Linear controllable demagnetization module for superconducting magnet power supply and control method of linear controllable demagnetization module

Abstract

The invention discloses a linear controllable demagnetization module for a superconducting magnet power line and a control method of the linear controllable demagnetization module. The linear controllable demagnetization module for the superconducting magnet power line comprises a commutation switch module, a first resistor and a plurality of 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; and each shunt branch is formed by connecting an IGBT device and a second resistor in series. The control method comprises the steps that when demagnetization is needed, an IGBT device of a shunt branch is turned on, and a commutation switch module is turned off, so that current is converted to the shunt branch; the demagnetization rate of the magnet is maintained by sequentially cutting out the shunt branches until the last shunt branch is cut out, the current is converted to the first resistor, and demagnetization is completed when the current is reduced to zero. According to the invention, the magnet can be demagnetized at a constant speed, and the demagnetization process is flexible and controllable.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting magnet power supply, and in particular to a superconducting magnet power supply linear controllable demagnetization module 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 many fields such as nuclear magnetic resonance imaging systems, high-energy physics research, and nuclear fusion research. At present, low-voltage and high-current superconducting magnet power supplies mainly use 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 losses, and improves work efficiency through high-frequency transformers and fully controlled switching devices. However, the superconducting magnet power supply solution based on the high-frequency synchronous rectification topology cannot achieve bidirectional energy flow because the magnet converter cannot output negative pressure. Therefore, an external structure is required to provide negative pressure and rely on energy-consuming components to withstand the energy discharged by the magnet.

[0003] In the prior art, the magnet demagnetization structure is mostly a mechanical switch in parallel with an energy transfer resistor, such as Figure 1 Although the magnet demagnetization scheme using a mechanical switch in parallel with a single resistor is reliable and stable, it cannot guarantee 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] In order to solve the above technical problems, the present invention provides a superconducting magnet power supply linear controllable demagnetization module and a control method thereof, which can demagnetize the magnet at a constant rate, and the demagnetization process is flexible and controllable.

[0005] The embodiment of the present invention provides a superconducting magnet power supply linear controllable demagnetization module, comprising: a commutation switch module, a first resistor and a plurality of shunt branches; The commutation switch module is connected in series between the magnetic converter 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 IGBT device and a second resistor connected in series.

[0006] Furthermore, the commutation switch module is composed of a plurality of IGBT devices connected in parallel.

[0007] Furthermore, the number of IGBT devices in the commutation switch module is N, wherein: , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, This is a round-up operation.

[0008] Furthermore, the number of the diversion branches is M, wherein: , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, This is a floor operation.

[0009] Further, the first resistor is greater than the second resistor; The resistance value of the second resistor is determined according to preset conditions, which 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.

[0010] The embodiment of the present invention further provides a control method for a superconducting magnet power supply linear controllable demagnetization module, which is applied to the above-mentioned superconducting magnet power supply linear controllable demagnetization module, and the control method includes: When the power supply needs to be demagnetized, the IGBT device of the shunt branch is turned on, and the commutation switch module is turned off, so that the current is commutated to the shunt branch; The demagnetization rate of the magnet is maintained by cutting out the shunt branches in sequence until the last shunt branch is cut out, the current is switched to the first resistor, and the demagnetization is completed when the current drops to zero.

[0011] As an improvement of the above solution, the method of maintaining the magnet demagnetization rate by sequentially cutting out the shunt branches includes: By adjusting the output voltage of the magnet converter, the voltage across the magnet is maintained at a first voltage; the first voltage is the magnet voltage required to maintain the magnet demagnetization rate; Acquire a second voltage across the linear controllable demagnetization module of the superconducting magnet power supply; When the second voltage is less than the first voltage, a shunt branch is cut out, and the process returns to the step of maintaining the voltage across the magnet at the first voltage by adjusting the output voltage of the magnet converter.

[0012] As an improvement of the above solution, the step of adjusting the output voltage of the magnet converter so that the voltage across the magnet is maintained at the first voltage includes: The first voltage is used as a reference voltage, and according to the actual voltage across the magnet, the output voltage of the magnet converter is adjusted by using a voltage loop feedback control, so that the voltage across the magnet is maintained at the first voltage.

[0013] As an improvement of the above solution, after the IGBT device that turns on the shunt branch turns off the commutation switch module to commutate the current to the shunt branch, the control method further includes: During the demagnetization process, the magnet output current is obtained; When the magnet output current is equal to the set target current, the commutation switch module is turned on and the IGBT device of the shunt branch is turned off to maintain the magnet output current at the target current.

