076] The modulation module 20 further comprises a first variable gain 62 comprising an input 63 connected to the output 46 of the second multiplier 44, an output 64, and a control input 65 connected to the control input 30 of the modulation module 20.

[0077] The modulation module 20 comprises a first adder 66 comprising an addition input 67 connected to the output 55 of the fourth adder 52, a subtraction input 68 connected to the output 64 of the first gain 62, and an output 69 connected to an input 71 of a saturator 70 of the module 20.

[0078] The saturator 70 further comprises an output 72 connected to the second output 27 of the module 20.

[0079] The modulation module 20 further comprises a second variable gain 73 comprising an input 74 connected to the output 51 of the third multiplier 48, an output 75, and a control input 76 connected to the control input 30 of the modulation module 20.

[0080] The module comprises a second adder 77 comprising a first addition input 78 connected to the output 43 of the first adder 40, a second addition input 79 connected to the output 75 of the second gain 73, and an output 80 connected to an input 82 of a second saturator 81 of the module 20.

[0081] The second saturator 81 further comprises an output 83 connected to the first output 25 of the module 20.

[0082] The saturators 70, 81 make it possible to avoid variable reversals relating to fixed-point algorithms.

[0083] The first and second gains 62, 73 are controlled so that they multiply the value received at their input 63, 74 by a multiplier coefficient taking the digital value 1 or -1 depending on the direction of rotation of the rotor 5.

[0084] If the direction of rotation of the rotor 5 is oriented from the axis V towards the axis W in the reference frame R (indirect direction), the multiplier coefficient is for example equal to 1, and if the direction of rotation of the rotor 5 is oriented from the axis W towards the axis V in the reference frame R (direct direction), the multiplier coefficient is equal to -1.

[0085] The value of the multiplier coefficient is determined by the detection device 17 as described below.

[0086] It is assumed that the first position sensor 7 delivers a sinusoidal signal Vcos and that the second position sensor 8 delivers a sinusoidal signal Vsin such that:

[0087] VCOS = ACO^O)(V

[0088] y sin = Asin(0) (2)

[0089] A being the amplitude of the signals and 0 being the angular position of the rotor 5.

[0090] When the rotor 5 rotates in the forward direction, the coefficient of the gains 62, 73 is equal to 1. A signal S25 on the first output 25 and a signal S27 on the second output 27 are equal to:

[0091] S25 = Asïn(0)sin(0) +Acos(6)cos(6) = A (3)

[0092] S27 = Asin(9)cos(9) -Acos(9)sin(9) = 0 (4)

[0093] When the rotor 5 rotates in the indirect direction, the coefficient of the gains 62 73 being equal to -1. The signal S25 on the first output 25 and the signal S27 on the second output 27 are equal to:

[0094] S25 = -Acos(0)sin(0)+Asïn(0)cos(0) = 0 (3)

[0095] S27 = Acos(6)cos(0) +Asin(0)sin(0) = A (4)

[0096] The first and second non-zero continuous values ​​delivered on the outputs 25, 27 are representative of the difference between the axis of rotation of the rotor 5 and the center of gravity of the rotor 5, and make it possible to quantify the unbalance of the rotor 5.

[0097] The module 20 makes it possible to filter the signals generated by the position sensors independently of the direction of rotation of the rotor 5 by selecting the gain of the gains 73, 62 equal to the multiplier coefficient, the selection being carried out by the detection device 17.

[0098] The gain of the variable gains 73, 62 is representative of the direction of rotation of the rotor 5.

[0099] [Fig.4] schematically illustrates an example of embodiment of the module of control 21 allowing compensation of the unbalance of the rotor 5 determined by the modulation module 20.

[0100] The modulation module 20 comprises two identical regulation loops 84, 85 each comprising an input 86 and an output 87.

[0101] The input 86 and the output 87 of a first regulation loop 84 are connected respectively to the first input 26 and to the first output 32 of the control module 21.

[0102] The input 86 and the output 87 of the second regulation loop 85 are connected respectively to the second input 28 and to the second output 34 of the control module 21.

[0103] As the control loops 84, 85 are identical, only the first loop 84 is detailed.

[0104] The first loop 84 comprises a summer 88, an integrator 89, a gain 91 and a saturator 92.

[0105] The adder 88 comprises an addition input 93 connected to the input 86, a subtraction input 94 connected to an output 95 of the saturator 92, and an output 96 connected to an input 97 of the integrator 89.

[0106] An output 98 of the integrator is connected to output 87 and to an input 99 of the gain.

