A power supply system for a superconducting magnet and a control method thereof

Abstract

The application discloses a power supply system suitable for superconducting magnets and a control method thereof, detects output current of a superconducting magnet, and performs difference between the output current and a pre-set current steady-state working value, and takes the difference as input of PID control; decoupling control is performed by using the pre-set current steady-state working value, current charging and discharging rate and current charging and discharging rate of another superconducting magnet, output S1 * is obtained; output S1 * is added to output of the PID control, and PWM modulation is performed on the addition result, and a drive signal of a front-stage one-way full-bridge result switch tube of an isolation type DC-DC converter is obtained. The application effectively solves the problem that two superconducting magnets are affected by self-induction and mutual induction in the charging, stable operation and discharging process, and can control the charging and discharging rates of the two superconducting magnets.

Description

Technical Field

[0001] This invention relates to high-power superconducting magnets, and in particular to a power supply system and control method suitable for superconducting magnets. Background Technology

[0002] The primary function of high-power superconducting magnets is to generate powerful magnetic fields to confine plasma and ensure its stable operation. Superconducting magnets play a crucial role in high-energy physics experiments such as nuclear fusion, serving as a key component for their successful execution. In nuclear fusion experiments, hydrogen plasma is heated to sufficiently high temperatures and densities to allow the fusion reaction to occur under the confinement of a magnetic field. Superconducting magnets can generate extremely high magnetic field strengths, providing sufficiently strong confinement forces to stabilize the plasma within the reaction region and prevent it from contacting materials, thus protecting the equipment and maintaining the reaction under suitable conditions. However, their operation is often affected by self-inductance and mutual inductance. These issues lead to variations in current, energy loss and waste, and also affect the stability and reliability of the superconducting magnet.

[0003] First, there is the issue of self-induction. When the current inside a superconducting magnet changes, it generates a reverse potential, resulting in self-induction. Self-induction impedes changes in current, limiting the superconducting magnet's operational capabilities and causing energy loss and waste. Furthermore, during discharge, self-induction slows down energy transfer, hindering the rapid transfer of energy to other loads or storage devices, increasing the complexity and cost of system design.

[0004] Secondly, there is mutual inductance. When a superconducting magnet interacts with other magnetic fields, mutual inductance occurs. This mutual inductance not only causes changes in current but also generates a residual magnetic field inside the superconducting magnet, potentially causing it to lose its superconducting state. Once a superconducting magnet loses its superconducting state, it will generate significant heat and electrical losses, and may also cause serious consequences such as mechanical damage or fire, posing great risks and difficulties to high-energy physics experiments such as nuclear fusion.

[0005] Currently, research on power supply systems for superconducting magnets in high-energy physics experiments such as nuclear fusion is limited. Existing technologies often employ methods such as magnetoresistive modulation and soft-switching to control the magnitude and duration of the charging and discharging current of the superconducting magnet. However, these methods are complex and difficult to implement. Therefore, designing a simple circuit topology and control method for controlling the charging and discharging rate of superconducting magnets in high-energy physics experiments such as nuclear fusion is of paramount importance.

[0006] In practical applications, superconducting magnets are mainly used in fields such as power, energy, medicine, and scientific research. Taking MRI (Magnetic Resonance Imaging) as an example, the power of common superconducting magnets is typically between several kilowatts and tens of kilowatts. Large superconducting magnets used in high-energy physics experiments such as nuclear fusion can reach hundreds of megawatts in power. The high-power superconducting magnets referred to in this invention are used in high-energy physics experiments such as nuclear fusion, and therefore have a power of several hundred kilowatts or more. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a power supply system and control method suitable for superconducting magnets, which effectively solves the problem of self-inductance and mutual inductance affecting two superconducting magnets during charging, stable operation and discharging.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a power supply system suitable for superconducting magnets, characterized in that it includes two power supply units with identical structures; wherein the first power supply unit includes an AC-DC converter, the input side of which is connected to the power grid, and the output side is connected to the input side of an isolated DC-DC converter; the isolated DC-DC converter includes an isolation transformer, the two coils on the primary side of the isolation transformer are connected in series, and the two coils on the primary side are respectively connected to the output of a single-phase full-bridge structure, and the two coils on the secondary side of the isolation transformer are each connected to a bridge uncontrolled rectifier output circuit, and the two bridge uncontrolled rectifier output circuits are connected in parallel; both bridge uncontrolled rectifier output circuits are connected to the first superconducting magnet; the first superconducting magnet of the first power supply unit and the second superconducting magnet of the second current unit are coupled to each other.

