Superconducting magnet power supply with controllable demagnetization rate and control method

Abstract

The present invention provides a superconducting magnet power supply with controllable demagnetization rate and a control method, comprising an AC / DC primary conversion module, an AC / DC output voltage measurement module, a power supply output voltage measurement module, a current regulation module and a voltage control module, and also comprising a magnet current feedback control module; the output of the AC / DC primary conversion module is connected to the input of the AC / DC output voltage measurement module; the output of the AC / DC output voltage measurement module is connected to the input of the current regulation module; the output of the current regulation module is connected to the input of the power supply output voltage measurement module; the output of the power supply output voltage measurement module is connected to both ends of the magnet through positive and negative busbars respectively; the negative busbar is grounded; due to the rapid adjustment function of the magnet current feedback control module and the power switch tube T2, the power switch tube T2 operates in a linear adjustment state, which can ensure that Vm is controllable and adjustable, that is, the magnet current drop rate di / dt can be controlled and adjusted, thereby making the demagnetization rate of the superconducting magnet power supply described in the present invention controllable and adjustable.

Description

Technical Field

[0001] The present invention relates to the technical field of power supplies, and in particular to a superconducting magnet power supply with controllable demagnetization rate and a control method thereof. Background Art

[0002] Superconducting magnets are widely used in a wide range of fields, including large-scale scientific engineering, electronics, biology, and medicine. The power supply that powers a superconducting magnet is called a superconducting magnet power supply. The accuracy of its output current determines the performance and quality of the magnetic field generated by the superconducting magnet.

[0003] For some large superconducting magnets, such as those used in large scientific facilities such as steady-state strong magnetic fields, accelerators, and nuclear fusion, the power supply current sometimes needs to be as high as tens of kiloamperes. Generally, a thyristor rectifier power supply technology solution is used. This type of power supply can achieve high current output and energy feedback of the superconducting magnet. The current rise rate and fall rate of the superconducting magnet are adjustable during excitation and demagnetization, but an industrial frequency transformer and a large LC filter circuit are required. The equipment is large in size and has a low power factor. In particular, the low-frequency ripple output is difficult to filter out.

[0004] For some small superconducting magnets, such as those used in nuclear magnetic resonance (NMR), magnetic resonance imaging (MRI), scanning electron microscopy (STM), quantum computing, quantum measurement, superconducting particle detectors and other fields, the required power supply current is relatively small, only a few hundred amperes. Generally, a small power supply system without inverter function (such as DC / DC Buck converter) is used to meet the power supply output current requirements. Compared with thyristor rectifier power supplies, there is no need for power frequency transformers and large filters. Their size and weight are reduced, and their dynamic response is significantly improved. However, when the superconducting magnet is demagnetized, the current drop rate can only be a designed fixed value. When used by the user, the demagnetization rate cannot be adjusted and controlled, which cannot meet the needs of some specific experiments.

[0005] When demagnetizing, this type of small superconducting magnet power supply needs to discharge energy through multiple diodes connected in series and parallel to form a diode group to reduce the current. For the circuit schematic, see Figure 1 At this time, according to the circuit equation of the power supply discharge circuit U = L·(di / dt), the circuit inductance L is the inductance of the magnet, and the discharge voltage U is determined by the conduction voltage drop of the diode and is a fixed value. Therefore, the current drop rate di / dt during demagnetization is also a fixed value, and the demagnetization rate is not adjustable. (Related literature: Deng Tianbai et al., Modeling and simulation of demagnetization protection circuit of small superconducting power supply system [J]. High Power Laser and Particle Beams, 2019, 31(3):5.)

[0006] For these small and medium-sized superconducting magnet power supplies, some scholars have proposed using three-phase PWM rectification plus H-bridge technology solutions, full-bridge DC / AC-AC / DC solutions, and other solutions to achieve energy feedback during demagnetization. However, this increases the complexity of the power supply's main circuit and control, and the number of switches increases exponentially, increasing costs accordingly. Furthermore, in these small superconducting magnets, the inductance and rated operating current of the superconducting magnets are relatively small, and the superconducting magnets do not store much energy. Therefore, the use of such power supplies that can achieve energy feedback is not very meaningful, and instead increases cost and complexity. Currently, there are few reports on their actual application.

