CN115877293A - Gradient power amplifier control device and gradient power amplifier - Google Patents

Abstract

The present application relates to a control device of a gradient power amplifier and a gradient power amplifier. The control device includes: a first differential module, which is used to differentiate the expected current to form a second adjustment signal; The difference between the output current of the output current and the expected current is generated to generate a difference signal; the adjustment module is used to perform proportional integral adjustment on the difference signal to generate a first adjustment signal; the first summation module is used to adjust the signal according to the first and the second The adjustment signal generates a first control signal, and the output current of the gradient power amplifier is controlled by the first control signal. The control device can improve the control accuracy of the output current of the gradient power amplifier, and reduce the image quality problem caused by the change of the equivalent load inductance of the gradient power amplifier.

Description

Gradient power amplifier control device and gradient power amplifier

technical field

The present application relates to the technical field of medical equipment, in particular to a control device for a gradient power amplifier and the gradient power amplifier.

Background technique

Magnetic resonance imaging equipment is a type of tomography, which uses magnetic resonance phenomena to obtain electromagnetic signals from the human body and reconstruct human body information. Magnetic resonance imaging equipment applies a radio frequency pulse of a certain frequency to the human body in a static magnetic field, so that the hydrogen protons in the human body are excited and magnetic resonance occurs. After the pulse is stopped, the protons generate magnetic resonance signals during relaxation. Corresponding magnetic resonance signals are obtained, and image reconstruction is performed on the magnetic resonance signals to obtain medical images. Magnetic resonance imaging (MRI) is a very powerful imaging method. This technology can obtain high-contrast and clear images inside the sample/tissue without damage and ionizing radiation, and has been widely used in various fields, especially in medical diagnosis. Compared with other auxiliary imaging methods, MRI has the advantages of multiple imaging parameters, fast scanning speed, high tissue resolution and clearer images. It can detect early lesions and has become a sharp tool for early screening of tumors, heart disease and cerebrovascular diseases.

The gradient filter is an indispensable component in the magnetic resonance imaging equipment. The gradient filter is located between the gradient power amplifier and the gradient coil, and its function is to prevent the noise between the equipment from interfering with the scanning room. The gradient filter and the gradient coil together constitute the control object of the gradient power amplifier. When the gradient coil generates an alternating gradient magnetic field, it will couple eddy currents in its shielding layer. In terms of gradient power amplifiers, their equivalent load inductance will change due to coupling and other reasons, which will affect the imaging quality.

Contents of the invention

Based on this, it is necessary to provide a control device for a gradient power amplifier and a gradient power amplifier for improving the imaging quality in view of the above technical problems.

A control device for a gradient power amplifier, comprising:

The first differential module is connected to the expected current of the gradient power amplifier, and the expected current is subjected to differential processing through the differential model of the first differential module to form a second adjustment signal;

The difference module is connected to the expected current of the gradient power amplifier, and is coupled to the output terminal of the gradient power amplifier, and is used to make a difference between the output current of the gradient power amplifier and the expected current to generate a difference signal;

An adjustment module, coupled to the output terminal of the difference seeking module, for performing proportional-integral adjustment on the difference signal to generate a first adjustment signal;

The first summation module is coupled to the adjustment module and the first differential module respectively, and is used to generate a first control signal according to the first adjustment signal and the second adjustment signal, and control the gradient power amplifier through the first control signal output current.

In one of the embodiments, the difference module includes a first input terminal, a second input terminal and an output terminal;

The first input terminal is connected to the expected current;

The second input terminal is connected to the output terminal of the gradient power amplifier;

The output end is connected to the adjustment module, and is used to make a difference between the output current of the gradient power amplifier and the expected current to generate the difference signal.

In one of the embodiments, the differential model of the first differential module includes a first-order differential model and/or a higher-order differential model, and the differential model includes a first variable parameter;

If the equivalent inductance increases in the equivalent load model of the gradient power amplifier, then the first variable parameter is a positive real number greater than 1; if the equivalent inductance decreases in the equivalent load model of the gradient power amplifier, then the The first variable parameter is a positive real number less than 1.

In one of the embodiments, the differential model of the first differential module is K ₁ *L ₁ *s;

Among them, K ₁ is the first variable parameter obtained from the measured waveform, L ₁ is the equivalent inductance of the gradient power amplifier, and s is the operator of the pull transformation.

