A high-precision current control method for a programmed degaussing current source

Abstract

The application provides a high-precision current control method for a program-controlled degaussing current source. First, a mathematical model of the program-controlled degaussing current source under a nonlinear load is established according to the Kirchhoff law, and a state space expression of the program-controlled degaussing current source is constructed based on the mathematical model. Then, aiming at the current fluctuation caused by the time-varying of the nonlinear load parameters and the parameter perturbation of electronic components and other disturbances in the program-controlled degaussing current source system, a cascaded extended state observer is designed to observe the lumped disturbance, and the observed lumped disturbance is compensated through a feedforward channel. Finally, a composite controller based on the cascaded extended state observer and the sliding mode control is designed to suppress the influence of the lumped disturbance on the output current of the program-controlled degaussing current source, and high-precision degaussing current output is realized. The application realizes high-precision degaussing current output under the existence of various disturbances such as time-varying of nonlinear load parameters, so as to improve the degaussing performance of the magnetic shielding device.

Description

Technical Field

[0001] This invention belongs to the field of demagnetizing power supply control technology, specifically relating to a high-precision current control method for a programmable demagnetizing current source. Background Technology

[0002] Currently, near-zero magnetic field environments have wide and unique applications in various fields such as quantum information technology, bioelectromagnetics, aerospace, and defense engineering. Magnetic shielding devices are an effective method for shielding external magnetic fields and achieving near-zero magnetic field environments. They often combine passive shielding systems and active magnetic compensation systems to meet the requirements of near-zero magnetic fields. The shielding layer of a magnetic shielding device is typically composed of highly permeable materials (such as permalloy) and highly conductive materials. The highly permeable materials shield low-frequency magnetic fields based on the magnetic flux shunting effect, while the highly conductive materials shield high-frequency magnetic fields based on the eddy current effect.

[0003] Typically, passive shielding systems in magnetic shielding devices employ multiple layers of soft magnetic materials such as permalloy to form the shielding layers. Therefore, while shielding against external magnetic fields, the shielding layers become incompletely and reversibly magnetized, resulting in residual magnetism within the shielding material itself. Furthermore, stress during installation and transportation can also cause residual magnetism in the shielding material. The magnitude of the residual magnetic field in a magnetic shielding device depends on the sum of the external static magnetic field and the shielding material's own magnetic field. Excessive residual magnetism in the shielding material can negatively impact the shielding performance of the device. Therefore, demagnetizing the shielding material is a key technology for reducing the residual magnetic field and improving the shielding performance of magnetic shielding devices.

[0004] Common demagnetizing methods include static demagnetization, thermal demagnetization, and dynamic demagnetization. Static demagnetization requires a strong reverse magnetic field, the intensity of which varies with the operating temperature. Thermal demagnetization involves heating the material to be demagnetized to above the Curie temperature. While this method effectively eliminates residual magnetization, it also damages other physical properties of the material and is not suitable for large and medium-sized magnetic shielding devices that have already been assembled. Dynamic demagnetization can be divided into direct current (DC) demagnetization and alternating current (AC) demagnetization. Its working principle involves placing the workpiece in an alternating, decaying magnetic field, demagnetizing along a decreasing hysteresis loop. DC demagnetization requires frequent changes in the direction of the DC current, and the attenuation amplitude of the current should be as small as possible. AC demagnetization can be divided into the through-current method and the attenuation method. The through-current method is suitable for batch demagnetization of small and medium-sized workpieces but is not suitable for large and medium-sized multi-layered complex magnetic shielding devices. Currently, most demagnetization of magnetic shielding devices uses the relatively easy-to-implement attenuation method. This involves winding a demagnetizing coil around the magnetic shielding device and introducing an alternating attenuating sinusoidal demagnetizing current into the coil to demagnetize the entire magnetic shielding device. To achieve effective demagnetization of the magnetic shielding material, the demagnetizing current needs to meet the following requirements: (1) The initial value of the demagnetizing current should be large enough to saturate the magnetic shielding material; (2) The attenuation step of the demagnetizing current should be as small as possible; (3) The parameters of the demagnetizing current should be adjustable. These special requirements for the demagnetizing current place higher demands on the design of the demagnetizing power supply. Unlike ordinary inverter power supplies, the demagnetizing power supply requires a large dynamic range of output current, needs to generate a variety of controllable attenuating sinusoidal currents, and has high control accuracy for small-amplitude currents. In addition, as the load of the demagnetizing power supply, the electrical parameters of the demagnetizing coil of the magnetic shielding device have nonlinear and time-varying characteristics, causing distortion of the current at different amplitudes and frequencies. The non-sinusoidal demagnetizing current will affect the demagnetization effect of the shielding material, thereby affecting the shielding performance of the magnetic shielding device. Furthermore, disturbances in the inverter power supply system, such as the non-ideal characteristics and parameter uncertainties of electronic components, can also generate harmonics in the output current, affecting the output current quality and increasing the uncertainty of the demagnetizing effect. Therefore, how to achieve high-precision current disturbance rejection control under the premise of high power and wide current range output is a major problem that needs to be solved in the development of demagnetizing power supplies.