[0007] In summary, in current practical applications, the power supply for this type of small and medium-sized superconducting magnets can achieve a controllable and adjustable current rise rate when the superconducting magnet is excited, but during demagnetization, there is currently no good way to achieve a controllable and adjustable current fall rate. Summary of the Invention

[0008] The present invention provides a superconducting magnet power supply with controllable demagnetization rate, which can realize controllable and adjustable current drop rate during demagnetization of the superconducting magnet.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A superconducting magnet power supply with controllable demagnetization rate, comprising an AC / DC primary conversion module, an AC / DC output voltage measurement module, a power supply output voltage measurement module, a current regulation module and a voltage control module, characterized in that it also comprises a magnet current feedback control module;

[0011] The output of the AC / DC primary conversion module is connected to the input of the AC / DC output voltage measurement module; the output of the AC / DC output voltage measurement module is connected to the input of the current regulation module; the output of the current regulation module is connected to the input of the power output voltage measurement module; the output of the power output voltage measurement module is connected to the two ends of the magnet through the positive and negative busbars respectively; the negative busbar is grounded;

[0012] The output Vdc of the AC / DC output voltage measurement module and the output Vm of the power supply output voltage measurement module are both connected to the input of the voltage control module. Vts is the set voltage difference between the two ends of the power switch tube T1, which is a fixed value. The output Vset of the voltage control module is connected to the voltage control terminal of the AC / DC primary conversion module.

[0013] The output Vm of the power supply output voltage measurement module, the output Im of the DC current sensor, and the power supply output current setting value Iref are all connected to the input end of the magnet current feedback control module, and the output Vk of the magnet current feedback control module is connected to the control end of the power switch tube T2, and at the same time is connected to the control end of the power switch tube T1 through the voltage regulator tube D2.

[0014] Furthermore, the AC / DC primary conversion module is an adjustable output voltage source, whose input is 220V or 380V AC power and output is a DC voltage with a set voltage ripple.

[0015] Furthermore, a DC current sensor DCCT is installed on the negative busbar to measure the DC current value passing through the magnet.

[0016] Furthermore, the AC / DC primary conversion module is a controllable output voltage source and is integrated with a PFC function, so that the power supply has a high power factor on the AC side.

[0017] Furthermore, the AC / DC output voltage measurement module is connected in parallel to the output end of the AC / DC primary conversion module, and is used to measure the DC output voltage Vdc of the AC / DC primary conversion module in real time, specifically by measuring the voltage by connecting resistors R1 and R2 in series to divide the voltage.

[0018] Furthermore, the power supply output voltage measurement module is connected in parallel to the output end of the current regulation module to measure the output voltage of the current regulation module, specifically by using resistors R3 and R4 connected in series to divide the voltage.

[0019] Furthermore, the output positive electrode of the AC / DC output voltage measurement module is connected to the drain of the power switch tube T1 in the current regulation module, the source of the power switch tube T1 and the source of the power switch tube T2 and one end of the resistor R5 are connected together, and the other end of the resistor R5 is the positive output end of the current regulation module, which is connected to the positive input end of the power supply output voltage measurement module, that is, the positive busbar of the power supply; the drain of the power switch tube T2 is connected to the cathode of the diode D1 through the resistor R6, and the anode of D1 is connected to the negative input end and negative output end of the current regulation module; the negative output end of the current regulation module is connected to the negative input end of the power supply output voltage measurement module, that is, the negative busbar of the power supply.

[0020] On the other hand, the present invention also discloses a method for controlling a superconducting magnet power supply with controllable demagnetization rate, which uses the above-mentioned superconducting magnet power supply with controllable demagnetization rate, and includes the following steps:

[0021] The voltage control module detects the output voltage Vdc of the AC / DC primary conversion module and the output voltage Vm of the superconducting magnet power supply in real time. The difference Vdc-Vm is the sum of the real-time voltage value between the drain and source of the power switch tube T1 and the voltage value across the resistor R5. The difference Vdc-Vm is used as a feedback value for comparison and calculation with the set voltage Vts across the power switch tube, that is, PID calculation is performed on Vts-(Vdc-Vm). The output value Vset after the PID calculation is the control voltage of the AC / DC primary conversion module. Vset can adjust the output voltage Vdc of the AC / DC primary conversion module to increase and decrease, so as to ensure that the voltage between the drain and source of the power switch tube T1 remains constant, that is, Vdc-Vm=Vset;

[0022] The magnet current feedback control module detects the superconducting magnet power supply output current Im as the feedback current value and the superconducting magnet power supply output voltage Vm as the feedback voltage value in real time, compares and calculates Im with the magnet current setting value Iref, that is, performs PID calculation on Iref-Im, and then compares the calculation result with Vm and performs PID calculation. The output value Vk after calculation is the control voltage of the power switch tubes T1 and T2.