[0009] In this invention, the AC-DC converter and DC-DC converter have simple structures and are easy to implement. Both converters use fewer power electronic devices, have lower costs, and also have high energy transmission efficiency.

[0010] The input side of the AC-DC converter is connected to the power grid via an LCL filter.

[0011] The present invention also provides a control method for the above-mentioned power supply system, which includes the following steps:

[0012] The output current of a superconducting magnet is detected, and the difference between the output current and the preset steady-state operating value of the current is calculated. The difference is used as the input for PID control.

[0013] By using a pre-set steady-state current operating value, current charging / discharging rate, and the current charging / discharging rate of another superconducting magnet for decoupling control, the output S1 is obtained. * ;

[0014] Output S1 *The signal is added to the output of the PID control, and the result is modulated by PWM to obtain the drive signal of the switching transistor of the front-stage unidirectional full-bridge converter of the isolated DC-DC converter.

[0015] This invention calculates the duty cycle through decoupling control and performs duty cycle feedforward, thereby eliminating the influence of self-inductance and mutual inductance.

[0016] In this invention, the expressions for the decoupling control outputs S1* and S2* corresponding to the first superconducting magnet and the second superconducting magnet are as follows:

[0017]

[0018] Where n is the turns ratio of the isolation transformer, U dc The input voltage of the isolated DC-DC converter is given by L1 and R1, which are the inductance and resistance of the first superconducting magnet, respectively. L2 and R2 are the inductance and resistance of the second superconducting magnet, respectively. M is the mutual inductance between the first and second superconducting magnets. 1ref i 2ref These are the preset steady-state operating values ​​of the current corresponding to the first and second superconducting magnets, respectively.

[0019] In this invention, decoupling control is simple and effective. The duty cycle can be directly calculated by the relationship between the self-inductance and mutual inductance of the inductor. Then, the difference between the duty cycle signal calculated by the single current loop PID controller and the duty cycle signal is used to control the switching transistor. In this way, the two superconducting magnets can be operated without being affected by self-inductance and mutual inductance, and the control accuracy is high.

[0020] The present invention also provides a control system suitable for high-power superconducting magnet power supply systems, comprising:

[0021] One or more processors;

[0022] A memory having stored one or more programs that, when executed by one or more processors, cause the one or more processors to implement the steps of the method described above.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. This invention effectively solves the problem of self-inductance and mutual inductance affecting two superconducting magnets during charging, stable operation and discharging, and can control the charging and discharging rates of the two superconducting magnets.

[0025] 2. This invention uses a high-power PWM rectifier and an isolated DC-DC converter to power the superconducting magnet. The topology is simple and has high transmission efficiency. Attached Figure Description

[0026] Figure 1This is a structural diagram of a high-power PWM rectifier according to an embodiment of the present invention;

[0027] Figure 2 This is a structural diagram of an isolated DC-DC converter according to an embodiment of the present invention;

[0028] Figure 3 The following are the expected operating waveforms of the two superconducting magnets in an embodiment of the present invention;

[0029] Figure 4 The diagram shows the effect of using the control method of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Figure 1 A typical high-power three-phase full-bridge PWM rectifier circuit is usually divided into voltage-source and current-source structures. The current-source structure refers to a three-phase bridge PWM rectifier circuit where the load side uses inductor filtering. This structure has advantages such as stable output current and low harmonics, and is therefore widely used in applications requiring high output current accuracy. However, due to the use of inductor filtering on the load side, its output voltage is unstable and prone to fluctuations, and overvoltage may occur with loads having high inductance. The voltage-source structure refers to a three-phase bridge PWM rectifier circuit where the load side uses capacitor filtering. This structure has advantages such as stable output voltage and low noise, and is therefore widely used in applications requiring high output voltage accuracy. However, due to the use of capacitor filtering on the load side, its output current is unstable and prone to harmonics, and overcurrent may occur with loads having low inductance. To obtain a stable output voltage, a voltage-source three-phase bridge PWM rectifier structure is considered, with LCL filters used on the input side, and active damping methods used to suppress the resonant spikes of the LCL filter. Figure 1 As shown, this rectifier circuit can rectify the 380V AC mains voltage into a 600V DC voltage.

