A linear controllable demagnetization module for a superconducting magnet power supply and its control method

Abstract

The present invention discloses a superconducting magnet power supply linear controllable demagnetization module and its control method. The superconducting magnet power supply linear controllable demagnetization module includes: a commutation switch module, a first resistor, and multiple shunt branches; the commutation switch module is connected in series between the magnet converter and the magnet; the first resistor and each shunt branch are connected in parallel with the commutation switch module; each shunt branch is composed of an IGBT device and a second resistor connected in series. The control method includes: when demagnetization is required, turn on the IGBT device of the shunt branch and turn off the commutation switch module to make the current commutate to the shunt branch; by sequentially cutting out the shunt branches, maintain the demagnetization rate of the magnet until the last shunt branch is cut out and the current commutates to the first resistor, and demagnetization is completed when the current drops to zero. The present invention can demagnetize the magnet at a constant rate, and the demagnetization process is flexible and controllable.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting magnet power supplies, and particularly to a linearly controllable demagnetization module for a superconducting magnet power supply and a control method thereof. Background Art

[0002] With the development of superconducting magnet materials and technologies, superconducting magnet power supplies have been widely used in multiple fields such as nuclear magnetic resonance imaging systems, high-energy physics research, and nuclear fusion research. Currently, low-voltage high-current superconducting magnet power supplies mainly adopt semi-controlled device solutions such as thyristors. Although the technology is mature, there are problems such as low power density, high loss, and insufficient flexibility. The high-frequency power supply solution effectively reduces the volume, reduces the loss, and improves the working efficiency through high-frequency transformers and fully controlled switching devices. However, for the superconducting magnet power supply solution based on the high-frequency synchronous rectification topology, since the magnet inverter cannot output a negative voltage, bidirectional energy flow cannot be achieved. Therefore, an external structure is required to provide a negative voltage, and energy-consuming components are relied on to withstand the energy released by the magnet.

[0003] In the prior art, the magnet demagnetization structure mostly adopts the method of a mechanical switch in parallel with an energy transfer resistor, as Figure 1 shown. Although the magnet demagnetization scheme of using a mechanical switch in parallel with a single resistor is reliable and stable, it cannot ensure a constant demagnetization rate during the demagnetization process, nor can it accurately control the demagnetization to a specified current value, and its demagnetization process is uncontrollable. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a linearly controllable demagnetization module for a superconducting magnet power supply and a control method thereof, which can demagnetize the magnet at a constant rate, and the demagnetization process is flexible and controllable.

[0005] An embodiment of the present invention provides a linearly controllable demagnetization module for a superconducting magnet power supply, including: a commutation switch module, a first resistor, and a plurality of shunt branches;

[0006] The commutation switch module is connected in series between the magnet inverter and the magnet;

[0007] The first resistor and each of the shunt branches are connected in parallel with the commutation switch module;

[0008] Each of the shunt branches is composed of an IGBT device and a second resistor connected in series.

[0009] Further, the commutation switch module is composed of a plurality of IGBT devices connected in parallel.

[0010] Further, the number of IGBT devices in the commutation switch module is N, where, , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, is the ceiling operation.

[0011] Further, the number of the shunt branches is M, where , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, is the floor operation.

[0012] Further, the first resistor is greater than the second resistor;

[0013] The resistance value of the second resistor is determined according to preset conditions, and the preset conditions include: making the voltage across the linear controllable demagnetization module of the superconducting magnet power supply in the initial stage after commutation greater than the magnet voltage required to maintain the magnet demagnetization rate.

[0014] The embodiment of the present invention also provides a control method for a linear controllable demagnetization module of a superconducting magnet power supply, which is applied to the above-mentioned linear controllable demagnetization module of the superconducting magnet power supply. The control method includes:

[0015] When the power supply needs to be demagnetized, turn on the IGBT device of the shunt branch and turn off the commutation switch module so that the current commutes to the shunt branch;

[0016] By sequentially cutting out the shunt branches, maintain the magnet demagnetization rate until the last shunt branch is cut out and the current commutes to the first resistor. When the current drops to zero, the demagnetization is completed.

[0017] As an improvement of the above solution, the maintaining the magnet demagnetization rate by sequentially cutting out the shunt branches includes:

[0018] By adjusting the output voltage of the magnet current converter, maintain the voltage across the magnet at a first voltage; the first voltage is the magnet voltage required to maintain the magnet demagnetization rate;

[0019] Obtain the second voltage across the linear controllable demagnetization module of the superconducting magnet power supply;

[0020] When the second voltage is less than the first voltage, cut out a shunt branch and return to the step of maintaining the voltage across the magnet at the first voltage by adjusting the output voltage of the magnet current converter.