In one of the embodiments, the equivalent load of the gradient power amplifier includes multiple zero-pole points, and the differential model of the first differential module is:

Among them, C _grd is the capacitance of the gradient filter, R is the equivalent resistance of the gradient power amplifier, _L is the equivalent inductance of the gradient power amplifier, and s is the operator of the pull transformation.

In one of the embodiments, the control device also includes:

The first resistance module is used to access the expected current of the gradient power amplifier, and the expected current and the resistance of the first resistance module can obtain an expected voltage;

A second summation module, coupled to the first resistance module and the first differential module, for generating a third adjustment signal according to the expected voltage and the second adjustment signal;

The first summation module is further configured to generate a first control signal according to the third adjustment signal and the first adjustment signal, and control the output current of the gradient power amplifier through the first control signal. In one of the embodiments, the control device also includes:

The second resistance module is connected to the expected current of the gradient power amplifier, and is used to obtain the expected voltage according to the expected current and the resistance of the second resistance module;

The first summation module is respectively coupled to the second resistance module and the adjustment module, and is used to generate a first control signal according to the expected voltage and the first adjustment signal;

A third summation module, coupled to the first summation module and the first differential module, respectively, for generating a second control signal according to the first control signal and the second adjustment signal;

A second differential module, coupled to the output terminal of the first differential module, for performing differential processing on the second adjustment signal to generate a third adjustment signal;

The fourth summation module is respectively coupled to the third summation module and the second differential module, and is used to generate a third control signal according to the third adjustment signal and the second control signal, and control the third control signal through the third control signal The output current of the gradient power amplifier.

In one of the embodiments, the second differential module includes a differential model, and the second differential module includes a differential model for performing differential processing on the second adjustment signal to generate the third adjustment signal;

The differential model of the second differential module is K ₂ *, wherein, ₂ is the second variable parameter and obtained through the measured waveform, and s is the operator of the pull transformation;

If the equivalent inductance in the equivalent load model of the gradient power amplifier increases, the second variable parameter is a positive real number;

If the equivalent inductance in the equivalent load model of the gradient power amplifier decreases, the second variable parameter is a negative real number.

In one of the embodiments, the control device also includes:

A delay module, connected to the difference module, the delay module is used to access the expected current of the gradient power amplifier, delay the expected current, generate a delayed expected current, and transmit the delayed expected current to the difference module;

The difference module is configured to access the delayed expected current and be coupled to the output terminal of the gradient power amplifier, and is used to generate the difference signal by combining the output current of the gradient power amplifier with the delayed expected current.

A gradient power amplifier, comprising a gradient power amplifier and any one of the control devices described above.

In the above implementation process, the second adjustment signal is generated by performing differential processing on the expected current through the first differential module, and the difference between the output current of the gradient power amplifier and the expected current is generated through the difference module to generate a difference signal, and the difference is generated through the adjustment module The proportional-integral adjustment of the value signal is performed to generate a first adjustment signal. Further, the first control signal is generated by the summation module according to the first adjustment signal and the second adjustment signal, and the output current of the gradient power amplifier is controlled by the first control signal. By The above control device can improve the control accuracy of the output current of the gradient power amplifier, thereby reducing the image quality problems caused by the change of the equivalent load inductance of the gradient power amplifier, thereby improving the imaging quality.

Description of drawings

Fig. 1 is the schematic diagram of the control device of gradient power amplifier in an embodiment;

Fig. 2 is the schematic diagram of the control device of gradient power amplifier in another embodiment;

Fig. 3 is the schematic diagram of the control device of gradient power amplifier in another embodiment;

Fig. 4 is the equivalent load model of gradient power amplifier in an embodiment;

Fig. 5 is the electromagnetic coupling schematic diagram of gradient coil and PET module shielding layer in an embodiment;

Fig. 6 is a schematic diagram of the change of equivalent load inductance with the rate of change of current in one embodiment;

Fig. 7 is the schematic diagram of each control component in an embodiment;

Fig. 8 is an output waveform obtained by different control schemes in an embodiment.

Reference signs: first differential module 1, adjustment module 2, difference module 3, first summation module 4, gradient power amplifier 5, first resistance module 6, second summation module 7, second resistance module 8, The third summation module 9 , the second differential module 10 , and the fourth summation module 11 .

