Control system and anti-disturbance method of electromagnetic bearing

Abstract

The invention provides a control system and an anti-disturbance method of an electromagnetic bearing, a rotor position outer ring is controlled by a non-singular fast terminal sliding mode controller, external disturbance borne by the system is estimated in real time by introducing a non-linear disturbance observer, and an estimation result is fed back to a position controller for compensation; the input of the position controller is the difference value between the given position and the feedback position of the magnetic bearing rotor, and the output value is the reference value of the current loop control current; a stator coil inner ring is controlled by a nonsingular fast terminal sliding mode controller, input values of the controller comprise a current bias value + a current reference value output by a position ring and a current bias value-a current reference value output by the position ring, and an output quantity is a driving PWM signal duty ratio of a magnetic bearing stator coil; driving the PWM signal to be output to the power amplifier; the power amplifier supplies power to the stator coil; the axial thrust load sudden change anti-disturbance capability can be enhanced, it is ensured that when the thrust load suddenly changes, the magnetic bearing maintains stable suspension of the rotor, and anti-disturbance control is achieved.

Description

Technical Field

[0001] This invention relates to the technical field of disturbance rejection control for magnetic bearings, and in particular to a control system and disturbance rejection method for an electromagnetic bearing. Specifically, it relates to a control system for an electromagnetic bearing and a disturbance rejection method for sudden changes in axial thrust load, which is used for disturbance rejection control of magnetic bearings in a magnetically levitated centrifugal compressor. Background Technology

[0002] Magnetic bearings are the core supporting components of magnetically levitated centrifugal compressors, mainly composed of radial bearings, axial bearings, protective bearings, and sensors. Radial bearings are further divided into front and rear radial bearings, thus allowing for four degrees of freedom of movement in the radial direction. Controlling a rotor requires controlling at least five degrees of freedom (four radial and one axial). The effectiveness of rotor control directly affects whether the entire unit can achieve oil-free and friction-free operation. Under high-capacity operating conditions, if a sudden power outage or inverter alarm occurs during high-speed rotor operation, the motor speed will drop instantly, causing a step jump in the axial thrust load. This leads to the rotor's levitation position deviating from the set value, and in severe cases, rotor instability or even rotor fall.

[0003] Existing technologies generally employ linear control strategies, which have limited ability to suppress the aforementioned nonlinear and time-varying disturbances, making it difficult to guarantee the accuracy and robustness of axial suspension of magnetic bearings across the entire operating range. Traditional terminal sliding mode control suffers from problems such as jitter and singularity due to frequent switching near the sliding surface. Summary of the Invention

[0004] This invention proposes a control system and anti-disturbance method for electromagnetic bearings, which can enhance the anti-disturbance capability of electromagnetic bearings under sudden changes in axial thrust load, and ensure that the electromagnetic bearing can still maintain stable rotor suspension when the thrust load changes suddenly, thus achieving anti-disturbance control.

[0005] The present invention adopts the following technical solution.

[0006] A control system for an electromagnetic bearing, wherein both the outer loop of the rotor position and the inner loop of the current of the electromagnetic bearing employ non-singular fast terminal sliding mode control to achieve dynamic levitation control; the outer loop of the rotor position is controlled by a non-singular fast terminal sliding mode controller of the control system, the input of which is the difference between the given position and the feedback position of the electromagnetic bearing rotor, and the output value is the reference value of the control current of the current loop; the inner loop of the electromagnetic bearing stator coil is controlled by a non-singular fast terminal sliding mode controller, the input values ​​of which include the current bias value + the current reference value output by the position loop and the current bias value - the current reference value output by the position loop, and the output quantity is the duty cycle of the drive PWM signal of the electromagnetic bearing stator coil; the drive PWM signal is controlled and output by the CPU of the control system, and passes through a level conversion circuit and an optocoupler isolation circuit to a power amplifier; the power amplifier, under the action of the drive level, converts the DC power supply into a controllable current required for the operating conditions to power the stator coil of the electromagnetic bearing, so that the electromagnetic bearing operates under the required operating conditions.

[0007] The electromagnetic bearing is used in the magnetic bearing mechanism of a magnetic levitation centrifugal compressor. The control system of the electromagnetic bearing includes a CPU, a reset circuit, a clock configuration circuit, an A / D conversion circuit, a level conversion circuit, a signal processing circuit, an optocoupler isolation circuit, and a power amplifier. The signal processing circuit is connected to the displacement sampling circuit of the electromagnetic bearing. The displacement sampling circuit is used to monitor and sample the rotor and stator positions of the electromagnetic bearing. The control method is in software form and is run by the CPU controller. The A / D conversion circuit receives the signal from the signal processing circuit, processes it to obtain the magnetic bearing rotor position data and the bearing stator coil current signal, and then sends the processed signal to the CPU via the A / D conversion circuit.