[0014] As an improvement of the above solution, the control method further includes: When the power supply is in steady-state operation or needs to be excited, the commutation switch module is turned on, the IGBT device of the shunt branch is turned off, and the magnet output current is maintained by adjusting the magnet converter output voltage.

[0015] Compared with the prior art, the beneficial effects of a linear controllable demagnetization module of a superconducting magnet power supply and a control method thereof provided in an embodiment of the present invention are: by connecting a controllable demagnetization module composed of multiple IGBT devices and resistors in series between the magnet and the magnet inverter, the module adopts multiple branches in parallel. During the demagnetization process, by cutting out the shunt branches in sequence, the voltage adjustment range of the module can be guaranteed, the magnet demagnetization rate can be maintained, and linear controllable demagnetization can be achieved, so that the magnet can be demagnetized at a constant rate, and the demagnetization time is reduced. In addition, the demagnetization process is flexible and controllable, and the current can be demagnetized to a specified current value, which is conducive to the precise regulation of the superconducting magnet power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a demagnetization topology diagram of a magnetic converter; Figure 2 It is a structural schematic diagram of a linear controllable demagnetization module of a superconducting magnet power supply provided by an embodiment of the present invention; Figure 3 It is a flow chart of a control method of a linear controllable demagnetization module of a superconducting magnet power supply provided by an embodiment of the present invention; Figure 4 It is a control loop diagram of a linear controllable demagnetization module of a superconducting magnet power supply provided by an embodiment of the present invention; Figure 5 It is a demagnetization curve diagram of a linear controllable demagnetization module of a superconducting magnet power supply provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] See also Figure 2 , Figure 2It is a structural schematic diagram of a superconducting magnet power supply linear controllable demagnetization module provided by an embodiment of the present invention. The superconducting magnet power supply linear controllable demagnetization module includes: a commutation switch module (i.e., IGBT1), a first resistor (i.e., R1) and a plurality of shunt branches; The commutation switch module is connected in series between the magnet converter (i.e., AD / DC converter) and the magnet (i.e., L); 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 IGBT device (ie, IGBT2, ..., IGBTn) and a second resistor (ie, R2, ..., Rn) connected in series.

[0019] As one of the optional embodiments, the commutation switch module is composed of a plurality of IGBT devices connected in parallel.

[0020] Specifically, a demagnetization module is connected in series on the magnet side, and the module is composed of multiple IGBTs and resistors, including multiple parallel shunt branches, and a commutation switch module branch and a first resistor branch. Each shunt branch is composed of an IGBT device and a resistor in series. Among them, the commutation switch module is used to commutate the current to other parallel branches when demagnetization is required. When the power supply is excited and in steady state operation, the output current passes through the commutation switch module branch. The commutation switch module can use switching devices such as thyristors, field effect transistors MOSFET, and IGBT. Since the thyristor needs to add an auxiliary zero-crossing shutdown circuit in the circuit to turn off, the design is relatively complicated, and the pressure-bearing capacity of MOSFET is relatively weak, and rapid shutdown is prone to overvoltage breakdown. Therefore, the commutation switch module is preferably set to multiple IGBT devices in parallel. The IGBT device has a high withstand voltage and can pass a large current after multiple modules are connected in parallel. The opening and closing of the IGBT can be controlled by the drive circuit, and the control method is relatively simple and safe. The first resistor and the second resistor are used to consume magnet energy, and when other modules in the module fail, the first resistor can transfer the loop current to the first resistor to ensure that the magnet side will not be short-circuited to protect the circuit. Compared with the traditional parallel single resistor solution, the resistance parameter of the first resistor in the embodiment of the present invention can be greatly reduced.

[0021] When the magnet needs to be demagnetized, the current on the commutation switch module is commutated to the remaining branches. By adjusting the voltage across 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 is demagnetized at a constant rate.

[0022] As one of the optional embodiments, the number of IGBT devices in the commutation switch module is N, wherein: , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, This is a round-up operation.

[0023] As an optional embodiment, the number of the shunt branches is M, wherein: , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, This is a floor operation.

[0024] Specifically, if the rated output current of the magnet power supply is kA, the maximum operating current of the selected IGBT is In order 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, it can be expressed as kA, then the commutation switch module needs to be IGBTs are connected in parallel. The module requires parallel shunt branches, The remaining current that cannot be divided evenly flows through R1.

[0025] As one of the optional embodiments, the first resistor is greater than the second resistor; The resistance value of the second resistor is determined according to preset conditions, which 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.

[0026] Specifically, by Figure 2 It can be seen that the loop voltage formula is: in, is the output voltage of the magnetic 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 output current of the magnet. When the magnet is excited, the required voltage is positive, when the magnet is demagnetized, the required voltage is negative.