[0021] As an improvement of the above solution, the adjusting the output voltage of the magnet current converter to maintain the voltage across the magnet at the first voltage includes:

[0022] Taking the first voltage as the reference voltage, according to the actual voltage across the magnet, the output voltage of the magnet current converter is adjusted by using voltage loop feedback control so that the voltage across the magnet is maintained at the first voltage.

[0023] As an improvement to the above solution, after the IGBT device in the conducting shunt branch turns off the commutation switch module so that the current commutates to the shunt branch, the control method further includes:

[0024] During the demagnetization process, obtain the magnet output current;

[0025] When the magnet output current is equal to the set target current, turn on the commutation switch module and turn off the IGBT device in the shunt branch so that the magnet output current is maintained at the target current.

[0026] As an improvement to the above solution, the control method further includes:

[0027] During the steady-state operation of the power supply or when excitation is required, turn on the commutation switch module and turn off the IGBT device in the shunt branch, and maintain the magnet output current by adjusting the output voltage of the magnet current converter.

[0028] Compared with the prior art, the beneficial effects of a linear controllable demagnetization module and its control method for a superconducting magnet power supply provided by an embodiment of the present invention are as follows: By connecting a controllable demagnetization module composed of multiple IGBT devices and resistors in series between the magnet and the magnet current converter, the module adopts multi-branch parallel connection. During the demagnetization process, by sequentially cutting out the shunt branches, the voltage regulation range of the module can be guaranteed, the magnet demagnetization rate can be maintained, linear controllable demagnetization can be achieved, so that the magnet can demagnetize at a constant rate, the demagnetization time is also reduced, and the demagnetization process is flexibly controllable, and the current can be demagnetized to the specified current value, which is beneficial to the precise regulation of the superconducting magnet power supply. Description of the Drawings

[0029] Figure 1 is a demagnetization topology diagram of a magnet current converter;

[0030] Figure 2 is a schematic structural diagram of a linear controllable demagnetization module for a superconducting magnet power supply provided by an embodiment of the present invention;

[0031] Figure 3 is a schematic flow diagram of a control method for a linear controllable demagnetization module for a superconducting magnet power supply provided by an embodiment of the present invention;

[0032] Figure 4 is a control circuit diagram of a linear controllable demagnetization module for a superconducting magnet power supply provided by an embodiment of the present invention;

[0033] Figure 5It is the demagnetization curve diagram of a linear controllable demagnetization module for a superconducting magnet power supply provided by an embodiment of the present invention. Specific Embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0035] Please refer to Figure 2 , Figure 2 It is the structural schematic diagram of a linear controllable demagnetization module for a superconducting magnet power supply provided by an embodiment of the present invention. The linear controllable demagnetization module for a superconducting magnet power supply includes: a commutation switch module (i.e., IGBT1), a first resistor (i.e., R1), and a plurality of shunt branches;

[0036] The commutation switch module is connected in series between a magnet converter (i.e., an AD / DC converter) and a magnet (i.e., L);

[0037] The first resistor and each of the shunt branches are connected in parallel with the commutation switch module;

[0038] Each of the shunt branches is composed of an IGBT device (i.e., IGBT2,..., IGBTn) and a second resistor (i.e., R2,..., Rn) connected in series.

[0039] As an optional embodiment, the commutation switch module is composed of a plurality of IGBT devices connected in parallel.

[0040] Specifically, a demagnetization module is connected in series on the magnet side. This module is composed of multiple IGBTs and resistors, including multiple parallel shunt branches, as well as a commutation switch module branch and a first resistor branch. Each shunt branch is composed of a series connection of an IGBT device and a resistor. Among them, the commutation switch module is used to commutate the current to other parallel branches when demagnetization is required. During power excitation and steady-state operation, the output current passes through the commutation switch module branch. The commutation switch module can adopt switching devices such as thyristors, MOSFETs, and IGBTs. Since the thyristor needs to add an auxiliary zero-crossing turn-off circuit in the loop, the design is relatively complex, and the voltage-bearing capacity of the MOSFET is relatively weak. Quick turn-off is likely to cause overvoltage breakdown. Therefore, the commutation switch module is preferably set as multiple parallel IGBT devices. The IGBT device has a high withstand voltage. After multiple modules are connected in parallel, a large current can be passed. Moreover, the turn-on and turn-off of the IGBT can be controlled by a drive circuit, and the control method is relatively simple and safe. The first resistor and the second resistor are used to consume the energy of the magnet. And when other modules in the module fail, the first resistor can transfer the loop current to the first resistor to ensure that no open circuit is formed on the magnet side to protect the circuit. Compared with the traditional parallel single-resistor scheme, the resistance parameter of the first resistor in the embodiment of the present invention can be greatly reduced.