[0023] Furthermore, during the superconducting magnet excitation and steady-field operation stages, the voltage control module adjusts the output voltage Vdc of the AC / DC primary conversion module to keep the drain-source voltage of the power switch tube T1 in the current regulation module constant, and the control voltage Vk output by the magnet current feedback control module causes the power switch tube T1 in the current regulation module to operate in a linear adjustment state, and the power switch tube T2 to operate in a fully on state, but due to the reverse blocking of the diode D1, no current flows through the switch tube T2; at this time, the power switch tube T1 can be equivalent to a rapidly adjustable variable resistor due to the rapid adjustment effect of the magnet current feedback control module and the power switch tube T1.

[0024] Furthermore, the method also includes a stage in which the superconducting magnet is demagnetized. Initially, the current is reduced through linear regulation of the switch tube T1. The induced voltage generated at both ends of the magnet causes Vm to gradually decrease from a positive value to a negative value. When Vm decreases, causing the diode D1 to begin conducting, the switch tube T2 begins to slowly shunt the current of the switch tube T1. As Vm further decreases, the magnet current will all flow through the switch tube T2. At this time, the switch tube T1 is turned off, and the control voltage Vk of the switch tube is adjusted through the current feedback control module, so that the switch tube T2 operates in a linear adjustment state. The switch tube T2 can be equivalent to a rapidly adjustable variable resistor R.

[0025] The magnet current drop rate di / dt = -Vm / L, L is the magnet inductance. If the demagnetization rate di / dt needs to be controllable and adjustable, then Vm needs to be controllable and adjustable.

[0026] And -Vm=V(d1)+V(T2)+V(R6)+V(R5)=V(d1)+i·R(T2)+i·R6+i·R5, where R5, R6, and V(d1) are fixed values. During demagnetization, the magnet current i gradually decreases, so it is only necessary to control the switch tube T2 so that the switch tube T2 can be quickly adjusted in the linear state, that is, to change the on-resistance R(T2) of the switch tube T2 in the above formula, so as to achieve Vm remaining constant or controllable and adjustable.

[0027] It can be seen from the above technical solution that a superconducting magnet power supply with controllable demagnetization rate of the present invention, due to the rapid adjustment of the magnet current feedback control module and the power switch tube T2, the power switch tube T2 operates in a linear adjustment state, which can ensure that Vm is controllable and adjustable, that is, the magnet current decrease rate di / dt can be controlled and adjusted, thereby controlling the demagnetization rate of the superconducting magnet power supply described in the present invention to be controllable and adjustable.

[0028] The present invention has the following beneficial effects:

[0029] (1) The present invention discloses a superconducting magnet power supply with controllable demagnetization rate. The power supply adopts a conventional AC / DC adjustable voltage source module and uses the current regulation module and control method disclosed in the present invention to adjust the power switches T1 and T2 to operate in different states, such as linear regulation, conduction, and cutoff. This not only enables the superconducting magnet power supply disclosed in the present invention to have high precision and stability during excitation and field stabilization, but also makes the rate at which the current of the power supply decreases controllable and adjustable. The present invention uses a simple main circuit and relatively low cost to achieve controllable and adjustable current decrease rate during demagnetization of such small and medium-sized superconducting magnets, thus meeting various applications and experimental requirements of superconducting magnets.

