A high-stability DC excitation power supply for superconducting magnet based on double closed-loop control

Abstract

The application provides a high-stability direct-current excitation power supply of a superconducting magnet based on double closed-loop control, relates to the technical field of precise electromagnetic control and high-stability power supply of a superconducting magnet, and through the cooperative closed-loop adjustment of a magnetic field and current, the magnetic field output precision and stability are improved while the external interference and system drift are inhibited, and the superconducting nuclear magnetic resonance system is supported to clearly image. The application feeds back the magnetic field state in real time through the introduction of a magnetic field detection module, and the cooperative control mode of current adjustment and magnetic field correction is combined, so that the magnetic field control is no longer dependent on the current set value, thereby the influence of coil parameter change, magnetic circuit nonlinearity, environmental temperature fluctuation and external magnetic disturbance on the magnetic field output can be effectively compensated. While the magnetic field adjustment response capability is ensured, the precision, stability and long-term operation reliability of the magnetic field output are improved, and the application is suitable for application scenarios with high requirements for magnetic field control.

Description

Technical Field

[0001] This invention relates to the field of precision electromagnetic control and high-stability power supply technology for superconducting magnets, specifically to a high-stability DC excitation power supply for superconducting magnets based on dual closed-loop control. Background Technology

[0002] Superconducting magnet excitation power supply control technology achieves precise control of magnetic field strength and stability through precise adjustment of the current in the excitation coil. It has significant application value in fields such as superconducting magnet actuation, precision physics experiments, nuclear magnetic resonance, magnetic measurement, and electromagnetic compatibility testing. High-performance DC excitation power supplies typically feature high output stability, high adjustment resolution, and low long-term drift, enabling them to maintain a constant target magnetic field or allow it to change smoothly according to a set pattern over extended periods, thus meeting the needs of high-precision experiments and engineering applications.

[0003] Existing high-stability DC excitation power supplies for superconducting magnets mostly employ constant current control, indirectly controlling the magnetic field by detecting the coil current and performing closed-loop regulation. This type of superconducting magnet excitation power supply has a relatively mature structure and fast response speed, and can meet the basic stability requirements of the magnetic field output to a certain extent. However, since the magnetic field is not solely determined by the current magnitude, factors such as coil parameter variations, magnetic circuit nonlinearity, ambient temperature fluctuations, and external magnetic disturbances can all cause deviations between the actual magnetic field and the theoretical value. Therefore, relying solely on current closed-loop control is insufficient to achieve high-precision and long-term stable control of the superconducting magnet's magnetic field.

[0004] Furthermore, while some existing technologies incorporate magnetic field sensors to monitor the magnetic field, they are mostly used for open-loop calibration or offline compensation, lacking a real-time coordinated adjustment mechanism with current control. During dynamic adjustment, issues such as response lag, insufficient accuracy, or high system complexity persist. Therefore, how to achieve precise closed-loop control of the magnetic field output while ensuring the dynamic response capability of the superconducting magnet excitation power supply, thereby improving system stability, disturbance rejection capability, and long-term operational reliability, remains a pressing technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-stability DC excitation power supply for superconducting magnets based on dual closed-loop control. Through coordinated closed-loop regulation of the magnetic field and current, it improves the accuracy and stability of the magnetic field output while suppressing external interference and system drift, supporting clear imaging in superconducting nuclear magnetic resonance systems. The coordinated closed-loop regulation of the magnetic field and current includes: a cascaded dual closed-loop structure: the inner loop is a current closed loop, where the coil current is detected in real time through a sampling resistor, and the control module quickly adjusts the output of the power amplifier module to achieve high dynamic response constant current control; the outer loop is a magnetic field closed loop, where a magnetic field detection module (such as a Hall sensor, fluxgate magnetometer, etc.) acquires the measured magnetic field value in real time, and the control module calculates the actual magnetic field based on this value, compares it with the current setpoint to generate a current correction value, and dynamically updates the target value of the inner current loop. Meanwhile, by combining the factory-calibrated coil constants and background field parameters, and introducing an online estimation mechanism to compensate for background field drift, a feedforward compensation term based on the actual load model can also be superimposed on the inner current loop. This effectively suppresses magnetic field deviations caused by coil parameter changes, magnetic circuit nonlinearity, temperature fluctuations, and external magnetic disturbances, significantly improving the accuracy, stability, and long-term reliability of the magnetic field output while ensuring response speed.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A high-stability DC excitation power supply for superconducting magnets based on dual closed-loop control, comprising:

[0008] AC input power;

[0009] The first and second DC power supplies, which are arranged in parallel, are respectively connected to the AC input power supply;

[0010] A first step-down module connected to a first DC power supply and a second step-down module connected to a second DC power supply, wherein the output terminals of the first step-down module and the second step-down module are respectively connected to the power supply terminal of the power amplifier module;

[0011] The magnetic field detection module is used to acquire external measurements corresponding to the coil load and provide real-time feedback on the magnetic field status.

