Active magnetic compensation closed-loop control system and method for open type magnetic shielding box based on model predictive control

Abstract

The invention provides an open type magnetic shielding box active magnetic compensation closed-loop control system and method based on model prediction control, and relates to the technical field of magnetic shielding cabin active magnetic compensation systems, and the system comprises an open type magnetic shielding box, a fluxgate sensor, a model prediction controller and the like. The system realizes effective compensation of a magnetic field by simultaneously considering input and output coupling, reduces cost, solves the problem of opaque optics, and is simple in structure and easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of active magnetic compensation systems for magnetic shielding cabins, and particularly to an active magnetic compensation closed-loop control system and method for an open magnetic shielding box based on model predictive control. Background Art

[0002] With the development of science and technology, the measurement of magnetocardiogram and magnetoencephalogram signals plays an increasingly important role in the prevention and treatment of biological diseases. The intensities of magnetocardiogram and magnetoencephalogram signals are generally on the order of magnitude, which are much smaller than the Earth's magnetic field. Therefore, it is first necessary to use a magnetic shielding cabin to shield the Earth's magnetic field and form a zero magnetic region inside the magnetic shielding cabin before the measurement of magnetocardiogram and magnetoencephalogram signals can be carried out. Currently, the commonly used method to achieve a zero magnetic region inside the magnetic shielding cabin is the active magnetic field compensation technology.

[0003] For the active magnetic compensation closed-loop control system, current magnetic shielding cabins are all closed cavities, which are optically opaque, heavy, and there are concerns about causing claustrophobia to the human body. And currently, the main methods used are PI closed-loop or PID closed-loop control. Although a good compensation effect can be obtained to a certain extent, there are problems in the closed-loop compensation of the internal residual magnetic field by traditional classical PID control, such as a large overshoot in the control process and a slow response speed. And most importantly, there will be a coupling problem in the multi-input multi-output system for PID control; if an active magnetic compensation closed-loop control system and method for an open magnetic shielding box based on model predictive control can be designed, the compensation effect can be improved through the control method, but there is no relevant research at home and abroad currently.

[0004] Therefore, aiming at the characteristics of the active magnetic compensation control system, selecting an extended observer and a model predictive controller to achieve the suppression of the external disturbance magnetic field of the open magnetic shielding box and the stable control of the internal magnetic field is of great significance for reducing the cost of the magnetic shielding cabin, solving the problem of optical opacity, and solving the coupling problem of the magnetic compensation control system. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide an active magnetic compensation closed-loop control system and method for an open magnetic shielding box based on model predictive control, which can reduce the cost of the magnetic shielding cabin, solve the problem of optical opacity, and solve the coupling problem of the magnetic compensation control system.

[0006] To achieve the above purpose, the present invention provides the following solutions:

[0007] An active magnetic compensation closed-loop control system for an open magnetic shielding box based on model predictive control, comprising: an open magnetic shielding box, a fluxgate sensor, a model predictive controller, an extended observer, a current source, and a square compensation coil;

[0008] The open magnetic shielding box has a cubic structure, which is composed of nested longitudinal magnetic shielding bands and transverse magnetic shielding bands; the fluxgate sensor is placed inside the open magnetic shielding box, and the fluxgate sensor is used to measure the residual magnetic field and the disturbing magnetic field; the model predictive controller is used to generate a control signal; the extended observer is used to observe the disturbance signal of the external magnetic field and feed back the disturbance signal to the model predictive controller to achieve disturbance suppression; the current source is used to generate a compensation current according to the control signal; the square compensation coil is used to generate a compensation magnetic field.

[0009] Preferably, the longitudinal magnetic shielding bands and the transverse magnetic shielding bands are nested to form an arrayed perforated structure.

[0010] Preferably, the longitudinal magnetic shielding bands and the transverse magnetic shielding bands are made of permalloy material.

