阅读说明：本技术 一种磁共振超导磁体电源及其控制方法 (Magnetic resonance superconducting magnet power supply and control method thereof ) 是由 王恒 于 2020-07-10 设计创作，主要内容包括：本发明公开了一种磁共振超导磁体电源及其控制方法,该磁共振超导磁体电源包括第一变换器即PWM整流器(单元),第二变换器即双有源桥DC-DC变换器单元,第三变换器即H桥单元以及超导磁体升降场及闭环控制模块。本发明可完成电网向(磁共振)超导磁体正向传输能量,超导磁体向电网反向回馈能量以及超导磁体励磁完成后可靠的切入超导开关。本发明所述的一种磁共振超导磁体电源,第二变换器采用高频变压器完成电气隔离,省去了第一变换器的工频变压器,大大减小电源整机体积；第三变换器不仅实现了励磁退磁过程中输出电压极性切换,而且励磁完成后超导磁体电流在第三变换器开关管和超导磁体中流动,提高了之后超导磁体闭环的可靠性。(The invention discloses a magnetic resonance superconducting magnet power supply and a control method thereof. The invention can complete the forward energy transmission from the power grid to the (magnetic resonance) superconducting magnet, the superconducting magnet feeds back energy to the power grid in a reverse direction, and the superconducting switch is reliably switched on after the excitation of the superconducting magnet is completed. According to the magnetic resonance superconducting magnet power supply, the second converter adopts the high-frequency transformer to complete electrical isolation, so that a power frequency transformer of the first converter is omitted, and the overall volume of the power supply is greatly reduced; the third converter not only realizes the output voltage polarity switching in the excitation and demagnetization process, but also improves the reliability of the later superconducting magnet closed loop because the superconducting magnet current flows in the third converter switch tube and the superconducting magnet after the excitation is finished.)

1. A magnetic resonance superconducting magnet power supply is characterized by comprising a first converter (100), a second converter (200), a third converter (300) and a power supply load superconducting magnet unit (400) which are sequentially arranged, wherein the first converter (100) is a PWM rectifier unit, the second converter (200) is an isolated DC/DC converter unit with double active bridges, and the third converter (300) is an H-bridge unit;

the power supply load superconducting magnet unit (400) comprises a superconducting magnet (410), a superconducting switch (420) and a magnet power supply (440), wherein the superconducting switch (420) is connected to the end part of the superconducting magnet (410) in parallel;

the second converter (200) comprises two full bridges H1(110) and H2(120), a high-frequency transformer TF, an inductor L, and voltage stabilizing capacitors C1 and C2, and the alternating current output phase shift angle of the output voltage VAB of the H1 bridge and the input voltage VCD of the H2 bridge is adjusted by controlling the switching tubes S1, S2, S3, S4, Q1, Q2, Q3 and Q4 of the H1 bridge and the H2 bridge to drive pulse signals;

the third converter (300) comprises a first switching tube K1, a second switching tube K2, a third switching tube K3 and a fourth switching tube K4, all the switching tubes are in a conducting state or a cut-off state, and the input voltage of the third converter (300) is the output voltage V of the second converter (200)₂The output voltage is the voltage V at the end of the power supply load superconducting magnet unit (400)_O。

2. A magnetic resonance superconducting magnet power supply according to claim 1, wherein the first converter (100) topologically comprises a two-level PWM rectifier, a three-level PWM rectifier.