[0012] The control module outputs a digital setting signal to the input of the digital-to-analog converter module. The control module receives the digital feedback signal output by the analog-to-digital converter module and the measurement signal output by the magnetic field detection module. It performs coordinated closed-loop regulation of the magnetic field and current to compensate for the effects of coil parameter changes, magnetic circuit nonlinearity, ambient temperature fluctuations and external magnetic disturbances on the magnetic field output.

[0013] The digital-to-analog converter module has its output connected to the input of the power amplifier module;

[0014] The power amplifier module has its output connected to the input of the coil load;

[0015] The feedback sampling module has its output connected to the input of the analog-to-digital converter module;

[0016] A sampling resistor is connected in series in the current loop of the coil load, and the detection signal across the sampling resistor is output to the input of the feedback sampling module.

[0017] Furthermore, the first DC power supply and the second DC power supply form a symmetrical power supply channel.

[0018] Furthermore, the control module is connected to the first buck module and the second buck module respectively via PWM control signals to adjust the output voltage of the first buck module and the second buck module.

[0019] Furthermore, the power amplifier module amplifies and converts the analog setting signal output by the digital-to-analog converter module into voltage and current, and outputs a bidirectional constant current to the coil load.

[0020] Furthermore, the control module determines or updates the target current based on the measurement signal output by the magnetic field detection module, and sends the updated target current to the digital-to-analog conversion module.

[0021] Furthermore, the control module includes at least a PWM generation unit, a communication interface unit, a closed-loop control calculation unit, and a status management unit.

[0022] Furthermore, the control module performs magnetic field calculation processing on the measurement signal output by the magnetic field detection module, converting the measurement signal into a magnetic field measurement value through linear mapping, piecewise linear mapping, or lookup table mapping.

[0023] Furthermore, the control module performs online estimation of the background field and bias term and forms an estimate, and uses the estimate to replace or correct the background field and bias term in the calculation of the outer loop of the magnetic field; when the preset stability condition is met, the control module updates the estimate.

[0024] Furthermore, the control module generates a feedforward compensation term based on the actual load model and superimposes the feedforward compensation term onto the voltage command candidate value of the inner current loop. The feedforward compensation term is calculated based on the magnet inductance parameters, equivalent resistance parameters, and current change rate.

[0025] Furthermore, it also includes a liquid crystal display module, which is connected to the control module and is used to display set values, feedback values, and working status information.

[0026] Beneficial effects:

[0027] This invention introduces a magnetic field detection module to provide real-time feedback on the magnetic field state, and combines current regulation and magnetic field correction in a coordinated control method. This allows magnetic field control to no longer rely solely on the current setpoint, thereby effectively compensating for the effects of coil parameter changes, magnetic circuit nonlinearity, ambient temperature fluctuations, and external magnetic disturbances on the magnetic field output. While ensuring the magnetic field regulation response capability, this invention improves the accuracy, stability, and long-term operational reliability of the magnetic field output, making it suitable for applications with high magnetic field control requirements, such as superconducting magnet driving, precision physics experiments, nuclear magnetic resonance, and magnetic measurement. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a high-stability DC excitation power supply for superconducting magnets based on dual closed-loop control according to the present invention.

