CN111208460B - Method for prolonging service life of gradient power amplifier and monitoring device of gradient power amplifier - Google Patents

Method for prolonging service life of gradient power amplifier and monitoring device of gradient power amplifier Download PDF

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CN111208460B
CN111208460B CN202010076537.1A CN202010076537A CN111208460B CN 111208460 B CN111208460 B CN 111208460B CN 202010076537 A CN202010076537 A CN 202010076537A CN 111208460 B CN111208460 B CN 111208460B
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林应锋
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Neusoft Medical Systems Co Ltd
Shanghai Neusoft Medical Technology Co Ltd
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Abstract

The embodiment of the invention provides a method for prolonging the service life of a gradient power amplifier and a monitoring device of the gradient power amplifier. The gradient power amplifier comprises X, Y, Z axis gradient power amplifiers which are respectively used for controlling the current of the X, Y, Z axis gradient coil. The method comprises the following steps: determining key components for restricting X, Y, Z the service life of the axial gradient power amplifier; establishing X, Y, Z a model of a key component of the axial gradient power amplifier, wherein the model takes the current of a gradient coil of a corresponding axis as input, and the output of the model is used for predicting the performance of the key component; in a preset period, current of an X, Y, Z-axis gradient coil during the work of the gradient power amplifier is obtained every other preset time period, and based on a model, output values of models corresponding to X, Y, Z axes are respectively calculated; predicting the value difference of the output value on an X, Y, Z axis in a preset period; and interchanging gradient power amplifiers of at least two axes when a preset period comes on the basis of the value difference of the output values on the X, Y, Z axes.

Description

Method for prolonging service life of gradient power amplifier and monitoring device of gradient power amplifier
Technical Field
The embodiment of the invention relates to the technical field of medical equipment, in particular to a method for prolonging the service life of a gradient power amplifier and a monitoring device of the gradient power amplifier.
Background
An MRI (magnetic Resonance Imaging) system obtains electromagnetic signals from a human body by using a magnetic Resonance phenomenon and reconstructs human body information, and is one of the most advanced medical Imaging means at present.
The gradient power amplifier is a core component of the MRI system, is used for driving a gradient coil and is responsible for spatial position coding required by MRI imaging. The gradient power amplifier provides a current imaging sequence with a specific waveform to the gradient coil, so that the gradient coil generates a gradient magnetic field which changes linearly in an imaging space. An Insulated Gate Bipolar Transistor (IGBT) module is a main component element of a gradient power amplifier. When current flows through the IGBT module, the IGBT module generates losses. Fig. 1 shows a waveform diagram of IGBT losses as a function of gradient coil current. The change in IGBT losses when the gradient coil current jumps from 10A to 400A is shown in fig. 1. As is clear from fig. 1, the IGBT losses increase with increasing gradient coil current. With the generation of power consumption of the IGBT module, the IGBT module will inevitably generate heat. Fig. 2 shows a waveform of IGBT junction temperature as a function of gradient coil current. As shown in fig. 2, when the gradient coil current is small, the power consumption of the IGBT module is low, and the IGBT junction temperature is low; when the current of the gradient coil is large, the power consumption of the IGBT module is high, and the junction temperature of the IGBT is increased. In the imaging process, the current amplitude of the current imaging sequence of the gradient power amplifier is randomly changed. MRI systems image different parts of the human body, requiring the use of different imaging current sequences. When the current amplitude is switched between a large current and a small current, the power consumption of the IGBT module is continuously switched between high and low as shown in fig. 1, and is modulated by the current sequence amplitude, thereby causing the fluctuation of the IGBT junction temperature as shown in fig. 2.
Fig. 3 shows an internal configuration diagram of an IGBT module. As shown in fig. 3, the junction and the case of the IGBT module are formed by packaging different materials, the IGBT module includes a substrate 100, a substrate solder layer 104, a copper substrate 105 for heat conduction, a heat dissipation paste layer 106, a heat sink 107, and the like, which are sequentially formed by an upper copper layer 101, a ceramic layer 102 for insulation and heat conduction, and a lower copper layer 103, the IGBT 108 and the diode 109 are respectively connected to the upper copper layer 101 of the substrate 100 by a chip solder 110, and the IGBT 108, the diode 109, and the upper copper layer 101 are electrically connected by bonding wires 111. The inside of IGBT module is through bonding wire 111, usually for aluminium pin connection, and when the temperature cycle of IGBT module fluctuates by a wide margin, because the thermal coefficient of the material is different between aluminium lead wire and the silicon chip, the contact surface will produce stress to lead to metal fatigue, the time of having a specified duration will appear leading to the coming off between wire and the silicon chip, thereby lead to the inefficacy of IGBT module, this life and the reliability that can restrict whole gradient power amplifier.
