Method and device for conditioning a measurement signal

Abstract

Method and device for conditioning a measurement signal. The device for conditioning a measurement signal delivered by an inductive position sensor (7, 8) for a rotor (3) of an electrical machine (1) supported by at least one active magnetic bearing (4), the inductive position sensor (7, 8) measuring a displacement of the rotor (3) and being powered by an alternating voltage source (10a) delivering a sinusoidal voltage at a predetermined constant frequency, comprises: - a sampler (15), and - first means (16). Figure 2

Description

Title of the invention: Method and device for conditioning a measurement signal. Technical field of the invention

[0001] The present invention relates to electrical machines comprising a rotor supported by magnetic bearings and particularly to the processing of a signal delivered by an inductive position sensor of such an electrical machine.

[0002] The present invention relates more particularly to a method of conditioning a measurement signal delivered by an inductive position sensor of the rotor of such an electrical machine. Prior art

[0003] Magnetic bearings are used in various rotating machines such as electric motors, compressors, turbines, or the like in order to maintain the axial and / or radial positions of a rotor by means of magnetic fields acting on the rotor of the machine.

[0004] Inductive position sensors are used in magnetic bearing control (MBC) devices to measure the position of the rotor.

[0005] The measurements delivered by the position sensors are used to control the magnetic bearings.

[0006] An inductive position sensor comprises two inductive elements connected in series.

[0007] An alternating supply voltage is applied to the ends of the elements inductive.

[0008] A displacement of the rotor causes a variation in the air gap, generating a variation in the inductance of the inductive elements.

[0009] A modulated alternating voltage is measured between the two inductive elements, representative of the variation of the inductance.

[0010] The rotor displacement is determined from the alternating voltage measured between the two inductive elements.

[0011] When the rotor is centered in the magnetic bearings and the displacement of said rotor is zero, the inductive components of the two inductive elements are equal, the alternating voltage delivered by the sensor has a zero amplitude.

[0012] Moving the rotor in one direction along an axis causes a proportional increase in the amplitude of the alternating voltage emitted by the sensor. Moving the rotor in the opposite direction along the axis causes a proportional increase in the amplitude of the alternating voltage delivered by the sensor, with a phase shift of 180°.

[0013] In practice, the inductive elements include parasitic resistive elements so that a phase shift appears between the supply voltage and the modulated alternating voltage at the output of the inductive sensor.

[0014] The phase shift or quadrature error makes it difficult to measure the alternating voltage delivered by the sensor and prevents determining the position of the rotor with sufficient accuracy to control the magnetic bearings.

[0015] To eliminate the quadrature error, the modulated alternating voltage is demodulated and filtered, notably by a low-pass filter, to determine the DC component of the signal representative of the rotor position. The low-pass filter creates a phase delay that degrades the ability to control the rotor position.

[0016] In addition, the low-pass filter removes the quadrature component of the alternating voltage delivered by the sensor which includes information allowing the position of the rotor to be determined more precisely. Summary of the invention

[0017] Therefore, the present invention aims to overcome these drawbacks totally or partially.

[0018] According to one aspect, a method for conditioning a measurement signal delivered by an inductive position sensor for a rotor of an electrical machine supported by at least one active magnetic bearing.

[0019] The inductive position sensor measures a displacement of the rotor and is powered by an alternating voltage source delivering a sinusoidal supply voltage at a predetermined constant period.

[0020] The process comprises:

[0021] - a sampling of the measurement signal at a first sampling instant for determine a first sample of the measurement signal,

[0022] - sampling the measurement signal at a second sampling instant to determine a second sample of the measurement signal, the second sampling instant being separated from the first sampling instant by a duration equal to one quarter of the predetermined constant period of the sinusoidal supply voltage, and

[0023] - a decomposition of the measurement signal into a sum of a sine function and of a cosine function from the first and second samples of the measurement signal and a predetermined phase shift between the phase of the sinusoidal supply voltage and the phase of a sampling signal associated with the first and second sampling instants.

[0024] The conditioning process allows the measurement signal to be decomposed into a phase component corresponding to the sine function and a quadrature component corresponding to the cosine function.

