CN117562543A - Active magnetic compensation method and system - Google Patents
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Abstract
The invention discloses an active magnetic compensation system, comprising: the output end of the reference magnetometer is connected with the input end of the signal processor, and the output end of the signal processor is connected with the compensation coil through a voltage-controlled current source; wherein, the reference magnetometer collects the magnetic field intensity T in the magnetic shielding barrel environment at regular time 1 And the magnetic field intensity T 1 Transmitting to a signal processor, the signal processor outputting a compensation voltage to a voltage-controlled current source, the voltage-controlled current source converting the compensation voltage into a compensation current of a compensation coil so as to make the magnetic field intensity T in the magnetic shielding barrel environment 1 Near or reaching target magnetic field strength T 0 . The compensation precision of the active magnetic compensation system can reach pT level, and the active magnetic compensation system can also generate good inhibition effect on low-frequency magnetic noise in the environment, and is suitable for a magnetocardiograph system with higher precision requirement.
Description
Technical Field
The invention belongs to the technical field of magnetic compensation, and particularly relates to an active magnetic compensation method and system.
Background
The heart of a person can be accompanied by the generation of a very weak biological magnetic field during electrophysiological activity, and magnetocardiography detection is an essential part in the process of diagnosing heart-related diseases. As a noninvasive function detection technique, magnetocardiography (MCG) has been widely used in clinical medicine such as localization of myocardial ischemia, judgment of arrhythmia, diagnosis of cardiac load, and the like. The typical intensity of the MCG signal is about several tens of pT (10 -12 Tesla), and the geomagnetic field strength is 30 μT to 50 μT (10) -6 Tesla), which means that the acquisition of MCG signals is often affected by the ambient magnetic field.
In order to suppress the interference of environmental magnetic noise, a passive magnetic shielding technology such as a magnetic shielding room and a magnetic shielding barrel is generally used, but the magnetic shielding room has the defects of high cost and large volume, and the shielding performance of the magnetic shielding barrel is also influenced by the material characteristics of the magnetic shielding room. These disadvantages of the passive shielding technology limit the measurement range of the high-precision measuring instrument, and cannot bring a stable magnetic field environment to the high-precision magnetic detection sensor, so that in order to ensure the quality of the MCG signal and control the cost at the same time, the current mainstream scheme is to further inhibit the environmental magnetic noise by setting up an active magnetic compensation system.
The compensation algorithm applied to the active magnetic compensation system at present has the characteristics of simple parameter adjustment and convenient operation, and can generate corresponding magnetic compensation quantity in a stable magnetic field environment, but when a sudden magnetic field and electronic magnetic noise appear in the environment, the compensation effect is greatly reduced, and the compensation precision is unsatisfactory.
Disclosure of Invention
The present invention provides an active magnetic compensation method, which aims to improve the above problems.
The invention is embodied in an active magnetic compensation system, the system comprising:
the output end of the reference magnetometer is connected with the input end of the signal processor, and the output end of the signal processor is connected with the compensation coil through a voltage-controlled current source;
wherein, the reference magnetometer collects the magnetic field intensity T in the magnetic shielding barrel environment at regular time 1 And the magnetic field intensity T 1 Transmitting to a signal processor, the signal processor outputting a compensation voltage to a voltage-controlled current source, the voltage-controlled current source converting the compensation voltage into a compensation current of a compensation coil so as to make the magnetic field intensity T in the magnetic shielding barrel environment 1 Near or reaching target magnetic field strength T 0 。
Further, the signal processor includes:
the magnetic noise monitoring module, the expected signal tracking module and the magnetic compensation processing module are connected with each other,
the magnetic noise monitoring module refers to the magnetic field intensity T acquired by the magnetometer 1 As feedback signal y, differential signal monitoring value y of feedback signal y is output 1 、y 2 Monitoring the total value y 3 ；
The expected signal tracking module sets the target magnetic field intensity T 0 As the desired signal v, the desired signal v and the differential signal monitoring value v thereof are output 1 、v 2 ；
Differential signal monitoring value y of magnetic compensation quantity processing module based on feedback signal y 1 、y 2 Differential signal monitoring value v from desired signal v 1 、v 2 Is the difference of (2)To calculate the voltage compensation component u 0 And then based on the total monitored value y of magnetic noise 3 For the voltage compensation component u 0 And compensating to obtain the total compensation quantity U of the voltage, namely outputting the compensation voltage by the signal processor.