[0107] An output 100 of the gain 91 is connected to an input 101 of the saturator 92.

[0108] [Fig.5] discloses an exemplary embodiment of the detection device 17.

[0109] The device 17 comprises comparison means 1000 comprising a first input 1001 connected to the input 170 of the device 17, a second input 1002 connected to a memory 103, and an output 104.

[0110] The memory 103 may be disposed within the device 17 as shown or disposed outside the device 17.

[0111] The device 17 further comprises first determination means 105 comprising an output 106, and second determination means 107 comprising a first input 108 connected to the output 104 of the comparison means 1000, a second input 109 connected to the output 106 of the first determination means 105, and an output 110 connected to the output 31 of the detection device 17.

[0112] The device 17 further comprises a second processing unit 111 implementing the comparison means 1000, the memory 103, the first and second determination means 105, 107.

[0113] The memory 103 stores a predefined speed threshold Se representative of the minimum rotation speed of the rotor 5 measured by the speed sensor 9, the sensor 9 measuring for example a minimum frequency of 10 Hz or 600 revolutions per minute.

[0114] It is assumed in the following that the speed measured by the speed sensor 9 is the absolute value of the speed so that the measured speed is positive or zero.

[0115] The first determination means 105 determine the rotation speed gradient of the rotor 5.

[0116] The speed gradient is for example transmitted to the first determination means 105 by a control computer of the drive system (not shown).

[0117] The speed gradient can for example be determined from the calculation of the derivative of the rotational speed of the rotor.

[0118] Alternatively, the speed gradient is provided by a control member for means for rotating the rotor, the means for rotating the rotor comprising, for example, an electric motor.

[0119] The comparison means 100 compare the absolute value of the rotation speed Q of the rotor with the speed threshold Se.

[0120] Now, an example of implementation of the example embodiment of the detection device 17 illustrated in [Fig.5].

[0121] [Fig.6] illustrates an example of temporal evolution of the rotation speed Q of the rotor 5, of a signal S106 delivered on the output 106 of the first determination means 105, and of a signal S31 delivered on the output 31 of the detection device 17 representative of the direction of rotation of the rotor 5.

[0122] It is assumed that before time tl, the rotor 5 rotates in the indirect direction at a rotation speed having an absolute value greater than the threshold Se.

[0123] The speed gradient determined by the first determination means 105 is zero. The signal S106 is zero, and the comparison means 1000 deliver a signal S104 on the output 104 representative of the comparison, for example the signal S104 is equal to “1” when the absolute value of the rotation speed is greater than the threshold Se, and “0” otherwise.

[0124] In this case, the signal S104 is equal to “1”.

[0125] As the signal S104 is equal to “1” and the signal S106 is zero, the second determination means 107 deliver a signal representative of the value of the multiplier coefficient of the gains 62, 73 equal to “1” so that the signal S31 is equal to “1” so that the multiplier coefficient of the gains 62, 73 is equal to “1”.

[0126] At time t1, the rotational speed of the rotor 5 decreases. The speed gradient determined by the first determination means 105 is negative. The signal S106 is negative and takes for example a value SN.

[0127] As the absolute value of the rotation speed Q is greater than the threshold Se between times t1 and t2, the output S31 remains at “1”.

[0128] The second determination means 107 deliver a signal representative of the value of the multiplier coefficient of the gains 62, 73 is equal to “1” so that the signal S31 is equal to “1”.

[0129] The multiplier coefficient of the gains 62, 73 is equal to “1”.

[0130] At time t2, as the absolute value of the rotation speed Q of the rotor is lower than the threshold Se the comparison means 1000 deliver a signal S104 equal to “-1”. Furthermore, since the speed gradient is negative, the signal S106 is equal to a value SN indicative of a negative gradient.

[0131] The second determination means 107 detect a reversal of the direction of rotation of the rotor 5 from the indirect direction to the direct direction opposite to the indirect direction, and deliver a signal representative of the value of the multiplier coefficient of the gains 62, 73 equal to “-1” so that the signal S31 is equal to “-1”.

[0132] The multiplier coefficient of the gains 62, 73 is equal to “-1”.

[0133] Between times t2 and t3, the rotation speed Q continues to decrease and becomes negative because rotor 5 rotates in the indirect direction. The absolute value of the rotation speed Q remains lower than the threshold Se.

[0134] Signal S31 remains at “-1”.

[0135] Between times t3 and t4, the negative rotation speed Q continues to decrease.