[0041] When demagnetizing the magnet is required, the current on the commutation switch module is commutated to the remaining branches. By adjusting the voltage at both ends of the demagnetization module and the output voltage E of the magnet converter, the voltage at the magnet end is maintained unchanged, so that the magnet demagnetizes at a constant rate.

[0042] As one optional embodiment, the number of IGBT devices in the commutation switch module is N, where , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, is the ceiling operation.

[0043] As one optional embodiment, the number of shunt branches is M, where , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, is the floor operation.

[0044] Specifically, if the rated output current of the magnet power supply is kA, and the maximum operating current of the selected IGBT is , to leave a certain margin, if the rated operating current of the IGBT device on the shunt branch is set to 1 / 2 of the maximum operating current, denoted as kA, then in the commutation switch module, it is required that Parallel connection of IGBTs. The module requires parallel shunt branches, The residual current that cannot be evenly divided passes through R1.

[0045] As an optional embodiment, the first resistor is greater than the second resistor;

[0046] The resistance value of the second resistor is determined according to preset conditions, and the preset conditions include: making the voltage across the superconducting magnet power supply linear controllable demagnetization module in the initial stage after commutation greater than the magnet voltage required to maintain the magnet demagnetization rate.

[0047] Specifically, from Figure 2 it can be known that the loop voltage formula is:

[0048]

[0049]

[0050]

[0051] Among them, is the output voltage of the magnet current converter, is the voltage across the demagnetization module, is the magnet inductance, dI / dt is the magnet excitation and demagnetization rate, is the equivalent resistance of the demagnetization module, is the magnet output current. Among them, when the magnet is excited, the required voltage is positive, and when the magnet is demagnetized, the required voltage is negative.

[0052] If the magnet needs to be excited and demagnetized at a rate of A / s, according to the inductance voltage formula, the magnet voltage needs to be , that is is the magnet voltage required to maintain the magnet excitation / demagnetization rate.

[0053] Obtained by transforming the loop voltage formula , where the output voltage of the converter has an adjustment range of 0 - E. Since the loop voltage is usually relatively small, subject to the actual application situation, it is ignored here. Therefore, the loop voltage formula can be simplified as:

[0054]

[0055] From the above formula, it can be obtained that to make the magnet demagnetize at a constant rate, it is necessary to satisfy ≥ To leave a certain margin, design a reasonable resistance value for the branch circuit so that the module terminal voltage in the initial stage after commutation is greater than , ensuring the voltage regulation range of the module.

[0056] During the demagnetization process, as the current decreases, detect the module terminal voltage , when , timely cut out the shunt branch. Since the equivalent resistance of the module is:

[0057]

[0058] Among them, the resistance values of R2 to Rn are the same. Therefore, after cutting out one branch, according to the equivalent resistance formula, it can be known that becomes larger. For example, when is , after cutting out one branch, , is greater than , then the module terminal voltage is greater than , and the voltage regulation can continue. By sequentially cutting out the branches and combining the adjustment of the converter output voltage, the magnet voltage is maintained at , thereby maintaining a constant demagnetization rate.

[0059] Based on the above superconducting magnet power supply linear controllable demagnetization module, the present invention also provides a control method for the superconducting magnet power supply linear controllable demagnetization module. Please refer to Figure 3 , Figure 3 is a schematic flow chart of a control method for a superconducting magnet power supply linear controllable demagnetization module provided by an embodiment of the present invention. The control method includes:

[0060] S1: When the power supply needs to be demagnetized, turn on the IGBT device of the shunt branch and turn off the commutation switch module so that the current commutates to the shunt branch;

[0061] S2: By sequentially cutting out the shunt branch, maintain the magnet demagnetization rate until the last shunt branch is cut out and the current commutates to the first resistor, and the demagnetization is completed when the current drops to zero.