Further, the voltage compensation component u 0 The calculation formula of (2) is specifically as follows:
wherein,k p is a proportionality coefficient, k d As a result of the differential coefficient,as a nonlinear function, alpha 1 、α 2 The value of β is a constant which is 0 to 1.
Further, the calculation formula of the total voltage compensation amount U is specifically as follows:
U＝u 0 -y 3 /c
wherein c is a constant.
Further, the differential signal monitoring value y of the feedback signal y 1 、y 2 Monitoring the total value y 3 The tracking formula of (2) is as follows:
y 1 ＝y′ 1 +q(y′ 2 -K 01 z′ 1 )；
wherein K is 01 、K 02 、K 03 Three adjustable parameters; z'. 1 、z′ 2 、z′ 3 Respectively the monitoring value y 'of the feedback signal at the last moment' 1 、y′ 2 、y′ 3 A difference from the feedback signal y; q is a filtering factor, c is a constant, U' is a compensation voltage output by the signal processor at the previous moment,as a nonlinear function.
Further, a nonlinear functionThe expression is specifically as follows:
wherein z is the difference between the monitored value of the feedback signal and the feedback signal, alpha is an adjustable parameter, the value range is 0-1, beta is a parameter factor, and sign is a sign function.
Further, a differential signal v of the desired signal v 1 、v 2 The tracking formula of (2) is as follows:
v 1 ＝v′ 1 +qv′ 2 ；
v 2 ＝v′ 2 qf(x 1 ,x 2 ,p,q)；
wherein v' 1 、v′ 2 Differential signal monitoring values, f (x) 1 ,x 2 P, q) is a discrete domain control function.
Further, a discrete control function f (x 1 ,x 2 P, q) is specifically as follows:
y＝x 1 +qx 2 ；
m＝pq，m 0 ＝mq
wherein x is 1 、x 2 、m、n 0 、m 0 And p and q are respectively set tracking speed factors and filtering factors for intermediate parameters.
The invention is realized in such a way that an active magnetic compensation method based on an active magnetic compensation system comprises the following steps:
(1) Reading a set expected signal v;
(2) When the sampling time is reached, the expected signal v enters an expected signal tracking module, and the feedback signal y enters a magnetic noise monitoring module;
(3) After the expected signal tracking module receives the expected signal v, the expected signal v and the differential signal thereof are tracked, and then v is respectively used for 1 ＝v′ 1 +qv′ 2 、v 2 ＝v′ 2 +qf(x 1 ,x 2 P, q) output trace value v 1 And v 2 ；
(4) After receiving the feedback signal y, the magnetic noise monitoring module tracks the feedback signal y and its differential signal, and then uses y 1 ＝y′ 1 +q(y′ 2 -K 01 z′ 1 ) Andoutputting the monitored value y 1 And y 2 At the same time +.>Output of the total monitored value y of magnetic noise 3 ；
(5) To be used forAnd->Calculating deviation +.>And->Outputting a voltage compensation component u by a magnetic compensation amount processing module 0 Then extracting low-voltage compensation component and total monitoring value of magnetic noise to compensate magnetic noise, finally using U=u 0 -y 3 C outputting a compensation voltage U;
(6) The voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil so as to lead the magnetic field intensity T in the magnetic shielding barrel environment 1 Near or reaching target magnetic field strength T 0 。
The active magnetic compensation system provided by the invention has the following beneficial technical effects:
(1) The compensation control is not needed until the magnetic noise is generated, the differentiation of the expected magnetic field value can be accurately tracked through the expected signal tracking module and the magnetic noise detection module, and meanwhile, the monitored magnetic noise is compensated to the control output end in the first time, so that the response speed is faster than that of a common compensation algorithm.