[0027] If the magnet needs to A / s rate of excitation and demagnetization, according to the inductance voltage formula, the magnet voltage needs to be ,Right now The magnet voltage required to maintain the magnet excitation / demagnetization rate.

[0028] By transforming the loop voltage formula, we can get , where the converter output voltage The adjustment range is 0-E. Due to the loop voltage Usually it is relatively small, and the specific situation depends on the actual application. It is ignored here. Therefore, the loop voltage formula can be simplified as: From the above formula, it can be obtained that in order to demagnetize the magnet at a constant rate, it is necessary to satisfy ≥ In order to leave a certain margin, the branch resistance is designed to make the module terminal voltage greater than , ensuring the module voltage control range.

[0029] During the demagnetization process, as the current decreases, the voltage at the module terminal is detected. ,when When the current is shunted, the shunt branch is cut out in time, because the module equivalent resistance is: Among them, the resistance values ​​of R2~Rn are the same, so after cutting out a branch, the equivalent resistance formula shows that For example, when for When a branch is cut out, , Greater than , then the module terminal voltage is greater than , the voltage can be controlled continuously. By cutting out the branches one by one and adjusting the output voltage of the converter, the magnet voltage is maintained at , thereby maintaining the demagnetization rate constant.

[0030] Based on the above-mentioned 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. Figure 3 , Figure 3 1 is a flow chart of a control method of a linearly controllable demagnetization module of a superconducting magnet power supply provided by an embodiment of the present invention. The control method comprises: S1: When the power supply needs to be demagnetized, the IGBT device of the shunt branch is turned on and the commutation switch module is turned off to commutate the current to the shunt branch; S2: The magnet demagnetization rate is maintained by sequentially cutting out the shunt branches until the last shunt branch is cut out, the current is switched to the first resistor, and the demagnetization is completed when the current drops to zero.

[0031] As one of the optional embodiments, the maintaining the magnet demagnetization rate by sequentially cutting out the shunt branches includes: By adjusting the output voltage of the magnet converter, the voltage across the magnet is maintained at a first voltage; the first voltage is the magnet voltage required to maintain the magnet demagnetization rate; Acquire a second voltage across the linear controllable demagnetization module of the superconducting magnet power supply; When the second voltage is less than the first voltage, a shunt branch is cut out, and the process returns to the step of maintaining the voltage across the magnet at the first voltage by adjusting the output voltage of the magnet converter.

[0032] Specifically, when the power supply receives a current reduction instruction and needs to be demagnetized, the IGBT on the shunt branch is first triggered and turned on. Since the IGBTs on the branches are all connected in series with resistors, the current still mainly passes through the commutation switch module. Then the IGBT in the commutation switch module is turned off to commutate the current to the remaining branches. The commutation current is divided to a certain extent according to the size of the parallel resistance of each branch.

[0033] When the current is commutated from the commutation switch module to the other branches, in order to maintain the magnet speed, the voltage at the magnet terminal must be .

[0034] According to the formula , the voltage required to maintain the magnet demagnetization rate ,when As the demagnetization process decreases When the converter output voltage E needs to be 0V, the magnet voltage can be , which means that the converter output voltage E has reached the output limit. By real-time detection of the voltage at both ends of the module , when the voltage across the module Down to When , it indicates that the output voltage of the magnetic converter is 0V and the magnetic converter has reached the adjustment limit, so the shunt branches are cut out from the modules one by one at this time.

[0035] After the branch is cut off, the module equivalent resistance increases, and the voltage at both ends of the module increases. The voltage can be adjusted by combining the magnet converter to maintain the voltage at the magnet end. .

[0036] Furthermore, when the shunt branches in the module are cut out one after another until the last branch is cut out, the magnet current is all commutated to the first resistor R1. By designing a suitable resistor value, the demagnetization rate cannot be maintained under low current conditions. Considering the actual demagnetization of the magnet power supply, the magnet power supply has very little demand for operation at this stage. Therefore, when the current is all commutated to R1, the magnet demagnetization rate is not controlled, and the magnet energy is naturally consumed through R1 to complete the demagnetization.

[0037] As one of the optional embodiments, the step of adjusting the output voltage of the magnet converter so that the voltage across the magnet is maintained at a first voltage includes: The first voltage is used as a reference voltage, and according to the actual voltage across the magnet, the output voltage of the magnet converter is adjusted by using a voltage loop feedback control, so that the voltage across the magnet is maintained at the first voltage.

[0038] Specifically, see Figure 4 Based on the converter control foundation, the control module is introduced to set the voltage required to maintain the magnet demagnetization rate as the reference voltage. o The voltage loop is controlled based on the comparison result. By controlling 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.