[0032] refer to Figure 2This is an isolated DC-DC converter circuit structure. The front-end adopts a single-phase full-bridge structure with the transformer primary side connected in series and the secondary side has two bridge uncontrolled rectifier outputs connected in parallel. The output side is connected to a high-power superconducting magnet. Typically, the superconducting magnet consists of two parts: a high-field coil and a low-field coil, named Superconducting Magnet 1 (first superconducting magnet) and Superconducting Magnet 2 (second superconducting magnet), respectively. Two isolated DC-DC converters are connected to Superconducting Magnet 1 and Superconducting Magnet 2, respectively.

[0033] The isolated DC-DC converter has an input voltage of 600V and converts it to provide the necessary power to two superconducting magnets. Taking the first parallel bridge uncontrolled rectifier circuit as an example, the output is connected in parallel with diode D1 and resistor R3, and in series with inductor L3. During discharge, the high-power superconducting magnet will gradually lose its superconducting state, and its resistance will increase significantly. At this time, the discharge current will reach several thousand amperes, as given by the formula: P = I 2 As can be seen from R, a large amount of heat energy will be generated, which may damage the superconducting magnet. At this time, the current forms a circuit through diode D3 and resistor R1. Resistor R1 divides the voltage of the superconducting magnet, thereby reducing the Joule heat generated by the superconducting magnet during the discharge process, and playing a certain protective role for the superconducting magnet.

[0034] refer to Figure 2 A current sensor is used to collect the current in a superconducting magnet. A current loop can then be used to control the charging rate, steady-state operating current, and discharge rate of a high-power superconducting magnet. However, during the operation of two high-power superconducting magnets, due to differences in inductance parameters, if the steady-state operating currents of the two magnets are required to be different, but the charging and discharging rates are the same, then the charging time to reach the steady-state operating current will not be the same. Therefore, the two superconducting magnets will inevitably be affected by self-inductance and mutual inductance when their operating states change. Therefore, decoupling control is used to eliminate this influence. Taking superconducting magnet 1 as an example, the principle of decoupling control is as follows: Current sensor 1 monitors the output current i1 of superconducting magnet 1 in real time, and compares it with the preset steady-state operating current value i. 1ref The difference is calculated, and the result is sent to the PID controller. At the same time, the preset steady-state current value i of the superconducting magnet 1 is set. 1ref The current charging and discharging rates di1 / dt and di2 / dt of the superconducting magnet 2 are fed into the decoupling control loop for calculation and output S1*. S1* is added to the output of the current control PID and output to the PWM loop. The PWM wave is used to control the operation of the four power switching transistors of the front-stage single-phase full-bridge structure of the isolated DC-DC converter.

[0035]

[0036] The control method for superconducting magnet 2 is the same as that for superconducting magnet 1. The decoupled control outputs S1* and S2* can be expressed by formulas, where n is the transformer turns ratio and Udc L1 is the input voltage of the isolated DC-DC converter, L2 and R2 are the inductance and resistance of superconducting magnet 1, and M is the mutual inductance of superconducting magnet 1 and 2.

[0037] Figure 3 The desired operating waveforms for two high-power superconducting magnets are given. Superconducting magnet 1 is set as a high-field coil and superconducting magnet 2 as a low-field coil. The inductance of superconducting magnet 1 is L1 = 0.555H, the inductance of superconducting magnet 2 is L2 = 4.34H, and the mutual inductance between the two superconducting magnets is M = 0.869H. From the waveforms, it can be seen that the charging and discharging rates of the two superconducting magnets are both 5A / s. At the same time, the steady-state current of superconducting magnet 1 is i1 = 10kA, and the steady-state current of superconducting magnet 2 is i2 = 15kA.

