Reactive power compensation method, associated control system and sensor driver circuit

Abstract

A control system (15) is proposed for controlling a full-bridge converter to compensate for the reactive power consumed by an inductive position sensor for a rotor of an electrical machine supported by at least one active magnetic bearing. The inductive position sensor is powered by an alternating current source.The control system (15) comprises: - a phase-shift determination means (26) configured to determine a phase shift (SP) between a supply voltage (VS) and a supply current (IS) delivered by the source, - a first control loop (22) configured to control the amplitude (Ac) of a control signal (SC) from the phase shift (SP), - a second control loop (23) configured to control the phase of the control signal (SC), - a third control loop (24) configured to control a voltage reference (VR), and - a control means (25) configured to control a full-bridge converter as a function of the control signal (SC). Figure 4.

Description

Title of the invention: Reactive power compensation method, associated control system and sensor driver circuit Technical field

[0001] The present invention relates to magnetic bearings and more particularly to the reactive power compensation of inductive position sensors in magnetic bearings.

[0002] The present invention relates more particularly to a method for compensating the reactive power consumed by such a sensor, a control system and a sensor driver circuit. Context

[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 rotor position.

[0005] Inductive position sensors are generally inductive loads.

[0006] The value of the inductive load varies significantly from one sensor to another.

[0007] Additionally, the inductive position sensors may be located far from the MBCs such that the cable connecting the inductive position sensors to the MBCs adds additional capacitive and inductive load depending on the length and size of the cable.

[0008] Since inductive position sensors are powered by alternating current (AC) sources, inductive position sensors consume a large amount of reactive power that must be compensated.

[0009] Document US 9,966,892 discloses an automatic reactive power compensation device for automatically compensating the reactive power consumed by an inductive position sensor.

[0010] The device generates a reactive current proportional to the current consumed by the inductive position sensor.

[0011] The automatic reactive power compensation device uses a half-bridge converter comprising two switches and two capacitors, the switches being controlled so that the capacitors deliver a compensation current to compensate for the reactive current.

[0012] Sensors and filters are required to determine the reactive current.

[0013] A time delay caused by said sensors and filters is introduced.

[0014] Additionally, since the voltage of the capacitors is fixed, the range of sensors that will work with the prior art is limited. Summary

[0015] Therefore, the present invention aims to overcome these drawbacks totally or partially.

[0016] According to one aspect, a method for compensating the reactive power consumed by at least one inductive position sensor for a rotor of an electrical machine supported by at least one active magnetic bearing is proposed.

[0017] The inductive position sensor is powered by an alternating current (AC) source and measures an axial or radial displacement of the rotor.

[0018] The method comprises:

[0019] - the determination of a phase shift between a supply voltage and a current power supplied by the alternating current source,

[0020] - determining the amplitude of a control signal from the phase shift determined,

[0021] - determining a voltage reference value for a storage device energy from the amplitude of the control signal and a reference duty cycle value,

[0022] - determining the phase of the control signal from the voltage of the energy storage device and voltage reference, and

[0023] - the control of the full bridge converter as a function of the control signal to generate the compensation current to bring the supply current into phase with the supply voltage.

[0024] The method can compensate for the reactive power consumed by different sensor / cable combinations without changing the values ​​of circuit elements.

[0025] In addition, the method is resistant to time delay caused by sensors / filters.

[0026] Preferably, the determination of the phase shift comprises the determination of the sign of the supply voltage, the sign of the supply current and the sign of the derivative of the supply voltage:

[0027] - the supply current lags behind the supply voltage when the sign of the supply voltage is positive, the sign of the supply current is negative, and the sign of the derivative of the supply voltage is positive or when the sign of the supply voltage is negative, the sign of the supply current is positive, and the sign of the derivative of the supply voltage is negative,

[0028] - the supply current is ahead of the supply voltage when the sign of the supply voltage is positive, the sign of the supply current is negative, and the sign of the derivative of the supply voltage is negative or when the sign of the supply voltage is negative, the sign of the supply current is positive, and the sign of the derivative of the supply voltage is positive, and

[0029] - the supply current is in phase with the supply voltage when the The sign of the supply voltage is always equal to the sign of the supply current.

[0030] Advantageously, the control signal is a periodic function having the same frequency as the frequency of the supply voltage.