[0005] Extended state observers, as a crucial component of active disturbance rejection control (ADRC), treat parameter uncertainties, external disturbances, and unmodeled dynamics as lumped disturbances, expanding them into new state variables of the original system. By estimating the lumped disturbances and compensating for them in the controller, the adverse effects of disturbances on the system are suppressed. However, when the controlled system order is greater than 2, configuring the parameters of the extended state observer becomes extremely difficult in practical engineering applications. Sliding mode control, a variable structure control, employs different control laws based on changes in the system's current state variables, causing the system state to move along a predetermined sliding mode trajectory. The sliding mode can be designed automatically, and once the system enters the sliding mode, it is independent of the original system state and external disturbances, thus exhibiting strong robustness. However, discontinuous switching of the controller can lead to chattering problems. A composite control method combining sliding mode controllers with disturbance estimation compensation can effectively suppress chattering. Summary of the Invention

[0006] To achieve high-precision demagnetizing current output under various disturbances, including time-varying nonlinear load parameters, this invention proposes a high-precision current control method for a programmable demagnetizing current source. This method employs a cascaded extended state observer to monitor lumped disturbances and compensates for these disturbances using a feedforward channel. A composite controller combining the cascaded extended state observer and sliding mode control suppresses the impact of lumped disturbances on the output current of the programmable demagnetizing current source, achieving high-precision demagnetizing current output. The designed method reduces the number of observer parameters that need to be tuned for higher-order systems, lowers the complexity of parameter configuration for extended state observers in practical engineering applications of higher-order systems, improves the disturbance rejection capability of the programmable demagnetizing current source system, and further enhances the accuracy of the output current.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A high-precision current control method for a programmable demagnetizing current source includes the following steps:

[0009] Step 1: Establish a mathematical model of the programmable demagnetizing current source under a nonlinear load based on Kirchhoff's laws, and construct the state-space expression of the programmable demagnetizing current source based on this mathematical model.

[0010] Step 2: Design a cascaded extended state observer to observe the lumped disturbances in the programmable demagnetizing current source system, and compensate for the observed disturbances in the controller through a feedforward channel; the lumped disturbances include various disturbances, such as current fluctuations caused by time-varying nonlinear load parameters and perturbations of electronic component parameters;

[0011] Step 3: Design a composite controller based on a combination of cascaded extended state observer and sliding mode control to suppress the influence of lumped disturbances on the output current of the programmable demagnetizing current source and achieve high-precision demagnetizing current output.

[0012] Further, step 1 includes:

[0013] According to Kirchhoff's laws, the mathematical model of a single-phase full-bridge inverter under nonlinear load is as follows:

[0014]

[0015] Among them, V dc V in V o These represent the DC bus voltage, inverter output voltage, and load voltage, respectively; u is the control input; i L i C i o These represent the inductor current, capacitor current, and load current, respectively. e L is the equivalent resistance of the inverter. f C f These are the inductor and capacitor of an LC filter, respectively. l R l These are the inductance and resistance of the nonlinear load, respectively;

[0016] Select system state variables as x1 represents the load current i o x2 represents the first derivative of the load current. x3 represents the second derivative of the load current. The system state equations are written as follows:

[0017]

[0018] Furthermore, in step 2, designing the cascaded extended state observer includes:

[0019] Considering the disturbance, the system state equation can be further written as:

[0020]

[0021] in, Δ1, Δ2, and Δ3 represent the system parameter uncertainties, and w(t) represents the external disturbance.

[0022] The system state-space expression can then be further expressed as:

[0023]

[0024] Let the lumped disturbance f′ include parameter uncertainty, internal unknown disturbance, and external unknown disturbance, and be expressed as:

[0025] f′=f(x1,x2,x3)+w(t)

[0026] =-(a1+Δ1)x1-(a2+Δ2)x2-(a3+Δ3)x3

[0027] Treating the lumped disturbance f′ as the extended state variable of the system, i.e., x4 = f′, h represents the first derivative of the lumped disturbance f′. Assuming the disturbance and its derivative are bounded and continuous, the extended state equation of the programmable demagnetizing current source system can be written as:

[0028]

[0029] y = x1

[0030] Where y represents the output of the state equation.