3. A method of controlling a magnetic resonance superconducting magnet power supply according to claim 1 or 2, characterized in that the first converter (100) performs a conversion of the grid side AC alternating voltage Vgrid to the input side DC voltage V1 of the second converter (200), wherein the V1 side voltage is kept constant by control; when the power grid transmits energy to the superconducting magnet (410), the first converter (100) works in a rectification mode, and the phase angle between the power grid voltage and the power grid current is smaller than 90 degrees; when the energy of the superconducting magnet (410) is fed back to a power grid, the first converter (100) works in an active inversion mode, and the included angle between the voltage of the power grid and the current of the power grid is larger than 90 degrees;

the second converter (200) completes the conversion from the DC side input V1 to the DC side output V2, and the voltage V2 is regulated by the second converter (200) module;

when the power grid transmits energy to the superconducting magnet (410), the H1 bridge output voltage VAB leads the H2 bridge input voltage VCD in phase; when the superconducting magnet (410) feeds energy back to the power grid, the phase of the H1 bridge output voltage VAB lags behind the phase of the H2 bridge input voltage VCD;

when the power grid transmits energy to the superconducting magnet (410), namely the superconducting magnet (410) is in an excitation state, the first switching tube K1 is conducted, the backward diode D4 of the fourth switching tube K4 continues current, the second switching tube K2 and the third switching tube K3 are cut off, and the voltage of the end of the superconducting magnet (410) is positive;

when the power grid transmits energy to the superconducting magnet (410), namely the superconducting magnet (410) is in a demagnetization state, the second switching tube K2 is conducted, the backward diode D3 of the third switching tube K3 continues current, the first switching tube K1 and the fourth switching tube K4 are cut off, and the end voltage of the superconducting magnet (410) is negative;

when the current of the superconducting magnet (410) reaches a set value, the first switch tube K1 is conducted, the backward diode D3 of the third switch tube K3 continues current, the second switch tube K2 and the fourth switch tube K4 are cut off, and the superconducting switch (420) is changed into a superconducting state.

Technical Field

The invention relates to the field of superconducting magnets, in particular to a magnetic resonance superconducting magnet power supply and a control method thereof.

Background

Magnetic Resonance Imaging (MRI) is a method for detecting the energy released by energy level jump of a target nuclide by using the principle of Nuclear Magnetic Resonance, thereby detecting the distribution of the target nuclide in a living body, is widely applied to the fields of clinical medicine and scientific research, and is an important Imaging device. Superconducting magnets are important components of MRI, producing a high uniformity magnetic field distribution within the target region. The lifting field of the superconducting magnet is controlled by a magnet power supply, and the power supply is required to have the capacity of bidirectional energy transmission and high reliability.

On one hand, the superconducting magnet is often excited and demagnetized, for example, magnetic resonance is generally free of magnetic field in the transportation process, and the field is raised and debugged when the magnetic resonance reaches the site, so that the magnet power supply is required to be small in size and convenient to transport. The early superconducting magnet power supply adopts a silicon controlled rectifier circuit based on power frequency transformer isolation, and the structure is analyzed in the thesis of parallel operation of double anti-star rectifier circuits, so that the power supply is large in size, low in response speed and large in ripple. The scheme of the power frequency transformer isolated PWM rectifier is a topological structure developed in the later period, such as the paper 'topological design and analysis of Ganchang magnetic resonance superconducting magnet power supply', although the dynamic response speed is improved, a power frequency transformer is required to be adopted, and the volume of the whole machine is still larger.

On the other hand, there are few specific control circuits for switching the magnetic resonance superconducting magnet into the superconducting switch. The superconducting switch is an essential component for steady-state operation of the magnetic resonance superconducting magnet and is connected in parallel at two ends of the superconducting magnet, so that high uniformity of a magnetic field in a target area is ensured. When the current of the (magnetic resonance) superconducting magnet reaches a set value, the superconducting switch is converted into a superconducting state through control, the current of the superconducting magnet gradually flows through the superconducting switch, the output current of the power supply gradually decreases to 0, and the power supply is disconnected; in the process, the load suddenly changes, the output current suddenly changes, the power supply is in a transient operation condition, the problems of magnetic biasing of the transformer and the like can occur, and the reliable operation of the power supply is influenced.

In addition, miniaturization and high reliability are an important trend in the development of power conversion devices, and are also requirements of magnetic resonance superconducting magnet systems for magnet power supplies.

