A magnetic field interference compensation device for a magnetic shielding cabin

Abstract

The present invention discloses a device for compensating for external magnetic field interference in a magnetic shielding cabin, comprising: a linear external magnetic field interference compensator, a linear extended state observer, a fluxgate sensor, a voltage-controlled current source, and a square Helmholtz coil; the voltage-controlled current source is connected to the linear external magnetic field interference compensator, which is connected to the linear extended state observer, which is connected to the fluxgate sensor, which is connected to the square Helmholtz coil. The present invention can reduce the number of passive magnetic shielding layers required for a magnetic shielding cabin, thereby lowering costs; the external magnetic field interference compensation method employed can improve the active magnetic compensation device's ability to resist magnetic field interference; and the voltage-controlled current source with bias adjustment can offset the effects of the fluxgate bias voltage and provide the current required to compensate for static residual magnetism and external interference magnetic fields.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic shielding cabins, and in particular to a device for compensating for external magnetic field interference in a magnetic shielding cabin. Background Art

[0002] The multi-layer passive shielding of the magnetic shielding cabin can effectively attenuate the Earth's magnetic field and form a weak magnetic environment in the central area of ​​the shielding cabin, providing conditions for scientific research such as clinical medicine research, brain science research, and weak magnetic field measurement and testing.

[0003] While the passive shielding of a magnetic shielding cabin can significantly attenuate external magnetic fields, static residual magnetism cannot be completely eliminated, dynamic magnetic fields cannot be compensated in real time, and the extremely weak magnetic field environment in the central area cannot be maintained stable in the presence of multiple sources of magnetic field interference. While adding a passive shielding layer can further improve the magnetic shielding effect, the alloy material used in the shielding layer is expensive, increasing the cost of the magnetic shielding cabin. Therefore, active magnetic field compensation can be added to compensate for interfering magnetic fields in real time. Existing active magnetic field compensation methods mostly use a proportional-differential-integral control method. While this method can compensate for dynamic magnetic fields in real time, it has poor anti-interference capabilities and cannot quickly and effectively eliminate interfering magnetic fields. Summary of the Invention

[0004] In order to solve the problems of high cost of passive shielding layer and insufficient suppression ability of dynamic magnetic field interference in the above-mentioned prior art of the magnetic shielding cabin, the present invention provides an external magnetic field interference compensation device for the magnetic shielding cabin. By combining a voltage-controlled current source with external magnetic field interference compensation, it can simultaneously eliminate static residual magnetism and dynamic magnetic field interference in the central area inside the magnetic shielding cabin. It has low cost, fast response and strong anti-interference ability.

[0005] In order to achieve the above technical objectives, the present invention provides a magnetic shield cabin external magnetic field interference compensation device, comprising: a linear external magnetic field interference compensator, a linear expansion state observer, a fluxgate sensor, a voltage-controlled current source and a square Helmholtz coil;

[0006] The voltage-controlled current source is connected to the linear external magnetic field interference compensator, the linear external magnetic field interference compensator is connected to the linear extended state observer, the linear extended state observer is connected to the fluxgate sensor, and the fluxgate sensor is connected to the square Helmholtz coil.

[0007] Optionally, the linear external magnetic field interference compensator, the linear extended state observer and the fluxgate sensor constitute an external magnetic field interference compensation module;

[0008] The voltage-controlled current source and the square Helmholtz coil form a current loop module;

[0009] The external magnetic field interference compensation module is used to generate a reference control variable to act on the current loop module;

[0010] The current loop module is used to generate a controlled magnetic field in the central area of ​​the magnetic shielding cabin to compensate for the external disturbance magnetic field and the static internal residual magnetism.

[0011] Optionally, the current source of the current loop module adopts a proportional feedback control circuit.

[0012] Optionally, the output current of the current source is:

[0013] i sum =i bias +i ctrl

[0014] Where i sum is the output current; i bias is the bias current; i ctrl To control the current in real time.