Detailed ways

In order to facilitate the understanding of the present application, and to make the above-mentioned purpose, features and advantages of the present application more obvious and understandable, the specific implementation manners of the present application will be described in detail below in conjunction with the accompanying drawings. In the following description, numerous specific details are set forth to facilitate a full understanding of the application, and preferred embodiments of the application are shown in the accompanying drawings. However, the present application can be embodied in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the application more thorough and comprehensive. The present application can be implemented in many other ways that are different from those described here, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present application, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined. In the description of the present application, "several" means at least one, such as one, two, etc., unless otherwise specifically defined.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein are for the purpose of describing specific embodiments only, and are not intended to limit the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Positron Emission Tomography (PET) is a relatively advanced clinical examination imaging technology in the field of nuclear medicine. The principle is to inject a certain substance, generally a necessary substance in the metabolism of biological life, such as glucose, protein, nucleic acid, fatty acid, and a short-lived radionuclide (such as 18F, 11C, etc.) into the human body, the radionuclide A positron is released during the decay process, and a positron encounters an electron after traveling a few tenths of a millimeter to a few millimeters and then annihilates, resulting in two gamma photons of equal energy and opposite directions. Due to the different paths of the two gamma photons in the body, the arrival time of the two PET detectors also has a certain difference. If the probe system on the response line detects two photons at 180 degrees to each other within the specified time window, Once a coincidence event is formed, the processing device will record the response data, and use the recorded response data to obtain the required PET image through image reconstruction technology.

Nuclear magnetic resonance (magnetic resonance, MR) examination is to place the human body in a special magnetic field, and use radio frequency pulses to excite the hydrogen nuclei in the human body, causing the hydrogen nuclei to resonate and absorb energy. After the radio frequency pulse is stopped, the hydrogen nucleus emits a radio signal at a specific frequency, and releases the absorbed energy, which is collected by an external receiver and processed by an electronic computer to obtain an image, which is called nuclear magnetic resonance imaging. MRI has completely got rid of the damage of ionizing radiation to the human body, and has many parameters, large amount of information, multi-directional imaging, and high resolution of soft tissues. It is widely used in the diagnosis of clinical diseases. Lesions become an essential inspection method.

PET-MR is a large-scale functional metabolic and molecular imaging diagnostic equipment that combines positron emission tomography imaging equipment and nuclear magnetic resonance equipment. In the PET-MR system, there is electromagnetic coupling between the gradient coil and the shielding layer of the PET module. From the perspective of the gradient power amplifier, its equivalent load inductance will increase or decrease due to the degree of coupling.

In one embodiment, as shown in FIG. 1 , FIG. 1 is a schematic diagram of a control device for a gradient power amplifier. The control device includes: a difference module 3, connected to the expected current of the gradient power amplifier 5, and coupled to the output terminal of the gradient power amplifier 5, for making a difference between the output current of the gradient power amplifier and the expected current, and generating a difference signal; an adjustment module 2, coupled to the output terminal of the difference seeking module 3, for performing proportional-integral adjustment on the difference signal to generate a first adjustment signal; the first differential module 1, connected to the expected gradient power amplifier The current is used to perform differential processing on the expected current through a differential model to form a second adjustment signal; the first summation module 4 is respectively coupled to the adjustment module 2 and the first differential module 1, and is used to adjust according to the first signal and the second adjustment signal generate a first control signal, through which the output current of the gradient power amplifier is controlled.

In one of the embodiments, a control device for a gradient power amplifier is provided, and the gradient power amplifier is applied to occasions where the load has electromagnetic coupling; the control device includes a load model, and the load model includes variable parameters, so The above variable parameters are changed according to the degree of coupling.

Specifically, the gradient power amplifier is applied to the scenario where there is electromagnetic coupling between the gradient coil and the shielding layer of the PET module. The control device includes a load model, wherein the load model includes a differential model of differential control in the control device, and the load model includes a first-order differential model and/or a higher-order differential model. By adjusting the variable parameters of the load model, and then adjusting the output current of the gradient power amplifier, the image quality problem caused by the change of the equivalent load inductance of the gradient power amplifier is reduced.

