A three-axis active magnetic compensation system based on decoupling control and parameter design method

Abstract

The application discloses a three-axis active magnetic compensation system based on decoupling control and a parameter design method, and belongs to the technical field of active magnetic shielding. The three-axis active magnetic compensation system based on decoupling control adopts a three-axis PID magnetic field controller to perform closed-loop control on three-axis magnetic field components of a center point in a magnetic shielding cabin. Parameter design of the three-axis PID magnetic field controller includes three steps. Firstly, a mathematical model of the three-axis active magnetic compensation system is obtained by using a sweep frequency method. Then, a coupling channel of the model is equivalent to a main channel to obtain a mathematical model of the three-axis active magnetic compensation system in a decoupling state. Finally, parameters of the three-axis PID magnetic field controller are designed according to the decoupling model of the three-axis active magnetic compensation system. The three-axis active magnetic compensation system based on decoupling control can realize decoupling between variables of the three-axis active magnetic compensation system, suppresses an interference magnetic field in an environment around the magnetic shielding cabin, and improves dynamic stability of a center magnetic field of the magnetic shielding cabin.

Description

TECHNICAL FIELD

[0001] The application relates to the field of active magnetic shielding, in particular to a three-axis active magnetic compensation system based on decoupling control and a parameter design method. BACKGROUND

[0002] Neural activities of human brain can generate neural current, according to the Biot-Savart law, the neural current can form a synchronous biomagnetic field outside the skull, the signal strength of the magnetic field is usually in the range of 50-500fT, which is extremely weak, and the magnetoencephalography (MEG) technology can directly detect such signal and has the characteristics of non-invasive and non-radiation. In the frequency range of the magnetic field generated by the neural current, the biological tissue almost does not interact with it, that is, the magnetoencephalography signal is basically not affected by the brain tissue, skull and scalp, so the magnetoencephalography technology suffers less interference in the brain than the electroencephalography (EEG) technology, and can detect the signal of the deep brain area. Therefore, as a high temporal and spatial resolution neuroimaging technology for detecting neural activities of brain, the magnetoencephalography technology has important role and wide application prospect in brain science research and clinical diagnosis.

[0003] Detecting such extremely weak magnetic signal of magnetoencephalography needs a low-frequency disturbance environment, which requires low residual magnetic field, low magnetic field gradient and low residual magnetic field drift. Generally, the total size of the magnetic field is about 50000nT, the magnetic field fluctuation is more than nT, and there is also urban magnetic noise generated by power lines, railways, motor vehicles moving in the earth's magnetic field, electrical equipment and other sources, therefore, the suppression of interference magnetic field is an important technical problem. According to the different principles of magnetic field suppression, the commonly used magnetic field suppression methods mainly include two types: passive magnetic shielding method and active magnetic compensation method, among which, the high permeability material shielding is a commonly used passive magnetic shielding method, due to the physical characteristics of the material with high magnetic permeability, the magnetic force lines of the magnetic field in the external environment pass through the surface of the material, so that the magnetic field inside the closed room formed by the material is reduced; in addition, shielding alternating magnetic field by using the induced eddy current effect of high-conductivity material is also a commonly used passive shielding method, which is mainly used for the suppression of high-frequency magnetic noise. Active magnetic compensation utilizes the magnetic effect of coil, that is, a controllable current is passed through the coil to generate a magnetic field with the same size and opposite direction as the interference magnetic field, combined with the closed-loop negative feedback control mode, the suppression of the environmental magnetic field can be realized, the active magnetic compensation method can effectively suppress the low-frequency and high-frequency magnetic field, and the final shielding effect depends on the efficiency of the compensation algorithm and the stability of the current source.

[0004] When the requirement of zero magnetic environment is higher, the passive magnetic shielding and active magnetic compensation are often combined to realize the near zero magnetic field environment. The magnetic shielding cabin is large in size, so it consumes more materials and is expensive. Moreover, the complex manufacturing process of high-quality metal sheet is also expensive. Therefore, it is necessary to apply the active magnetic compensation technology to improve the shielding performance and reduce the use of shielding materials.