In the existing gradient power amplifier, mainly in the manufacturing process of an IGBT power tube, the switching performance of the IGBT is improved through the optimization of a semiconductor processing technology, and an encapsulation material is optimized when the IGBT power tube is encapsulated, so that the capability of the IGBT for bearing junction temperature fluctuation is improved, and the service life of the IGBT is further prolonged. However, this places high demands on the manufacturing process, high manufacturing costs and high customization costs.
Disclosure of Invention
The embodiment of the invention aims to provide a method for prolonging the service life of a gradient power amplifier on the premise of not increasing the cost and a monitoring device of the gradient power amplifier.
One aspect of the embodiments of the present invention provides a method for prolonging a lifetime of a gradient power amplifier. The gradient power amplifier comprises an X, Y, Z-axis gradient power amplifier, and the X, Y, Z-axis gradient power amplifier is respectively used for controlling the current of a X, Y, Z-axis gradient coil in the MRI system. The method comprises the following steps: determining key components for restricting X, Y, Z the service life of the axial gradient power amplifier; establishing X, Y, Z a model of the key component of the axial gradient power amplifier, wherein the model takes the current of the gradient coil of the corresponding axis as input, and the output of the model is used for predicting the performance of the key component; in a preset period, current of an X, Y, Z-axis gradient coil during the work of the gradient power amplifier is obtained every preset time period, and based on the model, output values of models corresponding to X, Y, Z axes are respectively calculated; predicting the value difference of the output value on the X, Y, Z axis in the preset period according to the output value of the model corresponding to the X, Y, Z axis calculated every preset time period in the preset period; and interchanging gradient power amplifiers of at least two axes in the X, Y, Z-axis gradient power amplifier when the predetermined period comes based on the numerical difference of the output value predicted in the predetermined period on the X, Y, Z axis.
Further, predicting the value difference of the output value on the X, Y, Z axis in the predetermined period comprises: the axis on which the output value is largest and the axis on which the output value is smallest among the X, Y, Z axes in the predetermined period are predicted by statistical analysis of data.
Further, the axes for which the output value is the largest and the axes for which the output value is the smallest among the three axes X, Y, Z in the predetermined period, which are predicted by the statistical analysis of the data, include: calculating an average value of the output values of the model for each axis over the predetermined period; finding X, Y, Z the axis with the largest average value and the axis with the smallest average value from the three axes; and taking the axis with the maximum average value and the axis with the minimum average value as the axis with the maximum output value and the axis with the minimum output value respectively.
Further, interchanging the gradient power amplifiers of at least two axes in the X, Y, Z-axis gradient power amplifier comprises: and interchanging the gradient power amplifiers of the axis with the maximum output value and the axis with the minimum output value.
Further, the predetermined period is a periodic maintenance period of the gradient power amplifier.
Further, the critical components include IGBT modules.
Further, modeling the critical component includes: and establishing a power consumption model of the IGBT module.
Further, the power consumption model of the IGBT module includes switching losses and conduction losses of the IGBT module, which are related to the current of the gradient coil.
Further, modeling the critical component further comprises: establishing a thermal model of the IGBT module, the thermal model being related to the material of the IGBT module; and creating the model of the IGBT module based on the power consumption model and the thermal model.
Further, the model of the IGBT module includes a junction temperature fluctuation model of the IGBT module, the junction temperature fluctuation model is a product of the power consumption model and the thermal model, and an output of the model includes junction temperature fluctuation of the IGBT module.
Further, the gradient power amplifier of each of the X, Y, Z-axis gradient power amplifiers includes three H-bridges connected in series, each H-bridge includes a first bridge arm and a second bridge arm connected in parallel, the first bridge arm includes a first IGBT module and a second IGBT module connected in series, and the second bridge arm includes a third IGBT module and a fourth IGBT module connected in series.
Further, acquiring currents of X, Y, Z-axis gradient coils during the operation of the gradient power amplifier at intervals of a predetermined time period, and respectively calculating output values of models corresponding to X, Y, Z axes based on the models includes: obtaining X, Y, Z axial gradient coil current every other preset time period when the gradient power amplifiers work so as to obtain the current flowing through the first IGBT module of the first bridge arm of any one H bridge in each axial gradient power amplifier and the turn-on duty ratio; and calculating junction temperature fluctuation of the first IGBT module of any H bridge in each axial gradient power amplifier based on the model according to the current flowing through the first IGBT module and the turn-on duty ratio.
Further, predicting a value difference of the output value on the X, Y, Z axis in the predetermined period according to the output value of the model corresponding to the X, Y, Z axis calculated every predetermined time period in the predetermined period comprises: predicting the axis with the largest junction temperature fluctuation and the axis with the smallest junction temperature fluctuation in X, Y, Z three axes in the preset period based on the junction temperature fluctuation of the first IGBT module of any H-bridge in each axial gradient power amplifier calculated every preset time period in the preset period.
Further, each H-bridge further comprises an electrolytic capacitor connected in parallel with the first bridge arm and the second bridge arm, and the key component further comprises the electrolytic capacitor.
