A magnetic field disturbance compensation method based on state observation PID

Abstract

This invention discloses a magnetic field disturbance compensation method based on state-observation PID control. First, the residual magnetic field inside the shielded room is obtained through a triaxial magnetic field measurement and amplification circuit. Then, an active compensation system is built, and the closed-loop transfer relationship model of the compensation coil is analyzed. A PID control circuit based on a disturbance observer is used to compensate for the residual magnetic field inside the shielded room and suppress magnetic field disturbances in the active magnetic compensation coil. Compared with traditional PID controllers, the state-observator-based control method not only compensates for the residual magnetic field inside the shielded room but also effectively suppresses the influence of external uncertainties on the compensated magnetic field, improving the stability of the active magnetic compensation system during magnetic field compensation and significantly enhancing the dynamic performance when compensating for the residual magnetic field inside the magnetic shielded room.

Description

Technical Field

[0001] This invention relates to the field of disturbance suppression in active magnetic compensation closed-loop control systems, and specifically to a magnetic field disturbance compensation method based on state observation PID. Background Technology

[0002] Optically pumped magnetometers (OPMs) can measure magnetic fields with a sensitivity of up to 0.16 fT / Hz. 1 / 2 Commercially available atomic magnetometers, such as QuSpinOPM, have a sensitivity of <15 fT / Hz. 1 / 2 The magnetic field signals generated by neural activity in the human body have extremely low amplitudes (fT~pT) and low frequencies (1-80Hz). In recent years, the rapid development of atomic magnetometer technology has led to its increasing application in human magnetoencephalography (MEG) measurements. However, active magnetic field meters (OPMs) can only operate within a range of ±5nT. Even in a typical two-layer molybdenum magnetic shielding room using passive shielding, the remaining magnetic field can still reach tens of nT. Therefore, the development of OPMs requires active magnetic compensation technology to compensate for the residual magnetic field inside the magnetic shielding room.

[0003] An active magnetic compensation closed-loop system measures the residual magnetic field inside a magnetically shielded room. The control system, based on the values ​​from the magnetic field sensor sampling circuit, measures the ambient magnetic field data. This data is then imported into a computer via an ADC conversion unit. A compensation algorithm in the computer processes this data and controls the output voltage of a DAC conversion unit. This voltage controls the output current of a current source, which flows into the compensation coil to compensate for the ambient magnetic field. A PID circuit is commonly used for this control. However, unpredictable external factors, such as trains and vibrations, can cause disturbances to the magnetic field inside the magnetically shielded room, affecting the stability of the entire system. For example, when the floor assembly of the magnetically shielded room is directly connected to the floor, the movement of personnel can cause vibrations within the room. Measurements show that the vibration of the magnetic sensor produces artifact disturbances of 7Hz to 30Hz in the magnetic field inside the shielded room, and a 2.5mm displacement of the magnetic sensor causes a 1nT change in the magnetic field. Furthermore, the passage of trains, subways, and other vehicles also generates magnetic field disturbances, with disturbances on the order of 1–2nT.

[0004] For an unknown controlled object, a disturbance observer can be used to estimate and compensate for external disturbances in the system. The principle is to use the difference between the actual output and the nominal model output as an estimate of the disturbance and feed it back to the control terminal to cancel out external disturbances. Since the closed-loop control system of active magnetic compensation is a second-order system, a state observer can theoretically also be applied to magnetic field compensation systems to eliminate unpredictable external disturbances. Summary of the Invention

[0005] To address the issue of unpredictable external disturbances during magnetic field compensation, this invention provides a state-observation PID-based magnetic field disturbance compensation method. By constructing a nominal model and a low-pass filter, external disturbances are fed back to the control terminal, thereby suppressing their impact on the magnetic field compensation process. This method is used in active magnetic compensation closed-loop control systems to eliminate the influence of unpredictable external disturbances on the overall system's magnetic field measurement and compensation, achieving stable magnetic field compensation. This provides technical support for the realization of extremely weak magnetic environments and the application of atomic magnetometers.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A magnetic field disturbance compensation method based on state observation PID includes the following steps:

[0008] Step (1): Measure the magnitude of the remaining magnetic field in the shielded room. The three-axis magnetic field signal is obtained by the magnetic field sensor and filtered and amplified by the magnetic field measurement amplifier circuit. The three-axis magnetic field signal is converted into a voltage signal and output in three paths.

[0009] Step (2): Define the transfer function G of the magnetic field compensation system. p (s) is a second-order system, and a disturbance observer is defined based on the transfer function. As an equivalent model of the disturbance, the three-axis signal is output by the PID control system based on the state observer to remove the magnetic field disturbance, quickly obtain the stable current signal that needs to be compensated and output it, and drive the three-axis Helmholtz coil to generate the corresponding compensation magnetic field.

[0010] Furthermore, by applying the disturbance observer to the active magnetic field compensation system, the disturbance observer can be used to observe the impact of external disturbances on the compensation magnetic field and feed the disturbances back to the control input terminal of the control coil to generate the magnetic field, thereby suppressing the impact of external disturbances on the compensation magnetic field generated by the active magnetic field compensation system.