[0031] Preferably, the control signal is a periodic function resulting from the multiplication of a supply voltage reference phase-shifted by a reference angle by the amplitude of the control signal.

[0032] Advantageously, the reference angle is determined from the supply voltage.

[0033] Preferably, the periodic function is a sinusoidal function.

[0034] According to another aspect, a control system is provided.

[0035] The control system is configured to control a full bridge converter to compensate for reactive power consumed by at least one inductive position sensor for a rotor of an electrical machine supported by at least one active magnetic bearing, the inductive position sensor measuring the displacement of the rotor and being powered by an alternating current source.

[0036] The control system comprises:

[0037] - a phase shift determining means configured to determine the phase shift between a supply voltage and a supply current delivered by the alternating current source,

[0038] - a first control loop configured to control the amplitude of a control signal from the determined phase shift,

[0039] - a second control loop configured to control the phase of the signal control from the voltage of the energy storage device and a voltage reference,

[0040] - a third control loop configured to control the voltage of reference for an energy storage device from the amplitude of the control signal and a duty cycle reference value, and

[0041] - a control means configured to control the bridge converter complete according to the control signal to generate the compensation current to bring the supply current in phase with the supply voltage.

[0042] Advantageously, the phase shift determination means comprises a logic circuit comprising at least three logic comparators, a plurality of logic gates, a plurality of summation operators, a control device and at least one differentiator. The logic circuit is configured to determine the phase shift from the sign of the supply voltage, the sign of the supply current and the sign of the derivative of the supply voltage.

[0043] - The supply current lags behind the supply voltage when the sign of the supply voltage is positive, the sign of the supply current is negative, and the sign of the derivative of the supply voltage is positive or when the sign of the supply voltage is negative, the sign of the supply current is positive, and the sign of the derivative of the supply voltage is negative.

[0044] - The supply current is ahead of the supply voltage when the sign of the supply voltage is positive, the sign of the supply current is negative, and the sign of the derivative of the supply voltage is negative or when the sign of the supply voltage is negative, the sign of the supply current is positive, and the sign of the derivative of the supply voltage is positive.

[0045] - The supply current is in phase with the supply voltage when the The sign of the supply voltage is always equal to the sign of the supply current.

[0046] According to another aspect, a system for compensating the reactive power consumed by at least one inductive position sensor for a rotor of an electrical machine supported by at least one active magnetic bearing is proposed.

[0047] The system comprises a control system as defined above and a full bridge converter comprising four switches and an energy storage device, each switch being coupled to the control system to transfer the compensation current to and from the energy storage device.

[0048] According to another aspect, a sensor driver circuit for at least one inductive position sensor for a rotor of an electrical machine supported by at least one active magnetic bearing is provided.

[0049] The sensor driver circuit comprises a transformer having a main circuit and a secondary circuit configured to power the inductive position sensor, an alternating current source connected to the main circuit, and a system as defined above connected to the main circuit. Brief description of the drawings

[0050] Other advantages and characteristics of the invention will appear on examining the detailed descriptions of the embodiments, this being in no way restrictive. The attached drawings are described below:

[0051] [Fig.l] schematically illustrates a machine according to the invention;

[0052] [Fig.2] schematically illustrates an example of a sensor driver circuit inductive position according to the invention;

[0053] [Fig.3] schematically illustrates an example of a system for compensating the reactive power consumed by an inductive position sensor according to the invention;

[0054] [Fig.4] schematically illustrates an example of a control system according to the invention;

[0055] [Fig.5] schematically illustrates an example of a phase shift determination means according to the invention;

[0056] [Fig.6] schematically illustrates a second embodiment of the periodic function generator according to the invention;

[0057] [Fig.7] schematically illustrates an example of an angle conversion module according to the invention; and

[0058] [Fig.8] graphically illustrates an example of the waveforms of a supply voltage, a supply current and a compensation current according to the invention. Detailed description

[0059] Reference is made to [Fig.l] which schematically represents a partial longitudinal cross-section of a machine 1.

[0060] The machine 1 comprises a housing 2, a rotor 3 supported in the housing 2 by two active magnetic bearings 5.

[0061] The rotor 3 is surrounded by the active magnetic bearings 5.

[0062] The machine 1 uses at least two inductive position sensors 6 to measure the radial displacement of the rotor 3 between the active magnetic bearings 5.