[0015] Optionally, a controlled object of the magnetic field interference compensation device outside the magnetic shielding cabin is modeled, and the state equation of the controlled object is:

[0016]

[0017] Where y is the system output state; x1 and x2 are the system state and expansion state respectively; is the derivative of the system state; is the derivative of the expansion state; f sum is the lumped disturbance; k d is the current loop differential amplification factor; k p is the current loop proportional coefficient; k w is the amplification factor of the current loop power amplifier; L is the inductance of the magnetic compensation coil; r sum is the total resistance of the sampling resistor and the load resistor; r s k is the resistance of the sampling resistor; iv is the amplification factor of the instrument amplifier; Z is the number of turns of the coil; B s is the coil constant; k m is the fluxgate sensor conversion coefficient; k inad The amplification factor of the signal before entering the analog-to-digital converter; k ad is the analog-to-digital conversion coefficient; k da is the digital-to-analog conversion coefficient; d v is the current disturbance in the current loop; d b It is the sum of dynamic magnetic field interference and static remanence.

[0018] Optionally, the space equation of the expanded state is:

[0019]

[0020] Where z1 is the estimated value of the system output state; z2 is the estimated value of the system disturbance state; represents the coefficient matrix; Represents the input matrix when the input is u; is the input matrix when the input is y; is the derivative of the system state observation; is the derivative of the observation value of the expanded state.

[0021] Optionally, the output of the linear external magnetic field interference compensator is:

[0022]

[0023] Where, u is the control quantity; K p , b1 is the adjustment parameter; B ref is the magnetic field reference rate of the magnetic shielding cabin.

[0024] Optionally, the closed-loop transfer function of the magnetic field interference compensation device outside the magnetic shielding cabin is:

[0025]

[0026] in:

[0027]

[0028]

[0029] Where G clp (s) is the closed-loop transfer function; Y(s) is the result of Laplace transformation of the system output y; G B (s) is the transfer function of the controlled object; w0 is the adjustment parameter.

[0030] The present invention has the following technical effects:

[0031] 1. The present invention can reduce the number of passive magnetic shielding layers required for a magnetic shielding cabin, thereby reducing costs;

[0032] 2. The external magnetic field interference compensation method adopted by the present invention can improve the ability of the active magnetic compensation device to resist magnetic field interference;

[0033] 3. The present invention uses a voltage-controlled current source with bias adjustment, which can offset the influence of the fluxgate bias voltage and provide the required current to compensate for static residual magnetism and external interference magnetic fields;

[0034] 4. The present invention simultaneously realizes real-time compensation for static residual magnetism and dynamic magnetic field interference in the central area inside the magnetic shielding cabin, with low cost, fast response and strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 This is a structural block diagram of the external magnetic field interference compensation device for three-axis magnetic field compensation of the present invention;

[0037] Figure 2 Schematic diagram of the structure of the voltage-controlled current source with bias adjustment of the present invention;

[0038] Figure 3 It is the simulink simulation effect diagram of the present invention. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] like Figure 1 As shown, the present invention discloses a magnetic shield cabin external magnetic field interference compensation device, including: a linear external magnetic field interference compensator, a linear expansion state observer, a fluxgate sensor, a voltage-controlled current source and a square Helmholtz coil; the voltage-controlled current source is connected to the linear external magnetic field interference compensator, the linear external magnetic field interference compensator is connected to the linear expansion state observer, the linear expansion state observer is connected to the fluxgate sensor, and the fluxgate sensor is connected to the square Helmholtz coil.

[0041] The linear external magnetic field interference compensator, the linear expansion state observer and the fluxgate sensor constitute an external magnetic field interference compensation module; the voltage-controlled current source and the square Helmholtz coil constitute a current loop module, and the external magnetic field interference compensation module and the current loop module constitute an external magnetic field interference compensation system.