[0011] An active magnetic compensation closed-loop control method for an open magnetic shielding box based on model predictive control, which is applied to the above-mentioned active magnetic compensation closed-loop control system for an open magnetic shielding box based on model predictive control, includes:

[0012] S1. Establish an active magnetic compensation closed-loop control system, measure the magnitude of the residual magnetic field in the three-axis directions inside the open magnetic shielding box, convert the collected magnetic field signal into an electrical signal by the fluxgate sensor, and filter and amplify the electrical signal by the signal conditioning circuit, and output it in three paths;

[0013] S2. Design an extended observer based on the active magnetic compensation closed-loop control system to estimate the disturbing magnetic field;

[0014] S3. Based on the active magnetic compensation closed-loop control system and the extended observer, design a model predictive controller for the active magnetic compensation system, and realize the control of the magnetic field inside the open magnetic shielding box and the suppression of the magnetic field disturbance signal through the square compensation coil.

[0015] Preferably, in step S2, the system is converted into the form of a cascaded integrator by using the extended observer, the internal uncertainty and external disturbance of the system are defined as the total disturbance f, and through the input-output sweep analysis of the space magnetic field compensation system, the active magnetic compensation closed-loop control system of the open magnetic shielding box is written as a first-order system:

[0016]

[0017] Among them, represents the magnetic field signal measured by the fluxgate sensor, f(t) represents the total disturbance, b0 represents a control gain, z represents the estimated value of, u represents the control signal output by the space magnetic field compensation system.

[0018] Preferably, in step S3, in model predictive control, a controlled autoregressive integrated moving average model used in minimum variance control is adopted to describe the object affected by random interference; the expression of the object affected by random interference is:

[0019]

[0020] where u(t - 1) is the control signal of the space magnetic field compensation system at time t - 1, t represents the discrete time point of sampling control, q -1 is the backward shift operator, representing the corresponding quantity after retreating one sampling period, Δ = 1 - q -1 represents the difference operator, ξ(t) is an uncorrelated random sequence, representing the influence of a class of random noises, and A, B, and C are all polynomials of q -1

[0021] Preferably, in step S3, in model predictive control, the form of the optimization performance index at time t is:

[0022]

[0023] where E is the mathematical expectation, ω is the expected reference value of the object output, N1 and N2 are respectively the starting value and the ending value of the optimization time domain, NU is the control time domain, that is, the control quantity remains unchanged after NU steps: u(t + j - 1) = u(t + NU - 1), and λ(j) is the control weighting coefficient.

[0024] Preferably, the model predictive controller of the active magnetic compensation system is:

[0025] u(t) = u(t - 1) + d T (ω - f)

[0026] where u(t) is the control signal of the magnetic compensation system at time t, u(t - 1) is the control signal of the magnetic compensation system at time t - 1, d T =(10…0)(G T G + λI) -1 G T , G is a (N2 - N1 + 1)×NU - dimensional matrix, g j,i = g i+1 (i < j) is the unit step response coefficient, λ(j) is the control weighting coefficient, ω = [ω(t + N1)…ω(t + N2)] T , ω is the expected reference value of the object output, f is the matrix of f N (t), F j is a polynomial uniquely determined by A(q -1 ) and the prediction length j, F j (q​-1 ) = f j,0 + f j,0 q -1 + … + f j,n q -n , F j y(t) is only related to y(t), y(t - 1), etc.

[0027] According to the specific embodiments provided by the present invention, the following technical effects are disclosed by the present invention:

[0028] (1) The controlled object adopted in the present invention is an open magnetic shielding box. Currently, the relatively common magnetic shielding devices are all closed cavities, which are optically opaque, heavy, and there are concerns about causing claustrophobia to the human body. The open shielding box can effectively solve these problems.