[0063] The two inductive position sensors 6 measure the radial displacement of the rotor 4. Additional inductive position sensors can be used to measure the radial or axial displacement of the rotor 3.

[0064] For the sake of clarity, only one inductive position sensor 6 is shown in [Fig.l].

[0065] The machine 1 contains a sensor driver circuit 7 comprising an alternating current (AC) source 8.

[0066] The sensor driver circuit 7 supplies power to the inductive position sensor 6.

[0067] The sensor driver circuit 7 may be located outside the machine 1 as re presented.

[0068] The sensor driver circuit 7 can supply power to more than one inductive position sensor 6.

[0069] In a variant, the sensor driver circuit 7 is located inside the machine 1.

[0070] [Fig.2] schematically illustrates an example of the sensor driver circuit 7.

[0071] The sensor driver circuit 7 contains a transformer 9 with a main circuit 9a and a secondary circuit 9b.

[0072] The main circuit 9a is connected to the alternating current source 8 and the secondary circuit 9b is connected to the inductive position sensor 6.

[0073] The alternating current source 8 delivers a current Is and a voltage Vs having for example a sinusoidal waveform.

[0074] The sensor driver circuit 7 contains a system 10 with a first terminal 11 connected to one end of the main transformer circuit 9a and a second terminal 12 connected to the other end of the main transformer circuit 9a.

[0075] The system 10 generates a compensation current Ic so that the supply current Is is in phase with the supply voltage Vs.

[0076] When the supply current Is is in phase with the supply voltage Vs, the alternating current source 8 does not deliver reactive power. The reactive power consumed by the inductive position sensor 6 is compensated by the system 10 generating the compensation current Ic.

[0077] The system 10 extracts or delivers the compensation current Ic to the ends of the main circuit 9a.

[0078] The extracted compensation current Ic is stored in an energy storage device of the system 10.

[0079] The delivered compensation current Ic is delivered from an energy storage device of the system 10.

[0080] [Fig.3] schematically illustrates an example of the system 10.

[0081] The system 10 contains a full bridge converter connected to the first and second terminals 11, 12 and a filter inductor 14.

[0082] The system 10 further contains a control system 15 for controlling the full bridge converter 13.

[0083] The full bridge converter 13 contains four controlled switches 16, 17, 18, 19 and an energy storage device 20 using, for example, a capacitor.

[0084] The energy storage device 20 stores or delivers the compensation current I c-

[0085] The voltage between the terminals of the energy storage device 20 is denoted VDC.

[0086] Each controlled switch 16, 17, 18, 19 comprises a first link 16a, 17a, 18a, 19a, a second link 16b, 17b, 18b, 19b, and a control link 16c, 17c, 18c, 19c connected to the control system 15 through an interface (not shown).

[0087] The first connection 16a of a first controlled switch 16 and the first connection 17a of a second controlled switch 17 are connected to a first end of the energy storage device 20.

[0088] The second connection 18b of a third controlled switch 18 and the second connection 19b of the fourth controlled switch 19 are connected to the second end of the energy storage device 20.

[0089] The second connection 16b of the first controlled switch 16 and the first connection 18a of the third controlled switch 18 are connected to a first end of the filter inductor 14. The second end of the filter inductor 14 is connected to the first terminal 11.

[0090] The second connection 17b of the second controlled switch 17 and the first connection 19a of the fourth controlled switch 19 are connected to the second terminal 12.

[0091] Each controlled switch 16, 17, 18, 19 may be a transistor, for example a metal oxide semiconductor field effect transistor (MOSEFT) 21, containing a body diode (not shown).

[0092] Transistor 21 may be an insulated gate bipolar transistor (IGBT), a silicon carbide transistor (SiC) or a metal oxide semiconductor field effect transistor (MOSEFT).

[0093] The drain of transistor 21 is connected to the first connection 16a, 17a, 18a, 19a of the controlled switch 16, 17, 18, 19.

[0094] The source of transistor 21 is connected to the second connection 16b, 17b, 18b, 19b of the controlled switch 16, 17, 18, 19.

[0095] The gate of transistor 21 is connected to the control link 16c, 17c, 18c, 19c of the controlled switch 16, 17, 18, 19.

[0096] [Fig.4] schematically illustrates an example of the control system 15.

[0097] The control system 15 contains a first control loop 22 controlling the amplitude Ac of a control signal Sc, a second control loop 23 controlling the phase shift of the control signal Sc, and a third control loop 24 controlling the voltage reference for an energy storage device 20.