[0038] Figure 4 The simulation waveform is intended to be suitable for high-power superconducting magnet DC power supplies and control methods. The expected current waveform is as follows: Figure 3 Because high-power superconducting magnets take a long time to charge to a steady state, simulations often fail to match the actual operating waveforms. Therefore, only key components are demonstrated. Figure 4 It can be seen that the charging and discharging rates of both superconducting magnets are 5A / s. Both superconducting magnets L1 and L2 can stably transition between operating states during simultaneous charging (L1 operating stably), charging (L2 charging), discharging (L1 discharging), and stable operation (L2 operating stably). This verifies the rationality of the power system and eliminates the influence of self-inductance and mutual inductance on the two superconducting magnets during use.

[0039] Another embodiment of the present invention provides a control system corresponding to the above control method, including a memory, a processor, and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method of embodiment 1 above.

[0040] In some implementations, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0041] In other implementations, the processor can be any type of general-purpose processor, such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation here.

[0042] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0043] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A power supply system suitable for superconducting magnets, characterized in that, The system comprises two identical power supply units. The first power supply unit includes an AC-DC converter, whose input side is connected to the power grid and whose output side is connected to the input side of an isolated DC-DC converter. The isolated DC-DC converter includes an isolation transformer. The two coils on the primary side of the isolation transformer are connected in series and are respectively connected to the output of a single-phase full-bridge structure. The two coils on the secondary side of the isolation transformer are each connected to a bridge uncontrolled rectifier output circuit, and the two bridge uncontrolled rectifier output circuits are connected in parallel. Both bridge uncontrolled rectifier output circuits are connected to a first superconducting magnet. The first superconducting magnet of the first power supply unit and the second superconducting magnet of the second power supply unit are coupled to each other. The current sensor monitors the output current i1 of the first superconducting magnet in real time, and compares it with the preset steady-state operating value i. 1ref The difference is calculated, and the result is sent to the PID controller. At the same time, the preset steady-state current value i of the first superconducting magnet is set. 1ref The current charging / discharging rate di1 / dt and the second superconducting magnet current charging / discharging rate di2 / dt are fed into the decoupling control loop for calculation and output S1. * , will S1 * The output of the current-controlled PID controller is added to the PWM stage, and the PWM waveform is used to control the operation of the four power switches in the front-end single-phase full-bridge structure of the isolated DC-DC converter.

2. The power supply system for superconducting magnets according to claim 1, characterized in that, The input side of the AC-DC converter is connected to the power grid via an LCL filter.

3. A control method for the power supply system according to claim 1, characterized in that, Includes the following steps: The output current of a superconducting magnet is detected, and the difference between the output current and the preset steady-state operating value of the current is calculated. The difference is used as the input for PID control. By using a pre-set steady-state current operating value, current charging / discharging rate, and the current charging / discharging rate of another superconducting magnet for decoupling control, the output S1 is obtained. * ; Output S1 * The signal is added to the output of the PID control, and the result is modulated by PWM to obtain the drive signal of the switching transistor of the front-stage unidirectional full-bridge converter of the isolated DC-DC converter.

4. The control method according to claim 3, characterized in that, The decoupling control outputs S1 corresponding to the first and second superconducting magnets * S2 * The expression is: ； Where n is the turns ratio of the isolation transformer, U dc The input voltage of the isolated DC-DC converter is given by L1 and R1, which are the inductance and resistance of the first superconducting magnet, respectively. L2 and R2 are the inductance and resistance of the second superconducting magnet, respectively. M is the mutual inductance between the first and second superconducting magnets. 1ref i 2ref These are the preset steady-state operating values ​​of the current corresponding to the first and second superconducting magnets, respectively.

5. A control system suitable for high-power superconducting magnet power supply systems, characterized in that, include: One or more processors; A memory having stored one or more programs that, when executed by one or more processors, cause the one or more processors to perform the steps of the method of claim 3 or 4.

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