[0029] (2) The present invention designs an active magnetic compensation closed-loop control system and method for an open magnetic shielding box based on model predictive control, which can handle and solve the coupling problem of the closed-loop control of the multi-input multi-output active magnetic compensation system, so that the active magnetic compensation closed-loop control system can effectively compensate the residual magnetic field and disturbance magnetic field inside the open shielding box and achieve stable control of the internal magnetic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is a schematic structural diagram of the open magnetic shielding box provided by the embodiment of the present invention;

[0032] Figure 2 It is a block diagram of the active magnetic compensation closed-loop control system for the open magnetic shielding box based on model predictive control provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0034] The object of the present invention is to provide an active magnetic compensation closed-loop control system and method for an open magnetic shielding box based on model predictive control. The open magnetic shielding box can effectively solve problems such as the optical opacity, large weight of a closed cavity, and the concern of causing claustrophobia to the human body. Model predictive control is an optimal control strategy that can well handle multi-input multi-output systems. In model predictive control, all inputs and outputs of the system, as well as their interactions, can be considered through an optimization process. The extended observer can estimate and compensate for external disturbance magnetic fields to achieve stable control of the magnetic field inside the magnetic shielding cabin.

[0035] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] As Figure 1 and Figure 2 shown, an active magnetic compensation closed-loop control system for an open magnetic shielding box based on model predictive control in this embodiment includes an open shielding box, a fluxgate sensor, a model predictive controller, an extended observer, a current source, and a square compensation coil.

[0037] The open magnetic shielding box has a cubic structure and is composed of nested longitudinal magnetic shielding bands and transverse magnetic shielding bands with a certain width, forming the arrayed opening structure and being made of permalloy material. The fluxgate sensor is placed inside the open magnetic shielding box to measure the residual magnetic field and disturbance magnetic field. The model predictive controller is used to generate control signals. The extended observer is used to observe the external magnetic field disturbance signal and can feedback the disturbance signal to the model predictive controller to achieve disturbance suppression. The current source is used to generate compensation current according to the control signal. The square compensation coil is used to generate a compensation magnetic field.

[0038] Specifically, in this embodiment, a control input sequence is found such that the future output tracks a predetermined reference trajectory and satisfies all constraint conditions. In this process, all inputs and outputs are considered simultaneously rather than processed separately. Therefore, any coupling between the inputs and outputs will be naturally considered by the system model and optimization process, and model predictive control can achieve closed-loop control of the active magnetic compensation system with magnetic field coupling.

[0039] This embodiment also includes an active magnetic compensation closed-loop control method for an open magnetic shielding box based on model predictive control, which is applied to the above active magnetic compensation closed-loop control system and includes the following steps:

[0040] Step (1): Establish an active magnetic compensation closed-loop control system for the open magnetic shielding box based on model predictive control. Measure the magnitude of the residual magnetic field in the three-axis directions inside the open magnetic shielding box. The magnetic flux gate sensor converts the collected magnetic field signal into an electrical signal, and the signal conditioning circuit filters and amplifies the electrical signal, which is output in three paths.

[0041] Step (2): Design an extended observer based on the active magnetic compensation closed-loop control system of the open magnetic shielding box in Step (1) to estimate the disturbance magnetic field.

[0042] Step (3): Design a model predictive controller for the active magnetic compensation system based on the active magnetic compensation closed-loop control system of the open magnetic shielding box in Step (1) and the extended observer obtained in Step (2). Control the magnetic field inside the open shielding box and suppress the magnetic field disturbance signal through the square compensation coil.

[0043] Among them, in Step (2), the system is transformed into the form of a cascaded integrator by using the extended observer. The internal uncertainty and external disturbance of the system are defined as the total disturbance f. By performing input-output sweep analysis on the spatial magnetic field compensation system, the active magnetic compensation closed-loop control system of the open magnetic shielding box can be written as a first-order system:

[0044]

[0045] Among them, represents the magnetic field signal measured by the magnetic flux gate sensor, f(t) represents the total disturbance, b0 represents a control gain, z represents the estimated value of, u represents the control signal output by the spatial magnetic field compensation system.