[0011] In an active magnetic field compensation system, the coil and current source are modeled as a second-order system, and the equivalent transfer function is:

[0012]

[0013] Where K p1 K p2 K p3 K p4 is the scaling factor for the current source model, and R and L are the resistance and inductance of the coil, respectively;

[0014] Let d be the interference input. For observation interference, ε is the input error, and the output of the equivalent interference is:

[0015]

[0016] This allows for the initial and accurate estimation of disturbances in an active magnetic field compensation system.

[0017] Furthermore, the definition of the disturbance observer in step (2) specifically includes:

[0018] ①Establish the nominal model G of the magnetic field disturbance observer n (s):

[0019] ② Design a low-pass filter Q(s):

[0020] For the nominal model G n The noise introduced by (s) in the observation interference Add a low-pass filter to remove it;

[0021] Based on the structure of the magnetic field compensation closed-loop system, the transfer function G between the input u and the output y is... u (s) is obtained from Mason's formula:

[0022]

[0023] Similarly, the relationship between the disturbance d, the low-frequency measurement noise ξ, and the output is obtained as follows:

[0024]

[0025]

[0026] The design expression for a low-pass filter is as follows:

[0027] in

[0028] It is determined by parameters N, M, and τ, with N and M guaranteeing The regularity of M is given by τ, where τ represents the bandwidth of the filter, s represents the complex variable of the time-domain function after the Laplace transform, and k is a positive integer less than or equal to M.

[0029] The advantages of this invention compared to existing technologies are as follows: The active magnetic compensation closed-loop system can reduce the magnetic field inside the magnetic shielding chamber to the required operating range by measuring the residual magnetic field inside and then driving a coil with a current source to generate a compensating magnetic field. A PID circuit is commonly used for this purpose. However, unpredictable external factors, such as trains and vibrations, can cause disturbances to the magnetic field inside the magnetic shielding chamber, affecting the stability of the entire system. For unknown controlled objects, disturbance observers can be used to estimate and compensate for external disturbances in the system. The principle is to use the difference between the actual output and the nominal model output as an estimate of the disturbance and feed it back to the control terminal to cancel out external disturbances. The active magnetic compensation closed-loop control system is a second-order system, and state observers are theoretically also used in magnetic field compensation systems to eliminate unpredictable external disturbances. Attached Figure Description

[0030] Figure 1 This is a flowchart of the magnetic field disturbance compensation method based on state observation PID of the present invention;

[0031] Figure 2 This is a schematic diagram of the transfer function between the coil and the current source actuator in an active magnetic compensation system.

[0032] Figure 3 The control system block diagram for implementing the state observation-based PID magnetic field disturbance compensation method of the present invention is shown below;

[0033] Figure 4 This is a schematic diagram of the state observation-based PID control system of the present invention;

[0034] Figure 5 This is a simplified schematic diagram of a state-observation-based PID control system. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] like Figure 1 As shown, the state-observation PID control method of the present invention constructs a nominal model and a low-pass filter, designs a state-observation PID controller, and feeds back external disturbances to the control terminal, thereby suppressing the influence of external magnetic field disturbances on the magnetic field compensation process. Specifically, it includes the following steps:

[0037] Step (1): Measure the magnitude of the residual magnetic field inside the shielded room. The triaxial magnetic field signal is obtained by a magnetic field sensor, filtered and amplified by a magnetic field measurement amplifier circuit, and converted into a voltage signal for output in three paths. The transfer function of the coil and current source actuator in the active magnetic compensation system is as follows: Figure 2 As shown. Figure 3 As shown, the control system for implementing the state observation-based PID control method of the present invention includes a three-axis coil 1, a magnetic shielding chamber 2, and a magnetic field sensor 3. The control system also includes an A / D conversion circuit, a PID control circuit, a D / A conversion circuit, a current source, and a current drive.

[0038] Step (2): Define the magnetic field compensation closed-loop system, based on the state observation PID control system diagram as shown below. Figure 4 As shown, u is the input, y is the output, and the transfer function G is... p (s) is a second-order system, and a disturbance observer is defined based on the transfer function. As an equivalent model of the disturbance, the interference is filtered out by a filter Q(s). Let d be the disturbance input. For observational interference, ξ represents noise. ε is the filter residue, and ε is the input error. The triaxial signal is output by the PID control system based on the state observer to remove magnetic field disturbances, quickly obtain the stable current signal that needs to be compensated and output it, and drive the triaxial Helmholtz coil to generate the corresponding compensation magnetic field.

[0039] By applying a disturbance observer to an active magnetic field compensation system, the influence of external disturbances on the compensation magnetic field is observed using the disturbance observer, and the disturbance is fed back to the control input terminal of the control coil to generate the magnetic field, thereby suppressing the influence of external disturbances on the compensation magnetic field generated by the active magnetic field compensation system.