[0098] The controlled switches 16, 17, 18, 19 are controlled from the control signal Sc.

[0099] The control system 15 further contains a control means using for example a pulse signal generator 25.

[0100] The pulse signal generator 25 comprises an input 25a and four outputs 25b, 25c, 25d, 25e.

[0101] Each output 25b, 25c, 25d, 25e of the pulse signal generator 25 is connected to a different control link 16c, 17c, 18c, 19c.

[0102] The pulse signal generator 25 controls the switches 16, 17, 18, 19 of the full bridge converter 13 as a function of a control signal Sc received on the input 25a of the pulse signal generator 25.

[0103] The control signal Sc may be a modulation signal.

[0104] The pulse generator 25 may be based on pulse width modulation (PWM) or pulse frequency modulation (PFM).

[0105] For example, a first output 25b is coupled to the control link 16c of the first switch 16, a second output 25c is coupled to the control link 17c of the second switch 17, a third output 25d is coupled to the control link 18c of the third switch 18, and a fourth output 25e is coupled to the control link 19c of the fourth switch 19.

[0106] The first control loop 22 contains a phase shift determining means 26 intended to determine the phase shift between the supply voltage Vs and the supply current Is, as well as a control device 27.

[0107] The phase shift determination means 26 comprises a first input 26a receiving the supply voltage Vs, a second input 26b receiving the supply current Is, and an output 26c connected to an input 27a of the control device 27.

[0108] The phase shift determining means 26 delivers an output 26c. The output 26c is a signal SP representative of the phase shift between the supply voltage Vs and the supply current Is.

[0109] The first control device 27 has an output 27b connected to a first input 28a of a multiplier 28 of the control system 15.

[0110] The control device 27 determines the amplitude Ac of the control signal Sc from the phase shift delivered on the output 26c of the phase shift determining means 26.

[0111] The control device 27 may use a proportional integral (PI) control device.

[0112] The multiplier 28 comprises two inputs 28a and 28b, and an output 28c connected to the input 25 of the pulse signal generator 25.

[0113] The output 28c of the multiplier 28 delivers the control signal Sc.

[0114] The second control loop 23 is designed to determine the phase of the control signal Sc from the voltage VDC of the energy storage device 20 and the reference voltage VR.

[0115] The third control loop 24 is designed to determine the reference voltage VR from the amplitude Ac and a reference duty cycle Dv.

[0116] The control signal is determined by the control system 15 so that the supply current Is is in phase with the supply voltage Vs.

[0117] The second control loop 23 comprises a first comparator 29 comprising a first input 29a receiving the voltage VDC from the energy storage device 20, a second input 29b and an output 29c.

[0118] Output 29c is equal to the difference between the first input 29a and the second input 29b.

[0119] The output 29b of the first comparator 29 is connected to an input 30a of a control device 30.

[0120] The control device 30 may use a PI control device.

[0121] An output 30b of the first control device 30 is connected to an input 31a of a periodic function generator 31.

[0122] The first control device 30 delivers a signal S30 on the output 30b.

[0123] The periodic function generator 31 comprises an output 31b connected to the second input 28b of the multiplier 28.

[0124] The periodic function generator 31 delivers a signal S31 on the output 31b.

[0125] The periodic function generator 31 generates a periodic function from a signal delivered by the control device 30.

[0126] The periodic function generator 31 may be a sinusoidal function.

[0127] The third control loop 24 contains a comparator 32 which comprises a first input 32a connected to the output 27b of the first control loop 22, a second input 32b receiving the duty cycle reference value Dv, and an output 32c connected to an input 33a of a control device 33.

[0128] Output 32c delivers an error signal equal to the difference between the first input 32a and the second input 32b.

[0129] The control device 33 comprises an output 33b connected to the second input 29b of the comparator 29.

[0130] The control device 33 delivers the voltage reference VR.

[0131] The control device 33 may use a PL control device

[0132] The control signal Sc is equal to the multiplication of the amplitude Ac with the signal S31 delivered by the periodic function generator 31.

[0133] [Fig.5] schematically illustrates an example of the phase shift determining means 26.

[0134] The phase shift determining means 26 comprises a logic circuit comprising three logic comparators 35, 36, 37, three summation operators 38, 39, 40, a differentiator 41, two gains 45, 46, two NOT gates 47, 48, an exclusive OR gate 49, and four 3-input AND gates 50, 51, 52, 53.