[0030] (2) The power supply for a superconducting magnet with a controllable demagnetization rate described in the present invention has a conventional AC / DC adjustable voltage source module as its input end. This power supply module can be a common switching power supply module with adjustable output voltage on the market. Compared with the traditional thyristor rectifier power supply, the AC side of the power supply has a high power factor, does not require a large power frequency transformer and filter inductor, and has a smaller size and weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the schematic diagram of the demagnetization circuit currently used in small and medium-sized superconducting magnet power supplies;

[0032] Figure 2 This is a schematic diagram of a power supply circuit for a superconducting magnet with controllable demagnetization rate according to the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0034] like Figure 2 As shown, the superconducting magnet power supply with controllable demagnetization rate described in this embodiment includes a superconducting magnet power supply with controllable demagnetization rate, which is composed of an AC / DC primary conversion module 1, an AC / DC output voltage measurement module 5, a power supply output voltage measurement module 6, a current regulation module 8, a DC current sensor DCCT, a voltage control module 3, a magnet current feedback control module 4, a current setting value 7, etc.

[0035] The AC / DC primary conversion module 1 is an adjustable output voltage source, whose input is 220V or 380V AC power and output is a DC voltage with a certain voltage ripple; the output of the AC / DC primary conversion module 1 is connected to the input of the AC / DC output voltage measurement module 5; the output of the AC / DC output voltage measurement module 5 is connected to the input of the current regulation module 8; the output of the current regulation module 8 is connected to the input of the power output voltage measurement module 6; the output of the power output voltage measurement module 6 is connected to the two ends of the magnet 2 through the positive and negative busbars respectively; the negative busbar is grounded, and a DC current sensor DCCT is installed on the negative busbar for measuring the DC current value passing through the magnet.

[0036] The output Vdc of the AC / DC output voltage measurement module and the output Vm of the power supply output voltage measurement module are both connected to the input of the voltage control module. Vts is the set voltage difference across the power switch tube T1, which is a fixed value. The output Vset of the voltage control module is connected to the voltage control terminal of the AC / DC primary conversion module.

[0037] The output Vm of the power supply output voltage measurement module, the output Im of the DC current sensor, and the power supply output current setting value Iref are all connected to the input end of the magnet current feedback control module, and the output Vk of the magnet current feedback control module is connected to the control end of the power switch tube T2, and at the same time is connected to the control end of the power switch tube T1 through the voltage regulator tube D2. In the example of the present invention, the control end of the switch tube is the gate-source control end of the power MOSFET.

[0038] The AC / DC primary conversion module is a controllable output voltage source and is integrated with a PFC function, so that the power supply has a high power factor on the AC side.

[0039] The AC / DC output voltage measurement module is connected in parallel to the output end of the AC / DC primary conversion module and is used to measure the DC output voltage Vdc of the AC / DC primary conversion module in real time. In this embodiment, the voltage is measured by connecting resistors R1 and R2 in series to divide the voltage. The power supply output voltage measurement module is connected in parallel to the output end of the current regulation module and is used to measure the output voltage of the current regulation module, that is, the DC output voltage Vm of the superconducting magnet power supply of the present invention, that is, the voltage across the superconducting magnet. In this embodiment, the voltage is measured by connecting resistors R3 and R4 in series to divide the voltage.

[0040] The output positive electrode of the AC / DC output voltage measurement module is connected to the drain of the power switch tube T1 in the current regulation module, and the source of the power switch tube T1 and the source of the power switch tube T2 and one end of the resistor R5 are connected together. The other end of the resistor R5 is the positive output end of the current regulation module, which is connected to the positive input end of the power supply output voltage measurement module, that is, the positive busbar of the power supply; the drain of the power switch tube T2 is connected to the cathode of the diode D1 through the resistor R6, and the anode of D1 is connected to the negative input end and the negative output end of the current regulation module; the negative output end of the current regulation module is connected to the negative input end of the power supply output voltage measurement module, that is, the negative busbar of the power supply.

[0041] The voltage drop of the voltage regulator tube is Vd2. Due to the voltage stabilization function of the voltage regulator tube D2, the driving control voltage of the power switch tube T1 is lower than the driving control voltage of the power switch tube T2 by Vd2.

[0042] When the superconducting magnet is in excitation and steady-field operation, the power switch tube T1 in the current regulation module operates in a linear regulation state, and the power switch tube T2 operates in a conduction state. However, due to the reverse blocking of the diode D1, no current flows through the switch tube T2.