[0042] External magnetic field interference compensation module: The analog quantity of the fluxgate sensor is converted into a digital quantity by an analog-to-digital converter, and the digital quantity and the reference control quantity acting on the current loop module are used as the input quantity of the linear extended state observer. The linear extended state observer estimates the output state and lumped disturbance of the system, where the lumped disturbance refers to the sum of the internal disturbance of the system and the external disturbance of the system; the linear external magnetic field interference compensator performs a difference operation according to the system state, and uses the control quantity generated by the difference operation and the disturbance quantity observed by the linear extended state observer as the new reference control quantity of the current loop module to act on the current loop module.

[0043] Current loop module: The reference control quantity input by the voltage-controlled current source includes not only the reference control quantity from the external magnetic field interference compensation module, but also the variable bias quantity from the reference level chip. This control method can compensate for the bias voltage of the fluxgate sensor and the static residual magnetism in the shielding cabin while compensating for disturbances, thereby reducing the range of the current source and improving the control accuracy of the system; the square Helmholtz coil receives the control current from the voltage-controlled current source and generates a controlled magnetic field in the center area of ​​the magnetic shielding cabin to compensate for the external disturbance magnetic field and the static internal residual magnetism.

[0044] Specifically, the design process of the magnetic field interference compensation device outside the magnetic shielding cabin is as follows:

[0045] First, the controlled object of the device is modeled. The current source of the current loop module adopts a proportional feedback control circuit, and the state equation of the controlled object is:

[0046]

[0047] Where y is the system output state; x1 and x2 are the system state and expansion state respectively; is the derivative of the system state; is the derivative of the expansion state; f sum is the lumped disturbance; k d is the current loop differential amplification factor; k p k is the current loop proportional coefficient; w is the amplification factor of the current loop power amplifier; L is the inductance of the magnetic compensation coil; r sum is the total resistance of the sampling resistor and the load resistor; r s is the resistance of the sampling resistor; k iv is the amplification factor of the instrument amplifier; Z is the number of turns of the coil; B s is the coil constant; k m is the fluxgate sensor conversion coefficient; k inad The amplification factor of the signal before entering the analog-to-digital converter; k ad is the analog-to-digital conversion coefficient; k da is the digital-to-analog conversion coefficient; d v is the current disturbance in the current loop; db It is the sum of dynamic magnetic field interference and static remanence.

[0048] From formula (1), the expanded state space equation of the external magnetic field interference compensation system is:

[0049]

[0050] Where z1 is the estimated value of the system output state; z2 is the estimated value of the system disturbance state; is the derivative of the system state observation; is the derivative of the observation value of the expansion state; sorting (2) yields:

[0051]

[0052] by represents the coefficient matrix, Represents the input matrix when the input is u, Represents the input matrix when the input is y. Performing Laplace transform on input u yields U(s), and performing Laplace transform on input y yields Y(s). The system transfer function is solved by the system's expanded state space equation:

[0053] G(s)=C(sI-A) -1 B1U(s)+C(sI-A) -1 B2Y(s) (4)

[0054] G(s) represents the system transfer function. According to formula (4), the closed-loop pole configuration of the system can be uniformly configured to -w0+j0, where w0 is the bandwidth of the linear extended state observer, that is:

[0055] |(sI-A)|=s 2 +β1s+β2=(s+w0) 2 (5)

[0056] From formula (5), we can get:

[0057]

[0058] After the linear extended state observer observes the disturbance of the system and the output state of the system, a linear external magnetic field interference compensator is required to compensate. The output of the linear external magnetic field interference compensator is:

[0059]

[0060] Where B ref is the magnetic field reference rate of the magnetic shielding cabin;

[0061] From formula (4), we can see that the transfer function between the system output state estimate z1, the disturbance state estimate z2, the control variable u, and the system output variable y (the same as the input u and y in the input matrices B1 and B2, where the inputs are relative, u refers to the input of the controlled object, and y is the input of the extended state observer) can be expressed as:

[0062]

[0063] Where Z1(s) and Z2(s) represent the results of Laplace transform of the system output state estimate z1 and the disturbance state estimate z2, respectively; U(s) and Y(s) represent the results of Laplace transform of the control variable u and the system output variable y, respectively.