The method for prolonging the service life of the gradient power amplifier is combined with the model of the key part of the gradient power amplifier, the numerical difference of the output values of the model in X, Y, Z three axes after the gradient power amplifier operates for a period of time can be predicted, and partial gradient power amplifiers are exchanged according to the numerical difference of the output values of the model in X, Y, Z axes, so that the performances of the gradient power amplifiers in X, Y, Z three axes can be balanced mutually, the service lives of the gradient power amplifiers in X, Y, Z three axes are balanced mutually, and the service life of the gradient power amplifier can be prolonged.
The embodiment of the invention also provides a monitoring device of the gradient power amplifier, which comprises a model of key components of the X, Y, Z-axis gradient power amplifier, a calculation module, a prediction module and a prompt module. The key component restricts the service life of the gradient power amplifier, the current of the gradient coil of the corresponding shaft is used as the input of the model, and the output of the model is used for estimating the performance of the key component. The calculation module is used for respectively calculating output values of models corresponding to the X, Y, Z axes according to currents of X, Y, Z axis gradient coils obtained every other predetermined time period when the gradient power amplifier works and based on the models in a predetermined period. The prediction module is used for predicting the value difference of the output value on the X, Y, Z axis in the preset period according to the output value of the model corresponding to the X, Y, Z axis calculated every preset time period in the preset period. The prompting module is used for prompting interchange of gradient power amplifiers of at least two axes in the X, Y, Z-axis gradient power amplifier in the preset period based on the predicted numerical difference of the output value on the X, Y, Z axis in the preset period.
Further, the critical components include IGBT modules.
Further, the model of the critical component comprises a junction temperature fluctuation model of the IGBT module, and the output of the model comprises junction temperature fluctuation of the IGBT module.
Further, the prompting module is used for prompting that the axis with the largest temperature fluctuation and the axis with the smallest junction temperature fluctuation in the X, Y, Z three axes are interchanged in the preset period.
The monitoring device of the gradient power amplifier provided by the embodiment of the invention has the advantages of ingenious design concept and simple structure.
Drawings
FIG. 1 is a waveform diagram of IGBT loss as a function of gradient coil current;
FIG. 2 is a waveform diagram of IGBT junction temperature as a function of gradient coil current;
fig. 3 is an internal configuration diagram of the IGBT module;
FIG. 4 is a schematic block diagram of a gradient power amplifier and gradient coil;
FIG. 5 is a schematic block diagram of a gradient power amplifier for any axis;
FIG. 6 is a schematic circuit diagram of an H-bridge;
FIG. 7 is a flowchart of a method for prolonging the life of a gradient power amplifier according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a model of an IGBT module according to an embodiment of the invention;
FIG. 9 illustrates specific steps of a method for prolonging the lifetime of a gradient power amplifier according to an embodiment of the present invention;
fig. 10 discloses a schematic block diagram of a monitoring apparatus of a gradient power amplifier according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus consistent with certain aspects of the invention, as detailed in the appended claims.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, technical or scientific terms used in the embodiments of the present invention should have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. The use of "first," "second," and similar terms in the description and in the claims does not indicate any order, quantity, or importance, but rather is used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not denote a limitation of quantity, but rather denote the presence of at least one. "plurality" or "a number" means two or more. Unless otherwise indicated, "front", "rear", "lower" and/or "upper" and the like are for convenience of description and are not limited to one position or one spatial orientation. The word "comprising" or "comprises", and the like, means that the element or item listed as preceding "comprising" or "includes" covers the element or item listed as following "comprising" or "includes" and its equivalents, and does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. As used in this specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
Fig. 4 discloses a schematic block diagram of a gradient power amplifier 200 and a gradient coil 300. As shown in fig. 4, in the MRI system, the gradient coil 300 includes X, Y, Z-axis gradient coil 301, and accordingly, the gradient power amplifier 200 includes X, Y, Z-axis gradient power amplifiers 201, and X, Y, Z-axis gradient power amplifiers 201 are respectively used for controlling the current of X, Y, Z-axis gradient coil 301.
Fig. 5 discloses a schematic block diagram of the gradient power amplifier 201 for either axis. As shown in fig. 5, the gradient power amplifier 201 of each of the X, Y, Z-axis gradient power amplifiers includes three H-bridges H1, H2, H3 connected in series. Fig. 6 discloses a circuit schematic of an H-bridge. As shown in fig. 6, each H-bridge comprises a first leg 401 and a second leg 402 connected in parallel, the first leg 401 comprising a first IGBT module Q1 and a second IGBT module Q2 connected in series, the second leg 402 comprising a third IGBT module Q3 and a fourth IGBT module Q4 connected in series. The connection point of the first IGBT module Q1 and the second IGBT module Q2 and the connection point of the third IGBT module Q3 and the fourth IGBT module Q4 serve as two output terminals. Each of the first, second, third and fourth IGBT modules Q1, Q2, Q3, Q4 includes an IGBT and a freewheeling diode.