[0031] Based on the above extended state equations, in order to reduce the parameters of the observers to be tuned and simplify the parameter configuration, three cascaded second-order extended state observers with the same parameters are designed to observe the lumped disturbances.

[0032] Define the state variable as in, Estimate x1, Estimate x2, Estimate x3, Estimate the lumped disturbance f′, and For the cascaded extended state observer, the intermediate variable is defined as: The state equations of the cascaded extended state observer are as follows:

[0033]

[0034] in, For the parameters of the linear cascaded extended state observer, The observation error of the load current x1, The observation error is the first derivative of the load current, x2. The observation error is the second derivative of the load current, x3. The observation error is the lumped disturbance f′. This is the difference between the intermediate variable and the output of the previous level extended state observer.

[0035] Further, step 3 includes:

[0036] Subtracting the state equation of the cascaded extended state observer from the extended state equation, we obtain the error equation of the cascaded extended state observer as follows:

[0037]

[0038] Let the load current reference command be i ref Define the tracking error vector as Select the sliding surface s as:

[0039] s=c1ξ1+c2ξ2+ξ3

[0040] Where c1 and c2 are positive real numbers; differentiating the above equation, we have:

[0041]

[0042] in, The third derivative is used as a reference for the load current.

[0043] Combining the system state-space expression, the sliding mode control law is further obtained as follows:

[0044]

[0045] The exponential convergence law is selected as follows:

[0046]

[0047] Where ε is the switching gain, k is the approach speed parameter, and sgn() is the sign function;

[0048] By incorporating the exponential reaching law into the sliding mode control law, and using the lumped disturbance observed by the cascaded extended state observer to compensate for the disturbance in the sliding mode control law, the composite control law based on the cascaded extended state observer and sliding mode control is designed as follows:

[0049]

[0050] The advantages of this invention compared to the prior art are as follows:

[0051] 1. This invention utilizes a cascaded extended state observer to estimate the lumped disturbance of a programmable demagnetizing current source system, reducing the number of observer parameters that need to be tuned for higher-order systems. This significantly reduces the complexity of parameter configuration for extended state observers in practical engineering applications of higher-order systems, and makes engineering experiments relatively simple.

[0052] 2. This invention employs a robust sliding mode control method, which improves the disturbance suppression capability of the programmable demagnetizing current source and achieves high-precision demagnetizing current output under various disturbances such as time-varying nonlinear load parameters, thereby comprehensively improving demagnetizing accuracy and precision. Furthermore, the composite control method combining sliding mode controller disturbance estimation and compensation effectively suppresses chattering issues caused by sliding mode control.

[0053] 3. This invention is a composite control method for demagnetizing current source inverter systems based on cascaded extended state observers and sliding mode control. It improves the disturbance suppression capability and robustness of programmable demagnetizing current source systems, and realizes high-precision demagnetizing current output under various disturbances such as time-varying nonlinear load parameters, thereby improving demagnetizing performance. Attached Figure Description

[0054] Figure 1 This is a flowchart of the high-precision current control method for the programmable demagnetizing power supply of the present invention;

[0055] Figure 2 This is a schematic diagram of the programmable demagnetizing power supply system of the present invention;

[0056] Figure 3 This is a block diagram of the high-precision current control of the programmable demagnetizing power supply based on the cascaded extended state observer and sliding mode control of the present invention.

[0057] In the diagram: 1 is three-phase AC power, 2 is a single-phase full-bridge inverter, 3 is an LC filter, 4 is a nonlinear resistive-inductive load, 5 is a current sensor, 6 is an A / D acquisition module, 7 is a control unit, 8 is an SPWM generator, 9 is a sliding mode controller, and 10 is a cascaded expansion state observer. Detailed Implementation

[0058] 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.

[0059] like Figure 1 As shown, the high-precision current control method for a programmable demagnetizing power supply of the present invention first establishes a mathematical model of the programmable demagnetizing current source under nonlinear load based on Kirchhoff's laws, and constructs a state-space expression for the programmable demagnetizing current source based on this mathematical model; then, a cascaded extended state observer is designed to observe the lumped disturbances in the programmable demagnetizing current source system. The lumped disturbances include current fluctuations caused by time-varying nonlinear load parameters, perturbations of electronic component parameters, and other disturbances. The observed disturbances are compensated in the controller through a feedforward channel; finally, a composite controller based on the combination of the cascaded extended state observer and sliding mode control is designed to suppress the influence of lumped disturbances on the output current of the programmable demagnetizing current source, thereby achieving high-precision demagnetizing current output.