[0005] The three-axis active magnetic compensation system is a three-input three-output system, and the change of the current of any axis coil can simultaneously affect the three-axis magnetic field components in the cabin. The existence of the coupling between the variables of the three-axis active magnetic compensation system not only makes the system difficult to control, but also greatly reduces the control quality of the system. Therefore, the decoupling of the three-axis active magnetic compensation system is necessary to improve the dynamic stability of the magnetic field in the cabin. SUMMARY

[0006] In order to suppress the interference magnetic field in the magnetic shielding cabin and improve the dynamic stability of the magnetic field in the cabin, the application discloses a three-axis active magnetic compensation system based on decoupling control and a parameter design method. The three-axis PID magnetic field controller is used to perform closed-loop control on the three-axis magnetic field components at the center point in the magnetic shielding cabin. The parameter design of the three-axis PID magnetic field controller includes three steps. Firstly, the mathematical model of the three-axis active magnetic compensation system is obtained by using the sweep frequency method. Then, the coupling channel of the model is equivalent to the main channel to obtain the mathematical model of the three-axis active magnetic compensation system in the decoupling state. Finally, the parameters of the three-axis PID magnetic field controller are designed according to the decoupling model of the three-axis active magnetic compensation system.

[0007] In order to achieve the above purpose, the technical scheme adopted by the application is as follows:

[0008] A three-axis active magnetic compensation system based on decoupling control comprises a magnetic shielding cabin, three-axis compensation coils, three-axis fluxgate sensors, a three-axis PID magnetic field controller, a three-axis power amplifier and a three-axis signal conditioning circuit. The magnetic shielding cabin is a closed structure composed of two layers of permalloy and one layer of aluminum alloy. The three-axis compensation coils are installed outside the magnetic shielding cabin in an edge suspension winding manner. The three-axis fluxgate sensors are placed at the center point position in the magnetic shielding cabin. The three-axis PID magnetic field controller is used to generate three-axis coil control voltage signals. The three-axis power amplifier is used to amplify the coil control voltage signals to generate coil driving currents. The three-axis signal conditioning circuit is used to amplify and filter the output signals of the three-axis fluxgate sensors. The three-axis includes x-axis, y-axis and z-axis.

[0009] The magnetic field reference value of the three-axis active magnetic compensation system is set to 0. The error value between the magnetic field reference value and the output signal of the three-axis fluxgate sensor after the three-axis signal conditioning circuit is obtained by the three-axis PID magnetic field controller to obtain the control voltage of the three-axis compensation coil. After being amplified by the three-axis power amplifier, the driving current of the three-axis compensation coil is generated to drive the three-axis compensation coil to generate a magnetic field to compensate for the residual magnetism in the magnetic shielding cabin.

[0010] The triaxial active magnetic compensation system is a three-input, three-output system, and the parameters of the triaxial PID magnetic field controller are determined based on the mathematical model of the triaxial active magnetic compensation system under decoupled state.

[0011] This invention also provides a parameter design method for a three-axis active magnetic compensation system based on decoupling control. The parameter design method for the three-axis PID magnetic field controller includes the following steps:

[0012] Step 1: Establish the triaxial active magnetic compensation system model G(s) using the frequency sweep method:

[0013]

[0014] Among them, g ** (s) represent the mathematical model descriptions of the relationship between the control voltage of each axis compensation coil and the axial components of the magnetic field at the center point of the magnetic shielding cabin, respectively:

[0015]

[0016] Among them, B x B y and B z The output signals of the triaxial fluxgate sensor, which are the x-axis, y-axis, and z-axis magnetic field components of the center point of the magnetically shielded cabin, are respectively processed by the triaxial signal conditioning circuit. x u y and u z These are the control voltages for the compensation coils of the x-axis, y-axis, and z-axis, respectively.

[0017] Step 2: Equip the coupling channel of the triaxial active magnetic compensation system model G(s) to the main channel of G(s), thus obtaining the decoupled model G of the triaxial active magnetic compensation system. e (s):

[0018]

[0019] in, It is the x-axis compensation coil control voltage u x And the x-axis component B of the magnetic field at the center point of the magnetic shielding cabin x Equivalent models between them It is the y-axis compensation coil control voltage u y The y-axis component B of the magnetic field at the center point of the magnetic shielding cabiny the equivalent model between the x-axis compensation coil voltage control signal and the magnetic shield chamber internal center point three-axis response magnetic field signal, is the z-axis compensation coil control voltage u z and the equivalent model between the magnetic shield chamber center point magnetic field z-axis component B z

[0020] Step 3: According to the three-axis active magnetic compensation system decoupling model G e (s) design three-axis PID magnetic field controller parameters.