The design of the gradient power amplifier 200 is life-long and is mainly limited by the components that are designed for use. The embodiment of the invention provides a method for prolonging the service life of a gradient power amplifier in an MRI system. Fig. 7 discloses a flowchart of a method for prolonging the life of a gradient power amplifier according to an embodiment of the invention. As shown in fig. 7, the method for prolonging the lifetime of a gradient power amplifier according to an embodiment of the present invention may include steps S11 to S16.
In step S11, key components that restrict the lifetime of X, Y, Z-axis gradient power amplifiers are determined.
In step S12, a model of key components of the X, Y, Z-axis gradient power amplifier is established.
The model takes the current of the gradient coil corresponding to the axis as input, and the output of the model is related to the performance of the key component and used for predicting the performance of the key component.
In step S13, the current of the X, Y, Z-axis gradient coil at the time of the gradient power amplifier operation is acquired every predetermined period of time in a predetermined cycle. The interval of the predetermined period may be, for example, every 2 seconds.
In step S14, based on the models, output values of models corresponding to X, Y, Z axes are calculated, respectively.
In step S15, the numerical difference of the output value of the model on the X, Y, Z axis in the predetermined cycle is predicted from the output value of the model corresponding to X, Y, Z axis calculated at predetermined time intervals in the predetermined cycle.
In step S16, gradient power amplifiers of at least two axes of the X, Y, Z-axis gradient power amplifiers are interchanged at the time of arrival of the predetermined period based on the value difference of the predicted output value of the model on the X, Y, Z axis in the predetermined period.
The method for prolonging the service life of the gradient power amplifier is combined with the model of the key part of the gradient power amplifier, the numerical difference of the output values of the model in X, Y, Z three axes after the gradient power amplifier operates for a period of time can be predicted, and the numerical difference of the output values of the model is related to the performance of the key part, so that the performance difference of the key part can be directly caused by the numerical difference of the output values of the model, the service life of the key part is influenced, the service life of the key part is also a key factor for determining the service life of the gradient power amplifier, therefore, the performance difference of the predicted key part can be predicted through the numerical difference of the output values of the model in X, Y, Z axis, the service life difference of the gradient power amplifier is further predicted, and partial gradient power amplifiers are interchanged through the numerical difference of the output values of the model in X, Y, Z axis, so that X, Y, 3578, or the method for predicting the service life of the gradient power amplifier, The performances of the gradient power amplifiers on the three Z axes are balanced, so that the service lives of the gradient power amplifiers on the three axes X, Y, Z are balanced, and the service lives of the gradient power amplifiers can be prolonged.
The method for prolonging the service life of the gradient power amplifier can prolong the service life of the gradient power amplifier through a smart concept on the premise of not increasing any cost, thereby greatly reducing the cost of the gradient power amplifier and improving the reliability of the gradient power amplifier.
In one embodiment, the predetermined period may be a periodic maintenance period of the gradient power amplifier.
In practical application, the gradient power amplifier needs to be maintained and maintained regularly no matter whether the gradient power amplifier is damaged or not, for example, once a year, so that in the process of using the gradient power amplifier for one year, the numerical value difference of the output value of the model on the three axes X, Y, Z is found out through the model of the key component and the data analysis in the operation of the gradient power amplifier, and partial gradient power amplifiers in the model are exchanged when the regular maintenance period comes, so that the service life of the gradient power amplifier can be prolonged, and the normal operation of the gradient power amplifier cannot be influenced.
In one embodiment, predicting the difference in the values of the output values of the model on the X, Y, Z axis over the predetermined period comprises: the axis with the largest output value and the axis with the smallest output value among X, Y, Z axes within a predetermined period are predicted by statistical analysis of data. For example, the average value of the output values of the model for each axis in a predetermined period may be calculated, and then, the axis with the largest average value and the axis with the smallest average value among the three axes are found X, Y, Z, and the axis with the largest average value and the axis with the smallest average value are respectively taken as the axis with the largest output value and the axis with the smallest output value. Of course, the embodiment of the present invention is not limited to the mean value, and the axis with the largest output value and the axis with the smallest output value among X, Y, Z axes in the predetermined period may be determined by other big data statistical analysis and algorithm.
Therefore, based on this, in one embodiment, the gradient power amplifiers of the axis with the maximum output value and the axis with the minimum output value can be interchanged. Therefore, the service life of the gradient power amplifier can be maximized, and meanwhile, the product cost is not increased.
The applicant finds that the IGBT module is mainly used for restricting the service life of the gradient power amplifier at present. In the use process of the gradient power amplifier, the failure rate of the IGBT module is the highest, so that the service life and the reliability of the whole gradient power amplifier are limited. Thus, in one embodiment of the invention, the critical components may include IGBT modules. As shown in fig. 8, the modeling of the key component in step S12 may include: a model 500 of the IGBT module is established.