[0029] Figure 2 This is a functional schematic diagram of a high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control, according to the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] like Figure 1As shown, this embodiment of a high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control includes an AC input power supply, a first DC power supply, a second DC power supply, a first buck module, a second buck module, a control module, a digital-to-analog converter module, a power amplifier module, a coil load, a sampling resistor, a feedback sampling module, an analog-to-digital converter module, a backup feedback, an LCD display module, and a magnetic field detection module. The AC input power supply is connected to both the first and second DC power supplies, which are arranged in parallel without cascading. The first DC power supply is connected to the first buck module, and the second DC power supply is connected to the second buck module. The output terminals of the first and second buck modules are connected to the power supply terminals of the power amplifier module to provide symmetrical power. The control module outputs PWM (Pulse Width Modulation) control signals to the first and second buck modules to adjust their outputs. The control module outputs a digital setting signal to the digital-to-analog converter module, and the digital-to-analog converter module outputs an analog setting signal to the input terminal of the power amplifier module. The module's output is connected to the coil load to output a bidirectional constant current. A sampling resistor is connected in series in the current loop of the coil load. The detection signal from the sampling resistor is sequentially input to the feedback sampling module and the analog-to-digital converter (ADC). The digital feedback signal from the ADC is sent back to the control module, thus forming a closed-loop current inner loop. The backup feedback serves as an additional input port for the ADC, used for debugging or status acquisition. The backup feedback and the ADC can be optionally connected. The LCD module is connected to the control module to display setpoints, feedback values, and operating status information. The magnetic field detection module acquires external measurements corresponding to the coil load. Its measurement signal is input to the control module as an outer loop input to update the target current setting.

[0032] The AC input power supply provides external AC power to the system. The first and second DC power supplies convert the AC input power into DC power, forming positive and negative power supply channels or symmetrical power supply channels, respectively, providing the energy basis for subsequent voltage reduction and power output. The first and second buck modules regulate the output of the first and second DC power supplies, and their outputs serve as the power supply for the power amplifier module. The control module modulates the first and second buck modules using PWM control signals, ensuring that the power amplifier module obtains a matched supply voltage under different load conditions to reduce power loss.

[0033] The control module performs control calculations and coordination management, and includes at least a PWM generation unit, a communication interface unit, a closed-loop control calculation unit, and a status management unit. The control module outputs a digital setting signal to the digital-to-analog converter (DAC) module and receives digital feedback signals from the DAC module to achieve closed-loop regulation. The DAC module converts the digital setting signal output by the control module into an analog setting signal (which can be a bipolar analog quantity) and outputs the analog setting signal to the input terminal of the power amplifier module. The power amplifier module amplifies and converts the analog setting signal output by the DAC module into a voltage-to-current signal, outputting a bidirectional constant current that meets the target value to the coil load. The sampling resistor converts the current in the coil load circuit into a sampling voltage signal corresponding to the current. The feedback sampling module conditions the sampling voltage signal across the sampling resistor, and the signal conditioning includes at least one or more of amplification, filtering, or bias processing. The DAC module converts the analog feedback signal output by the feedback sampling module into a digital feedback signal and sends it to the control module. Backup feedback provides an additional analog input signal channel to the DAC module for debugging, calibration, or status monitoring. The LCD display module is used to display system status information output by the control module. The magnetic field detection module is used to acquire external measurement quantities corresponding to the coil load, and its output is sent to the control module as an outer loop input signal to update the target current setting.

[0034] The control logic in this embodiment includes an inner current loop and an optional outer loop (e.g., an outer magnetic field loop):

[0035] (a) Inner Current Loop: During operation, the control module generates a digital setpoint corresponding to the target current and outputs it to the digital-to-analog converter (DAC). The DAC outputs an analog setpoint signal to the power amplifier module, which then outputs current to the coil load. The coil load loop current flows through the sampling resistor to generate a sampling voltage. This sampling voltage is conditioned by the feedback sampling module and input to the DAC. The DAC outputs a digital feedback signal to the control module. The control module performs closed-loop adjustment based on the deviation between the target current and the feedback current, updating the setpoint output to the DAC, thereby ensuring that the coil load current stably follows the target current and achieves constant current output.

[0036] The closed-loop regulation of the control module can employ proportional regulation, proportional-integral regulation, proportional-integral-derivative regulation, or other equivalent digital control algorithms; the analog-to-digital conversion module and the digital-to-analog conversion module can communicate with the control module through a serial interface, and the communication method does not constitute a limitation on the present invention.

[0037] (b) Power Supply Matching and Adjustment: To adapt to the voltage requirements of the coil load under different operating conditions, the control module outputs a PWM control signal to the first and second buck modules, ensuring symmetrical power supply from the first and second buck modules to the power supply terminal of the power amplifier module. The control module can adjust the output voltage of the first and second buck modules based on information such as target current, feedback current, output margin, or temperature rise status, thereby reducing power loss in the power amplifier module while meeting output requirements.

[0038] (c) Outer Loop Input: When an external measurement is required as the control target, the magnetic field detection module outputs a measurement signal to the control module. The control module determines or updates the target current based on the outer loop input signal and sends the updated setpoint to the digital-to-analog converter module, so that the coil load current is adjusted according to the outer loop target. The existence of the outer loop does not change the structure of the inner loop closed loop; the outer loop is used to generate the target value of the inner loop.