[0021] Further, the step 1 comprises the following steps:

[0022] Step (1): Collecting three-axis active magnetic compensation system input and output data:

[0023] The three-axis coil voltage controller generates a sine voltage signal with a certain amplitude and a frequency from 0.1Hz to 200Hz in logarithmic coordinates, measures and records the x-axis compensation coil voltage control signal and the magnetic shield chamber internal center point three-axis response magnetic field signal.

[0024] Step (2): Data processing:

[0025] At each frequency point, the amplitude and phase changes of the x-axis compensation coil voltage control signal and the magnetic shield chamber internal center point three-axis response magnetic field signal are respectively counted, and the Bode plots of g 11 (s), g 21 (s) and g 31 (s) in the three-axis active magnetic compensation system model G(s) are drawn in logarithmic coordinates, including amplitude-frequency curves and phase-frequency curves.

[0026] Step (3): Fitting the three-axis active magnetic compensation system model:

[0027] According to the amplitude-frequency curves and phase-frequency curves obtained in step (2), g 11 (s), g 21 (s) and g 31 (s) in the three-axis active magnetic compensation system model G(s) are fitted.

[0028] Step (4): Repeating steps (1), (2), and (3) to determine g 12 (s), g 22 (s) and g 32 (s) related to the y-axis compensation coil voltage control signal; repeating steps (1), (2), and (3) to determine g 13 (s), g 23 (s) and g 33 (s) related to the z-axis compensation coil voltage control signal.

[0029] ​Furthermore, step 2 includes the following steps:

[0030] Step (1): Implement closed-loop control for the y-axis and z-axis magnetic fields and open-loop control for the x-axis magnetic field of the triaxial active magnetic compensation system. Derive the x-axis compensation coil control voltage u under this control structure. x And the x-axis component B of the magnetic field at the center point of the magnetic shielding chamber x The equivalent model between them, namely

[0031] Step (2): Implement closed-loop control for the x-axis and z-axis magnetic fields and open-loop control for the y-axis magnetic field of the triaxial active magnetic compensation system. Derive the y-axis compensation coil control voltage u under this control structure. y The y-axis component B of the magnetic field at the center point of the magnetic shielding cabin y The equivalent model between them, namely

[0032] Step (3): Implement closed-loop control for the x-axis and y-axis magnetic fields and open-loop control for the z-axis magnetic field of the triaxial active magnetic compensation system. Derive the z-axis compensation coil control voltage u under this control structure. z And the z-axis component B of the magnetic field at the center point of the magnetic shielding cabin z The equivalent model between them, namely

[0033] Furthermore, step 3 includes the following steps:

[0034] Step (1): For Conduct the McLaughlin unfold;

[0035] Step (2): Take the approximate model as a first-order model with time delay: And conduct the McLaughlin expansion; among them, K r1 T is the proportional element constant. r1 τ is the time constant of the inertial element. r1 The lag time for a pure time-delay element;

[0036] Step (3): Make the corresponding coefficients of the Maclaurin expansion in steps (1) and (2) equal, and determine K. r1 T r1 and τ r1 ;

[0037] Step (4): Repeat steps (1), (2), and (3) to confirm. corresponding and corresponding

[0038] Step (5): Based on the approximate model and Design the parameters of the three-axis PID magnetic field controllers for the x-axis, y-axis and z-axis of the three-axis active magnetic compensation system.

[0039] The beneficial effects of this invention can be seen in the following aspects:

[0040] (1) The present invention uses the frequency sweep method to model the three-axis active magnetic compensation system, which provides a basis for the parameter design of the controller and is conducive to designing the optimal controller parameters;

[0041] (2) The present invention performs equivalent processing on the coupling between variables in the three-axis active magnetic compensation system, converting the three-input three-output system of the three-axis active magnetic compensation into three single-input single-output systems, which facilitates the individual design of the controller for each loop.