[0043] When the superconducting magnet is demagnetized, initially, the current is reduced through the linear adjustment of the switch tube T1. The induced voltage generated at both ends of the magnet causes Vm to gradually decrease from a positive value to a negative value. When Vm drops to the point where the diode D1 begins to conduct, the switch tube T2 begins to slowly shunt the current of the switch tube T1. As Vm continues to decrease, the magnet current will all flow through the switch tube T2. At this time, the switch tube T1 is turned off, and the magnet current feedback control module can adjust its control voltage Vk to make the switch tube T2 work in a linear adjustment state, thereby controlling the demagnetization rate of the superconducting magnet power supply.

[0044] The power switch tubes T1 and T2 are exemplified by power MOSFETs in the present invention. In practice, other power switch devices capable of operating in a linear adjustment region, such as power IGBTs, may also be used. According to the rated output current of the superconducting magnet power supply and the current carrying capacity of the selected power switch tube, the current regulating module (8) may be implemented by connecting multiple power switch devices in parallel.

[0045] The DC current sensor is used to measure the DC current Im output by the superconducting magnet power supply of the present invention, that is, the current flowing through the superconducting magnet. In this embodiment, a DC current sensor current measurement solution is adopted to achieve isolation between the measured signal and the output signal. In a high-precision superconducting magnet power supply, a current sensor with high measurement accuracy and low temperature drift characteristics should also be selected;

[0046] The current setting value can be a digital quantity set by the host computer in a digital control system; in a high-precision superconducting magnet power supply and analog control system, it can be a high-precision, low-temperature drift analog value output by a high-performance DAC module (composed of a high-precision analog-to-digital converter chip and its peripheral circuits).

[0047] The voltage control module is used to control and adjust the DC output voltage Vdc of the AC / DC primary conversion module.

[0048] The magnet current feedback control module is used to control and adjust the output DC current Im of the superconducting magnet power supply with controllable demagnetization rate described in the present invention.

[0049] On the other hand, the present invention provides a superconducting magnet power supply with controllable demagnetization rate, which adopts the following control scheme:

[0050] The voltage control module detects the output voltage Vdc of the AC / DC primary conversion module and the output voltage Vm of the superconducting magnet power supply in real time. The difference (Vdc-Vm) between the two values ​​can be the sum of the real-time voltage value between the drain and source of the power switch tube T1 and the voltage value across the resistor R5. The voltage control module uses the difference (Vdc-Vm) as a feedback value and compares and calculates it with the set voltage Vts across the power switch tube (for the determined superconducting magnet power supply output parameters and its power switch tube, Vts should be a fixed value). That is, a PID operation is performed on Vts-(Vdc-Vm). The output value Vset after the PID operation is the control voltage of the AC / DC primary conversion module. Vset can adjust the output voltage Vdc of the AC / DC primary conversion module to increase and decrease, so as to ensure that the voltage between the drain and source of the power switch tube T1 remains constant, that is, Vdc-Vm=Vset.

[0051] The magnet current feedback control module detects the output current Im of the superconducting magnet power supply as the feedback current value and the output voltage Vm of the superconducting magnet power supply as the feedback voltage value in real time, compares and calculates Im with the magnet current setting value Iref, that is, performs PID calculation on (Iref-Im), and then compares the calculation result with Vm and performs PID calculation. The output value Vk after calculation is the control voltage of the power switch tubes T1 and T2;

[0052] During the superconducting magnet excitation and steady-field operation phases, the voltage control module can maintain a constant voltage between the drain and source of the power switch tube T1 in the current regulation module by adjusting the output voltage Vdc of the AC / DC primary conversion module. The control voltage Vk output by the magnet current feedback control module can cause the power switch tube T1 in the current regulation module to operate in a linear adjustment state, and the power switch tube T2 to operate in a fully conductive state. However, due to the reverse blocking of diode D1, no current flows through the switch tube T2. At this time, the power switch tube T1 can be equivalent to a rapidly adjustable variable resistor. Due to the rapid regulation of the magnet current feedback control module and the power switch tube T1, the output current of the superconducting magnet power supply described in the present invention has extremely low current ripple and a very stable output.