The junction temperature of the IGBT module can fluctuate due to a specific current imaging sequence, namely the current of the gradient coil, so that the service life of the IGBT module can be shortened, and the service life of the gradient power amplifier is further influenced. And the essential cause of junction temperature fluctuation of the IGBT module is due to IGBT losses. Thus, in one embodiment, as shown in fig. 8, modeling 500 the IGBT module may include: a power consumption model 501 of the IGBT module is established. The power consumption model 501 of the IGBT module may include switching losses and turn-on losses of the IGBT module.
The switching losses of the IGBT modules are related to the current of the gradient coil. Referring collectively to fig. 5 and 6, for example, the switching losses of an IGBT module can be expressed as follows:
Figure BDA0002378628340000091
the switching loss of the IGBT module is Psw, the turn-on energy and the turn-off energy of the IGBT module are Eon and Eoff respectively, Vbus is input voltage of an H bridge, Vbase is reference voltage, Ibase is reference current, fsw is switching frequency of the IGBT module, and Ice is current flowing through the IGBT module. In the case of IGBT module determination, other parameters are known, except Ice as a variable. On the other hand, the current Ice flowing through the IGBT module is directly determined by the current of the gradient coil, and thus it is understood that the switching loss of the IGBT module is related to the current of the gradient coil. Therefore, with knowledge of the gradient coil current, the switching losses of the IGBT module can be easily calculated from, for example, equation (1).
The conduction losses of the IGBT modules are also related to the current of the gradient coil. For example, the turn-on loss of an IGBT module can be expressed as follows:
Pcond＝Vce×Ice×D (2)
wherein, Pcond is the conduction loss of the IGBT module, Vce is the conduction voltage of the IGBT module, and D is the turn-on duty ratio of the IGBT module. With the IGBT module determination, Vce is known, while the on duty cycle of the IGBT module is related to the current of the gradient coil.
Referring to fig. 5 and fig. 6 in combination, the following relationship exists between the output voltage and the input voltage of the gradient power amplifier and the turn-on duty ratio of the IGBT module:
Vgc＝V1+V2+V3＝(2D-1)×(Vbus1+Vbus2+Vbus3) (3)
wherein Vgc is the output voltage of the gradient power amplifier, V1, V2 and V3 are the output voltages of three H-bridges respectively, and Vbus1, Vbus2 and Vbus3 are the input voltages of three H-bridges respectively.
In some embodiments, the input voltages of the three H-bridges are all the same, i.e., Vbus 1-Vbus 2-Vbus 3-Vbus, so equation (3) can be simplified as follows:
Vgc＝(2D-1)×Vbus×3 (4)
in addition, the output voltage Vgc of the gradient power amplifier is the voltage of the gradient coil. The calculation formula according to the voltage of the gradient coil is, for example, as follows:
Figure BDA0002378628340000101
wherein Lgc is the inductance of the gradient coil, Igc is the current of the gradient coil, and Rgc is the equivalent resistance of the gradient coil.
Therefore, according to the formula (4) and the formula (5), the relationship between the turn-on duty ratio of the IGBT module and the current of the gradient coil can be obtained. Therefore, when the current of the gradient coil is known, the on duty of the IGBT module can be easily calculated according to, for example, equations (4) and (5), and the on loss of the IGBT module can be easily calculated according to, for example, equation (2).
The total loss of the IGBT module can be expressed, for example, as follows:
P(t)＝Psw+Pcond (6)
in summary, the switching loss and the conduction loss of the IGBT module can be calculated respectively under the condition that the current of the gradient coil is known, and then the total loss of the IGBT module can be calculated according to, for example, formula (6). Therefore, the current of the gradient coil will directly affect the power consumption of the IGBT module. The power consumption of the IGBT module will be different if the currents of the gradient coils are different.
Therefore, the power consumption model of the IGBT module can be established according to the above equations (1) to (6). The total power consumption of the IGBT module can be calculated according to the formula after the current of the gradient coil is obtained.
In other embodiments, as shown in fig. 8, establishing a model 500 of the IGBT module may further include: a thermal model 502 of the IGBT module is established. Wherein the thermal model 502 of the IGBT module is related to the material of the IGBT module. The interior of the IGBT module may be divided into a plurality of layers, each layer of material having a respective thermal resistance and thermal capacity, and all the layers together form the thermal resistance of the IGBT module as a whole, as shown in the following equation:
Figure BDA0002378628340000111
wherein Z isthjc(t)Is the thermal resistance of the whole IGBT module, RiIs the thermal resistance of the respective layers, t is the time, τiIs the time constant of the thermal impedance in the IGBT module, whereiCan be further expressed as follows:
τi＝Ri×Ci (8)
wherein, CiThe heat capacity of the respective layers.