[0042] (3) The present invention performs a model reduction approximation on the decoupling model of the three-axis active magnetic compensation system, which simplifies the complex form of the decoupling model of the three-axis active magnetic compensation system and is beneficial to the design of each loop controller. Attached Figure Description

[0043] Figure 1 This is a block diagram of the triaxial active magnetic compensation system based on decoupling control according to the present invention;

[0044] Figure 2 The diagram shows the equivalent model block diagram of the active magnetic compensation system along the x-axis. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0046] like Figure 1 As shown, this invention employs a three-axis PID magnetic field controller to perform closed-loop control of the three-axis magnetic field components at the center point inside the magnetically shielded chamber. The parameter design of the three-axis PID magnetic field controller includes three steps: first, a mathematical model of the three-axis active magnetic compensation system is obtained using a frequency sweep method; then, the coupling channel of this mathematical model is equivalent to the main channel to obtain the mathematical model of the three-axis active magnetic compensation system in a decoupled state; finally, the parameters of the three-axis PID magnetic field controller are designed based on the decoupled model of the three-axis active magnetic compensation system.

[0047] The specific implementation of the triaxial active magnetic compensation system based on decoupling control of the present invention is as follows:

[0048] Figure 1 China B xref B yref and Bzref Bx, By and Bz are x-axis, y-axis and z-axis magnetic field reference value of three-axis active magnetic compensation system respectively, B x , B y and B z are x-axis, y-axis and z-axis magnetic field component of the center point of the magnetic shielding cabin through the three-axis magnetic flux gate sensor output signal of the three-axis signal conditioning circuit respectively, e x , e y and e z are error values of x-axis, y-axis and z-axis magnetic field reference value and x-axis, y-axis and z-axis magnetic field feedback value of the center point in the magnetic shielding cabin respectively, u x , u y and u z are x-axis, y-axis and z-axis compensation coil control voltage of three-axis active magnetic compensation system respectively, i x , i y and i z are x-axis, y-axis and z-axis compensation coil driving current of three-axis active magnetic compensation system respectively, B mx , B my and B mz are x-axis, y-axis and z-axis magnetic field measurement values of the three-axis magnetic flux gate sensor in the magnetic shielding cabin.

[0049] As shown in Figure 1 , a three-axis active magnetic compensation system based on decoupling control includes a magnetic shielding cabin, three-axis compensation coils, three-axis magnetic flux gate sensors, three-axis PID magnetic field controllers, three-axis power amplifiers and a three-axis signal conditioning circuit, wherein three-axis represents x-axis, y-axis and z-axis; the magnetic shielding cabin is a closed structure constructed by two layers of permalloy and one layer of aluminum alloy, wherein the aluminum alloy layer is located between the two layers of permalloy; the three-axis compensation coils are installed in an edge suspension winding manner outside the magnetic shielding cabin, wherein the x-axis compensation coil is installed in the north-south direction of the magnetic shielding cabin, the y-axis compensation coil is installed in the top-bottom direction of the magnetic shielding cabin, and the z-axis compensation coil is installed in the east-west direction of the magnetic shielding cabin; the three-axis magnetic flux gate sensors are placed at the center point position in the magnetic shielding cabin; the three-axis PID magnetic field controller is used to generate three-axis compensation coil control voltage signals; the three-axis power amplifier is used to amplify the three-axis compensation coil control voltage signals to generate three-axis compensation coil driving currents; the three-axis signal conditioning circuit is used to amplify and filter the three-axis magnetic flux gate sensor output signals; the three-axis magnetic flux gate sensor output signals contain residual magnetism at the center point of the magnetic shielding cabin, magnetic fields generated by the three-axis compensation coils and interference magnetic fields generated by environmental interference magnetic fields at the center point of the magnetic shielding cabin.

[0050] Taking the x-axis as an example, the three-axis active magnetic compensation system x-axis magnetic field reference value B xref is set to 0, and the error value e x of the magnetic field reference value and the center point x-axis magnetic field feedback value B xThe coil control voltage u is obtained after the triaxial PID magnetic field controller x , wherein B x The x-axis magnetic field measurement value B of the triaxial fluxgate sensor is obtained mx After being amplified and filtered by the x-axis signal conditioning circuit, u is obtained x After being amplified by the triaxial power amplifier, the x-axis compensation coil driving current i is generated x , i x The magnetic field generated by driving the compensation coil compensates for the residual magnetism in the magnetic shielding cabin.

[0051] Figure 1 The triaxial active magnetic compensation system shown is a three-input three-output system, and the parameters of the triaxial PID magnetic field controller are determined according to the mathematical model of the triaxial active magnetic compensation system in the decoupling state.