[0136] The absolute value of the rotation speed Q is greater than the threshold Se and the gradient remains negative.

[0137] Signal S31 remains at “-1”.

[0138] At time t4, the rotation speed Q is negative and increases so that the speed gradient becomes positive.

[0139] The first determination means 105 deliver the signal S106 equal to a Spindicative value of a positive or zero gradient.

[0140] The absolute value of the rotation speed is greater than the threshold Se.

[0141] Signal S31 remains at “-1”.

[0142] Between times t4 and t5, the negative rotation speed Q continues to increase.

[0143] The absolute value of the rotation speed Q is greater than the threshold Se and the gradient remains positive.

[0144] Signal S31 remains at “-1”.

[0145] At time t5, the absolute value of the rotation speed Q is less than the threshold Se, the comparison means 1000 deliver a signal S104 equal to “-1”. Furthermore, as the speed gradient is positive or zero, the signal S106 is equal to the Spindicative value of a positive or zero gradient.

[0146] The second determination means 107 detect a reversal of the direction of rotation of the rotor 5 from the direct direction to the indirect direction, and deliver a signal representative of the value of the multiplier coefficient of the gains 62, 73 equal to “1” so that the signal S31 is equal to “1”.

[0147] The multiplier coefficient of the gains 62, 73 is equal to “1”.

Claims

Claims

1. Method for detecting the change in direction of rotation of a rotor (5) of a magnetic bearing (1), comprising: - a determination of the rotational speed gradient of the rotor (5), - a comparison of the rotational speed of the rotor (5) with a predefined speed threshold (Se), and - the detection of the change in direction of rotation of the rotor (5) from the result of the comparison of the rotational speed of the rotor (5) with the predefined speed threshold (Se) and the determined rotational speed gradient of the rotor (5).

2. Method according to claim 1, wherein when the rotor rotates in a first direction of rotation, the method comprises: - detecting a first reversal of the direction of rotation of the rotor (5) in a second direction of rotation opposite to the first direction of rotation when the absolute value of the rotational speed of the rotor is less than the speed threshold (Se) and when the speed gradient is negative, and - detecting a second reversal of the direction of rotation of the rotor following the first reversal, when the speed gradient is greater than or equal to zero, and when the absolute value of the rotational speed of the rotor is less than the speed threshold.

3. Device (17) for detecting the change in direction of rotation of a rotor for a magnetic bearing, comprising: - comparison means (1000) configured to compare the rotation speed of the rotor (5) with a predefined speed threshold (Se), - first determination means (105) configured to determine the rotation speed gradient of the rotor (5), and - second determination means (107) configured to detect the change in direction of rotation of the rotor (5) from the result of the comparison of the rotation speed of the rotor (5) with the predefined speed threshold (Se) and the determined rotation speed gradient of the rotor (5).

4. Device according to claim 3, in which the second determining means (107) are configured to: - detect a first inversion of the direction of rotation of the rotor in a second direction of rotation opposite to the first direction of rotation when the absolute value of the rotation speed of the rotor is less than the speed threshold (Se) and when the speed gradient is negative, and - detect a second inversion of the direction of rotation of the rotor following the first inversion when the speed gradient is greater than or equal to zero, and when the absolute value of the rotation speed of the rotor is less than the speed threshold (Se).

5. Control system (3) for a magnetic bearing comprising a device (17) according to claim 3 or 4, and a synchronous filter (16) comprising at least one control algorithm (21) for the magnetic bearing (1), the algorithm comprising a variable gain (62, 73) controlled by said device according to the direction of rotation of the rotor.

6. Control system according to claim 5, wherein the synchronous filter comprises a demodulation module (20) and a demodulation module (22), the modulation module (20) comprising a first algorithm comprising at least one variable gain (62, 73) controlled by said device according to the direction of rotation of the rotor, and the demodulation module (22) comprising a second algorithm comprising at least one variable gain controlled by said device according to the direction of rotation of the rotor.

7. Control system according to claim 6, in which the synchronous filter further comprises a control module (21) connected on the one hand to the modulation module (20) and on the other hand to the demodulation module (22), the control module (21) implementing an algorithm for correcting the unbalance of the rotor (5).

8. Drive system comprising a magnetic bearing (1) comprising a rotor (5) and a stator (4) comprising coils (6a, 6b, 6c, 6d) distributed uniformly in the stator (4) forming at least one servo axis, a power converter (2) supplying the servo axis, and a control system (3) according to one of claims 5 to 7 controlling the power converter.

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