[0025] The determination of the in-phase and quadrature components is carried out in a simple manner, without the addition of processing means or a control loop.

[0026] Preferably, the first sampling instant is chosen when the sinusoidal supply voltage is zero and the second sampling instant is chosen when the absolute value of the sinusoidal supply voltage is maximum; the measurement signal is decomposed into a signal Sm according to the following equation:

[0027] Sm(t)=c. sin(cot+ 0)= a.sin(cot)+b.cos(cot)

[0028] where sin is the trigonometric function sine, cos is the trigonometric function cosine, t is time, co is such that , T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant,

[0029] The decomposition of the measurement signal includes determining the first coefficient a and the second coefficient b from the first sample of the measurement signal associated with the first sampling instant and the second sample of the measurement signal associated with the second sampling instant,

[0030] the first and second coefficients a and b being such that:

[0031] a = X90

[0032] b = Xv

[0033] Advantageously, the second sampling instant is chosen a quarter of a period after the first sampling instant, the measurement signal is decomposed into a signal Sm according to the following equation:

[0034] Sm(t)=c. sin(cot+ 0)= a.sin(cot)+b.cos(cot)

[0035] where sin is the trigonometric function sine, cos is the trigonometric function cosine, t is time, co is such that , T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant,

[0036] The decomposition of the measurement signal includes determining the first coefficient a and the second coefficient b from the first sample of the measurement signal associated with the first sampling instant and the second sample of the measurement signal associated with the second sampling instant,

[0037] the first and second coefficients a and b being such that:

[0039] sin^1 (S ) -(pÿxt^ + xa^, xw>0 ««(tan"1 ( S ) + TF - <^xrt02 + xr2(A ^20 < 0

[0040] tan1 being the arctangent trigonometric function and q> being the predetermined phase shift between the first sampling instant and the sinusoidal supply voltage, xd being the first sample of the measurement signal and xt2 0 being the second sample.

[0041] According to another aspect, the invention also relates to a device for conditioning a measurement signal delivered by an inductive position sensor for a rotor of an electrical machine supported by at least one active magnetic bearing.

[0042] The inductive position sensor measures a displacement of the rotor and is powered by an alternating voltage source delivering a sinusoidal supply voltage at a predetermined constant period.

[0043] The device comprises:

[0044] - a sampler configured to sample the measurement signal at a first sampling instant to determine a first sample of the measurement signal and sampling the measurement signal at a second sampling instant to determine a second sample of the measurement signal, the second sampling instant being separated from the first sampling instant by a duration equal to one-quarter of the predetermined constant period of the sinusoidal supply voltage, and

[0045] - of the first means configured to decompose the measurement signal into a sum of a sine function and a cosine function from the first and second samples of the measurement signal, and a predetermined phase shift between the phase of the sinusoidal supply voltage and the phase of a sampling signal associated with the first and second sampling instants.

[0046] Preferably, the first means are configured to decompose the measurement signal into a signal Sm according to the following equation

[0047] Sm(t)=c. sin(cot+ 0)= a.sin(cot)+b.cos(cot)

[0048] where sin is the trigonometric function sine, cos is the trigonometric function cosine, t is time, co is such that w , T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant,

[0049] the first means being further configured to determine the first coefficient a and the second coefficient b from the first sample of the measurement signal associated with the first sampling instant and from the second sample of the measurement signal associated with the second sampling instant,

[0050] the first and second coefficients a and b being such that:

[0051] « = *90'

[0052] b = XQ-

[0053] Advantageously, the first means are configured to decompose the measurement signal into a signal Sm according to the following equation

[0054] Sm(t)=c. sin(cot+ 0)= a.sin(cot)+b.cos(cot)

[0055] where sin is the trigonometric function sine, cos is the trigonometric function cosine, t is time, co is such that (j, -Al, T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant,

[0056] the first means being further configured to determine the first coefficient a and the second coefficient b from the first sample of the measurement signal associated with the first sampling instant and from the second sample of the measurement signal associated with the second sampling instant,

[0057] the first and second coefficients a and b being such that:

[0058] a =

[0059] b =

[0060] tan'1 being the arctangent trigonometric function and being the predetermined phase shift between the first sampling instant and the sinusoidal supply voltage, xü being the first sample of the measurement signal and xt2 0 being the second sample.