[0046] In model predictive control, the controlled autoregressive integrated moving average model used in minimum variance control is adopted to describe the object affected by random interference as:

[0047]

[0048] Among them, u(t - 1) is the control signal of the spatial magnetic field compensation system at time t - 1, t represents the discrete time point of sampling control, q -1 is the backward shift operator, representing the corresponding quantity after retreating one sampling period, Δ = 1 - q -1 represents the difference operator, ξ(t) is an uncorrelated random sequence, representing the influence of a class of random noises, and A, B, C are all polynomials of q -1 of.

[0049] Among them, in Step (3), in model predictive control, the form of the optimization performance index at time t is:

[0050]

[0051] Among them, E is the mathematical expectation, ω is the expected reference value of the object output, N1 and N2 are the starting value and the ending value of the optimization time domain respectively, NU is the control time domain, that is, the control quantity remains unchanged after NU steps: u(t + j - 1) = u(t + NU - 1), λ(j) is the control weighting coefficient, and generally it can be assumed to be a constant λ for simplifying the calculation.

[0052] The designed model predictive controller of the active magnetic compensation system is:

[0053] u(t) = u(t - 1) + d T (ω - f)

[0054] Among them, u(t) is the control signal of the magnetic compensation system at time t, u(t - 1) is the control signal of the magnetic compensation system at time t - 1, d T =(1 0…0)(G T G + λI) -1 G T , G is a matrix of (N2 - N1 + 1)×NU dimensions, g j,i =g i+1 (i < j) is the unit step response coefficient, λ(j) is the control weighting coefficient, ω = [ω(t + N1)…ω(t + N2)] T , ω is the expected reference value of the object output, f is the matrix of f N (t), F j is a polynomial uniquely determined by A(q -1 ) and the prediction length j, F j (q -1 ) = f j,0 +f j,0 q -1 +…+f j,n q -n , F j y(t) is only related to y(t), y(t - 1), etc.

[0055] Through the designed model predictive controller and the extended state observer, the closed-loop control of the active magnetic compensation system of the open magnetic shielding box can be realized, so that the active magnetic compensation closed-loop control system can effectively compensate the residual magnetic field and the disturbance magnetic field inside the open magnetic shielding box and realize the stable control of the internal magnetic field.

[0056] In summary, in this embodiment, an active magnetic compensation closed-loop control system and method for an open magnetic shielding box based on model predictive control are designed with a model predictive controller and an extended state observer for the open shielding box. The open shielding box has the advantages of light weight, optical transparency, and low cost. The model predictive controller can effectively handle and solve the coupling problem of the closed-loop control of the multi-input multi-output active magnetic compensation system, and the extended state observer can observe the external magnetic field disturbance and suppress the magnetic field disturbance through feedback. The active magnetic compensation closed-loop control system based on model predictive control compensates the residual magnetic field and the disturbance magnetic field inside the open magnetic shielding box to achieve stable control of the internal magnetic field.

[0057] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description in the method section.

[0058] Specific examples are used in this article to elaborate on the principles and implementation methods of the present invention. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention. At the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. An active magnetic compensation closed-loop control system for an open magnetic shielding box based on model predictive control, characterized in that, Including: An open magnetic shielding box, a fluxgate sensor, a model predictive controller, an extended observer, a current source, and a square compensation coil; The open magnetic shielding box is of a cube structure, which is composed of nested longitudinal magnetic shielding bands and transverse magnetic shielding bands; the fluxgate sensor is placed inside the open magnetic shielding box, and the fluxgate sensor is used to measure the residual magnetic field and the disturbance magnetic field; the model predictive controller is used to generate a control signal; the extended observer is used to observe the disturbance signal of the external magnetic field and feedback the disturbance signal to the model predictive controller to achieve disturbance suppression; the current source is used to generate a compensation current according to the control signal; the square compensation coil is used to generate a compensation magnetic field.

2. The active magnetic compensation closed-loop control system for an open magnetic shielding box based on model predictive control according to claim 1, wherein The longitudinal magnetic shielding band and the transverse magnetic shielding band are nested to form an arrayed hole structure.