[0135] Each logic comparator 35, 36, 37 comprises a positive input, a negative input, and an output.

[0136] When the value of the positive input is greater than the value of the negative input, the output delivers a high logic state “1”, and when the positive input is less than the value of the negative input, the output delivers a low logic state “0”.

[0137] The positive input of a first and a second logic comparator 35, 36, and the negative input of the third logic comparator 37 are connected to a ground GND.

[0138] The negative input of the first logic comparator 35 and an input of the differentiator 41 are connected to the first input 26a of the phase shift determination means 26 receiving the supply voltage Vs.

[0139] The output of the differentiator 41 is connected to the positive input of the third logic comparator 37.

[0140] The differentiator 41 determines the derivative of the supply voltage Vs.

[0141] The positive input of the second logic comparator 36 is connected to the second input 26b of the phase shift determination means 26 receiving the supply current Is.

[0142] The output of the first logic comparator 35 is connected to the input of a first NOT gate 47, to a first input of the exclusive OR gate 49, and to a second input of a first and a second AND gate 50, 51.

[0143] The output of the second logic comparator 36 is connected to a second input of the exclusive OR gate 49.

[0144] The output of the third logic comparator 37 is connected to the input of the second NOT gate 48, to a third input of a third AND gate 52, and to a second input of the second AND gate 51.

[0145] The output of the first NOT gate 47 is connected to a second input of the third AND gate 52 and to a first input of the fourth AND gate 53.

[0146] An output of the exclusive OR gate 49 is connected to a first input of the first, second, third and fourth AND gates 50, 51, 52, 53.

[0147] An output of the second NOT gate 48 is connected to a third input of the first and fourth AND gates 50, 53.

[0148] The output of the third AND gate 52 is connected to a first input of a first summation operator 38 and the output of the first AND gate 50 is connected to a second input of the first summation operator 38.

[0149] The output of the first summation operator 38 is connected to a first input of a second summation operator 39.

[0150] Each of the gains 45, 46 comprises an input and an output.

[0151] Gains 45, 46 have a negative unit value so that the output of each gain is equal to the negative value on the input of said gain.

[0152] The input of the first gain 45 is connected to the output of the second AND gate 51 and the input of the second gain 46 is connected to the output of the fourth AND gate 53.

[0153] The output of the first gain 45 is connected to a first input of the third summation operator 40 and the output of the second gain 46 is connected to a second input of the third summation operator 40.

[0154] The output of the third summation operator 40 is connected to a second input of the second summation operator 39.

[0155] An output of the second summation operator 39 is connected to the output 26c of the phase shift determination means 26.

[0156] Each summation operator 38, 39, 40 delivers on its output the sum of the values received on its entries.

[0157] The signal SP can have three states, a first state is “1”, a second state is “-1”, and the third state is “0”.

[0158] When the sign of the supply voltage Vs and the sign of the supply current Is are identical, the first and second logic comparators 35, 36 deliver the high logic state “1” or the low logic state “0” so that the output of the exclusive OR gate 49 is equal to “0”. Consequently, the outputs of the AND gate 50, 51, 52, 53 are in the low logic state “0”.

[0159] The signal SP is in the third state “0”.

[0160] When the sign of the supply voltage Vs is positive and the sign of the supply current Is is negative, the first logic comparator 35 delivers the low logic state “0” and the second logic comparator 36 delivers the high logic state “1” so that the exclusive OR gate 49 delivers the high logic state “1” and the first NOT gate 47 delivers the high logic state “1”.

[0161] If the supply voltage Vs increases, the differentiator 41 delivers a positive value so that the third logic comparator 37 delivers the high logic state “1”. The second NOT gate 48 delivers the low logic state “0”. The first, second and third inputs of the third AND gate 52 are in the high logic state “1” so that the output of the third AND gate 52 is in the high logic state “1”. The outputs of the first, second and fourth AND gates 50, 51, 53 are in the low logic state “0”. The signal SP is in the first state “1” in which the supply current Is lags behind the supply voltage.