[0039] As one of the optional embodiments, after the IGBT device that turns on the shunt branch turns off the commutation switch module to commutate the current to the shunt branch, the control method further includes: During the demagnetization process, the magnet output current is obtained; When the magnet output current is equal to the set target current, the commutation switch module is turned on and the IGBT device of the shunt branch is turned off to maintain the magnet output current at the target current.

[0040] Specifically, during the demagnetization process, if you want to reduce the current to the set target current, the output current is detected during the demagnetization process. When the output current reaches the target current, the IGBT in the commutation switch module is turned on to commutate the current from the branch to the commutation switch module branch, and then the IGBTs on the remaining branches are turned off to maintain the current at the target current.

[0041] As one of the optional embodiments, the control method further includes: When the power supply is in steady-state operation or needs to be excited, the commutation switch module is turned on, the IGBT device of the shunt branch is turned off, and the magnet output current is maintained by adjusting the magnet converter output voltage.

[0042] Specifically, when the power supply is in the excitation and operation stage, 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-state internal resistance of the IGBT is much smaller than R1, the current mainly passes through the commutation switch module.

[0043] See also Figure 5 , Figure 5It is the demagnetization curve diagram of a linearly controllable demagnetization module for a superconducting magnet power supply provided by an embodiment of the present invention. The dashed line is the demagnetization curve of the parallel single-resistance scheme, and the solid line is the demagnetization curve of the scheme adopted in the present invention. It can be seen that the embodiment of the present invention can maintain a constant demagnetization rate of the magnet and reduce the demagnetization time (T1 < T2). Moreover, by using 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.

[0044] An embodiment of the present invention provides a linearly controllable demagnetization module for a superconducting magnet power supply and its control method. The 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, and 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, and the demagnetization time is also reduced. Moreover, the demagnetization process is flexibly controllable, and the current can be demagnetized to a specified current value, which is beneficial to the precise regulation of the superconducting magnet power supply.

[0045] The above is the preferred implementation manner 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 superconducting magnet power supply linear controllable demagnetization module, characterized in that: include: A commutation switch module, a first resistor and a plurality of shunt branches; The commutation switch module is connected in series between the magnetic converter 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.

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

3. The superconducting magnet power supply linear controllable demagnetization module according to claim 2, characterized in that: The number of IGBT devices in the commutation switch module is N, wherein: , is the rated output current of the superconducting magnet power supply, is the rated operating current of the IGBT device, This is a round-up operation.

4. The superconducting magnet power supply linear controllable demagnetization module according to claim 1, characterized in that: 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, This is a floor operation.

5. The superconducting magnet power supply linear controllable demagnetization module according to claim 1, characterized in that: The first resistor is greater than the second resistor; The resistance value of the second resistor is determined according to preset conditions, which 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.

6. A control method for a linear controllable demagnetization module of a superconducting magnet power supply, characterized in that: Applied to the linear controllable demagnetization module of a superconducting magnet power supply as claimed in any one of claims 1 to 5, the control method comprises: When the power supply needs to be demagnetized, the IGBT device of the shunt branch is turned on, and the commutation switch module is turned off, so that the current is commutated to the shunt branch; The demagnetization rate of the magnet is maintained by cutting out the shunt branches in sequence until the last shunt branch is cut out, the current is switched to the first resistor, and the demagnetization is completed when the current drops to zero.

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

8. The control method of the linear controllable demagnetization module of the superconducting magnet power supply according to claim 7, characterized in that: The step of adjusting the output voltage of the magnet converter so that the voltage across the magnet is maintained at a first voltage includes: The first voltage is used as a reference voltage, and according to the actual voltage across the magnet, the output voltage of the magnet converter is adjusted by using a voltage loop feedback control, so that the voltage across the magnet is maintained at the first voltage.

9. The control method of the linear controllable demagnetization module of the superconducting magnet power supply according to claim 6, characterized in that: After the IGBT device that conducts the shunt branch turns off the commutation switch module to commutate the current to the shunt branch, the control method further includes: During the demagnetization process, the magnet output current is obtained; When the magnet output current is equal to the set target current, the commutation switch module is turned on and the IGBT device of the shunt branch is turned off to maintain the magnet output current at the target current.

10. The control method of the linear controllable demagnetization module of the superconducting magnet power supply according to claim 6, characterized in that: The control method further comprises: When the power supply is in steady-state operation or needs to be excited, the commutation switch module is turned on, the IGBT device of the shunt branch is turned off, and the magnet output current is maintained by adjusting the magnet converter output voltage.

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