[0040] In an active magnetic field compensation system, the coil and current source are modeled as a second-order system, such as... Figure 2 As shown, the transfer function is equivalent to:

[0041]

[0042] Where K p1 K p2 K p3 K p4 is the scaling factor for the current source model, and R and L are the resistance and inductance of the coil, respectively;

[0043] Let d be the interference input. For observation interference, ε is the input error, and the output of observation interference is:

[0044]

[0045] This allows for the initial and accurate estimation of interference in the active magnetic field compensation system.

[0046] The design of the disturbance observer mainly consists of the following two parts:

[0047] (1) Nominal model G of magnetic field disturbance observer n Establishment of (s):

[0048] Due to G in practical problems p Since the inverse physics of (s) is unrealizable, based on the second-order properties of the entire system, a nominal model G that can be realized is generally designed. n (s) is used instead. Nominal model G n The transfer function of (s) and G p The transfer function of (s) is similar, and the functions are similar, and it is G p The physically realizable model of (s). Such as observational disturbances. As shown in the output, the designed G... n (s) makes The value is approximately 1, used for observing disturbances.

[0049] (2) Design of low-pass filter Q(s):

[0050] To address the noise introduced by the nominal model, in the context of observational interference This is achieved by adding a low-pass filter. The simplified control system diagram is as follows: Figure 5 As shown, based on the structure of the magnetic field compensation closed-loop system, the transfer function G between the input u and the output y is... u (s) can be obtained from Mason's formula:

[0051]

[0052] Similarly, the relationship between the disturbances d and ξ and the output can be obtained as follows:

[0053]

[0054]

[0055] As can be seen from the above expressions, a low-pass filter can reduce the disturbance transfer function G in the low-frequency range. d (s) is 0, but the effect of noise will not be reduced.

[0056] The design expression for a low-pass filter is as follows, which is mainly determined by parameters N, M, and τ. N and M guarantee... The regularity of τ is given by τ, where τ represents the bandwidth of the filter, s represents the complex variable of the time-domain function after the Laplace transform, and k is a positive integer less than or equal to M.

[0057] in

[0058] It is known that the high-frequency interference in the magnetic compensation system has been shielded by the magnetic shielding cylinder. The remaining disturbance frequency is below 30Hz. Considering the characteristics that the larger the parameter, the narrower the frequency band and the sensitivity to noise but the weaker the ability to suppress interference, it is necessary to make a choice between the ability to suppress external disturbances and the measurement of noise.

[0059] The contents not described in detail in this specification are prior art known to those skilled in the art. Those skilled in the art will readily understand that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A magnetic field disturbance compensation method based on state-observation PID, characterized in that, Includes the following steps: Step (1): Measure the magnitude of the remaining magnetic field in the shielded room. The three-axis magnetic field signal is obtained by the magnetic field sensor and filtered and amplified by the magnetic field measurement amplifier circuit. The three-axis magnetic field signal is converted into a voltage signal and output in three paths. Step (2): Define the transfer function G of the magnetic field compensation system. p (s) is a second-order system, and a disturbance observer is defined based on the transfer function. As an equivalent model of the disturbance, the three-axis signal is output by the PID control system based on the state observer to remove the magnetic field disturbance, quickly obtain the stable current signal that needs to be compensated and output it, and drive the three-axis Helmholtz coil to generate the corresponding compensation magnetic field. By applying a disturbance observer to an active magnetic field compensation system, the influence of external disturbances on the compensation magnetic field is observed using the disturbance observer and fed back to the control input terminal of the control coil to generate the magnetic field, thereby suppressing the influence of external disturbances on the compensation magnetic field generated by the active magnetic field compensation system. In an active magnetic field compensation system, the coil and current source are modeled as a second-order system, and the equivalent transfer function is: Where K p1 K p2 K p3 K p4 is the scaling factor for the current source model, and R and L are the resistance and inductance of the coil, respectively; Let d be the interference input. For observation interference, ε is the input error, and the output of the equivalent interference is: This allows for the initial and accurate estimation of disturbances in an active magnetic field compensation system.

2. The magnetic field disturbance compensation method based on state observation PID according to claim 1, characterized in that, The definition of the disturbance observer in step (2) specifically includes: ① Establish the nominal model G of the magnetic field disturbance observer n (s): ② Design a low-pass filter Q(s): For the nominal model G n The noise introduced by (s) in the observation interference Add a low-pass filter to remove it; Based on the structure of the magnetic field compensation closed-loop system, the transfer function G between the input u and the output y is... u (s) is obtained from Mason's formula: Similarly, the perturbation is obtained. Low-frequency measurement noise The relationship between the output and the output is as follows: The design expression for a low-pass filter is as follows: ,in ; It is determined by parameters N, M, and τ, with N and M guaranteeing The regularity of M is given by τ, where τ represents the bandwidth of the filter, s represents the complex variable of the time-domain function after the Laplace transform, and k is a positive integer less than or equal to M.

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