Therefore, the IGBT module can be built according to the above equations (7) to (8)A thermal model 502. It follows that the thermal resistance Z of the IGBT module as a wholethjc(t)Only with respect to the material of the IGBT module. Therefore, when the IGBT module is determined, the thermal resistance Z of the IGBT module as a wholethjc(t)Is constant.
In the case where the power consumption model 501 and the thermal model 502 of the IGBT module are simultaneously established, the model 500 of the IGBT module may be created based on the power consumption model 501 and the thermal model 502. In one embodiment, the model 500 of the IGBT module includes a junction temperature fluctuation model of the IGBT module, which is a product of the power consumption model 501 and the thermal model 502, for example, as shown in the following formula:
ΔTjc＝P(t)×Zthjc(t) (9)
wherein Δ Tjc is junction temperature fluctuation of the IGBT module.
Therefore, in this case, the output of the model 500 of the IGBT module includes junction temperature fluctuations of the IGBT module, as shown in fig. 8. Therefore, under the condition that the current of the gradient coil is obtained, junction temperature fluctuation of the IGBT module can be calculated according to a junction temperature fluctuation model of the IGBT module.
Therefore, based on the model 500 of the IGBT module shown in fig. 8, in some embodiments, steps S13 through S16 shown in fig. 7 may specifically include steps S21 through S28.
As shown in fig. 9, in step S21, the current Igc _ X of the X-axis gradient coil at the time of the gradient power amplifier operation is acquired every predetermined period, and then the process proceeds to step S24.
Under the condition that the current Igc _ X of the X-axis gradient coil is obtained, the current flowing through the first IGBT module of the first bridge arm of any H bridge in the X-axis gradient power amplifier and the turn-on duty ratio can be obtained.
In step S22, the current Igc _ Y of the Y-axis gradient coil at the time of the gradient power amplifier operation is acquired every predetermined period, and then the process proceeds to step S25.
Under the condition of knowing the current Igc _ Y of the Y-axis gradient coil, the current flowing through the first IGBT module of the first bridge arm of any H bridge in the Y-axis gradient power amplifier and the turn-on duty ratio can be known.
In step S23, the current Igc _ Z of the Z-axis gradient coil at the time of the gradient power amplifier operation is acquired every predetermined period, and then the process proceeds to step S26.
Under the condition that the current Igc _ Z of the Z-axis gradient coil is obtained, the current flowing through the first IGBT module of the first bridge arm of any H bridge in the Z-axis gradient power amplifier and the turn-on duty ratio can be obtained.
In step S24, according to the current flowing through the first IGBT module in the X-axis gradient power amplifier and the turn-on duty ratio, the junction temperature fluctuation Δ Tjc _ X of the first IGBT module of any H-bridge in the X-axis gradient power amplifier may be calculated based on the junction temperature fluctuation model of the IGBT module established in fig. 8, and then the process proceeds to step S27.
In step S25, according to the current flowing through the first IGBT module in the Y-axis gradient power amplifier and the turn-on duty ratio, the junction temperature fluctuation Δ Tjc _ Y of the first IGBT module of any H-bridge in the Y-axis gradient power amplifier may be calculated based on the junction temperature fluctuation model of the IGBT module established in fig. 8, and then the process proceeds to step S27.
In step S26, according to the current flowing through the first IGBT module in the Z-axis gradient power amplifier and the turn-on duty ratio, the junction temperature fluctuation Δ Tjc _ Z of the first IGBT module of any H-bridge in the Z-axis gradient power amplifier may be calculated based on the junction temperature fluctuation model of the IGBT module established in fig. 8, and then the process proceeds to step S27.
In step S27, based on the junction temperature fluctuations Δ Tjc _ X, Δ Tjc _ Y, and Δ Tjc _ Z of the first IGBT module of any one H-bridge in each axial gradient power amplifier calculated every predetermined time period within a predetermined period, the axis with the largest temperature fluctuation and the axis with the smallest junction temperature fluctuation among the X, Y, Z three axes within the predetermined period can be predicted by analyzing data of the temperature fluctuations.
In step S28, when a predetermined period comes, for example, when the scheduled maintenance is performed, the gradient power amplifiers of the axis having the largest junction temperature fluctuation Δ Tjc and the axis having the smallest junction temperature fluctuation are interchanged.
Table 1 gives a comparison of junction temperature fluctuations in one embodiment X, Y, Z for the three axes over different gradient coil currents.
TABLE 1
Figure BDA0002378628340000131
From the comparison results in table 1, it can be seen that the X-axis junction temperature fluctuation is the smallest and only 3 ℃, while the Z-axis junction temperature fluctuation is the largest and only 8 ℃. Therefore, at the end of maintenance, the computer can automatically remind the maintenance personnel to interchange the gradient power amplifiers of the X axis and the Z axis.