[0062] As an optional embodiment, the maintaining the magnet demagnetization rate by sequentially cutting out the shunt branch includes:

[0063] By adjusting the output voltage of the magnet converter, maintain the voltage across the magnet at a first voltage; the first voltage is the magnet voltage required to maintain the magnet demagnetization rate;

[0064] Obtain the second voltage across the superconducting magnet power supply linear controllable demagnetization module;

[0065] When the second voltage is less than the first voltage, a shunt branch is cut out, and the step of adjusting the output voltage of the magnet converter to maintain the voltage across the magnet at the first voltage is returned.

[0066] Specifically, when the power supply receives a current reduction command and needs to demagnetize, first the IGBT on the shunt branch is triggered to conduct. Since the IGBTs on the branch are all in series with resistors, the current still mainly passes through the commutation switch module at this time. Then the IGBTs in the commutation switch module are turned off, causing the current to commutate to the other branches, and the commutation current is shunted to a certain extent according to the parallel resistance of each branch.

[0067] When the current commutates from the commutation switch module to the other branches, to maintain the magnet speed at this time, it is necessary to ensure that the voltage across the magnet is .

[0068] According to the formula , the voltage required to maintain the magnet demagnetization speed , when decreases to during the demagnetization process, the output voltage E of the converter needs to be 0V to make the magnet voltage , that is to say, the output voltage E of the converter has reached the output limit. By detecting the voltage across the module in real time , when the voltage across the module decreases to , it indicates that the output voltage of the magnet converter is 0V and the magnet converter has reached the adjustment limit. Therefore, the shunt branches are cut out from the module in sequence at this time.

[0069] After cutting out the branch, the equivalent resistance of the module increases and the voltage across the module increases, and the voltage can be continuously adjusted in combination with the magnet converter to maintain the voltage across the magnet .

[0070] Furthermore, when the shunt branches in the module are successively cut out until the last branch is cut out, at this time all the magnet current commutates to the first resistor R1. By designing an appropriate resistor value, the demagnetization speed cannot be maintained under the condition of low current. Considering the actual situation of the magnet power supply demagnetization, the operation demand of the magnet power supply is very small at this stage. Therefore, when all the current commutates to R1, the magnet demagnetization speed is not controlled, and the magnet energy is naturally consumed through R1 to complete demagnetization.

[0071] As one of the optional embodiments, the adjusting the output voltage of the magnet converter to maintain the voltage across the magnet at the first voltage includes:

[0072] Taking the first voltage as the reference voltage, and adjusting the output voltage of the magnet converter by using voltage loop feedback control according to the actual voltage across the magnet, so that the voltage across the magnet is maintained at the first voltage.

[0073] Specifically, please refer to Figure 4 , based on the converter control foundation, a regulation module link is introduced. The voltage required to maintain the demagnetization rate of the magnet is set as the reference voltage. According to the comparison result between the reference voltage and the actual magnet voltage U o , voltage loop control is performed. By controlling the magnitude of the output voltage E of the magnet converter, the voltage across the magnet is maintained at the first voltage, thereby achieving demagnetization at a constant rate.

[0074] As one of the optional embodiments, after the IGBT device in the conducting shunt branch turns off the commutation switch module to commutate the current to the shunt branch, the control method further includes:

[0075] During the demagnetization process, obtain the magnet output current;

[0076] When the magnet output current is equal to the set target current, turn on the commutation switch module and turn off the IGBT device in the shunt branch, so that the magnet output current is maintained at the target current.

[0077] Specifically, during the process of discharging current, if it is desired to reduce the current to the set target current, then during the demagnetization process, detect the output current. When the output current reaches the target current, turn on the IGBT in the commutation switch module to commutate the current from the branch to the commutation switch module branch, and then turn off the IGBTs on the other branches to maintain the current at the target current.

[0078] As one of the optional embodiments, the control method further includes:

[0079] When the power supply is in steady-state operation or needs excitation, turn on the commutation switch module and turn off the IGBT device in the shunt branch, and maintain the magnet output current by adjusting the output voltage of the magnet converter.

[0080] Specifically, when the power supply is in the excitation and operation stages, the IGBTs in the commutation switch module are all turned on, and the IGBTs on the other branches are all turned off. Since the on-resistance of the IGBT is much smaller than R1, the current mainly passes through the commutation switch module at this time.

[0081] Please refer to Figure 5 , Figure 5 is the demagnetization curve diagram of a superconducting magnet power supply linear controllable demagnetization module provided by an embodiment of the present invention. The dotted line is the demagnetization curve of the parallel single-resistance scheme, and the solid line is the demagnetization curve of the scheme adopted by the present invention. It can be seen that the embodiment of the present invention can maintain a constant magnet demagnetization rate, and the demagnetization time is reduced (T1 < T2). Moreover, using the IGBT as the commutation switch, the demagnetization process is flexibly controllable, can be demagnetized to a specified current value and maintained, the on-off control method is simple, and the voltage withstand and current-carrying capacity of the IGBT module are also relatively good.