[0162] If the supply voltage Vs decreases, the differentiator 41 delivers a negative value so that the third logic comparator 37 delivers the low logic state “0”. The second NOT gate 48 delivers the high logic state “1”. The first, second and third inputs of the fourth AND gate 53 are in the high logic state “1” so that the output of the fourth AND gate 53 is in the high logic state “1”. The outputs of the first, second and third AND gates 50, 51, 52 are in the low logic state “0”. The signal SP is in the second state “-1” in which the supply current Is is ahead of the supply voltage Vs.

[0163] When the sign of the supply voltage Vs is negative and the sign of the supply current Is is positive, the first logic comparator 35 delivers the high logic state “1” and the second logic comparator 36 delivers the low logic state “0” so that the exclusive OR gate 49 delivers the high logic state “1” and the first NOT gate 47 delivers the low logic state “0”.

[0164] If the supply voltage Vs increases, the differentiator 41 delivers a positive value so that the third logic comparator 37 delivers the high logic state “1”. The second NOT gate 48 delivers the low logic state “0”. The first, second and third inputs of the second AND gate 51 are in the high logic state "1" so that the output of the second AND gate 51 is in the high logic state "1". The outputs of the first, third and fourth AND gates 50, 52, 53 are in the low logic state "0". The signal SP is in the second state "-1" in which the supply current Is is ahead of the supply voltage Vs.

[0165] If the supply voltage Vs decreases, the differentiator 41 delivers a negative value so that the third logic comparator 37 delivers the low logic state “0”. The second NOT gate 48 delivers the high logic state “1”. The first, second and third inputs of the first AND gate 50 are in the high logic state “1” so that the output of the first AND gate 50 is in the high logic state “1”. The outputs of the second, third and fourth AND gates 51, 52, 53 are in the low logic state “0”. The signal SP is in the first state “1” in which the supply current IP lags behind the supply voltage VP.

[0166] In a first embodiment of the periodic function generator 31, the periodic function generator delivers the signal S31 equal to:

[0167] S31(0 = "> <wZ + 530(f) +w0)(D

[0168] where coO is a phase synchronized with the supply voltage Vs, and co is equal to:

[0169] w = 2tf / (2)

[0170] where f is the frequency of the alternating current source 8.

[0171] [Fig.6] illustrates a second embodiment of the periodic function generator 31.

[0172] Unlike the first embodiment of the periodic function generator 31 in which the frequency of the alternating current source 8 is known, in the second embodiment, a sinusoidal function is determined independently by measuring the output voltage Vs of the alternating current source 8.

[0173] The periodic function generator 31 comprises three transfer functions 55, 57, 60, a limiter 56, an angle conversion module 58 and a summation operator 59.

[0174] A first transfer function 55 comprises an input 55a receiving the supply voltage Vs and an output 55b connected to an input 56a of the limiter 56.

[0175] The first transfer function 55 delivers a signal S55 to the output 55b:

[0177] where rms is the root mean square function.

[0178] Signal S55 is the supply voltage reference phase.

[0179] The limiter 56 comprises an output 56b connected to an input 57a of a second transfer function 57 and delivers a signal S56 on output 56b between one and minus one.

[0180] The second transfer function 57 comprises an output 57b connected to an input 58a of the angle conversion module 58.

[0181] The second transfer function 57 delivers an angle 0; representing the phase of the supply voltage Vs on the output 57b equal to:

[0182] 0,. = arcsine(556)(4)

[0183] The value of angle 0; being between -90° and +90°.

[0184] The conversion module 58 converts the angle 0; into a reference angle 0f included between 0° and 360° to represent a complete period of the supply voltage Vs.

[0185] The reference angle 0f is delivered to an output 58b of the conversion module 58.

[0186] Output 58b is connected to a first input of the summation operator 59.

[0187] The conversion module 58 comprises a second input 58c receiving the supply voltage Vs.

[0188] The summation operator 59 has a second input connected to the input 31a of a periodic function generator 31.

[0189] The summation operator 59 comprises an output connected to an input 60a of the third transfer function 60.

[0190] The summation operator 59 delivers on its output a signal S59 equal to:

[0191] 559 = 530 + 0 / (5)

[0192] The third transfer function 60 comprises an output 60b connected to the output 31b of the periodic function generator 31.

[0193] The third transfer function 60 delivers the signal S31 on the output 31b equal to:

[0194] 531 = sin(S59) (6)

[0195] The periodic function S31 results from the multiplication of the supply voltage reference phase S55 shifted by the reference angle 0f.

[0196] [Fig.7] illustrates an example of the conversion module 58.