[0064] Perform Laplace transform on formula (7) and substitute formula (8) into it to obtain:

[0065]

[0066] Take the transfer function of the controlled object as G B (s);

[0067]

[0068]

[0069] Then, the closed-loop transfer function of the external magnetic field interference compensation device is:

[0070]

[0071] From formula (10), we can see that adjusting w0, K p The three parameters b and b1 can ensure the stability of the closed-loop system, accurately estimate and compensate for disturbances, and improve the dynamic performance of the system.

[0072] The design of the current loop module includes:

[0073] The current loop module uses a proportional feedback control circuit as the current source. A precision resistor is connected in series with the Helmholtz coil, and the current in the Helmholtz coil is controlled by controlling the voltage across the precision resistor. A precision op amp serves as the front-end operational circuit, and a low-noise power amplifier serves as the back-end driver to reduce current noise, thereby reducing the magnetic field noise generated by the current loop. The voltage across the precision resistor is detected by an instrumentation amplifier and fed back to the input to achieve proportional feedback control of the deviation.

[0074] Since the fluxgate itself has a bias voltage, a bias adjustment circuit is formed at the current loop input stage using a reference level chip, a sliding rheostat, and a precision op amp, so that the output current of the current source is as follows:

[0075] isum =i bias +i ctrl (11)

[0076] Where i sum is the output current; i bias is the bias current; i ctrl To control the current in real time, the current generated by the current source flows through the Helmholtz coil to generate a compensation magnetic field, reduce the static residual magnetism, compensate for the external interference magnetic field, and form a stable weak magnetic environment inside the magnetic shielding cabin.

[0077] The linear extended state observer in the external magnetic field interference compensation module receives the system's control variable and the system output quantity sensed by the fluxgate sensor, and outputs an estimate of the system's output state and disturbance state to the linear external magnetic field interference compensator. The linear external magnetic field interference compensator compares the system's output state with the reference state, generating a control variable to compensate for the system's state deviation and disturbance, which is then applied to the current loop module. The voltage-controlled current source in the current loop module provides the current required to compensate for static residual magnetism and the current required to compensate for dynamic interference magnetic fields. The current generated by the voltage-controlled current source flows through the Helmholtz coil, generating a magnetic field with the same phase and opposite direction as the interference magnetic field, thereby canceling the interference magnetic field.

[0078] like Figure 2 As shown in the figure, the resistance, capacitance and inductance are used as parameters to analyze the voltage controlled current source composed of the operational amplifier circuit. When R1 = R2, the first operational amplifier U1 outputs a voltage V out1 With input voltage V in , input bias reference voltage V ref The relationship between can be expressed as:

[0079]

[0080] The second operational amplifier U2 outputs a voltage V out2 The output voltage of the first operational amplifier U1 is V out1 , instrumentation amplifier output voltage V out4 The relationship between can be expressed as:

[0081]

[0082] The third power operational amplifier U3 outputs a voltage V out3 With input voltage V out2 The relationship between can be expressed as:

[0083]

[0084] Coil output current i out The output voltage of the third power operational amplifier U3 is Vout3 The relationship between them is:

[0085]

[0086] The output voltage across the sampling resistor and the instrumentation amplifier output voltage V out4 (Take AD8429 produced by ADI as an example) The relationship between them is:

[0087]

[0088] In summary, when the output of the current loop module is in steady state, the current i flowing through the Helmholtz coil is sum With input voltage V in 、V ref The relationship between can be expressed as:

[0089]

[0090] Take V in formula (6) ref The corresponding current is the bias current i bias 、V in Control current i ctrl The output current of the current source can be obtained as:

[0091] i sum =i bias +i ctrl (18)