In one of the embodiments, the control device includes a first differential module and/or a second differential module, the first differential module includes a first differential model, and the second differential module includes a second differential model; the first differential module includes a second differential model; The differential model and the second differential model are calculated based on the equivalent load model of the gradient power amplifier.

More specifically, the control device may be provided with one differential module, or may be provided with two differential modules, or may be provided with multiple differential modules. Each of the differential modules includes variable parameters. By adjusting the variable parameters, the output current of the gradient power amplifier is adjusted, thereby reducing image quality problems caused by changes in the equivalent load inductance of the gradient power amplifier. Setting two differentiating modules can better reduce the influence brought by the change of equivalent load inductance.

Specifically, the first input terminal of the difference seeking module 3 is connected to the expected current, the second input terminal of the difference seeking module 3 is connected to the output terminal of the gradient power amplifier 5, and the output terminal of the difference seeking module 3 is connected to the input terminal of the adjustment module 2 connected to make a difference between the output current of the gradient power amplifier 5 and the expected current to generate a difference signal; the output terminal of the adjustment module 2 is connected to the first input terminal of the first summation module 4 for performing difference signal Proportional-integral adjustment to generate a first adjustment signal; the input terminal of the first differential module 1 is connected to the expected current, and the output terminal of the first differential module 1 is connected to the second input terminal of the first summation module 4 for the expected current to pass through The differential model carries out differential processing to form the second adjustment signal; the output end of the first summation module 4 is connected with the gradient power amplifier 5, and is used to generate the first control signal according to the first adjustment signal and the second adjustment signal, through the The first control signal controls the output current of the amplifier. Among them, I is the expected current, and I ₀ is the output current of the gradient power amplifier 5 . According to the increase or decrease of the equivalent inductance in the equivalent load model of the gradient power amplifier 5, the variable parameters of the differential model are adjusted. The differential model of the first differential module includes a first-order differential model and/or a higher-order differential model, and the differential model includes a first variable parameter, and the first variable parameter performs an algebraic operation with the first differential model; if the gradient power If the equivalent inductance increases in the equivalent load model of the amplifier 5, then the first variable parameter is a positive real number greater than 1; if the equivalent inductance decreases in the equivalent load model of the gradient power amplifier 5, then the first variable parameter can be Change the parameter to a positive real number less than 1. Wherein, the algebraic operation may be one or a combination of operations such as addition, subtraction, multiplication, and division. The above control device can improve the control accuracy of the gradient power amplifier, and reduce the image quality problems caused by the change of the equivalent load inductance of the gradient power amplifier.

In one embodiment, as shown in FIG. 2 , FIG. 2 is a schematic diagram of another control device for a gradient power amplifier. The control device also includes on the basis of Fig. 1: a first resistance module 6 and a second summation module 7; the first resistance module 6 is connected to the expected current of the gradient power amplifier 5, and is used for according to the expected current and The resistance of the first resistance module 6 obtains the expected voltage; the second summation module 7 is respectively coupled to the first resistance module 6 and the first differential module 1, and is used to generate a third voltage according to the expected voltage and the second adjustment signal. Regulating signal; the first summation module 4 is further configured to generate a first control signal according to the third regulating signal and the first regulating signal, and control the output current of the gradient power amplifier 5 through the first control signal.