[0053] During the demagnetization phase of the superconducting magnet, initially, the current is reduced through the linear regulation of the switch tube T1. The induced voltage generated at both ends of the magnet causes Vm to gradually decrease from a positive value to a negative value. When Vm decreases, causing the diode D1 to begin to conduct, the switch tube T2 begins to slowly shunt the current of the switch tube T1. As Vm further decreases, the magnet current will all flow through the switch tube T2. At this time, the switch tube T1 is turned off, and the control voltage Vk of the switch tube is adjusted through the current feedback control module, so that the switch tube T2 operates in a linear adjustment state. The switch tube T2 can be equivalent to a rapidly adjustable variable resistor R(T2);

[0054] Then the magnet current drop rate di / dt = -Vm / L, L is the magnet inductance. If the demagnetization rate di / dt needs to be controllable and adjustable, then Vm needs to be controllable and adjustable;

[0055] And -Vm=V(d1)+V(T2)+V(R6)+V(R5)=V(d1)+i·R(T2)+i·R6+i·R5, in which R5, R6, and V(d1) are fixed values. During demagnetization, the magnet current i gradually decreases, so it is only necessary to control the switch tube T2 so that its R(T2) can be adjusted quickly to achieve Vm remaining constant or controllable and adjustable.

[0056] In summary, due to the rapid regulation of the magnet current feedback control module and the power switch tube T2, the power switch tube T2 operates in a linear adjustment state, which can ensure that Vm is controllable and adjustable, that is, the magnet current decrease rate di / dt can be controlled and adjusted, thereby making the demagnetization rate of the superconducting magnet power supply described in the present invention controllable and adjustable.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A superconducting magnet power supply with controllable demagnetization rate, comprising an AC / DC primary conversion module, an AC / DC output voltage measurement module, a power supply output voltage measurement module, a current regulation module, and a voltage control module, characterized in that: Also included is a magnet current feedback control module; The output of the AC / DC primary conversion module is connected to the input of the AC / DC output voltage measurement module; the output of the AC / DC output voltage measurement module is connected to the input of the current regulation module; the output of the current regulation module is connected to the input of the power output voltage measurement module; the output of the power output voltage measurement module is connected to the two ends of the magnet through the positive and negative busbars respectively; the negative busbar is grounded; The output Vdc of the AC / DC output voltage measurement module and the output Vm of the power supply output voltage measurement module are both connected to the input of the voltage control module. Vts is the set voltage difference between the two ends of the power switch tube T1, which is a fixed value. The output Vset of the voltage control module is connected to the voltage control terminal of the AC / DC primary conversion module. The output Vm of the power supply output voltage measurement module, the output Im of the DC current sensor, and the power supply output current setting value Iref are all connected to the input end of the magnet current feedback control module. The output Vk of the magnet current feedback control module is connected to the control end of the power switch tube T2, and is also connected to the control end of the power switch tube T1 through the voltage regulator tube D2. The magnet current feedback control module is used to generate a control voltage Vk based on the input power supply output voltage Vm, the output Im of the DC current sensor, and the power supply output current setting value Iref. The control voltage Vk is applied to the control end of the power switch tube T2 and then applied to the control end of the power tube T1 through the voltage regulator tube D2, so as to: a) During excitation and steady-field operation, the power switch tube T1 is controlled to operate in a linear adjustment state, while the power switch tube T2 remains on but no current flows; b) During demagnetization operation, the power switch tube T1 is controlled to be turned off, and the power switch tube T2 is operated in a linear adjustment state to adjust the rate of decrease of the magnet current.

2. The superconducting magnet power supply with controllable demagnetization rate according to claim 1, characterized in that: The AC / DC primary conversion module is a controllable and adjustable output voltage source. Its input is 220V or 380V AC power and it integrates a PFC function, which enables the power supply to have a high power factor on the AC input side; its output is a DC voltage with a certain voltage ripple.

3. The superconducting magnet power supply with controllable demagnetization rate according to claim 1, characterized in that: A DC current sensor DCCT is installed on the negative busbar to measure the DC current value passing through the magnet.

4. The superconducting magnet power supply with controllable demagnetization rate according to claim 1, characterized in that: The AC / DC output voltage measurement module is connected in parallel to the output end of the AC / DC primary conversion module and is used to measure the DC output voltage Vdc of the AC / DC primary conversion module in real time. Specifically, the voltage is measured by connecting resistors R1 and R2 in series to divide the voltage.

5. The superconducting magnet power supply with controllable demagnetization rate according to claim 1, characterized in that: The power supply output voltage measurement module is connected in parallel to the output end of the current regulation module and is used to measure the output voltage of the current regulation module. Specifically, the voltage is measured by connecting resistors R3 and R4 in series to divide the voltage.