[0052] The triaxial PID magnetic field controller parameter design method of the present application comprises the following steps:

[0053] Step (1) Sweep frequency method to establish a triaxial active magnetic compensation system model G(s):

[0054]

[0055] Wherein, g ** (s) is the mathematical model description between the control voltage of each axis compensation coil and the x-axis component of the magnetic field at the center point of the magnetic shielding cabin, that is:

[0056]

[0057] Wherein, B x , B y and B z are the x-axis, y-axis and z-axis magnetic field components of the center point of the magnetic shielding cabin, respectively, the output signals of the triaxial fluxgate sensor of the triaxial signal conditioning circuit, u x , u y and u z are the control voltages of the x-axis, y-axis and z-axis compensation coils, respectively.

[0058] Step (2) The coupling channel of the triaxial active magnetic compensation system model G(s) is equivalent to the main channel of G(s), and a decoupling model G e (s) of the triaxial active magnetic compensation system is obtained:

[0059]

[0060] Wherein, is the equivalent model between the x-axis compensation coil control voltage u x and the x-axis component B x of the magnetic field at the center point of the magnetic shielding cabin, is the equivalent model between the y-axis compensation coil control voltage uy and the equivalent model between the y-axis component of the magnetic field at the center point of the magnetic shielding cabin B y is the z-axis compensation coil control voltage u z and the equivalent model between the z-axis component of the magnetic field at the center point of the magnetic shielding cabin B z ;

[0061] Step (3) designs three-axis PID magnetic field controller parameters according to the active magnetic compensation system decoupling model G e (s).

[0062] Specifically, the step (1) comprises the following steps:

[0063] 1) Collecting three-axis active magnetic compensation system input and output data:

[0064] The coil voltage controller generates a sine voltage signal with a certain amplitude and a frequency from 0.1 Hz to 200 Hz selected by logarithmic coordinates at equal intervals on the x-axis of the system, measures and records the x-axis compensation coil voltage control signal u x and the three-axis magnetic flux gate sensor output signals B x , B y and B z of the x-axis, y-axis and z-axis magnetic field components at the center point of the magnetic shielding cabin through the three-axis signal conditioning circuit.

[0065] 2) Data processing:

[0066] At each frequency point, the amplitude variation and phase variation of the x-axis compensation coil voltage control signal u x and the three-axis magnetic flux gate sensor output signals B x , B y and B z of the x-axis, y-axis and z-axis magnetic field components at the center point of the magnetic shielding cabin through the three-axis signal conditioning circuit are respectively counted at each frequency point, and the Bode diagrams of g 11 (s), g 21 (s) and g 31 (s) in the three-axis active magnetic compensation system model G(s) are drawn in logarithmic coordinates, including amplitude-frequency curves and phase-frequency curves.

[0067] 3) Fitting the three-axis active magnetic compensation system model:

[0068] According to the amplitude-frequency curves and phase-frequency curves obtained by sweeping, g 11 (s), g 21 (s) and g 31 (s) in the active magnetic compensation system model G(s) are fitted.

[0069] 4) Repeat 1)-3), respectively determine y-axis compensation coil voltage control signal u y ​Related g 12 (s), g 22 (s) and g 32 (s) and z-axis compensation coil voltage control signal u z Related g 13 (s), g 23 (s) and g 33 (s);

[0070] Step (2) includes the following steps:

[0071] 1) The control voltage u of the x-axis compensation coil of the triaxial active magnetic compensation system x And the x-axis component B of the magnetic field at the center point of the magnetic shielding cabin x Equivalent model between For example, by separating the x-axis loop, the input-output relationship of the triaxial active magnetic compensation system can be obtained:

[0072]

[0073] Among them, B -x and u -x The B was removed respectively x and u x The subsequent input and output vectors of the triaxial active magnetic compensation system, G 1* (s) and G *1 (s) represent the first row and first column of G(s) after removing g 11 The row and column vectors obtained after (s), G -11 (s) is the matrix obtained by removing the first row and the first column from G(s);