The method for prolonging the service life of the gradient power amplifier according to the embodiment of the invention is schematically described above by taking a key component as an IGBT module as an example. However, the model for establishing the key components in the embodiment of the present invention is not limited to the IGBT module, and may include other components that may play a key role in the lifetime of the gradient power amplifier. With the continuous development of semiconductor technology, when the IGBT module will no longer become the bottleneck limiting the lifetime of the gradient power amplifier, the method described above can be similarly applied to other devices in the gradient power amplifier. For example, each H-bridge further comprises an electrolytic capacitor connected in parallel with the first leg and the second leg, and the critical component further comprises an electrolytic capacitor. Thus, in other embodiments, modeling the critical component may also include modeling the electrolytic capacitance. In other embodiments, the critical component may also include one or more elements, and thus, modeling the critical component may include modeling one or more elements. The method is within the protection scope of the invention as long as the method is used for carrying out life estimation and modeling on devices used in the gradient power amplifier and then carrying out life optimization through the analysis and guidance of system software for after-sale maintenance.
The method for prolonging the service life of the gradient power amplifier has ingenious conception, does not need to increase any cost, and can improve the reliability of the gradient power amplifier.
The embodiment of the invention also provides a monitoring device 600 of the gradient power amplifier. Fig. 10 discloses a schematic block diagram of a monitoring apparatus 600 of a gradient power amplifier according to an embodiment of the present invention. As shown in fig. 10, the monitoring apparatus 600 for a gradient power amplifier according to an embodiment of the present invention includes a model 601 of key components of X, Y, Z-axis gradient power amplifiers, a calculation module 602, a prediction module 603, and a prompt module 604. Critical components, which may include, for example, IGBT modules, limit the life of the gradient power amplifier. The model takes the current of the gradient coil of the corresponding axis as input, and the output of the model is used for predicting the performance of the key component. In case the critical component is an IGBT module, the model 601 of the critical component may comprise a model 500 of the IGBT module, for example a junction temperature fluctuation model of the IGBT module. Therefore, the output of the model includes junction temperature fluctuations of the IGBT module.
The calculating module 602 may calculate, in a predetermined period, output values of models corresponding to the X, Y, Z axes according to currents of X, Y, Z axis gradient coils obtained at predetermined time intervals when the gradient power amplifier operates, and based on the models.
The prediction module 603 may predict a value difference of the output value on the X, Y, Z axis in a predetermined period, based on the output value of the model corresponding to the X, Y, Z axis calculated every predetermined time period in the predetermined period.
The prompting module 604 may prompt interchanging of gradient power amplifiers of at least two axes of the X, Y, Z-axis gradient power amplifier at a predetermined period based on a difference in the predicted output values over the X, Y, Z-axis values over the predetermined period. In one embodiment, the prompting module 604 may prompt X, Y, Z to interchange the axis with the largest temperature fluctuation and the axis with the smallest junction temperature fluctuation among the three axes.
The prompt may include, but is not limited to, sounding an audible alarm, a text message, or a light signal, etc.
The monitoring device 600 of the gradient power amplifier of the embodiment of the invention has the advantages of ingenious design concept and simple structure.
The method for prolonging the service life of the gradient power amplifier and the monitoring device of the gradient power amplifier provided by the embodiment of the invention are described in detail above. The method for prolonging the service life of the gradient power amplifier and the monitoring device of the gradient power amplifier in the embodiments of the present invention are described herein by using specific examples, and the description of the above embodiments is only for assisting understanding of the core idea of the present invention and is not intended to limit the present invention. It should be noted that, for those skilled in the art, various improvements and modifications can be made without departing from the spirit and principle of the present invention, and these improvements and modifications should fall within the scope of the appended claims.

Claims (18)

1. A method for prolonging the service life of a gradient power amplifier, wherein the gradient power amplifier comprises an X, Y, Z-axis gradient power amplifier, and the X, Y, Z-axis gradient power amplifier is respectively used for controlling the current of a X, Y, Z-axis gradient coil in an MRI system, and is characterized in that: the method comprises the following steps:
determining key components for restricting X, Y, Z the service life of the axial gradient power amplifier;
establishing X, Y, Z a model of the key component of the axial gradient power amplifier, wherein the model takes the current of the gradient coil of the corresponding axis as input, and the output of the model is used for predicting the performance of the key component;
in a preset period, current of an X, Y, Z-axis gradient coil during the work of the gradient power amplifier is obtained every preset time period, and based on the model, output values of models corresponding to X, Y, Z axes are respectively calculated;
predicting the value difference of the output value on the X, Y, Z axis in the preset period according to the output value of the model corresponding to the X, Y, Z axis calculated every preset time period in the preset period; and
interchanging gradient power amplifiers of at least two axes of a X, Y, Z-axis gradient power amplifier when the predetermined period comes based on the numerical difference of the output value predicted within the predetermined period on an X, Y, Z axis.
2. The method of claim 1, wherein: predicting the difference in value of the output value on the X, Y, Z axis during the predetermined period comprises:
the axis on which the output value is largest and the axis on which the output value is smallest among the X, Y, Z axes in the predetermined period are predicted by statistical analysis of data.