(2) Three modules in the compensation algorithm can form a complete closed loop, the magnetic compensation quantity can be calculated only according to the expected magnetic field value and the magnetic noise monitoring value, the model of the controlled object can be suitable for various magnetic compensation systems without knowing, and the adaptability of the magnetic compensation algorithm is better than that of a common magnetic compensation algorithm;
(3) The compensation accuracy of the compensation algorithm can reach pT level, and the compensation algorithm can also generate a good inhibition effect on low-frequency magnetic noise in the environment, and is suitable for a magnetocardiograph system with high accuracy requirements.
Drawings
FIG. 1 is a schematic diagram of an active magnetic compensation system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of signal feedback of an active magnetic compensation system according to an embodiment of the present invention;
FIG. 3 is a flow chart of an active magnetic compensation method according to an embodiment of the present invention.
Detailed Description
The following detailed description of the embodiments of the invention, given by way of example only, is presented in the accompanying drawings to aid in a more complete, accurate, and thorough understanding of the inventive concepts and aspects of the invention by those skilled in the art.
FIG. 1 is a schematic structural diagram of an active magnetic compensation system according to an embodiment of the present invention, and for convenience of explanation, only a portion related to the embodiment of the present invention is shown, the system includes:
the output end of the reference magnetometer is connected with the input end of the signal processor, and the output end of the signal processor is connected with the compensation coil through a voltage-controlled current source;
wherein, the reference magnetometer collects the magnetic field intensity T in the magnetic shielding barrel environment at regular time 1 And the magnetic field intensity T 1 Send to a letterThe signal processor outputs compensation voltage to the voltage-controlled current source, and the voltage-controlled current source converts the compensation voltage into compensation current of the compensation coil so as to enable the magnetic field intensity T in the magnetic shielding barrel environment 1 Near or reaching target magnetic field strength T 0 。
In this embodiment, the reference magnetometer is disposed at the center of the magnetic shielding barrel, so as to mainly monitor the magnetic field strength of the environment of the magnetic shielding barrel, while the compensation coil is mainly used to generate a uniform compensation magnetic field in the magnetic shielding barrel, and offset the fluctuation of the magnetic field strength of the environment by the generated compensation magnetic field strength, and in addition, the magnetic shielding barrel is also provided with an induction magnetometer whose position is different from that of the reference magnetometer, which is mainly used to verify whether the magnetic field strength of other positions in the magnetic shielding barrel after compensation is close to the target magnetic field strength T 0 。
In an embodiment of the present invention, a signal processor includes:
the system comprises a magnetic noise detection module, a desired signal tracking module and a magnetic compensation amount processing module, wherein the magnetic noise detection module and the desired signal tracking module are connected with the magnetic compensation amount processing module, as shown in fig. 2.
(1) The magnetic noise monitoring module refers to the magnetic field intensity T acquired by the magnetometer 1 As feedback signal y, differential signal monitoring value y of feedback signal y is output 1 、y 2 Monitoring the total value y 3 。
The magnetic noise monitoring module is used for monitoring actual magnetic noise and total noise in the system, and the magnetic noise monitoring module can obtain the monitoring value of each state variable in the system only from the input quantity and the output quantity of the system without excessive information sources. Moreover, the magnetic noise monitoring module is used without considering the noise conditions inside and outside the system, and even if the magnetic noise monitoring module faces to an uncertain noise model, the magnetic noise monitoring module can also obtain the monitoring value of the total magnetic noise in real time, and meanwhile, the magnetic noise is compensated in feedback.
After receiving the feedback signal y, the magnetic noise monitoring module will perform differential signal y on the feedback signal y 1 、y 2 、y 3 Performing a tracking process in which：
y 1 ＝y′ 1 +q(y′ 2 -K 01 z′ 1 )；
Wherein K is 01 、K 02 、K 03 Three adjustable parameters; z'. 1 、z′ 2 、z′ 3 Respectively the monitoring value y 'of the feedback signal at the last moment' 1 、y′ 2 、y′ 3 A difference from the feedback signal y; q is a filtering factor, c is a constant, U' is a compensation voltage output by the signal processor at the previous moment,is a nonlinear function, and the expression is as follows:
wherein z is the difference between the monitored value of the feedback signal and the feedback signal, alpha is an adjustable parameter, the value range is 0-1, beta is a parameter factor, the parameter is adjustable, and sign is a sign function. Increasing the value of beta can increaseThe monitoring effect of the function can reduce the monitoring speed; decreasing the value of alpha can increase +.>The monitoring speed of the function will reduce the monitoring effect, so that the appropriate alpha and beta values can achieve the complementary effect according to different magnetic noise conditions.