[0061] Preferably, the device further comprises a processing unit configured to control the sampler so that the phase shift is equal to a predetermined target value.

[0062] According to yet another aspect, the invention also relates to a measuring assembly comprising a conditioning device as defined above, and an inductive position sensor connected to the conditioning device.

[0063] Advantageously, the inductive position sensor is a radial inductive position sensor configured to measure the radial position of the rotor.

[0064] Preferably, the inductive position sensor is an axial inductive position sensor configured to measure the axial position of the rotor. Brief description of the figures

[0065] Other advantages and features of the invention will become apparent upon examination of the detailed descriptions of the embodiments, this being in no way restrictive. The accompanying drawings are described below:

[0066] Fig. 1 schematically illustrates a machine according to the invention;

[0067] Figure 2 schematically illustrates an example of a measurement set according to the invention;

[0068] Figures 3 and 4 schematically illustrate a first example of a method for conditioning a measurement signal according to the invention; and

[0069] Figures 5 and 6 schematically illustrate a second example of a method for conditioning a measurement signal according to the invention. Detailed description of the invention

[0070] Reference is made to [Fig.1] which schematically represents a partial longitudinal cross-section of a machine 1.

[0071] The machine 1 comprises a housing 2, a rotor 3 supported in the housing 2 by two radial active magnetic bearings 4 and an axial active bearing 5.

[0072] The radial active magnetic bearings 4 radially surround the rotor 3.

[0073] The rotor 3 further comprises a disc 6 surrounded axially by the axial active bearing 5.

[0074] The machine 1 further includes two inductive position sensors 7 for measuring the radial position of the rotor 3, and two inductive position sensors 8 arranged on either side of the disk 5 for measuring the axial position of the rotor 3.

[0075] The measurements delivered by the inductive position sensors 6 measuring the radial position of the rotor 3 and the measurements delivered by the inductive position sensors 8 measuring the axial position of the rotor 3 are transmitted to control means 9 of the magnetic bearings 4 comprising for example a processing unit.

[0076] The machine 1 further comprises a plurality of power supply circuits 10 for sensors 7, 8 and a plurality of conditioning devices 11.

[0077] Each power supply circuit 10 is connected to a sensor 7, 8 to supply energy to said sensor 7,8.

[0078] The power supply circuit 10 can be located outside the machine 1 as shown.

[0079] In one variant, the power supply circuit 10 is located inside the machine 1.

[0080] Each conditioning device 11 is connected to a sensor 7, 8 to condition a measurement signal delivered by said sensor 7, 8.

[0081] The conditioning device 11 can be located outside the machine 1 as shown.

[0082] In one variant, the conditioning device 11 is located inside the machine 1.

[0083] A sensor 7, 8, the power supply circuit 10 connected to said sensor 7, 8 and the conditioning device 11 connected to said sensor 6, 7 form a measuring set.

[0084] It is assumed that the rotor 3 is separated from the inductive position sensors 7 measuring the radial displacement of the rotor 3 by an air gap Ji and that the disk 6 of the rotor 3 is separated from the inductive position sensors 8 measuring the axial displacement of the rotor 3 by an air gap J2.

[0085] Figure [Fig. 2] schematically illustrates an example of the measuring set.

[0086] The sensor 7, 8 comprises a first impedance Z1 and a second impedance Z2.

[0087] The first impedance Z1 comprises a first end connected to a first power supply terminal 12 of the sensor 7, 8 and a second end connected to a first end of the second impedance Z2.

[0088] The second impedance Z2 includes a second end connected to a second power supply terminal 13 of the sensor 7, 8.

[0089] A connection point between the second end of the first impedance Z1 and the first end of the second impedance Z2 is connected to an output terminal 14 of the sensor 7,8.