[0074] like Figure 2 As shown, the y-axis and z-axis magnetic fields are controlled in a closed loop, while the x-axis magnetic field is controlled in an open loop. Figure 2 C -1 (s) represents the controller matrix after removing the x-axis PID field controller, from... Figure 2 The control input u of loop x can be seen in the diagram. x In addition to via the main channel g 11 (s) Affects output B x In addition, it also uses G *1 (s)--C -1 (s)--G 1* (s) for B x To have an impact, i.e., u x For B x The actual effect is the superposition of the coupling effect of the x-loop itself and the y and z-loops. Figure 2 The control voltage u of the x-axis compensation coil of the triaxial active magnetic compensation system can be derived from the structure shown. xBx is the x-axis component of the magnetic field at the center point of the magnetic shield cabin x Bx is the x-axis component of the magnetic field at the center point of the magnetic shield cabin

[0075] 2) Let the x-axis magnetic field and the z-axis magnetic field of the three-axis active magnetic compensation system be closed-loop controlled, and the y-axis magnetic field be open-loop controlled, and derive the control voltage u of the y-axis compensation coil under this control structure y Bx is the x-axis component of the magnetic field at the center point of the magnetic shield cabin y Bx is the x-axis component of the magnetic field at the center point of the magnetic shield cabin

[0076] 3) Let the x-axis magnetic field and the y-axis magnetic field of the three-axis active magnetic compensation system be closed-loop controlled, and the z-axis magnetic field be open-loop controlled, and derive the control voltage u of the z-axis compensation coil under this control structure z Bx is the x-axis component of the magnetic field at the center point of the magnetic shield cabin z Bx is the x-axis component of the magnetic field at the center point of the magnetic shield cabin

[0077] The step (3) comprises the following steps:

[0078] 1) Perform a Maclaurin expansion on

[0079] 2) Take the approximate model as a first-order plus time delay model: And perform a Maclaurin expansion; wherein, K r1 is a proportional link constant, T r1 is an inertial link time constant, and τ r1 is a pure lag link lag time;

[0080] 3) Let the Maclaurin expansion coefficients in 1) and 2) correspond to each other, and determine K r1 , T r1 and τ r1 ;

[0081] 4) Repeat 1)-3), and determine corresponding and corresponding

[0082] 5) According to the approximate models and , design the three-axis active magnetic compensation system x-axis, y-axis and z-axis PID magnetic field controller parameters respectively.

[0083] ​While the foregoing specific embodiments of the application have been described in some detail to provide a thorough understanding of the application, it should be apparent that the application is not limited to the specifics of the foregoings as these can, of course, vary. As can be seen, the application can be carried out by specifically constructing devices in accordance with the teaching herein or by practicing acts consistent with the principles of this application. For a better understanding of the application, its operating principles and other objects and advantages, reference should be made to the drawings and to the accompanying descriptive matter.

Claims

1. A parameter design method for a triaxial active magnetic compensation system based on decoupling control, characterized in that, The decoupled control-based triaxial active magnetic compensation system includes a magnetic shielding chamber, triaxial compensation coils, a triaxial fluxgate sensor, a triaxial PID magnetic field controller, a triaxial power amplifier, and a triaxial signal conditioning circuit. The magnetic shielding chamber is a closed structure constructed of two layers of permalloy and one layer of aluminum alloy. The triaxial compensation coils are mounted outside the magnetic shielding chamber using a suspension-type winding method. The triaxial fluxgate sensor is placed at the center point inside the magnetic shielding chamber. The triaxial PID magnetic field controller generates a control voltage signal for the triaxial coils. The triaxial power amplifier amplifies the coil control voltage signal to generate the coil drive current. The triaxial signal conditioning circuit amplifies and filters the output signal of the triaxial fluxgate sensor. The three axes include an x-axis, a y-axis, and a z-axis. The magnetic field reference value of the three-axis active magnetic compensation system is set to 0. The error value between the magnetic field reference value and the output signal of the three-axis fluxgate sensor after the three-axis signal conditioning circuit is obtained by the three-axis PID magnetic field controller to obtain the control voltage of the three-axis compensation coil. After being amplified by the three-axis power amplifier, the driving current of the three-axis compensation coil is generated to drive the three-axis compensation coil to generate a magnetic field to compensate for the residual magnetism in the magnetic shielding cabin. The triaxial active magnetic compensation system is a three-input three-output system, and the parameters of the triaxial PID magnetic field controller are determined according to the mathematical model of the triaxial active magnetic compensation system under decoupled state. The parameter design method for a three-axis PID magnetic field controller includes the following steps: Step 1: Establish a model of the triaxial active magnetic compensation system using the frequency sweep method. : in, The mathematical models describe the relationship between the control voltage of each axis compensation coil and the components of the magnetic field at the center point of the magnetic shielding cabin, respectively: in, , and These are the output signals of a three-axis fluxgate sensor, which takes the x-axis, y-axis, and z-axis magnetic field components at the center point of the magnetic shielding chamber as inputs, and is processed by a three-axis signal conditioning circuit. , and These are the control voltages for the compensation coils of the x-axis, y-axis, and z-axis, respectively. Step 2: Model the triaxial active magnetic compensation system The coupling channel is equivalent to The main channel yields the decoupled model of the triaxial active magnetic compensation system. : in, It is the control voltage of the x-axis compensation coil. and the x-axis component of the magnetic field at the center point of the magnetic shielding chamber Equivalent models between them It is the control voltage of the y-axis compensation coil. y-axis component of the magnetic field at the center point of the magnetic shielding cabin Equivalent models between them It is the control voltage of the z-axis compensation coil. z-axis component of the magnetic field at the center point of the magnetic shielding chamber Equivalent models between them; Step 3: Based on the decoupling model of the triaxial active magnetic compensation system Design parameters for a three-axis PID magnetic field controller.