[0197] The conversion module 58 comprises two logic comparators 61, 62, a differentiator 63 and a state machine 64.

[0198] The state machine 64 comprises an input 64a connected to the input 58a of the angle conversion module 58, an output 64b connected to the output 58b of the angle conversion module 58, a first control input 64c connected to the output of a first logic comparator 70, and a second control input 64d connected to the output of the second logic comparator 62.

[0199] The negative input of the logic comparators 70, 71 is connected to ground GND.

[0200] The positive input of the first logic comparator 61 and the input of the differentiator 63 are connected to the second input 58c of the angle conversion module 58.

[0201] The output of the differentiator 63 is connected to the positive input of the second logic comparator 62.

[0202] When the supply voltage Vs is positive, the first logic comparator 61 delivers the high logic state “1”.

[0203] When the supply voltage Vs is negative, the first logic comparator 61 delivers the low logic state “0”.

[0204] When the supply voltage Vs increases, the second logic comparator 62 delivers the high logic state “1”.

[0205] When the supply voltage Vs decreases, the second logic comparator 62 delivers the low logic state “0”.

[0206] The state machine 64 determines the reference angle 0f as explained below.

[0207] When the first logic comparator 61 delivers the low logic state “0” and the second logic comparator 62 delivers the low logic state “0”, the state machine 64 converts the angle 0; between -90° and +90° into the corresponding reference angle 0f between 180° and 270°.

[0208] When the first logic comparator 61 delivers the low logic state “0” and the second logic comparator 62 delivers the high logic state “1”, the state machine 64 converts the angle 0; between -90° and +90° into the corresponding reference angle 0f between 270° and 360°.

[0209] When the first logic comparator 61 delivers the high logic state “1” and the second logic comparator 62 delivers the low logic state “0”, the state machine 64 converts the angle 0; between -90° and +90° into the corresponding reference angle 0f between 90° and 180°.

[0210] When the first logic comparator 61 delivers the low logic state “1” and the second logic comparator 62 delivers the low logic state “1”, the state machine 64 converts the angle 0; between -90° and +90° into the corresponding reference angle 0f between 0° and 90°.

[0211] [Fig.8] illustrates an example of the characteristic waveforms of the supply voltage Vs, the supply current Is and the compensation current Ic.

[0212] The supply voltage Vs is in phase with the supply current Is.

[0213] The system 10 controlled by the control system 15, also called an active capacitor, reactive power compensator or power factor correction circuit, can be used to compensate for many different sensor / cable combinations without changing the circuit element values ​​of the control system 15.

[0214] Furthermore, the control system 15 is not influenced by the time delay caused by the sensors / filters.

[0215] The control system 15 varies the voltage of the energy storage device 20 so that the system 10 is adapted to compensate for the reactive power consumed by different types of inductive position sensors 6.

Claims

Claims

1. Method for compensating the reactive power consumed by at least one inductive position sensor (6) for a rotor (3) of an electrical machine (1) supported by at least one active magnetic bearing (5), the inductive position sensor (6) measuring a displacement of a rotor (4) and being powered by an alternating current source (8), the method comprising: - the determination of a phase shift (SP) between a supply voltage (Vs) and a supply current (Is) delivered by the alternating current source (8), - the determination of the amplitude (Ac) of a control signal (Sc) from the determined phase shift (SP), - determining a voltage reference value (VR) for an energy storage device (20) from the amplitude (Ac) of the control signal (Sc) and a duty cycle reference value (Dv) - determining the phase of the control signal (Sc) from the voltage of the energy storage device (20) and the voltage reference (VR), and - controlling the full bridge converter (13) as a function of the control signal to generate the compensation current (Ic) to bring the supply current (Is) into phase with the supply voltage (Vs).

2. The method of claim 1, wherein determining the phase shift (SP) comprises determining the sign of the supply voltage (Vs), the sign of the supply current (Is), and the sign of the derivative of the supply voltage (Vs): - the supply current (Is) lags behind the supply voltage (Vs) when the sign of the supply voltage (Vs) is positive, the sign of the supply current (Is) is negative, and the sign of the derivative of the supply voltage (Vs) is positive or when the sign of the supply voltage (Vs) is negative, the sign of the supply current (Is) is positive, and the sign of the derivative of the supply voltage (Vs) is negative, - the supply current (Is) leads the supply voltage (Vs) when the sign of the supply voltage (Vs) is positive, the sign of the supply current (Is) is negative, and the sign of the derivative of the supply voltage (Vs) is negative or when the sign of the supply voltage (Vs) is negative, the sign of the supply current (Is) is positive and the sign of the derivative of the supply voltage (Vs) is positive, and - the supply current (Is) is in phase with the supply voltage (Vs) when the sign of the supply voltage is always equal to the sign of the supply current.