[0090] The sensor 7, 8 delivers a measurement signal S14 on its output terminal 14.

[0091] The first and second power supply terminals 12, 13 of the sensor 7, 8 are connected to the power supply circuit 10 comprising an alternating voltage source 10a delivering a sinusoidal voltage E at a predetermined constant period T according to the following equation:

[0092] e-£osin((ïtf) -.E0sin(ÿ7) (1)

[0093] Eo being the amplitude of the voltage E, sin is the trigonometric sine function, t being a time variable and co being the angular frequency such that:

[0094] w = ^(2)

[0095] The conditioning device 11 includes a sampler 15 capable of sampling the measurement signal S14 at a first sampling instant to determine a first sample of the measurement signal S14 and sampling the measurement signal S14 at a second sampling instant to determine a second sample of the measurement signal, the second sampling instant being separated from the first sampling instant by a duration equal to one quarter of the predetermined constant period T of the sinusoidal supply voltage E.

[0096] The conditioning device 10 further includes first means 16 capable of decomposing the measurement signal S14 into a sum of a function sine and a cosine function from the first and second samples of the measurement signal S14, and a predetermined phase shift between the phase of the sinusoidal supply voltage E and the phase of a sampling signal associated with the first and second sampling instants.

[0097] The first means 16 include, for example, a processing unit.

[0098] A first example of the method for conditioning the measurement signal S14 implementing the measurement assembly is now described with reference to Figures 3 and 4.

[0099] Fig. 3 describes a first example of the time evolution of the supply voltage E and the measurement signal S14.

[0100] In this example of the conditioning process, the measurement signal S14 is decomposed by the first means 16 into a signal Sm such that:

[0101] Sm(t)=c. sin(cot+ 0)= a.sin(cot)+b.cos(cot) (3)

[0102] where sin is the trigonometric function sine, cos is the trigonometric function cosine, t is time, co is the angular frequency according to equation (2), T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant.

[0103] The supply voltage E is represented by a curve Cl and the measurement signal S14 modeled by the function Sm(t)=c.sin(cot+ 0) is represented by the curve C2.

[0104] The coefficient c and the constant 0 are determined by identifying the signal Sm with the signal S14.

[0105] During a step 20 ([Fig.4]), the sampler 15 samples the measurement signal S14 at a first sampling instant tl to determine a first sample x0 of the measurement signal S14.

[0106] The first sampling instant tl is chosen when the supply voltage is zero.

[0107] The first sampling instant tl is determined by a time-measuring device, for example an analog-to-digital converter.

[0108] During a step 21, the sampler 15 samples the measurement signal S14 at a second sampling instant t2 to determine a second sample x90 of the measurement signal S14.

[0109] The second sampling instant t2 is separated from the first sampling instant tl by a duration equal to one quarter of the predetermined constant period T of the sinusoidal supply voltage E, when the absolute value of the sinusoidal supply voltage E is maximum.

[0110] During a step 22, the first means 16 decompose the measurement signal S14 according to equation (3) from the first and second samples xœ, x90« of the measurement signal S14.

[0111] The first and second coefficients a and b are such that:

[0112] « = X90(4)

[0113] ^ = X0(5)

[0114] The in-phase component of the signal S14 corresponding to the function a.sin(cot) is represented on [Fig.3] by the curve C3 and the quadrature component corresponding to the cosine function b.cos(cot) is represented on [Fig.3] by the curve C4.

[0115] A second example of the method for conditioning the measurement signal S14 implementing the measurement assembly 11 is now described with reference to Figures 5 and 6.

[0116] Fig. 5 describes a second example of the time evolution of the supply voltage E and the measurement signal S14.

[0117] In this example of the conditioning process, the first sampling and the supply voltage E are phase-shifted by a constant predetermined phase shift

[0118] The measurement signal S14 is decomposed by the first means 16 into a signal Sm such that:

[0119] Sm(t)=c. sin(cot+ 0)= a.sin(cot)+b.cos(cot) (6)

[0120] where sin is the trigonometric function sine, cos is the trigonometric function cosine, t is time, co is the angular frequency according to equation (2), T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant.