More specifically, the first input terminal of the difference seeking module 3 is connected to the expected current of the gradient power amplifier 5, the second input terminal of the difference seeking module 3 is connected to the output terminal of the gradient power amplifier 5, and the output terminal of the difference seeking module 3 is connected to the output terminal of the gradient power amplifier 5. The input end of the adjustment module 2 is connected to make a difference between the output current of the gradient power amplifier 5 and the expected current to generate a difference signal; the output end of the adjustment module 2 is connected to the first input end of the first summation module 4 for use To carry out proportional-integral adjustment to the differential signal, generate the first adjustment signal; the input terminal of the first differential module 1 is connected to the expected current of the gradient power amplifier 5, and the output terminal of the first differential module 1 is connected to the output terminal of the second summation module 7 The second input terminal connection is used for the expected current to be differentially processed through the differential model to form the second adjustment signal; the input terminal of the first resistance module 6 is connected to the expected current of the gradient power amplifier 5, and the output terminal of the first resistance module 6 is connected to the first resistance module 6. The first input terminal of two summing modules 7 is connected, and is used to obtain the expected voltage according to the resistance of the expected current and the first resistance module 6; The input end is connected to generate a third adjustment signal according to the expected voltage and the second adjustment signal; the output end of the first summation module 4 is connected to the gradient power amplifier 5, and is used to generate the third adjustment signal according to the third adjustment signal and the first adjustment signal. The adjustment signal generates a first control signal by which the output current of the amplifier is controlled. The differential model of the first differential module includes a first-order differential model and/or a higher-order differential model, and the differential model includes a first variable parameter, and the first variable parameter performs an algebraic operation with the first differential model; if the gradient power If the equivalent inductance increases in the equivalent load model of the amplifier 5, then the first variable parameter is a positive real number greater than 1; if the equivalent inductance decreases in the equivalent load model of the gradient power amplifier 5, then the first variable parameter can be Change the parameter to a positive real number less than 1. Wherein, the algebraic operation may be one or a combination of operations such as addition, subtraction, multiplication, and division. The value of the first resistance module 6 is the resistance of the gradient coil. The above-mentioned control device can use the reduced first-order differential to reduce the error of the output current of the gradient power amplifier, improve the control accuracy of the gradient power amplifier, and reduce the image quality problems caused by the change of the equivalent load inductance of the gradient power amplifier. .

In one embodiment, as shown in FIG. 3 , FIG. 3 is a schematic diagram of another control device for a gradient power amplifier. The control device also includes on the basis of FIG. 1: a second resistance module 8, a third summation module 9, a second differential module 10, and a fourth summation module 11; the second resistance module 8 is connected to a gradient power amplifier The expected current of 5 is used to obtain the expected voltage according to the expected current and the resistance of the second resistance module 8; the first summation module 4 is respectively coupled to the second resistance module 8 and the adjustment module 2 for Generate a first control signal according to the expected voltage and the first adjustment signal; the third summation module 9 is respectively coupled to the first summation module 4 and the first differential module 1, for according to the first control signal And the second adjustment signal generates a second control signal; the second differentiation module 10 is coupled to the output terminal of the first differentiation module 1, and is used to perform differential processing on the second adjustment signal to generate a third adjustment signal; the fourth A summation module 11, coupled to the third summation module 9 and the second differential module 10, respectively, for generating a third control signal according to the third adjustment signal and the second control signal, through the third control signal The output current of the gradient power amplifier 5 is controlled.

More specifically, the first input terminal of the difference seeking module 3 is connected to the expected current of the gradient power amplifier 5, the second input terminal of the difference seeking module 3 is connected to the output terminal of the gradient power amplifier 5, and the output terminal of the difference seeking module 3 is connected to the output terminal of the gradient power amplifier 5. The input end of the adjustment module 2 is connected to make a difference between the output current of the gradient power amplifier 5 and the expected current to generate a difference signal; the output end of the adjustment module 2 is connected to the first input end of the first summation module 4 for use To carry out proportional-integral adjustment to the differential signal, generate the first adjustment signal; the input terminal of the first differential module 1 is connected to the expected current of the gradient power amplifier 5, and the output terminal of the first differential module 1 is connected to the output terminal of the second differential module 10 respectively. The input end and the first input end connection of the third summation module 9 are used for the expected current to be differentially processed by the differential model to form the second adjustment signal; the input end of the first resistance module 6 is connected to the expected current of the gradient power amplifier 5, The output terminal of the first resistance module 6 is connected with the second input terminal of the first summation module 4, for obtaining the expected voltage according to the resistance of the expected current and the first resistance module 6; the output terminal of the first summation module 4 It is connected with the second input end of the third summing module 9, and is used to generate the first control signal according to the expected voltage and the first regulation signal; the output end of the second differential module 10 is connected with the first input end of the fourth summing module 11 The input end is connected, and is used for generating the third adjustment signal by differential processing to the second adjustment signal; the output end of the third summation module 9 is connected with the second input end of the fourth summation module 11, and is used for according to the described The first control signal and the second adjustment signal generate the second control signal; the output end of the fourth summation module 11 is connected with the gradient power amplifier 5, for generating the third control signal according to the third adjustment signal and the second control signal , the output current of the gradient power amplifier 5 is controlled by the third control signal. Wherein, the first differential module 1 includes a first differential model, and the second differential module 10 includes a second differential model; the first differential model includes a first-order differential model and/or a higher-order differential model, and the second differential model includes First-order differential models and/or higher-order differential models. The first differential model includes a first variable parameter, and the first variable parameter and the first differential model perform an algebraic operation; if the equivalent inductance in the equivalent load model of the gradient power amplifier 5 increases, the first The variable parameter is a positive real number greater than 1; if the equivalent inductance in the equivalent load model of the gradient power amplifier 5 decreases, the first variable parameter is a positive real number smaller than 1. The second differential model includes a second variable parameter, and the second variable parameter performs an algebraic operation with the second differential model; if the equivalent inductance in the equivalent load model of the gradient power amplifier 5 increases, the second The variable parameter is a positive real number; if the equivalent inductance in the equivalent load model of the gradient power amplifier 5 decreases, the second variable parameter is a negative real number. Wherein, the algebraic operation may be one or a combination of operations such as addition, subtraction, multiplication, and division. The value of the second resistance module 8 is the resistance of the gradient coil. The above-mentioned control device can use the reduced first-order differential and second-order differential to further reduce the error of the output current of the gradient power amplifier on the basis of the reduced first-order differential, improve the control accuracy of the gradient power amplifier, and reduce the error caused by The equivalent load inductance of the gradient power amplifier changes, which brings about image quality problems.