3. A method according to claim 1 or 2, wherein the control signal (Sc) is a periodic function having the same frequency as the frequency of the supply voltage (Vs).

4. Method according to claim 1 or 2, in which the control signal (Sc) is a periodic function resulting from the multiplication of a supply voltage reference phase-shifted by a reference angle (0f) by the amplitude (Ac) of the control signal (Sc).

5. Method according to claim 4, wherein the reference angle (0f) is determined from the supply voltage (Vs).

6. Method according to one of claims 3 to 5, in which the periodic function is a sinusoidal function.

7. Control system (15) for controlling a full-bridge converter (13) to compensate for the reactive power consumed by at least one inductive position sensor (6) for a rotor (3) of an electrical machine (1) supported by at least one active magnetic bearing (5), the inductive position sensor (6) measuring a displacement of a rotor (4) and being powered by an alternating current source (8), the control system (15) comprising: - a phase shift determining means (26) configured to determine the phase shift (SP) between a supply voltage (Vs) and a supply current (Is) delivered by the alternating current source (8), - a first control loop (22) configured to control the amplitude of a control signal (Sc) from the determined phase shift (SP),- a second control loop (23) configured to control the phase of the control signal (Sc) from the voltage of the energy storage device (20) and a voltage reference (VR), - a third control loop (24) configured to control a voltage reference (VR) for an energy storage device (20) from the amplitude (Ac) of the control signal (Sc) and a duty cycle reference value (Dv), and, - a control means (25) configured to control the full bridge converter (13) as a function of the control signal (Sc) to generate the compensation current (Ic) to bring the supply current (Is) into phase with the supply voltage (Vs).

8. A control system according to claim 7, wherein the phase shift determining means (26) comprises a logic circuit comprising at least three logic comparators (35, 36, 37), a plurality of logic gates (49, 50, 51, 52, 53), a plurality of summing operators (38, 39, 40), a controller (42), and at least one differentiator (41), the logic circuit being configured to determine the sign of the supply voltage (Vs) and the sign of the supply current, and the sign of the derivative of the supply voltage (Vs): - the supply current (Is) lags behind the supply voltage (Vs) when the sign of the supply voltage (Vs) is positive, the sign of the supply current (Is) is negative, and the sign of the derivative of the supply voltage (Vs) is positive or when the sign of the supply voltage (Vs) is negative, the sign of the supply current (Is) is positive, and the sign of the derivative of the supply voltage (Vs) is negative, - the supply current leads the supply voltage (Vs) when the sign of the supply voltage (Vs) is positive, the sign of the supply current (Is) is negative, and the sign of the derivative of the supply voltage (Vs) is negative or when the sign of the supply voltage (Vs) is negative, the sign of the supply current (Is) is positive, and the sign of the derivative of the supply voltage (Vs) is positive, and - the supply current is in phase with the supply voltage (Vs) when the sign of the supply voltage (Vs) is always equal to the sign of the supply current (Is).

9. System (10) for compensating the reactive power consumed by at least one inductive position sensor (6) for a rotor (3) of an electrical machine (1) supported by at least one active magnetic bearing (5), the inductive position sensor (6) measuring a displacement of a rotor (4), the system (10) comprising a control system (15) according to claim 7 or 8 and a full bridge converter (13) comprising four switches (16, 17, 18, 19) and an energy storage device (20), each switch being coupled to the system control (15) for transferring the compensation current (Ic) to and from the energy storage device (20).

10. A sensor driver circuit (7) for at least one inductive position sensor (6) for a rotor (3) of an electrical machine (1) supported by at least one active magnetic bearing (5), the inductive position sensor (6) measuring a displacement of a rotor (4), comprising a transformer (9) having a main circuit (9a) and a secondary circuit (9b) configured to power the inductive position sensor (6), an alternating current source (8) connected to the main circuit (9a), and a system (10) according to claim 9 connected to the main circuit (9a).

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