When magnetic noise appears inside and outside the system, the magnetic noise monitoring module can change the state of the noise to make the noise inFirst order state, and then re-using the nonlinear function defined aboveAnd parameter K 01 、K 02 、K 03 And obtaining the monitoring values of all noise states inside and outside the system.
(2) The expected signal tracking module sets the target magnetic field intensity T 0 As the desired signal v, the desired signal v and the differential signal monitoring value v thereof are output 1 、v 2 ；
The expected signal tracking module extracts the needed magnetic signals according to the input characteristics of the magnetic field, reduces the jump of the input quantity of the magnetic field, and is convenient for the magnetic compensation system to track in real time. The expected signal tracking module can obtain a differential signal of magnetic noise in a feedback mode and carry out transition processing on the response of the magnetic field signal, so that the system can rapidly obtain compensation expected and ensure smaller overshoot. Finally, the range of object parameters adapted to the magnetic field feedback gain and the magnetic noise differential gain can be enlarged, so that the robustness of the magnetic compensation system is improved.
After receiving the desired signal v, the desired signal tracking module processes the desired signal v and the differential signal v thereof 1 、v 2 The above tracking process is performed in which:
v 1 ＝v′ 1 +qv′ 2 ；
v 2 ＝v′ 2 +qf(x 1 ,x 2 ,p,q)；
wherein v' 1 、v′ 2 Differential signal monitoring values, f (x) 1 ,x 2 P, q) is a discrete domain control function, two parameters, namely a tracking speed factor p and a filtering factor q, are set to a second order systemFor example, the discrete control function is:
y＝x 1 +qx 2 ；
m＝pq，m 0 ＝mq
wherein x is 1 、x 2 Is an intermediate parameter in a second order system.
(3) Differential signal monitoring value y of magnetic compensation quantity processing module based on feedback signal y 1 、y 2 Differential signal monitoring value v from desired signal v 1 、v 2 Is the difference of (2)To calculate the voltage compensation component u 0 And then based on the total monitored value y of magnetic noise 3 For the voltage compensation component u 0 And compensating to obtain the total compensation quantity U of the voltage, namely outputting the compensation voltage by the signal processor.
The magnetic compensation quantity processing module adopts a nonlinear controller structure independent of an object model, can automatically detect magnetic noise and give out a voltage compensation component, and can accurately reflect the change condition of the magnetic noise as long as the speed of the magnetic noise monitoring module is fast enough, and after the magnetic field variable integration is connected in series, the magnetic compensation quantity processing module can achieve an ideal control effect. In general, the magnetic compensation amount processing module is a nonlinear combination of magnetic field state variable errors generated by the desired signal tracking module and the magnetic noise monitoring module, which forms a compensation voltage together with a voltage compensation component of the magnetic noise monitoring module to the overall magnetic noise (monitored total value); wherein the voltage compensation component u 0 The calculation formula of (2) is specifically as follows:
wherein k is p Is a proportionality coefficient, k d As a result of the differential coefficient,wherein,
monitoring value y in magnetic noise monitoring module 1 And y 2 Will be fed back to the desired signal tracking module to generate a desired signal tracking value v 1 And v 2 The magnetic compensation quantity processing module calculates a compensation component u through the expected signal tracking value 0 While monitoring the total value y 3 Will also be given to the compensation component u in combination with the system coefficient c in the form of negative feedback 0 It can thus be seen that the output of the total amount of magnetic compensation U and the compensation component U 0 Constant c and total monitored value y of magnetic noise monitoring module 3 In relation, the expression is:
U＝u 0 -y 3 /c。
FIG. 3 is a flowchart of an active magnetic compensation method according to an embodiment of the present invention, which specifically includes the following steps:
(1) The set expected signal v is read at the beginning, and the feedback signal y at the last moment is also read, and the initial value of the feedback signal y defaults to zero.