Disclosure of Invention

The invention aims to provide a miniaturized and high-reliability magnetic resonance superconducting magnet power supply and a control method. In particular, the topological structure of the PWM rectifier, the double active bridges and the H bridge, which is provided by the invention, uses the high-frequency transformer for electrical isolation and energy transmission, can omit a power frequency transformer, and reduces the volume of a power supply; the control circuit double-active-bridge module can change the polarity of the output voltage, and further, the closed-loop current of the superconducting magnet flows only in the double-active-bridge module and the superconducting magnet through control, so that the reliability of the power supply in the instant operation of sudden load change is improved.

In order to achieve the above purpose, the invention adopts the technical scheme that: a magnetic resonance superconducting magnet power supply comprises a first converter, a second converter, a third converter and a power supply load superconducting magnet unit which are sequentially arranged, wherein the first converter is a PWM rectifier unit, the second converter is an isolation DC/DC converter unit with double active bridges, and the third converter is an H-bridge unit;

the power supply load superconducting magnet unit comprises a superconducting magnet, a superconducting switch and a magnet power supply, wherein the superconducting switch is connected to the end part of the superconducting magnet in parallel;

the second converter comprises two full bridges H1 and H2, a high-frequency transformer TF, an inductor L, voltage stabilizing capacitors C1 and C2, and driving pulse signals are controlled by controlling switching tubes S1, S2, S3, S4, Q1, Q2, Q3 and Q4 of an H1 bridge and an H2 bridge, so that alternating current output phase shift angles of output voltage VAB of the H1 bridge and input voltage VCD of the H2 bridge are adjusted;

the third converter comprises a first switching tube K1, a second switching tube K2, a third switching tube K3 and a fourth switching tube K4, all the switching tubes are in a conducting state or a cut-off state, and the input voltage of the third converter is the output voltage V of the second converter₂The output voltage is the voltage V at the end of the superconducting magnet unit of the power supply load_O。

Further, the first converter topologically comprises a two-level PWM rectifier and a three-level PWM rectifier.

A control method of a magnetic resonance superconducting magnet power supply is characterized in that a first converter completes conversion of a power grid side AC alternating current voltage Vgrid to a second converter input side DC direct current voltage V1, wherein a voltage on a V1 side is kept constant through control; when the power grid transmits energy to the superconducting magnet, the first converter works in a rectification mode, and the included angle between the power grid voltage and the power grid current phase is smaller than 90 degrees; when the energy of the superconducting magnet is fed back to a power grid, the first converter works in an active inversion mode, and the included angle between the voltage of the power grid and the current phase of the power grid is larger than 90 degrees;

the second converter completes the conversion of the DC side input V1 to the DC side output V2, and the voltage V2 is regulated by the second converter module;

when the power grid transmits energy to the superconducting magnet, the phase of the H1 bridge output voltage VAB leads the phase of the H2 bridge input voltage VCD; when the superconducting magnet feeds energy back to the power grid, the phase of the output voltage VAB of the H1 bridge lags behind the input voltage VCD of the H2 bridge;

when the power grid transmits energy to the superconducting magnet, namely the superconducting magnet is in an excitation state, the first switch tube K1 is conducted, the backward diode D4 of the fourth switch tube K4 continues current, the second switch tube K2 and the third switch tube K3 are cut off, and the end voltage of the superconducting magnet is positive;

when the power grid transmits energy to the superconducting magnet, namely the superconducting magnet is in a demagnetizing state, the second switching tube K2 is switched on, the backward diode D3 of the third switching tube K3 continues current, the first switching tube K1 and the fourth switching tube K4 are switched off, and the voltage of the superconducting magnet terminal is negative;

when the current of the superconducting magnet reaches a set value, the first switching tube K1 is turned on, the backward diode D3 of the third switching tube K3 continues current, the second switching tube K2 and the fourth switching tube K4 are turned off, and the superconducting switch is changed into a superconducting state.