[0039] In this embodiment, the superconducting magnet, its current leads, and the connector resistance are equivalent to inductors. With equivalent resistance A series circuit, the control voltage applied by the power supply to the magnet end satisfy:

[0040] ;

[0041] The magnetic field quantity B and the coil current I satisfy the following:

[0042] ;

[0043] Where kB is the coil constant, I is the coil current, B0 is the background field and bias term, and t is time.

[0044] (d) Outer loop measurement signal processing, parameter calibration and drift compensation (optional).

[0045] In some embodiments, the measurement signal output by the magnetic field detection module can be an analog voltage signal, a digital signal, or a frequency-dependent signal. To enable the outer loop of the magnetic field to perform closed-loop calculations using the magnetic field quantity B as feedback, the control module performs magnetic field calculation and conversion processing on the measurement signal to obtain the measured magnetic field value. .

[0046] 1) Conversion of measurement signal to magnetic field quantity:

[0047] Let the original measurement signal output by the magnetic field detection module be... The control module can process the raw measurement signal according to the sensor type. After conversion, the measured magnetic field value is obtained. .

[0048] Optionally, the conversion relationship can take the form of linear mapping, piecewise linear mapping, or lookup table mapping, for example:

[0049] or ;

[0050] in, , The conversion coefficients are obtained from the calibration, and the LUT is a pre-stored mapping table.

[0051] For measuring devices that output frequency-dependent signals, frequency can be selected as an option. Linear mapping to magnetic field measurements: Where b1 and b0 are the conversion coefficients obtained from calibration.

[0052] Alternatively, a conversion relationship corresponding to the physical mechanism of the device (e.g., a conversion based on the gyromagnetic ratio) may be adopted. The above methods do not constitute a limitation of the present invention.

[0053] Optionally, to reduce the impact of noise on the outer loop, the control module can adjust the magnetic field measurement values. Digital filtering is performed to obtain the magnetic field disturbance B used for outer loop calculation. filt .

[0054] 2) Factory calibration of coil constant kB, background field, and bias term B0:

[0055] In some embodiments, the coil constant kB, background field, and bias term B0 can be obtained through factory calibration and stored in the non-volatile memory of the control module. Optionally, the calibration process includes: driving the coil load to output a stable current at at least two different current points (I1, I2), and measuring the corresponding magnetic fields (B1, B2) by the magnetic field detection module, thereby calculating:

[0056] ;

[0057] ;

[0058] Further, alternatively, multi-point current / magnetic field sampling can be used for least squares fitting or piecewise fitting to obtain higher accuracy coil constant kB and background field and bias term B0.

[0059] 3) Online drift estimation and compensation:

[0060] During long-term operation, the background field and bias term B0 may change slowly due to environmental magnetic disturbances, temperature variations, or zero-point drift of the measuring device. To improve the long-term stability of the outer-loop closed-loop control, the control module can optionally perform online estimation of the background field term to generate an estimate. and with estimates The background field and bias term B0 are replaced or corrected and included in the outer loop calculation. Optionally, when preset stability conditions are met (e.g., the current change rate |dI / dt| is less than a threshold and the absolute value of the current inner loop error is less than a threshold), the control module updates the estimate. ,For example:

[0061] ;

[0062] Where λ is the drift estimation coefficient (0 < λ < 1), and k is the number of iterations. For feedback current, This is a magnetic field disturbance.

[0063] When in a rapid climb or transient adjustment phase, the update of the estimator can be paused. This is to avoid transient errors introducing drift estimation.

[0064] By using the above-mentioned measurement signal calculation, factory calibration and online drift compensation methods, the outer loop of the magnetic field can obtain a feedback quantity corresponding to the actual magnetic field, and maintain the absolute accuracy and long-term stability of the magnetic field control under external disturbances and slow drift conditions.

[0065] Specifically, this invention employs a cascaded closed-loop control structure, including an inner current loop and an outer magnetic field loop: the inner current loop generates a control voltage command using the coil current as feedback to achieve rapid and stable current regulation; the outer magnetic field loop generates a current correction value using the magnetic field detection signal as feedback and superimposes it onto the current command to correct magnetic field deviation, thereby compensating for magnetic field drift caused by flux creep, temperature fluctuations, and environmental disturbances. Furthermore, to adapt to the large inductance characteristics of superconducting magnets, a slope limit is applied to the current command, and amplitude limiting and anti-integral saturation processing are performed at the voltage output; simultaneously, an ideal value based on the required voltage is introduced. Feedforward compensation is used to improve tracking performance during the magnet current ramp-up phase and reduce steady-state error.