[0121] The supply voltage E is represented by a CIO curve and the measurement signal S14 modeled by the function Sm(t)=c.sin(cot+ 0) is represented by the curve C20. The coefficient c and the constant 0 are determined by identifying the signal Sm with the signal S14.

[0122] During a step 30 ([Fig.6]), the sampler 15 samples the measurement signal S14 at a first sampling instant t10 to determine a first sample xd0 of the measurement signal S14.

[0123] During a step 31, the sampler 15 samples the measurement signal S14 at a second sampling instant t20 to determine a second sample xt 20 of the measurement signal S14.

[0124] The second sampling instant t20 is separated from the first sampling instant t10 by a duration equal to one quarter of the predetermined constant period T of the sinusoidal supply voltage E.

[0125] During a step 32, the first means 16 decompose the measurement signal S14 according to equation (6) from the first and second samples xt i0, xt 2o of the measurement signal S14.

[0126] The first and second coefficients a and b are such that:

[0127]

[0128] sinftan1 (g ) -^200 (8) b = ' . x . .---------------- sï^tair1 ( JS ) + æ - (p)^xtw2 + x^02, xf20 < 0

[0129] tan1 being the trigonometric function arctangent.

[0130] The phase component of the signal S14 corresponding to the function a.sin(cot) is represented on [Fig.5] by the curve C30 and the quadrature component corresponding to the cosine function b.cos(cot) is represented on [Fig.5] by the curve C40.

[0131] The conditioning process allows the measurement signal to be decomposed into a phase component corresponding to the sine function and a quadrature component corresponding to the cosine function.

[0132] The determination of the in-phase and quadrature components is carried out in a simple manner, without the addition of processing means or a control loop.

Claims

Demands

1. A method for conditioning a measurement signal (S 14) delivered by an inductive position sensor (7, 8) for a rotor (3) of an electrical machine (1) supported by at least one active magnetic bearing (4), the inductive position sensor (7, 8) measuring a displacement of the rotor (3) and being powered by an alternating voltage source (10a) delivering a sinusoidal supply voltage at a predetermined constant period, the method comprising: - sampling the measurement signal (S 14) at a first sampling instant (t1, t10) to determine a first sample (x0, xd0) of the measurement signal, - sampling the measurement signal at a second sampling instant (t2, t20) to determine a second sample (x90, xt20) of the measurement signal,the second sampling instant being separated from the first sampling instant by a duration equal to one quarter of the predetermined constant period of the sinusoidal supply voltage, and - a decomposition of the measurement signal into a sum of a sine function and a cosine function from the first and second samples of the measurement signal and a predetermined phase shift between the phase of the sinusoidal supply voltage and the phase of a sampling signal associated with the first and second sampling instants.

2. 2. A method according to claim 1, wherein the first sampling instant (t1) is chosen when the sinusoidal supply voltage is zero and the second sampling instant (t2) is chosen when the absolute value of the sinusoidal supply voltage is at its maximum, the measurement signal (S14) is decomposed into a signal Sm according to the following equation: Sm(t) = c sin(cot + 0) = a sin(cot) + b cos(cot) where sin is the sine function, cos is the cosine function, t is time, co is such that π, T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant, the decomposition of the measurement signal comprises determining the first coefficient a and the second coefficient b from the first sample (xœ) of the measurement signal associated with the first sampling instant (t1) and of the second sample (x90°) of the measurement signal associated with the second sampling instant (t2), the first and second coefficients a and b being such that: b = x^