2. The parameter design method according to claim 1, characterized in that, Step 1 includes the following steps: Step (1): Acquire input and output data of the triaxial active magnetic compensation system: The triaxial coil voltage controller generates a sinusoidal voltage signal with a constant amplitude and a frequency ranging from 0.1Hz to 200Hz at equal intervals on a logarithmic coordinate system x-axis. It measures and records the x-axis compensation coil voltage control signal and the triaxial response magnetic field signal at the center point inside the magnetic shielding cabin. Step (2): Data processing: At each frequency point, the amplitude and phase changes of the x-axis compensation coil voltage control signal and the triaxial response magnetic field signal at the center point inside the magnetic shielding chamber are statistically analyzed, and the triaxial active magnetic compensation system model is plotted on logarithmic coordinates. middle , and Bode plot, including amplitude frequency curve and phase frequency curve; Step (3): Fitting the triaxial active magnetic compensation system model: Based on the amplitude-frequency curve and phase-frequency curve obtained in step (2), the model of the triaxial active magnetic compensation system is obtained by fitting. In , and ; Step (4): Repeat steps (1), (2), and (3) to determine the voltage control signal related to the y-axis compensation coil. , and Repeat steps (1), (2), and (3) to determine the voltage control signal related to the z-axis compensation coil. , and .

3. The parameter design method according to claim 1, characterized in that, Step 2 includes the following steps: Step (1): Implement closed-loop control for the y-axis and z-axis magnetic fields and open-loop control for the x-axis magnetic field of the triaxial active magnetic compensation system. Derive the control voltage of the x-axis compensation coil under this control structure. and the x-axis component of the magnetic field at the center point of the magnetic shielding chamber The equivalent model between them, namely ; Step (2): Implement closed-loop control for the x-axis and z-axis magnetic fields and open-loop control for the y-axis magnetic field of the triaxial active magnetic compensation system. Derive the control voltage of the y-axis compensation coil under this control structure. y-axis component of the magnetic field at the center point of the magnetic shielding cabin The equivalent model between them, namely ; Step (3): Implement closed-loop control for the x-axis and y-axis magnetic fields and open-loop control for the z-axis magnetic field of the triaxial active magnetic compensation system. Derive the control voltage of the z-axis compensation coil under this control structure. z-axis component of the magnetic field at the center point of the magnetic shielding chamber The equivalent model between them, namely .

4. The parameter design method according to claim 1, characterized in that, Step 3 includes the following steps: Step (1): For Conduct the McLaughlin unfold; Step (2): Take the approximate model as a first-order model with time delay: And conduct the McLaughlin expansion; among them, The constant of the proportional element, The time constant of the inertial element, The lag time for a pure time-delay element; Step (3): Set the corresponding coefficients of the Maclaurin expansion in steps (1) and (2) to be equal, and determine... , and ; Step (4): Repeat steps (1), (2), and (3) to confirm. corresponding and corresponding ; Step (5): Based on the approximate model , and Design the parameters of the three-axis PID magnetic field controllers for the x-axis, y-axis and z-axis of the three-axis active magnetic compensation system.

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