[0066] ;

[0067] Among them, U idel The ideal value for the required voltage. This is a current command. Through the above control method, the absolute accuracy and long-term stability of the magnetic field output are improved while ensuring system safety and controllability.

[0068] Optionally, the magnetic field detection module includes one or more of a spectrometer, a magnetic resonance probe, a fluxgate sensor, or a Hall magnetic field sensor, used to convert magnetic field changes into electrical signals or frequency-related signals for output.

[0069] Optionally, the control module performs magnetic field calculation processing on the detection signal output by the magnetic field detection module, converting the detection signal into a magnetic field measurement value. It can obtain conversion coefficients, coil constant kB, background field, and bias term B0 through factory calibration, and perform online estimation and compensation for zero-point drift of background field during operation to improve the absolute accuracy and long-term stability of magnetic field closed-loop control.

[0070] Optionally, the control module includes a current control unit and a magnetic field correction unit; the current control unit uses the current signal of the excitation coil as feedback to achieve rapid adjustment of the drive current; the magnetic field correction unit uses the detection signal output by the magnetic field detection module as feedback to finely adjust the magnetic field output.

[0071] Optionally, both the first and second step-down modules include a linear constant current circuit, a switching modulation circuit, or a combination of both, to balance the stability of the magnetic field output and the system energy utilization efficiency.

[0072] Optionally, the magnetic field detection module and the control module adopt a digital signal transmission method to improve the anti-interference capability of the detection signal in complex electromagnetic environments.

[0073] Optionally, the digital-to-analog conversion module further includes a reference power supply module for providing a stable reference signal to the magnetic field detection module and the control module.

[0074] Optionally, the control module adjusts the control parameters according to the system operating status to coordinate the magnetic field adjustment speed and the stability of the magnetic field output.

[0075] Example:

[0076] The superconducting magnet in this embodiment can be equivalent to an inductor. With equivalent resistance Series circuit, magnet terminal voltage satisfy:

[0077] ;

[0078] Where t represents time.

[0079] The control module adopts a cascaded double closed-loop structure of an outer magnetic field loop and an inner current loop:

[0080] (1) Outer ring of magnetic field: based on the measured value of magnetic field With magnetic field setting value Deviation is the input, magnetic field error Defined as:

[0081] ;

[0082] Correction amount of current generated in the outer loop of the magnetic field (Branch A) or (Branch B), and update the current target accordingly. The outer loop of the magnetic field only updates the target current and does not directly output a PWM control signal.

[0083] (2) Inner current loop: based on the target current With feedback current The deviation is the input, current error. Defined as:

[0084] ;

[0085] Inner current loop calculation magnet terminal voltage command This signal is mapped to a PWM control signal to drive a switching bidirectional power converter, enabling the magnet current to quickly follow the target current. .

[0086] (3) Control cycle setting:

[0087] The inner current loop period is The outer loop period of the magnetic field is And satisfy:

[0088] ;

[0089] Where N is an integer multiple of the outer loop period and the inner loop period, used to characterize the update frequency of the outer loop relative to the inner loop. That is, for every update performed by the outer magnetic field loop, the inner current loop performs N control operations. The inner current loop executes at a high frequency (sampling current → calculation → updating PWM pulse width), while the outer magnetic field loop executes at a low frequency (sampling magnetic field → updating target current). ).

[0090] Specifically, the working process of the present invention includes the following steps, which are executed by the control module:

[0091] S1 Initialization and Mode Entry:

[0092] S1.1 Read and set the magnetic field setting value and base current The relationship is determined (either by user setting or by calibration).

[0093] S1.2 Set current limit Current slope limitation Voltage command limiting And protection thresholds (overcurrent, overvoltage, overtemperature, sensor malfunction).

[0094] S1.3 Start-up current inner loop control task (cycle) ), initiate the outer loop control task of the magnetic field (cycle) ).

[0095] S2 Magnetic Field Outer Ring Update Target Current (Period) ).

[0096] S2.1 Sampling magnetic field measurement value Calculate the magnetic field error:

[0097] ;

[0098] S2.2 Generate the current correction amount based on the outer loop strategy (select branch A or branch B as shown below).