6. The superconducting magnet power supply with controllable demagnetization rate according to claim 1, characterized in that: The output positive electrode of the AC / DC output voltage measurement module is connected to the drain of the power switch tube T1 in the current regulation module, and the source of the power switch tube T1 and the source of the power switch tube T2 and one end of the resistor R5 are connected together. The other end of the resistor R5 is the positive output end of the current regulation module, which is connected to the positive input end of the power supply output voltage measurement module, that is, the positive busbar of the power supply; the drain of the power switch tube T2 is connected to the cathode of the diode D1 through the resistor R6, and the anode of D1 is connected to the negative input end and the negative output end of the current regulation module; the negative output end of the current regulation module is connected to the negative input end of the power supply output voltage measurement module, that is, the negative busbar of the power supply.

7. A method for controlling a superconducting magnet power supply with controllable demagnetization rate, using the superconducting magnet power supply with controllable demagnetization rate according to claim 6, characterized in that: The following steps are included: The voltage control module detects the output voltage Vdc of the AC / DC primary conversion module and the output voltage Vm of the superconducting magnet power supply in real time. The difference Vdc-Vm is the sum of the real-time voltage value between the drain and source of the power switch tube T1 and the voltage value across the resistor R5. The difference Vdc-Vm is used as a feedback value for comparison and calculation with the set voltage Vts across the power switch tube, that is, PID calculation is performed on Vts-(Vdc-Vm). The output value Vset after the PID calculation is the control voltage of the AC / DC primary conversion module. Vset can adjust the output voltage Vdc of the AC / DC primary conversion module to increase and decrease, so as to ensure that the voltage between the drain and source of the power switch tube T1 remains constant, that is, Vdc-Vm=Vset; The magnet current feedback control module detects the superconducting magnet power supply output current Im as the feedback current value and the superconducting magnet power supply output voltage Vm as the feedback voltage value in real time, compares and calculates Im with the magnet current setting value Iref, that is, performs PID calculation on Iref-Im, and then compares the calculation result with Vm and performs PID calculation. The output value Vk after calculation is the control voltage of the power switch tubes T1 and T2; The present invention also includes the following steps: during the superconducting magnet excitation and steady-field operation phase, the voltage control module adjusts the output voltage Vdc of the AC / DC primary conversion module to maintain a constant voltage between the drain and source of the power switch tube T1 in the current regulation module; the control voltage Vk output by the magnet current feedback control module causes the power switch tube T1 in the current regulation module to operate in a linear adjustment state, and the power switch tube T2 to operate in a fully conductive state; however, due to the reverse blocking of the diode D1, no current flows through the switch tube T2; at this time, the power switch tube T1 can be equivalent to a rapidly adjustable variable resistor; due to the rapid adjustment of the magnet current feedback control module and the power switch tube T1, the output current of the superconducting magnet power supply has extremely low current ripple and very stable output; The process also includes a demagnetization operation phase of the superconducting magnet. Initially, the current is reduced through linear regulation of the switch tube T1. The induced voltage generated across the magnet causes Vm to gradually decrease from a positive value to a negative value. When Vm decreases, causing the diode D1 to begin conducting, the switch tube T2 begins to slowly shunt the current of the switch tube T1. As Vm further decreases, the magnet current will all flow through the switch tube T2. At this time, the switch tube T1 is turned off, and the control voltage Vk of the switch tube is adjusted through the current feedback control module, so that the switch tube T2 operates in a linear adjustment state. The switch tube T2 can be equivalent to a rapidly adjustable variable resistor R. The magnet current drop rate di / dt = -Vm / L, L is the magnet inductance. If the demagnetization rate di / dt needs to be controllable and adjustable, then Vm needs to be controllable and adjustable. And -Vm=V(D1)+V(T2)+V(R6)+V(R5)= V(d1)+i•R(T2)+i•R6+i•R5, where R5, R6, and V(d1) are fixed values. During demagnetization, the magnet current i gradually decreases, so it is only necessary to control the switch tube T2 so that the switch tube T2 can be quickly adjusted in the linear adjustment state, dynamically adjust and change the on-resistance of the switch tube T2, that is, quickly change R(T2) in the above formula, so as to achieve Vm remaining constant or controllable and adjustable.

Images