其中，C_grd为梯度滤波器电容、R梯度功率放大器等效电阻、L₁为梯度功率放大器等效电感、s为s为拉式变换的算子。In one of the embodiments, the gradient power amplifier equivalent load model considering the gradient filter capacitance is shown in Figure 4. When the gradient filter capacitance connected to the gradient power amplifier and the gradient coil is not negligible, under the action of the capacitance, The equivalent load of the gradient power amplifier includes multiple zero-pole points. In this embodiment, the control device shown in FIG. 1 is used to propose a feed-forward control scheme including multiple zero-pole points, wherein the differential model of the first differential module can be:

Among them, C _grd is the capacitance of the gradient filter, R is the equivalent resistance of the gradient power amplifier, L ₁ is the equivalent inductance of the gradient power amplifier, and s is the operator of the pull transformation.

In one embodiment, in the PET-MR system, there is electromagnetic coupling between the gradient coil and the shielding layer of the PET module, and when the gradient coil generates an alternating gradient magnetic field, eddy currents will be coupled out of the shielding layer of the PET module. In particular, in the PET-MR system, dozens of PET modules are installed near the gradient coils, and each module is covered by a copper foil shield, which intensifies the coupling effect. This effect changes the equivalent load of the gradient power amplifier. The gradient current forms a gradient magnetic field, which passes through the shielding layer to generate an induced current. The direction of the magnetic field generated by the induced current is opposite to the direction of the gradient magnetic field, so that the total magnetic field generated by the gradient power amplifier is partially offset. Therefore, in the view of the gradient power amplifier, The equivalent load inductance is reduced. When the coupling effect is severe, there is a large distortion in the gradient current, which affects the imaging quality. As shown in Figure 5, where L ₁ and I ₁ are the gradient coil self-inductance and gradient current respectively, L ₂ , R ₂ and I ₂ respectively represent the equivalent self-inductance, equivalent resistance and equivalent current of the PET module shielding layer, M is the mutual inductance coefficient. According to Figure 5, the following equation can be obtained (neglecting the coil impedance):

Among them, s is the operator of the pull transformation, which represents the rate of change of the current, U ₁ is the voltage of the gradient coil; U ₂ is the voltage of the shielding layer of the PET module. The shielding layer is closed at the end, and U ₂ =0, then:

Substituting it into formula (1), we can get:

That is, the equivalent inductive load of the gradient power amplifier is:

Among them, M ² ≤ L ₁ L ₂ , when the conversion rate of current I ₁ is very large, the impedance of the shielding layer can be ignored, as follows:

Extending it to N PET modules without loss of generality, assuming that the parameters of the PET module itself are the same, and the mutual inductance of the gradient coil is the same, and the mutual inductance between the modules can be ignored, then:

It can be seen from equations (5) and (6) that under the coupling effect of the gradient coil and the shielding layer of the PET module, the equivalent load inductance faced by the gradient power amplifier decreases, and the degree of reduction is proportional to the number of PET modules. As shown in Figure 6, a schematic diagram of the change of the equivalent load inductance with the rate of change of the current is given. This embodiment uses the control device shown in Figure 2 to propose a reduced first-order differential feedforward control scheme, wherein the differential model of the first differential module can be K ₁ *L ₁ *s, where K ₁ is the first possible variable parameters, the first variable parameter is a positive real number less than 1, and K ₁ can be obtained through the measured waveform. Specifically, change the value of K ₁ up and down, observe the current error displayed by the oscilloscope, and take the first variable parameter corresponding to when the absolute value of the error peak value is minimum.