[0099] S2.3 Target Current:

[0100] ;

[0101] in, The initial target current, without amplitude limiting or slope limiting, is obtained from the outer loop of the magnetic field. Subsequent amplitude limiting and slope limiting are typically applied to generate the final inner loop target current. . The current setting value is corresponding to the set magnetic field. To determine the magnetic field error e B The obtained current correction amount.

[0102] S2.4 applies engineering constraints to the target current:

[0103] (a) Amplitude limiting: ;sat represents the amplitude limiting function, This indicates the maximum current value.

[0104] (b) Slope constraints: ;ramp represents the slope function. This represents the maximum value of the rate of change of current.

[0105] S2.5 will update the target current Send it to the inner current loop.

[0106] Branch A: Discrete fine-tuning outer loop (using threshold time and fixed step), including:

[0107] A1 sets the magnetic field threshold band. Bth, threshold time Fine-tuning the step current and current correction limit .

[0108] A2 When the magnetic field error At the same time, maintain the current correction amount constant.

[0109] A3 When magnetic field error (The magnetic field is too low, and current needs to be increased) The duration reaches the threshold time. When, execute And reset the "low" timing.

[0110] A4 When magnetic field error (Magnetic field too high, current reduction required) Duration reaches threshold time When, execute And reset the "too high" timer.

[0111] A5 Current Correction Amount Limiting the amplitude: .

[0112] As an example, the outer ring of the magnetic field can be fine-tuned using a discrete fine-tuning method that measures the magnetic field every 5 seconds, adjusts it only once every 15 consecutive seconds when the threshold is exceeded, and the step size is 4.4µA (approximately 0.1µT).

[0113] Branch B: Proportional-integral continuous correction outer loop, including:

[0114] B1 Calculates candidate values ​​for current correction. , The proportionality coefficient of the outer loop of the magnetic field:

[0115] ;

[0116] And update the points system:

[0117] ;

[0118] Among them, K iB The integral coefficient of the outer loop of the magnetic field. For magnetic field error, This is the outer loop control cycle of the magnetic field. It is the integral state quantity of the outer current loop.

[0119] B2 Candidate values ​​for current correction Limiting: Current correction amount after limiting ; This is the maximum correction amount for the current.

[0120] B3 When it happens At that time, the integral state quantity of the outer current loop Perform anti-integral saturation processing (freeze or backcalculate) to suppress overshoot during recovery.

[0121] B4 Current Correction Amount Apply slope constraints: ;

[0122] in, This represents the maximum rate of change of current under magnetic field quantity B.

[0123] B5 will adjust the current amount. Input S2.3~S2.4 to update the target current.

[0124] S3 current inner loop execution (cycle) ),include:

[0125] S3.1 Sample Feedback Current Calculate the current error : ;

[0126] S3.2 Output voltage command candidate value via current regulator (e.g., using PI control):

[0127] ;

[0128] And update the points system: ;

[0129] in, The candidate voltage command values ​​are calculated using the inner-loop proportional-integral (PI) PI algorithm. This is the integral state quantity of the inner current loop. This is the proportionality coefficient for the inner current loop. This is the integral coefficient of the inner current loop.

[0130] S3.3 (Optional) Generate and superimpose feedforward compensation terms based on the actual load model:

[0131] ;

[0132] in, For feedforward voltage, The equivalent inductance of the magnet is... For equivalent series resistance, This is the target current within the previous inner loop cycle. The feedforward coefficient is used to adjust the feedforward ratio. These are candidate values ​​for the voltage command after the feedforward is superimposed.

[0133] When feedforward is not used, let: ;

[0134] S3.4 Limits the voltage command: ;

[0135] in, This indicates the maximum voltage value.

[0136] S3.5 When it occurs At that time, the integral state quantity of the inner current loop Perform anti-integral saturation processing (freeze or backcalculate) to reduce overshoot during saturation recovery.

[0137] S3.6 will send voltage command The signal is mapped to a PWM control signal, and the modulation amount is constrained within the allowable range; the PWM control signal is updated to drive the bidirectional switching power stage to generate a magnet terminal voltage at the magnet terminal. , so that the feedback current Rapidly follow the target current .

[0138] Preferably, the outer ring period is an integer multiple of the inner ring period. .

[0139] Preferably, the safety margin is determined based on the voltage margin, for example, satisfying: And set a safety margin.

[0140] Preferably, the outer loop period of the magnetic field Preferred time: 1s to 10s; Threshold time Preferred time: 5s to 60s; fine-tuning of step current. Preferably, the voltage is 1µA to 20µA. Maximum voltage value. Determined by bus voltage and topology.