3. The method of claim 2, wherein: predicting, by statistical data analysis, an axis whose output value is the largest and an axis whose output value is the smallest among the X, Y, Z axes in the predetermined period includes:
calculating an average value of the output values of the model for each axis over the predetermined period;
finding X, Y, Z the axis with the largest average value and the axis with the smallest average value from the three axes; and
and taking the axis with the maximum average value and the axis with the minimum average value as the axis with the maximum output value and the axis with the minimum output value respectively.
4. The method of claim 2, wherein: interchanging the gradient power amplifiers of at least two axes of the X, Y, Z-axis gradient power amplifiers comprises:
and interchanging the gradient power amplifiers of the axis with the maximum output value and the axis with the minimum output value.
5. The method of claim 1, wherein: the preset period is a periodic maintenance period of the gradient power amplifier.
6. The method of claim 1, wherein: the critical components include IGBT modules.
7. The method of claim 6, wherein: modeling the critical component includes:
and establishing a power consumption model of the IGBT module.
8. The method of claim 7, wherein: the power consumption model of the IGBT module comprises switching losses and conduction losses of the IGBT module, and the switching losses and the conduction losses are related to the current of the gradient coil.
9. The method of claim 7, wherein: establishing a model of the critical component further comprises:
establishing a thermal model of the IGBT module, the thermal model being related to the material of the IGBT module; and
creating the model of the IGBT module based on the power consumption model and the thermal model.
10. The method of claim 9, wherein: the model of the IGBT module comprises a junction temperature fluctuation model of the IGBT module, the junction temperature fluctuation model is a product of the power consumption model and the thermal model, and the output of the model comprises junction temperature fluctuation of the IGBT module.
11. The method of claim 10, wherein: the gradient power amplifier of each shaft in the X, Y, Z shaft gradient power amplifier comprises three H-bridges connected in series, each H-bridge comprises a first bridge arm and a second bridge arm which are connected in parallel, the first bridge arm comprises a first IGBT module and a second IGBT module which are connected in series, and the second bridge arm comprises a third IGBT module and a fourth IGBT module which are connected in series.
12. The method of claim 11, wherein: obtaining X, Y, Z axis gradient coil current at preset time intervals when the gradient power amplifier works, and respectively calculating X, Y, Z axis corresponding model output values based on the model, wherein the model output values comprise:
obtaining X, Y, Z axial gradient coil current every other preset time period when the gradient power amplifiers work so as to obtain the current flowing through the first IGBT module of the first bridge arm of any one H bridge in each axial gradient power amplifier and the turn-on duty ratio; and
and calculating junction temperature fluctuation of the first IGBT module of any H bridge in each axial gradient power amplifier based on the model according to the current flowing through the first IGBT module and the turn-on duty ratio.
13. The method of claim 12, wherein: predicting a value difference of the output value on the X, Y, Z axis in the predetermined period according to the output value of the model corresponding to the X, Y, Z axis calculated every predetermined time period in the predetermined period comprises:
predicting the axis with the largest junction temperature fluctuation and the axis with the smallest junction temperature fluctuation in X, Y, Z three axes in the preset period based on the junction temperature fluctuation of the first IGBT module of any H-bridge in each axial gradient power amplifier calculated every preset time period in the preset period.
14. The method of claim 11, wherein: each H-bridge further comprises an electrolytic capacitor connected in parallel with the first bridge arm and the second bridge arm, and the key component further comprises the electrolytic capacitor.
15. The utility model provides a monitoring device of gradient power amplifier which characterized in that: it includes:
x, Y, Z model of key components of the gradient power amplifier, wherein the key components restrict the service life of the gradient power amplifier, and the model takes the current of the gradient coil of the corresponding axis as input, and the output of the model is used for estimating the performance of the key components;
the calculation module is used for respectively calculating output values of models corresponding to X, Y, Z axes according to currents of X, Y, Z axis gradient coils obtained every other predetermined time period during the work of the gradient power amplifier in a predetermined period and based on the models;
a prediction module, configured to predict a value difference of the output value on the X, Y, Z axis in the predetermined period according to the output value of the model corresponding to the X, Y, Z axis calculated every predetermined time period in the predetermined period; and
a prompting module for prompting interchange of gradient power amplifiers of at least two axes of a X, Y, Z-axis gradient power amplifier at the predetermined period based on the predicted numerical difference of the output value on X, Y, Z-axis within the predetermined period.
16. The apparatus of claim 15, wherein: the critical components include IGBT modules.
17. The apparatus of claim 16, wherein: the model of the critical component comprises a junction temperature fluctuation model of the IGBT module, and the output of the model comprises junction temperature fluctuation of the IGBT module.
18. The apparatus of claim 17, wherein: the prompting module is used for prompting that the axis with the largest temperature fluctuation and the axis with the smallest junction temperature fluctuation in the X, Y, Z three axes are interchanged in the preset period.
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