The invention has the technical effects that: according to the topological structure of the PWM rectifier, the double active bridges and the H bridge, the high-frequency transformer is used for electrical isolation and energy transmission, a power frequency transformer can be omitted, and the size of a power supply is reduced; the control circuit double-active-bridge module can change the polarity of the output voltage, and further, the closed-loop current of the superconducting magnet flows only in the double-active-bridge module and the superconducting magnet through control, so that the reliability of the power supply in the instant operation of sudden load change is improved.

Drawings

FIG. 1 is a schematic diagram of a magnetic resonance superconducting magnet power supply configuration of the present invention;

FIG. 2 is a schematic of the topology of a second converter of the present invention;

FIG. 3 is a schematic of the topology of a third converter of the present invention;

FIG. 4 is a simplified schematic wiring diagram of the (magnetic resonance) superconducting magnet, magnet power supply, and superconducting switch of the power-supply-loaded superconducting magnet unit of the present invention;

FIG. 5 is a schematic diagram of the third converter circuit operating when the superconducting magnet of the present invention is energized;

FIG. 6 is a schematic diagram of the third converter circuit operating when the superconducting magnet of the present invention is demagnetized;

fig. 7 is a schematic diagram of the third converter circuit operating after excitation of the superconducting magnet of the present invention is complete.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to the drawings, the present invention discloses a magnetic resonance superconducting magnet power supply and a control method thereof, the magnetic resonance superconducting magnet power supply includes a first converter 100, i.e., a PWM rectifier (unit), a second converter 200, i.e., a dual active bridge DC-DC converter unit, a third converter 300, i.e., an H-bridge unit, and a superconducting magnet lifting field and closed loop control module. The invention can complete the forward energy transmission from the power grid to the (magnetic resonance) superconducting magnet, the superconducting magnet feeds back energy to the power grid in a reverse direction, and the superconducting switch is reliably switched on after the excitation of the superconducting magnet is completed. According to the magnetic resonance superconducting magnet power supply, the second converter 200 adopts the high-frequency transformer to complete electrical isolation, so that a power frequency transformer of the first converter 100 is omitted, and the overall volume of the power supply is greatly reduced; the third converter 300 not only realizes the polarity switching of output voltage in the process of excitation and demagnetization, but also the current of the superconducting magnet flows in the switch tube of the third converter 300 and the superconducting magnet 410 after the excitation is finished, thereby improving the reliability of the later superconducting magnet closed loop.

With reference to the drawings, the first converter 100 is a PWM rectifier, which performs conversion from a grid-side ac voltage to an input-side dc voltage of the second converter 200, wherein the input-side dc voltage of the second converter 200 is controlled to be constant; the second converter 200 is a double active bridge, also called a dc transformer, which completes the conversion from dc side input to dc side output, and the dc side output voltage is regulated by the second converter 200; the third converter 300 is an H-bridge and performs output voltage polarity switching and closed loop high reliability operation. During excitation, the first converter 100 transmits energy to the second converter 200, the second converter 200 transmits energy to the third converter 300, the output voltage of the third converter 300 is positive, the current of the superconducting magnet 410 is controllably increased, and the magnet stores energy. When in demagnetization, through control, the output voltage of the third converter 300 is negative, the current of the superconducting magnet is controllable to be reduced, the magnet leaks energy, the third converter 300 transmits energy to the second converter 200, and the second converter 100 feeds back energy to the power grid. When the superconducting magnet is in a closed loop, the first converter 100 and a power grid do not transfer energy through control, the first switch tube of the third converter 300 is conducted, the backward diode of the third switch tube continues current, the second switch tube and the fourth switch tube are cut off, the current of the superconducting magnet continues current in the backward diodes of the first switch tube and the third switch tube, the superconducting switch is controlled to be in a superconducting state, the current is transferred to the superconducting switch branch, and the current closed loop of the superconducting magnet is completed.