(2) Waiting for the sampling time, the sampling time can be set to different values as required. When the sampling time is reached, the expected signal v enters the expected signal tracking module, the feedback signal y enters the magnetic noise monitoring module, and when the sampling time is not reached, the expected signal and the feedback signal continue to wait.
(3) After the expected signal tracking module receives the expected signal v, the expected signal v and the differential signal thereof are tracked, and then v is respectively used for 1 ＝v′ 1 +qv′ 2 、v 2 ＝v′ 2 +qf(x 1 ,x 2 P, q) output trace value v 1 And v 2 ；
(4) After receiving the feedback signal y, the magnetic noise monitoring module tracks the feedback signal y and its differential signal, and then uses y 1 ＝y′ 1 +q(y′ 2 -K 01 z′ 1 ) Andoutputting the monitored value y 1 And y 2 At the same time +.>Output of the total monitored value y of magnetic noise 3 ；
(5) Subsequently byAnd->Calculating deviation +.>And->Outputting a voltage compensation component u by a magnetic compensation amount processing module 0 Then extracting low-voltage compensation component and total monitoring value of magnetic noise to compensate magnetic noise, finally using U=u 0 -y 3 And/c outputting the compensation voltage U.
(6) The voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil so as to lead the magnetic field intensity T in the magnetic shielding barrel environment 1 Near or reaching target magnetic field strength T 0
The active magnetic compensation system is placed in a passive magnetic shielding environment, and the magnetic compensation method can be integrated in a signal processor after parameter setting, and can also be directly used for real-time parameter adjustment in an upper computer. The desired signal tracking module and the magnetic noise monitoring module in the present invention receive the digital signal from the ADC, which represents the magnetic field measurement in the real environment, and are called real in the feedback processAn inter-feedback signal. The magnetic noise monitoring module needs to track the differential signal monitoring value y according to the actual feedback signal 1 、y 2 Monitoring the total value y 3 The desired signal tracking module tracks a differential signal v of the desired signal v 1 、v 2 The magnetic compensation amount processing module is used for processing the magnetic compensation amount according to the difference amountAnd calculating the magnetic compensation quantity and outputting the calculated magnetic compensation quantity through a digital-to-analog converter. The schematic block diagram of the compensation algorithm in an active magnetic compensation system is shown in fig. 2.
Wherein, the magnetometer is responsible for collecting a magnetic field signal B OUT And apply the magnetic field signal B OUT Converted into a voltage signal V OUT The magnetic compensation algorithm embedded in the signal processor calculates the magnetic compensation amount U according to the set expected value, and the signal processor uses the voltage signal V to calculate the magnetic compensation amount U COMP Is output to the voltage-controlled current source, and the voltage-controlled current source outputs a corresponding current signal I COMP Inputting into a magnetic compensation coil, and finally generating a magnetic field B with the same size and opposite direction as the magnetic noise by the magnetic compensation coil COMP Thereby achieving the purpose of magnetic compensation.
While the present invention has been described by way of example, it should be apparent that the practice of the invention is not limited by the foregoing, but rather is intended to cover various insubstantial modifications of the method concepts and teachings of the invention, either as applied to other applications without modification, or as applied directly to other applications, without departing from the scope of the invention.
Claims (9)
1. An active magnetic compensation system, the system comprising:
the output end of the reference magnetometer is connected with the input end of the signal processor, and the output end of the signal processor is connected with the compensation coil through a voltage-controlled current source;
wherein, the reference magnetometer collects the magnetic field intensity T in the magnetic shielding barrel environment at regular time 1 And the magnetic field intensity T 1 Send to signalThe processor outputs the compensation voltage to the voltage-controlled current source, and the voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil so as to ensure that the magnetic field intensity T in the magnetic shielding barrel environment 1 Near or reaching target magnetic field strength T 0 。
2. The active magnetic compensation system of claim 1, wherein the signal processor comprises:
the magnetic noise monitoring module, the expected signal tracking module and the magnetic compensation processing module are connected with each other,
the magnetic noise monitoring module refers to the magnetic field intensity T acquired by the magnetometer 1 As feedback signal y, differential signal monitoring value y of feedback signal y is output 1 、y 2 Monitoring the total value y 3 ；
The expected signal tracking module sets the target magnetic field intensity T 0 As the desired signal v, the desired signal v and the differential signal monitoring value v thereof are output 1 、v 2 ；
Differential signal monitoring value y of magnetic compensation quantity processing module based on feedback signal y 1 、y 2 Differential signal monitoring value v from desired signal v 1 、v 2 Is the difference of (2)To calculate the voltage compensation component u 0 And then based on the total monitored value y of magnetic noise 3 For the voltage compensation component u 0 And compensating to obtain the total compensation quantity U of the voltage, namely outputting the compensation voltage by the signal processor.