[0082] An embodiment of the present invention provides a superconducting magnet power supply linear controllable demagnetization module and its control method, and its beneficial effects are as follows: By connecting a controllable demagnetization module composed of multiple IGBT devices and resistors in series between the magnet and the magnet current converter, the module adopts multi-branch parallel connection. During the demagnetization process, by sequentially cutting out the shunt branches, the voltage regulation range of the module can be ensured, the demagnetization rate of the magnet can be maintained, linear controllable demagnetization can be realized, so that the magnet can demagnetize at a constant rate, the demagnetization time is also reduced, and the demagnetization process is flexibly controllable, and the current can be demagnetized to the specified current value, which is beneficial to the precise regulation of the superconducting magnet power supply.

[0083] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A linear controllable demagnetization module for a superconducting magnet power supply, characterized in that Comprising: A commutation switch module, a first resistor, and a plurality of shunt branches; The commutation switch module is connected in series between the magnet inverter and the magnet; The first resistor and each of the shunt branches are connected in parallel with the commutation switch module; Each of the shunt branches is composed of an insulated gate bipolar transistor (IGBT) device and a second resistor connected in series; The first resistor is greater than the second resistor; The resistance value of the second resistor is determined according to a preset condition, and the preset condition includes: making the voltage across the superconducting magnet power supply linear controllable demagnetization module in the initial stage after commutation greater than the magnet voltage required to maintain the magnet demagnetization rate.

2. The linear controllable demagnetization module of the superconducting magnet power supply according to claim 1, characterized in that, The commutation switch module is composed of a plurality of IGBT devices connected in parallel.

3. The linear controllable demagnetization module of the superconducting magnet power supply according to claim 2, wherein The number of IGBT devices in the commutation switch module is N, where, , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, is the ceiling operation.

4. The linear controllable demagnetization module of the superconducting magnet power supply according to claim 1, wherein The number of the shunt branches is M, where , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, is the floor operation.

5. A control method for a linear controllable demagnetization module of a superconducting magnet power supply, characterized in that, Applied to the superconducting magnet power supply linear controllable demagnetization module according to any one of claims 1 to 4, the control method includes: When the power supply needs to be demagnetized, turn on the IGBT device of the shunt branch and turn off the commutation switch module to make the current commutate to the shunt branch; By sequentially cutting out the shunt branches, maintain the magnet demagnetization rate until the last shunt branch is cut out and the current commutates to the first resistor, and complete demagnetization when the current drops to zero.

6. The control method of the linear controllable demagnetization module of the superconducting magnet power supply according to claim 5, characterized in that, The maintaining the magnet demagnetization rate by sequentially cutting out the shunt branches includes: By adjusting the output voltage of the magnet inverter, maintain the voltage across the magnet at a first voltage; the first voltage is the magnet voltage required to maintain the magnet demagnetization rate; Obtain the second voltage across the superconducting magnet power supply linear controllable demagnetization module; When the second voltage is less than the first voltage, cut out a shunt branch and return to the step of adjusting the output voltage of the magnet inverter to maintain the voltage across the magnet at the first voltage.

7. The control method of the linear controllable demagnetization module of the superconducting magnet power supply according to claim 6, characterized in that, The adjusting the output voltage of the magnet inverter to maintain the voltage across the magnet at the first voltage includes: Taking the first voltage as the reference voltage, according to the actual voltage across the magnet, adjust the output voltage of the magnet inverter by using voltage loop feedback control so that the voltage across the magnet is maintained at the first voltage.

8. The control method of the linear controllable demagnetization module of the superconducting magnet power supply according to claim 5, wherein After turning on the IGBT device of the shunt branch and turning off the commutation switch module to make the current commutate to the shunt branch, the control method further includes: During the demagnetization process, obtain the magnet output current; When the magnet output current is equal to the set target current, turn on the commutation switch module and turn off the IGBT device of the shunt branch to maintain the magnet output current at the target current.

9. The control method of the linear controllable demagnetization module for the superconducting magnet power supply according to claim 5, characterized in that, The control method further includes: When the power supply is in steady-state operation or needs to be excited, turn on the commutation switch module and turn off the IGBT device of the shunt branch, and maintain the magnet output current by adjusting the output voltage of the magnet inverter.

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