The first inverter 100, the second inverter 200, and the third inverter 300 are explained in detail below:

the first converter 100 is a PWM (Pulse-Width-Modulation) rectifier. When the power grid transmits energy to the superconducting magnet 410, the PWM rectifier works in a rectification mode, and the included angle between the power grid voltage and the power grid current phase is smaller than 90 degrees; when the energy of the superconducting magnet 410 is fed back to the power grid, the PWM rectifier works in an active inversion mode, and the phase angle between the power grid voltage and the power grid current is greater than 90 degrees. In particular, the PWM rectifier of the first converter 100 may topologically include a two-level PWM rectifier, a three-level PWM rectifier, and the like.

The second converter 200 is a Dual-Active-Bridge (DAB), also called dc transformer, and the topology is shown in fig. 2. The high-frequency transformer TF comprises two full bridges H1 and H2, a high-frequency transformer TF, a high-frequency inductor L and two voltage-stabilizing capacitors C1 and C2. The output voltage of the H1 bridge and the alternating current output phase shift angle of the input voltage of the H2 bridge can be adjusted by controlling driving pulse signals of switching tubes of the H1 bridge and the H2 bridge. When the grid transmits energy to superconducting magnet 410, the H1 bridge output voltage phase leads the H2 bridge input voltage; when superconducting magnet 410 feeds energy back to the grid, the H1 bridge output voltage phase lags the H2 bridge input voltage.

The third converter 300 is an H-bridge converter. When the power grid transmits energy to the superconducting magnet 410, that is, the superconducting magnet is in an excitation state, the first switch tube is turned on, the backward diode of the fourth switch tube continues current, the second switch tube and the third switch tube are turned off, and the voltage of the superconducting magnet terminal is positive. When the power grid transmits energy to the superconducting magnet 410, that is, the superconducting magnet is in a demagnetizing state, the second switching tube is turned on, the backward diode of the third switching tube continues current, the first switching tube and the fourth switching tube are turned off, and the voltage across the superconducting magnet is negative. When the current of the superconducting magnet reaches a set value, the first switch tube is switched on, the backward diode of the third switch tube continues current, the second switch tube and the fourth switch tube are switched off, the current of the superconducting magnet continues current in the backward diodes of the first switch tube and the third switch tube (the switch tube in the branch without the switch state), the superconducting switch 420 is controlled to be in the superconducting state, the current is transferred to the superconducting switch branch, and the current closed loop of the superconducting magnet is completed.

Specifically, the method comprises the following steps:

referring to fig. 1, a magnetic resonance superconducting magnet power supply includes a first converter, namely a PWM rectifier unit 100, a second converter, namely a dual active bridge, namely an isolated DC/DC converter unit 200, a third converter 300, namely an H-bridge unit, and a power-supply-load superconducting magnet unit 400.

The first converter 100 performs a conversion of the grid-side AC voltage Vgrid into the input-side DC voltage V1 of the second converter 200, wherein the voltage on the V1 side is kept constant by control. When the power grid transmits energy to the superconducting magnet 410, the PWM rectifier (unit) works in a rectification mode, and the included angle between the power grid voltage and the power grid current phase is smaller than 90 degrees; when the energy of the superconducting magnet 410 is fed back to the power grid, the PWM rectifier works in an active inversion mode, and the phase angle between the power grid voltage and the power grid current is greater than 90 degrees. In particular, the first converter 100PWM rectifier may topologically include a two-level PWM rectifier, a three-level PWM rectifier, and the like.