[0141] like Figure 2 As shown, the present invention can be generally divided into a control loop, a measurement feedback loop, a power loop, and a protection and status monitoring part and a protection control part coupled thereto. The loops and parts are coordinated in a closed loop through current commands, modulation signals and measurement feedback signals.

[0142] The control loop includes a host computer, a control module, and a slope / limiting management unit. The host computer is used to input and send operating parameters, which include at least: magnetic field setpoint. The controller specifies the operating mode and various limits. It performs closed-loop control calculations and includes at least a current control unit and a magnetic field correction unit. The current control unit generates a current control quantity based on the deviation between the target current and the feedback current; the magnetic field correction unit generates a current correction quantity based on the deviation between the set magnetic field and the measured magnetic field, and corrects the current target. The controller outputs a current command. To the slope / limiting management unit. The slope / limiting management unit is used to perform engineering constraint processing on the current command, including at least: Applying slope limits prevents excessively rapid current changes and allows for unified management of protection thresholds, thereby outputting control quantities that meet safety constraints.

[0143] The measurement feedback loop includes at least a magnetic field detection module and a current sampling module, used to provide closed-loop feedback signals to the controller. The magnetic field detection module is used to acquire the measured magnetic field value. This can be achieved using sensors such as spectrometers, fluxgate magnetometers, and Hall effect probes, and the magnetic field measurement signal is output to the controller. The current sampling module is used to acquire the current measurement value. It may include a sampling resistor or current sensor, as well as signal conditioning circuits such as amplification and filtering circuits and analog-to-digital conversion circuits, and outputs the current measurement signal to the controller. The controller then calculates the magnetic field measurement value. With current measurement value The outer loop correction of the magnetic field and the inner loop control of the current are completed separately, thus forming a cascaded double closed loop.

[0144] The power circuit converts the control signal output from the control circuit into a controlled output voltage / current for the superconducting magnet / excitation coil. The power circuit is fronted by the main power supply / DC bus, providing energy input. A pre-regulator / voltage regulator module (optional) can be placed between the main power supply and the constant current drive module to improve the controllability or efficiency of subsequent stages over a wider input range. The constant current drive module converts the control signal into an output drive quantity, which can be linear, switching, or a hybrid linear / switching mode. The constant current drive module outputs drive quantities such as "output drive voltage / duty cycle". Following the constant current drive module is an output stage / protection module, which at least implements freewheeling, interlocking, and overvoltage / overcurrent protection functions, and is linked with the protection and status monitoring unit on the right. The output terminal is connected to the superconducting magnet / excitation coil load.

[0145] The protection and status monitoring unit monitors the operating status and triggers protection controls in case of abnormalities. The protection and status monitoring unit detects at least the following conditions: overvoltage, overcurrent, overtemperature, and sensor malfunction, and outputs protection trigger signals. The protection control unit executes safety actions based on the protection trigger signals. These actions include at least current reduction, shutdown, and alarm, and feeds back protection constraints to the slope / limiting management unit and / or controls the power circuit, thereby achieving closed-loop safety protection.

[0146] Through the above structure, the system achieves closed-loop control and protection coordination of "magnetic field setting - magnetic field measurement - current target correction - constant current drive output - current / magnetic field feedback".

[0147] This embodiment provides the control logic, data path, and timing update relationship of the outer and inner loops of the magnetic field. The core of this embodiment is that the outer loop of the magnetic field generates a current correction amount and writes it into the cache. The inner loop of the current reads the cache at a specified boundary to update the target current, thus avoiding oscillation caused by the two loops competing with each other in terms of timing.

[0148] Input magnetic field setting value and basic current command Magnetic field measurement values (Obtained from the magnetic field detection module) Enters the outer loop control module of the magnetic field. The outer loop of the magnetic field is in the outer loop period. The following is executed according to the magnetic field setting value. With magnetic field measurement value The deviation is used to calculate the correction amount for the outer loop current of the magnetic field, and the result is output as the correction amount for the outer loop current of the magnetic field. The updated value. This is the correction amount for the outer loop current of the magnetic field. It is used to compensate for the effects of magnetic field drift, zero-point offset or other slowly changing errors on magnetic field stability.