3. 3. A method according to claim 1, wherein the second instant (t20) sampling is chosen a quarter of a period after the first instant (t10) of sampling, the measurement signal (S 14) is decomposed into a signal Sm according to the following equation: Sm(t)= c. sin(cot+ 0)= a.sin(cot)+b.cos(cot) where sin is the trigonometric function sine, cos is the trigonometric function cosine, t is time, co is such that , T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant, The decomposition of the measurement signal includes determining the first coefficient a and the second coefficient b from the first sample (xü 0) of the measurement signal associated with the first sampling instant (t10) and the second sample (xt2 0) of the measurement signal associated with the second sampling instant (t20), the first and second coefficients a and b being such that: [ co^tan' 1 ( £ ) - ^x t} ^ + x t 20 2 , x t2Q > 0 «= s ---------- lco^tan 1 (3^) + 7F-(p)^ / +x z20 2 , x z20 <0 ««(tan- 1 ( § ) - x f20 > 0 b = , x . .---------------- . (â) + Æ - WtW2 + W ' ^20 < 0 tan1 being the arctangent trigonometric function and being the predetermined phase shift between the first sampling instant and the sinusoidal supply voltage, xd being the first sample of the measurement signal and xt2 0 being the second sample.

4. A device for conditioning a measurement signal delivered by an inductive position sensor (7, 8) for a rotor (3) of an electrical machine (1) supported by at least one active magnetic bearing (4), the inductive position sensor (7, 8) measuring a displacement of the rotor (3) and being powered by an alternating voltage source (10a) delivering a sinusoidal supply voltage at a predetermined constant period, the device comprising: - a sampler (15) configured to sample the measurement signal (S 14) at a first sampling instant (t1, t10) to determine a first sample (x0, xd0) of the measurement signal and to sample the measurement signal at a second sampling instant (t2, t20) to determine a second sample (x90”, xt20) of the measurement signal, the second sampling instant being separated from the first sampling instant by a duration equal to one quarter of the predetermined constant period of the sinusoidal supply voltage, and - first means (16) configured to decompose the measurement signal into a sum of a sine function and a cosine function from the first and second samples of the measurement signal, and a predetermined phase shift between the phase of the sinusoidal supply voltage and the phase of a sampling signal associated with the first and second sampling instants.

5. 5. Device according to claim 4, wherein the first means (16) are configured to decompose the measurement signal into a signal Sm according to the following equation Sm(t) = c.sin(cot+0) = a.sin(cot) + b.cos(cot) where sin is the trigonometric sine function, cos is the trigonometric cosine function, t is time, co is such that is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant, the first means being further configured to determine the first coefficient a and the second coefficient b from the first sample (x0°) of the measurement signal associated with the first sampling instant (t1) and the second sample (x90°) of the measurement signal associated with the second sampling instant (t2), the first and second coefficients a and b being such that: b = X^

6. 6. Device according to claim 4, wherein the first means (16) are configured to decompose the measurement signal into a signal Sm according to the following equation

7.

8.

9.

10. Sm(t)= c. sin(cot+ 0)= a.sin(cot)+b.cos(cot) where sin is the trigonometric sine function, cos is the trigonometric cosine function, t is time, co is such that w, T is the predetermined constant period, a is a first coefficient and b is a second coefficient, a, b, c being real numbers, and 0 is a constant, the first means being further configured to determine the first coefficient a and the second coefficient b from the first sample (xü 0) of the measurement signal associated with the first sampling instant (t10) and the second sample (xt2 0) of the measurement signal associated with the second sampling instant (t20), the first and second coefficients a and b being such that: ( co^tan' 1 (g) - ^20 0 has - { | cosftan-' ( §” ) + æ - x^o < 0 swz(tan' ! (¾ ) -x r20 >0 b = , .-------------- "fl'1^) +7r-^xri02 + xf202, xr20<0 tan'1 being the arctangent trigonometric function and being the predetermined phase shift between the first sampling instant and the sinusoidal supply voltage, xd being the first sample of the measurement signal and xt2 0 being the second sample. Device according to any one of claims 4 to 6 further comprising a processing unit configured to control the sampler so that the phase shift is equal to a predetermined target value. Measurement assembly comprising a conditioning device according to any one of claims 4 to 7, and an inductive position sensor (6, 7) connected to the conditioning device." Measurement assembly according to claim 8, wherein the inductive position sensor (7) is a radial inductive position sensor configured to measure the radial position of the rotor. 0 Measuring assembly according to claim 8, wherein the inductive position sensor (7) is an axial inductive position sensor configured to measure the axial position of the rotor.