3. The active magnetic compensation closed-loop control system for an open magnetic shielding box based on model predictive control according to claim 1, characterized in that, The longitudinal magnetic shielding band and the transverse magnetic shielding band are made of permalloy material.

4. A method for active magnetic compensation closed-loop control of an open magnetic shielding box based on model predictive control, which is applied to the active magnetic compensation closed-loop control system of the open magnetic shielding box based on model predictive control according to any one of claims 1 to 3, characterized in that, Including: S1. Establish an active magnetic compensation closed-loop control system, measure the magnitude of the residual magnetic field in the three-axis directions inside the open magnetic shielding box, convert the collected magnetic field signal into an electrical signal by the fluxgate sensor, and filter and amplify the electrical signal by the signal conditioning circuit, and output it in three paths; S2. Design an extended observer based on the active magnetic compensation closed-loop control system to estimate the disturbance magnetic field; S3. Based on the active magnetic compensation closed-loop control system and the extended observer, design a model predictive controller for the active magnetic compensation system, and realize the control of the magnetic field inside the open magnetic shielding box and the suppression of the magnetic field disturbance signal through the square compensation coil.

5. The active magnetic compensation closed-loop control method for an open magnetic shielding box based on model predictive control according to claim 4, characterized in that In step S2, the active magnetic compensation closed-loop control system is converted into the form of a cascaded integrator by using the extended observer, and the internal uncertainty and external disturbance of the active magnetic compensation closed-loop control system are defined as the total disturbance f. By performing input-output sweep analysis on the spatial magnetic field compensation system, the active magnetic compensation closed-loop control system is written as a first-order system as: Among them, represents the magnetic field signal measured by the fluxgate sensor, f(t) represents the total disturbance, and b0 represents a control gain, is a preset parameter, z represents the estimated value of, and u represents the control signal output by the space magnetic field compensation system.

6. The active magnetic compensation closed-loop control method for an open magnetic shielding box based on model predictive control according to claim 5, wherein, In step S3, in the model predictive control, the controlled autoregressive integrated moving average model used in the minimum variance control is adopted to describe the object affected by random interference; the expression of the object affected by random interference is: Among them, u(t - 1) is the control signal of the spatial magnetic field compensation system at time t - 1, t represents the discrete time point of sampling control, q -1 is the backward shift operator, representing the corresponding quantity after moving back one sampling period, Δ = 1 - q -1 represents the difference operator, ξ(t) is an uncorrelated random sequence, representing the influence of a class of random noise, and A, B, and C are all polynomials of q -1 ​ 7. The active magnetic compensation closed-loop control method for an open magnetic shielding box based on model predictive control according to claim 6, wherein In step S3, in the model predictive control, the form of the optimization performance index at time t is: where E is the mathematical expectation, ω is the expected reference value of the object output, N1 and N2 are respectively the initial value and the final value of the optimization time domain, NU is the control time domain, that is, the control quantity remains unchanged after NU steps: u(t + j - 1) = u(t + NU - 1), and λ(j) is the control weighting coefficient.

8. The active magnetic compensation closed-loop control method for an open magnetic shielding box based on model predictive control according to claim 6, characterized in that, The model predictive controller of the active magnetic compensation system is: u(t) = u(t - 1) + d T (ω - f) where u(t) is the control signal of the spatial magnetic field compensation system at time t, d T =(1 0 … 0)(G T G + λI) -1 G T , G is an (N2 - N1 + 1)×NU dimensional matrix, g j,i = g i+1 (i < j) is the unit step response coefficient, λ(j) is the control weighting coefficient, ω = [ω(t + N1) … ω(t + N2)] T , ω is the desired reference value of the object output, f is the matrix of f N (t), F j is a polynomial uniquely determined by A(q -1 ) and the prediction length j, F j (q -1 ) = f j,0 + f j,0 q -1 + … + f j,nq -n , F j y(t) is only related to y(t) and y(t - 1).

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