3. The active magnetic compensation system of claim 1, wherein the voltage compensation component u 0 The calculation formula of (2) is specifically as follows:
wherein k is p Is a proportionality coefficient, k d As a result of the differential coefficient,as a nonlinear function, alpha 1 、α 2 The value of β is a constant which is 0 to 1.
4. The active magnetic compensation system of claim 4, wherein the total compensation amount U is calculated by the following formula:
U＝u 0 -y 3 /c
wherein c is a constant.
5. The active magnetic compensation system of claim 1, wherein the differential signal monitor value y of the feedback signal y 1 、y 2 Monitoring the total value y 3 The tracking formula of (2) is as follows:
y 1 ＝y′ 1 +q(y′ 2 -K 01 z′ 1 )；
wherein K is 01 、K 02 、K 03 Three adjustable parameters; z'. 1 、z′ 2 、z′ 3 Respectively the monitoring value y 'of the feedback signal at the last moment' 1 、y′ 2 、y′ 3 A difference from the feedback signal y; q is a filtering factor, c is a constant, U' is a compensation voltage output by the signal processor at the previous moment,as a nonlinear function.
6. The active magnetic compensation system of claim 5, wherein the nonlinear functionThe expression is specifically as follows:
wherein z is the difference between the monitored value of the feedback signal and the feedback signal, alpha is an adjustable parameter, the value range is 0-1, beta is a parameter factor, and sign is a sign function.
7. The active magnetic compensation system of claim 1, wherein a differential signal v of the desired signal v 1 、v 2 The tracking formula of (2) is as follows:
v 1 ＝v′ 1 +qv′ 2 ；
v 2 ＝v′ 2 +qf(x 1 ,x 2 ,p,q)；
wherein v' 1 、v′ 2 Differential signal monitoring values, f (x) 1 ,x 2 P, q) is a discrete domain control function.
8. The active magnetic compensation system of claim 1, wherein the discrete control function f (x 1 ,x 2 P, q) is specifically as follows:
y＝x 1 +qx 2 ；
m＝pq，m 0 ＝mq
wherein x is 1 、x 2 、m、n 0 、m 0 And p and q are respectively set tracking speed factors and filtering factors for intermediate parameters.
9. Active magnetic compensation method based on an active magnetic compensation system according to any of claims 1 to 8, characterized in that it comprises in particular the following steps:
(1) Reading a set expected signal v;
(2) When the sampling time is reached, the expected signal v enters an expected signal tracking module, and the feedback signal y enters a magnetic noise monitoring module;
(3) After the expected signal tracking module receives the expected signal v, the expected signal v and the differential signal thereof are tracked, and then v is respectively used for 1 ＝v′ 1 +qv′ 2 、v 2 ＝v′ 2 +qf(x 1 ,x 2 P, q) output trace value v 1 And v 2 ；
(4) After receiving the feedback signal y, the magnetic noise monitoring module tracks the feedback signal y and its differential signal, and then uses y 1 ＝y′ 1 +q(y′ 2 -K 01 z′ 1 ) Andoutputting the monitored value y 1 And y 2 At the same time +.>Output of the total monitored value y of magnetic noise 3 ；
(5) To be used forAnd->Calculating deviation +.>And->Outputting a voltage compensation component u by a magnetic compensation amount processing module 0 Then extracting the low-voltage compensation component and the total monitored value y 3 Compensating for magnetic noise with u=u 0 -y 3 C outputting a compensation voltage U;
(6) The voltage-controlled current source converts the compensation voltage into the compensation current of the compensation coil so as to lead the magnetic field intensity T in the magnetic shielding barrel environment 1 Near or reaching target magnetic field strength T 0 。
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