[0149] The current target update module is configured to execute at a relatively long update period Tc. At each Tc boundary time, the current target update reads the correction amount of the outer loop current of the magnetic field from the cache. and link it with the base current command The target current is generated after superposition. :

[0150] ;

[0151] Here, ramp(·) represents applying a slope limit to the target current so that the change in the target current meets the preset current change rate dI / dt constraint, thereby avoiding the risk of voltage saturation or oscillation under large inductive loads. Reads only occur at specified boundaries ("read only at Tc boundary"), thus achieving a decoupling mechanism between outer-loop write caching and inner-loop fixed-point value retrieval.

[0152] The control module of the current inner loop uses feedback current. With target current As input, it performs current closed-loop calculation within the inner loop cycle and outputs voltage control commands. The inner current loop includes limiting and anti-integral saturation measures: when a voltage control command is given... When voltage limiting occurs due to limitations in the power stage voltage capability, the inner current loop freezes or backcalculates the integral term to suppress overshoot during saturation recovery. The inner current loop outputs a voltage control command. It enters the output drive, forming a bidirectional drive output for the power stage, thereby driving current to flow through the coil load.

[0153] The power output is applied to the coil load, and the current is sampled to form the feedback current. Returning to the inner current loop, the coil current I simultaneously generates a magnetic field output through the magnetic field-current relationship, i.e., utilizing... This indicates the correspondence between a magnetic field and an electric current; the magnetic field is measured by a sensor to form a magnetic field measurement value. Return to the outer loop of the magnetic field.

[0154] Preferably, the outer loop updates the magnetic field outer loop current correction only during the Tb cycle. Target current Read the target current only at the Tc boundary And update. By using a combination of cache write-boundary read-slope limit mechanism, the system avoids the double-loop coupling oscillation caused by the outer and inner loops simultaneously and frequently contending for the same target variable, thereby improving system stability and feasibility.

[0155] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0156] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control, characterized in that, include: AC input power; The first and second DC power supplies, which are arranged in parallel, are respectively connected to the AC input power supply; A first step-down module connected to a first DC power supply and a second step-down module connected to a second DC power supply, wherein the output terminals of the first step-down module and the second step-down module are respectively connected to the power supply terminal of the power amplifier module; The magnetic field detection module is used to acquire external measurements corresponding to the coil load and provide real-time feedback on the magnetic field status. The control module outputs a digital setting signal to the input of the digital-to-analog converter module. The control module receives the digital feedback signal output by the analog-to-digital converter module and the measurement signal output by the magnetic field detection module. It performs coordinated closed-loop regulation of the magnetic field and current to compensate for the effects of coil parameter changes, magnetic circuit nonlinearity, ambient temperature fluctuations and external magnetic disturbances on the magnetic field output. The digital-to-analog converter module has its output connected to the input of the power amplifier module; The power amplifier module has its output connected to the input of the coil load; The feedback sampling module has its output connected to the input of the analog-to-digital converter module; A sampling resistor is connected in series in the current loop of the coil load, and the detection signal across the sampling resistor is output to the input of the feedback sampling module.

2. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, The first DC power supply and the second DC power supply form a symmetrical power supply channel.

3. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, The control module is connected to the first buck module and the second buck module respectively via PWM control signals to adjust the output voltage of the first buck module and the second buck module.

4. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, The power amplifier module amplifies and converts the analog setting signal output by the digital-to-analog converter module into voltage and current, and outputs a bidirectional constant current to the coil load.

5. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, The control module determines or updates the target current based on the measurement signal output by the magnetic field detection module, and sends the updated target current to the digital-to-analog conversion module.

6. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, The control module includes at least a PWM generation unit, a communication interface unit, a closed-loop control calculation unit, and a status management unit.

7. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, The control module performs magnetic field calculation processing on the measurement signal output by the magnetic field detection module, converting the measurement signal into a magnetic field measurement value through linear mapping, piecewise linear mapping, or lookup table mapping.

8. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 7, characterized in that, The control module performs online estimation of the background field and bias term and forms an estimate, and uses the estimate to replace or correct the background field and bias term in the calculation of the outer loop of the magnetic field; when the preset stability condition is met, the control module updates the estimate.

9. The high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, The control module generates a feedforward compensation term based on the actual load model and superimposes the feedforward compensation term onto the voltage command candidate value of the inner current loop. The feedforward compensation term is calculated based on the magnet inductance parameters, equivalent resistance parameters, and current change rate.

10. A high-stability DC excitation power supply for a superconducting magnet based on dual closed-loop control according to claim 1, characterized in that, It also includes a liquid crystal display module, which is connected to the control module and is used to display set values, feedback values ​​and working status information.

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