In one of the embodiments, for severe electromagnetic coupling between the gradient coil and the shielding layer of the PET module, it is not enough to use only the reduced first-order differential feed-forward control. As shown in Figure 6, within the range of the current change rate (S _p -S _z ), the equivalent load inductance decreases with the increase of the current climbing rate, and the differential control amount needs to be reduced even more. At this time, only adjustment The value of the first variable parameter is insufficient to minimize the control error. Based on this, this embodiment uses the control device shown in Figure 3 to propose a second-order differential feedforward control scheme, where the differential model of the first differential module can be K ₁ *L ₁ *s, where K ₁ is the first Variable parameters, the first variable parameter is a positive real number less than 1, and K ₁ can be obtained through the measured waveform. Specifically, change the value of K ₁ up and down, observe the current error displayed by the oscilloscope, and take the first variable parameter corresponding to when the absolute value of the error peak value is minimum. Wherein, the differential model of the second differential module may be K ₂ *s, wherein K ₂ is a second variable parameter, and the second variable parameter is a negative real number. K ₂ can be obtained by measuring the waveform. Specifically, change the value of _K2 up and down, observe the current error displayed by the oscilloscope, and take the second variable parameter corresponding to when the absolute value of the error peak value is minimum. As shown in FIG. 7, FIG. 7 is a schematic diagram of each control component in this embodiment. It can be seen from Figure 7 that when the current rises from 0, the second-order differential generates negative narrow pulses, thereby limiting the rate of rise of the load current.

As shown in Figure 8, Figure 8 shows the output waveforms obtained by different control schemes. Line 1 in the figure represents the gradient current; line 2 in the figure represents the current tracking error using traditional feedforward control; line 3 in the figure represents the current tracking error using the first-order differential The current error of the feedforward control (the control method shown in Figure 2); the line 4 in the figure represents the current error of the first-order differential and second-order differential feedforward control (the control method shown in Figure 3). It can be seen from Figure 8 that the feedforward control current error of the first-order differential and second-order differential (control mode shown in Figure 3) is the smallest.

In one of the embodiments, on the basis of the control method in Figure 3, the first variable parameter can be directly adjusted without adjusting the second variable parameter, and then the output current of the gradient power amplifier can be adjusted, thereby reducing the Image quality problems caused by changes in equivalent load inductance.

In one of the embodiments, before the difference seeking module is connected to the expected current, the expected current can first pass through the delay module, and the delay module delays the expected current signal for a period of time before sending it to the difference seeking module, the function is to offset the closed-loop control loop delay.

In one of the embodiments, a gradient power amplifier is provided, including the gradient power amplifier and any control device for the above gradient power amplifier.

In one of the embodiments, a PET-MR device is provided, including the above-mentioned gradient power amplifier, gradient coil and shielding assembly; when there is electromagnetic coupling between the gradient coil and the shielding assembly, the first differential module can The variable parameter is a positive real number less than 1, and the second variable parameter of the second differential module is a negative real number.

The technical features of the above embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be It is considered to be within the range described in this specification.

The above-mentioned embodiments only represent several implementation modes of the present application, and the description thereof is relatively specific and detailed, but it should not be construed as limiting the scope of the patent for the invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the scope of protection of the patent application should be based on the appended claims.