[0060] like Figure 2As shown, the programmable demagnetizing current source consists of a three-phase AC power supply 1, a single-phase full-bridge inverter 2, an LC filter 3, a nonlinear resistive-inductive load 4, a current sensor 5, an A / D acquisition module 6, a controller 7, and an SPWM generator 8. The three-phase AC power supply 1 generates a DC bus voltage after rectification, which is then inverted into a demagnetizing current by the single-phase full-bridge inverter 2. The LC filter 3 filters out high-frequency harmonics in the demagnetizing current. The nonlinear resistive-inductive load 4 is an equivalent load model of the demagnetizing coil of the magnetically shielded cabin. The current sensor 5 acquires the current of the nonlinear resistive-inductive load 4, i.e., the demagnetizing current. The current information is acquired by the A / D acquisition module 6 and sent to the controller 7. The controller 7 outputs a duty cycle control quantity based on the input reference current signal and the acquired current information. This quantity is then used by the SPWM generator 8 to generate the switching signal for the single-phase full-bridge inverter 2, thereby achieving sinusoidal current tracking and generating the required demagnetizing current.

[0061] like Figure 3 As shown, the high-precision current control block diagram of the programmable demagnetizing current source is presented. The load current and the control output of the sliding mode controller 9 are used as the input of the cascaded extended state observer 10. The cascaded extended state observer 10 observes the lumped disturbance and uses the estimated disturbance, the reference current and related variables, and the load current and related variables as the input of the sliding mode controller 9.

[0062] The specific implementation steps of this invention are as follows:

[0063] Step (1): Establish a mathematical model for a nonlinear load under a programmable demagnetizing current source:

[0064] According to Kirchhoff's laws, the mathematical model of a single-phase full-bridge inverter under nonlinear load is as follows:

[0065]

[0066] Among them, V dc V in V o These represent the DC bus voltage, inverter output voltage, and load voltage, respectively; u is the control input; i L i C i o These represent the inductor current, capacitor current, and load current, respectively. e L is the equivalent resistance of the inverter. f C f These are the inductor and capacitor of an LC filter, respectively. l R l These are the inductance and resistance of the nonlinear load, respectively.

[0067] Select system state variables as x1 represents the load current i o x2 represents the first derivative of the load current. x3 represents the second derivative of the load current. The system state equation can be written as:

[0068]

[0069] Step (2): Design the cascaded extended state observer:

[0070] Many uncertainties exist in actual inverter systems, such as deviations between actual and theoretical parameters of the filter inductor and capacitor, the inability to accurately measure their equivalent resistance, aging of the filter inductor and capacitor, and temperature variations during system operation. Furthermore, since the demagnetizing coil is a nonlinear load, it exhibits time-varying characteristics under the influence of the demagnetizing current. Considering the disturbance, the system state equation can be further written as:

[0071]

[0072] in, Δ1, Δ2, and Δ3 represent the system parameter uncertainties, and w(t) represents the external disturbance.

[0073] The system state-space expression can then be further expressed as:

[0074]

[0075] Let the "lumped disturbance" include parameter uncertainty, internal unknown disturbance, and external unknown disturbance, and express it as:

[0076] f′=f(x1,x2,x3)+w(t)

[0077] =-(a1+Δ1)x1-(a2+Δ2)x2-(a3+Δ3)x3

[0078] Treating the lumped disturbance f′ as the extended state variable of the system, i.e., x4 = f′, h represents the first derivative of the lumped disturbance f′, assuming the disturbance and its derivative are bounded and continuous. Then the extended state equation of the programmable demagnetizing current source system can be written as:

[0079]

[0080] Where y represents the output of the state equation.

[0081] Based on the above extended state equations, to reduce the number of observer parameters to be tuned and simplify the observer parameter configuration, three cascaded second-order extended state observers with identical parameters are designed to observe the lumped disturbance. The state variables are defined as follows: in, Estimate x1, Estimate x2, Estimate x3, Estimate the lumped disturbance f′, and These are intermediate variables for the cascaded extended state observer. The estimation error is defined as... The state equations of the cascaded extended state observer are as follows:

[0082]

[0083] in, For the parameters of the linear cascaded extended state observer, The observation error of the load current x1, The observation error is the first derivative of the load current, x2. The observation error is the second derivative of the load current, x3. The observation error is the lumped disturbance f′. This is the difference between the intermediate variable and the output of the previous level extended state observer. Step (3): [Example] Figure 3 As shown, a composite sliding mode controller based on a cascaded extended state observer is designed:

[0084] Subtracting the state equation of the cascaded extended state observer from the extended state equation, we obtain the error equation of the cascaded extended state observer as follows:

[0085]

[0086] Let the load current reference command be i ref Define the tracking error vector as Select the sliding surface s as:

[0087] s=c1ξ1+c2ξ2+ξ3

[0088] Where c1 and c2 are positive real numbers. Taking the derivative of the above equation, we have:

[0089]

[0090] in, The third derivative is used as a reference for the load current.