[0092] like Figure 3 As shown, curve 1 and curve 2 respectively represent the magnetic field changes in the central area of ​​the magnetic shielding cabin after adding sin(45t) and sin(45t)+sin(360t), and the amplitude unit is nT. Curve 3 is the magnetic field in the central area of ​​the magnetic shielding cabin under the external magnetic field interference compensation device of the present invention, and the corresponding parameters of the linear extended state observer are β1=100, β2=2500, and the corresponding linear external magnetic field interference compensator parameters K p =500, from Figure 3 It can be seen that the peak-to-peak value of the magnetic field change is attenuated from 1nT to 0.04nT, which can effectively attenuate external magnetic field interference.

[0093] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. The magnetic field interference compensation device for the external magnetic shielding cabin is characterized by: include: Linear external magnetic field disturbance compensator, linear extended state observer, fluxgate sensor, voltage-controlled current source and square Helmholtz coil; The voltage-controlled current source is connected to the linear external magnetic field interference compensator, the linear external magnetic field interference compensator is connected to the linear extended state observer, the linear extended state observer is connected to the fluxgate sensor, and the fluxgate sensor is connected to the square Helmholtz coil; The controlled object of the magnetic shielding cabin external magnetic field interference compensation device is modeled, and the state equation of the controlled object is: Where y is the system output state; x1 and x2 are the system state and expansion state respectively; is the derivative of the system state; is the derivative of the expansion state; f sum is the lumped disturbance; k d is the current loop differential amplification factor; k p k is the current loop proportional coefficient; w is the amplification factor of the current loop power amplifier; L is the inductance of the magnetic compensation coil; r sum is the total resistance of the sampling resistor and the load resistor; r s is the resistance of the sampling resistor; k iv is the amplification factor of the instrument amplifier; Z is the number of turns of the coil; B s is the coil constant; k m is the fluxgate sensor conversion coefficient; k inad The amplification factor of the signal before entering the analog-to-digital converter; k ad is the analog-to-digital conversion coefficient; k da is the digital-to-analog conversion coefficient; d v is the current disturbance in the current loop; d b It is the sum of dynamic magnetic field interference and static residual magnetism; The spatial equation of the expanded state is: Where z1 is the estimated value of the system output state; z2 is the estimated value of the system disturbance state; represents the coefficient matrix; Represents the input matrix when the input is u; is the input matrix when the input is y; is the derivative of the system state observation; is the derivative of the observation value of the expansion state; The output of the linear external magnetic field interference compensator is: Where, u is the control quantity; K p , b1 is the adjustment parameter; B ref is the magnetic field reference rate of the magnetic shielding cabin.

2. The magnetic shielding cabin external magnetic field interference compensation device according to claim 1, characterized in that: The linear external magnetic field interference compensator, the linear extended state observer and the fluxgate sensor constitute an external magnetic field interference compensation module; The voltage-controlled current source and the square Helmholtz coil form a current loop module; The external magnetic field interference compensation module is used to generate a reference control variable to act on the current loop module; The current loop module is used to generate a controlled magnetic field in the central area of ​​the magnetic shielding cabin to compensate for the external disturbance magnetic field and the static internal residual magnetism.

3. The magnetic shielding cabin external magnetic field interference compensation device according to claim 2, characterized in that: The current source of the current loop module adopts a proportional feedback control circuit.

4. The magnetic shielding cabin external magnetic field interference compensation device according to claim 3, characterized in that: The output current of the current source is: i sum =i bias +i ctrl ; Where i sum is the output current; i bias is the bias current; i ctrl To control the current in real time.

5. The magnetic shielding cabin external magnetic field interference compensation device according to claim 1, characterized in that: The closed-loop transfer function of the magnetic field interference compensation device outside the magnetic shielding cabin is: in: Where G clp (s) is the closed-loop transfer function; Y(s) is the result of Laplace transformation of the system output y; G B (s) is the transfer function of the controlled object; w0 is the adjustment parameter.

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