Referring to fig. 2, the second converter 200 is a Dual-Active-Bridge (DAB), also called dc transformer, which performs conversion from the dc-side input V1 to the dc-side output V2, and the voltage V2 is regulated by the second converter 200 module; the third converter is an H-bridge and completes voltage polarity switching and closed-loop high-reliability operation. The second converter 200 includes two full bridges H1(110 in fig. 2) and H2(120 in fig. 2), a high frequency transformer TF, an inductor L, and voltage stabilizing capacitors C1 and C2. By controlling the switching tubes S1, S2, S3 and S4 of the H1 bridge and the H2 bridge and driving pulse signals of Q1, Q2, Q3 and Q4, the alternating current output phase shift angle of the bridge output voltage VAB of the H1 bridge and the bridge input voltage VCD of the H2 can be adjusted. When the power grid transmits energy to the superconducting magnet 410, the H1 bridge output voltage VAB phase leads the H2 bridge input voltage VCD; when the superconducting magnet 410 feeds energy back to the grid, the H1 bridge output voltage VAB phase lags the H2 bridge input voltage VCD.

Referring to fig. 3, third inverter 300 is an H-bridge (unit) including a first switching transistor K1, a second switching transistor K2, a third switching transistor K3, and a fourth switching transistor K4, all of which are in an on or off state. The input voltage of the third converter 300 is the output voltage V of the second converter 200 unit₂The output voltage is the voltage V at the end of the superconducting magnet unit 400, namely the superconducting magnet 410, of the power supply load_O。

Referring to fig. 4, a schematic diagram of the wiring of the magnetic resonance superconducting magnet, the magnet power supply and the superconducting switch according to the present invention is shown, and the magnetic resonance superconducting magnet, the magnet power supply and the superconducting switch are composed of a superconducting magnet 410, a superconducting switch 420, a low temperature dewar and low temperature environment section 430 and a magnet power supply 440, wherein the superconducting switch 420 is connected in parallel with the end of the superconducting magnet 410.

Referring to fig. 5, a schematic diagram of the circuit operation of the third converter 300 when the superconducting magnet 410 of the present invention is excited is shown. The red line is a current path (of course, this is only illustrated here, and the gray scale is adjusted by correction at the later stage), and the dotted switch tube is a cut-off switch tube. When the power grid transmits energy to the superconducting magnet 410, that is, the superconducting magnet 410 is in an excited state, the first switching tube K1 is turned on, the backward diode D4 of the fourth switching tube K4 continues current, the second switching tube K2 and the third switching tube K3 are turned off, and the end voltage of the superconducting magnet 410 is positive.

Referring to fig. 6, a schematic diagram of the operation of the third transformer 300 when the superconducting magnet 410 of the present invention is demagnetized is shown. The red line is a current path (of course, this is only illustrated here, and the gray scale is adjusted by correction at the later stage), and the dotted switch tube is a cut-off switch tube. When the power grid transmits energy to the superconducting magnet 410, that is, the superconducting magnet 410 is in a demagnetizing state, the second switching tube K2 is turned on, the backward diode D3 of the third switching tube K3 continues current, the first switching tube K1 and the fourth switching tube K4 are turned off, and the voltage across the superconducting magnet 410 is negative.

Referring to fig. 7, a schematic diagram of the operation of the third transformer 300 when the superconducting magnet 410 of the present invention is demagnetized is shown. The red line is a current path (of course, this is only illustrated here, and the gray scale is adjusted by correction at the later stage), and the dotted switch tube is a cut-off switch tube. When the current of the superconducting magnet 410 reaches a set value, the first switching tube K1 is turned on, the backward diode D3 of the third switching tube K3 continues current, and the second switching tube K2 and the fourth switching tube K4 are turned off, that is, the current of the superconducting magnet 410 is transferred to a red line portion in the schematic diagram 7. Compared with the traditional mode of reducing the output current of the power supply, the branch switch tube is not in a switch state, only in a conduction state and a reverse diode freewheeling state, has high operation reliability, changes the superconducting switch 420 into a superconducting state at the moment, and transfers the current from the red branch to the branch of the superconducting switch 420 to complete the closed loop.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.