Claims (10)

1. A control device for a gradient power amplifier, comprising: The first differential module is connected to the expected current of the gradient power amplifier, and the expected current is subjected to differential processing through the differential model of the first differential module to form a second adjustment signal; The difference module is connected to the expected current of the gradient power amplifier, and is coupled to the output terminal of the gradient power amplifier, and is used to make a difference between the output current of the gradient power amplifier and the expected current to generate a difference signal; An adjustment module, coupled to the output terminal of the difference seeking module, for performing proportional-integral adjustment on the difference signal to generate a first adjustment signal; The first summation module is coupled to the adjustment module and the first differential module respectively, and is used to generate a first control signal according to the first adjustment signal and the second adjustment signal, and control the gradient power amplifier through the first control signal output current. 2. the control device of gradient power amplifier according to claim 1, is characterized in that, described difference module comprises first input end, second input end and output end; The first input terminal is connected to the expected current; The second input terminal is connected to the output terminal of the gradient power amplifier; The output end is connected to the adjustment module, and is used to make a difference between the output current of the gradient power amplifier and the expected current to generate the difference signal. 3. The control device of the gradient power amplifier according to claim 1, wherein the differential model of the first differential module comprises a first-order differential model and/or a high-order differential model, and the differential model comprises a first variable parameter ; If the equivalent inductance increases in the equivalent load model of the gradient power amplifier, then the first variable parameter is a positive real number greater than 1; if the equivalent inductance decreases in the equivalent load model of the gradient power amplifier, then the The first variable parameter is a positive real number less than 1. 4. the control device of gradient power amplifier according to claim 3, is characterized in that, The differential model of the first differential module is K ₁ *L ₁ *s; Among them, K ₁ is the first variable parameter obtained from the measured waveform, L ₁ is the equivalent inductance of the gradient power amplifier, and s is the operator of the pull transformation. 5. the control device of gradient power amplifier according to claim 1, is characterized in that, the equivalent load of described gradient power amplifier comprises a plurality of zero poles, and the differential model of described first differential module is:

Among them, C _grd is the capacitance of the gradient filter, R is the equivalent resistance of the gradient power amplifier, _L is the equivalent inductance of the gradient power amplifier, and s is the operator of the pull transformation. 6. the control device of gradient power amplifier according to claim 1, is characterized in that, described control device also comprises: The first resistance module is used to access the expected current of the gradient power amplifier, and the expected current and the resistance of the first resistance module can obtain an expected voltage; A second summation module, coupled to the first resistance module and the first differential module, for generating a third adjustment signal according to the expected voltage and the second adjustment signal; The first summation module is further configured to generate a first control signal according to the third adjustment signal and the first adjustment signal, and control the output current of the gradient power amplifier through the first control signal. 7. the control device of gradient power amplifier according to claim 1, is characterized in that, described control device also comprises: The second resistance module is connected to the expected current of the gradient power amplifier, and is used to obtain the expected voltage according to the expected current and the resistance of the second resistance module; The first summation module is respectively coupled to the second resistance module and the adjustment module, and is used to generate a first control signal according to the expected voltage and the first adjustment signal; A third summation module, coupled to the first summation module and the first differential module, respectively, for generating a second control signal according to the first control signal and the second adjustment signal; A second differential module, coupled to the output terminal of the first differential module, for performing differential processing on the second adjustment signal to generate a third adjustment signal; The fourth summation module is respectively coupled to the third summation module and the second differential module, and is used to generate a third control signal according to the third adjustment signal and the second control signal, and control the third control signal through the third control signal The output current of the gradient power amplifier. 8. The control device of the gradient power amplifier according to claim 7, wherein the second differential module includes a differential model, and the second differential module includes a differential model for differentiating the second adjustment signal processing to generate said third conditioning signal; The differential model of the second differential module is K ₂ *s, wherein, K ₂ is the second variable parameter and obtained by the measured waveform, and s is the operator of the pull transformation; If the equivalent inductance in the equivalent load model of the gradient power amplifier increases, the second variable parameter is a positive real number; If the equivalent inductance in the equivalent load model of the gradient power amplifier decreases, the second variable parameter is a negative real number. 9. The control device of the gradient power amplifier according to any one of claims 1-8, wherein the control device further comprises: A delay module connected to the difference module, the delay module is used to access the expected current of the gradient power amplifier, delay the expected current, generate a delayed expected current, and transmit the delayed expected current to the difference module; The difference module is configured to access the delayed expected current and be coupled to the output terminal of the gradient power amplifier, and is used to generate the difference signal by combining the output current of the gradient power amplifier with the delayed expected current. 10. A gradient power amplifier, characterized by comprising a gradient power amplifier and the control device according to any one of claims 1-9.

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