[0091] Combining the system's state-space expression, the sliding mode control law can be further obtained as follows:

[0092]

[0093] The exponential convergence law is selected as follows:

[0094]

[0095] Where ε is the switching gain, k is the approach speed parameter, and sgn() is the sign function.

[0096] By incorporating the exponential reaching law into the control law, and using the lumped disturbance observed through the cascaded extended state observer to compensate for the disturbance in the sliding mode control law, the final composite control law based on the cascaded extended state observer and sliding mode control is designed as follows:

[0097]

Claims

1. A high-precision current control method for a programmable demagnetizing current source, characterized in that, Includes the following steps: Step 1: Establish a mathematical model of the programmable demagnetizing current source under a nonlinear load based on Kirchhoff's laws, and construct the state-space expression of the programmable demagnetizing current source based on this mathematical model. Step 2: Design a cascaded extended state observer to observe the lumped disturbances in the programmable demagnetizing current source system, and compensate for the observed disturbances in the controller through a feedforward channel; the lumped disturbances include various disturbances, including current fluctuations caused by time-varying nonlinear load parameters and perturbations of electronic component parameters; Step 3: Design a composite controller based on a combination of cascaded extended state observer and sliding mode control to suppress the influence of lumped disturbances on the output current of the programmable demagnetizing current source and achieve high-precision demagnetizing current output.

2. The high-precision current control method for a programmable demagnetizing current source according to claim 1, characterized in that, Step 1 includes: According to Kirchhoff's laws, the mathematical model of a single-phase full-bridge inverter under nonlinear load is as follows: ； in, , , These represent the DC bus voltage, inverter output voltage, and load voltage, respectively, with u being the control input. , , These are the inductor current, capacitor current, and load current, respectively. This is the equivalent resistance of the inverter. , These are the inductor and capacitor of an LC filter, respectively. , These are the inductance and resistance of the nonlinear load, respectively; Select system state variables as , Indicates load current , The first derivative of the load current , The second derivative of the load current The system state equations can be written as: 。 3. The high-precision current control method for a programmable demagnetizing current source according to claim 2, characterized in that, In step 2, designing the cascaded expansion state observer includes: Considering the disturbance, the system state equation can be further written as: ； in, , , , , , , Due to the uncertainty of system parameters, External disturbance; The system state-space expression can then be further expressed as: ； Cause collective disturbance Including parameter uncertainty, internal unknown disturbances, and external unknown disturbances, expressed as: ； aggregated disturbance As an extended state variable of the system, i.e. , , Indicates aggregate disturbance Assuming the first derivative of the disturbance and the derivative of the disturbance are bounded and continuous, the extended state equation of the programmable demagnetizing current source system can be written as: ； in, The output of the state equation is represented. Based on the above extended state equation, in order to reduce the parameters of the observer to be tuned and simplify the parameter configuration of the observer, three cascaded second-order extended state observers with the same parameters are designed to observe the lumped disturbance. Define the state variable as ,in, estimate , estimate , estimate , Estimate lumped disturbance , and For the intermediate variables of the cascaded extended observer; the estimation error is defined as , , , , , The state equations of the cascaded extended state observer are as follows: ； in, , For the parameters of the linear cascaded extended state observer, Load current The observation error, The first derivative of the load current The observation error, The second derivative of the load current The observation error, For aggregated disturbance The observation error, , This is the difference between the intermediate variable and the output of the previous level extended state observer.

4. The high-precision current control method for a programmable demagnetizing current source according to claim 3, characterized in that, Step 3 includes: Subtracting the state equation of the cascaded extended state observer from the extended state equation, we obtain the error equation of the cascaded extended state observer as follows: Let the load current reference command be Define the tracking error vector as Select the sliding surface for: in, , It is a positive real number; for Taking the derivative, we have: in, The third derivative is used as a reference for the load current; combined with the system state-space expression, the sliding mode control law is further obtained as follows: The exponential reaching law is selected as follows: in, For switching gain, To approximate the velocity parameters, It is a symbolic function; By incorporating the exponential reaching law into the sliding mode control law, and using the lumped disturbance observed through a cascaded extended state observer to compensate for the disturbance in the sliding mode control law, the composite control law based on the cascaded extended state observer and sliding mode control is designed as follows: 。

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