[0008] An anti-disturbance method for an electromagnetic bearing control system is provided, specifically an axial thrust load mutation anti-disturbance method. First, the position feedback value in the axial direction of the magnetic bearing is obtained in real time through a displacement sampling circuit, and the difference between this value and the given position is calculated. A non-singular fast terminal sliding mode surface is formed based on this difference to accelerate the system's convergence speed and improve tracking accuracy. A switching function is used to avoid singularity problems that may occur in traditional terminal sliding mode control. Simultaneously, an adaptive reaching law is designed using a hyperbolic tangent function to adaptively adjust the convergence rate according to the system's operating state, optimizing the system's dynamic response characteristics and reducing overshoot. Then, a nonlinear disturbance observer is introduced to estimate the external disturbances experienced by the system in real time, and the estimation results are fed back to the controller for compensation, thereby enhancing the robustness and anti-interference capability of the control system.

[0009] The method includes the following steps;

[0010] Step 1: Taking the axial magnetic bearing system as the controlled object, establish a rotor dynamics model of the axial magnetic bearing with sudden changes in axial thrust load; Step 2: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] ,

[0011] Non-singular fast terminal sliding surface designed based on difference;

[0012] Step 3: Based on the nonsingular fast terminal sliding surface and the hyperbolic tangent function, construct the required functional form and design an adaptive reaching law; [The text then abruptly shifts to a different topic:] ...the nonsingular fast terminal sliding surface... Combined with the adaptive reaching law, the non-singular fast terminal sliding mode controller is derived by substituting it into the rotor dynamics model of the axial magnetic bearing system; Step 4: The difference between the actual model and the ideal model output caused by the sudden change in axial thrust load and parameter perturbation is equivalent to the control input, and a nonlinear disturbance observer is designed.

[0013] The electromagnetic bearing is an active magnetic bearing system, including a radial bearing, an axial thrust disk, a protective bearing, a sensor, and a rotor. The radial bearings are distributed at both ends of the rotor and have four degrees of freedom of radial displacement. It has a single degree of freedom displacement z in the axial direction.

[0014] Step one includes the following steps;

[0015] Step 1.1, according to Newton's second law, the basic dynamic equation of the magnetic bearing in the axial direction is as follows:

[0016]

[0017] Step 1.2: Under high-capacity operating conditions, if a sudden power outage or inverter alarm occurs while the compressor unit is running at high speed, the motor speed will drop instantly, causing a sudden change in axial thrust load. This will lead to the rotor's suspension position deviating from the set value, and in severe cases, rotor instability or even rotor fall may occur. Let the sudden change in axial thrust load be...

[0018] ;

[0019] Step 1.3, Electromagnetic force It is a nonlinear function of control current and deviation displacement; generally, when the rotor makes small displacement movements near the equilibrium position, it can be expressed by a Taylor expansion near the equilibrium position as follows:

[0020]

[0021]

[0022] Step 1.4, based on the above analysis, the dynamic equation of the axial magnetic bearing rotor with abrupt change in axial thrust load is:

[0023]

[0024] Step 1.5, let The dynamic equation of the axial magnetic bearing rotor with abrupt change in axial thrust load is expressed as follows:

[0025]

[0026] Step 1.6, let The standard form of the state-space model for an axial magnetic bearing control system with a sudden change in axial thrust load is:

[0027] .

[0028] In step two, a non-singular fast-end sliding surface is designed through the following steps to improve the robustness of the axial magnetic bearing control system;

[0029] Step 2.1, Define the output reference displacement value of the axial magnetic bearing system. The displacement error is ;

[0030] Step 2.2 yields the following non-singular fast terminal sliding surface:

[0031]

[0032] Step 2.3, Switch Function Expressed as a formula

[0033]

[0034]

[0035] .

[0036] Step three includes the following steps;

[0037] Step 3.1, first construct the first term of the adaptive reaching law, and then... The hyperbolic tangent function, followed by the coefficient Multiply;

[0038] Step 3.2, regarding The hyperbolic tangent function and the function term with respect to z Multiplication constructs the second term of the adaptive reaching law;

[0039] Step 3.3: Add the above two items together to design an adaptive reaching law, the specific construction of which is expressed by the following formula;

[0040]

[0041] Step 3.4: Combine the non-singular fast terminal sliding surface with the adaptive reaching law, and substitute it into the rotor dynamics model of the axial magnetic bearing system to derive the non-singular fast terminal sliding controller, which is expressed by the following formula;

[0042] .

[0043] Step four, for the axial magnetic bearing control system, involves using a nonlinear disturbance observer to calculate sudden changes in axial thrust load and compensating for them in the controller to achieve disturbance-resistant control, thereby avoiding performance degradation caused by sudden changes in axial thrust load. This specifically includes the following steps:

[0044] Step 4.1, the matrix of nonlinear observer gain Expressed as a formula

[0045]

[0046] Step 4.2, through Estimates of the abrupt change in axial thrust load Exponential approach disturbance

[0047] ,

[0048] ;

[0049] Step 4.3, the specific construction of the nonlinear disturbance observer is expressed by the following formula:

[0050]

[0051]

[0052]

[0053] Step 4.4, calculate the estimated fault value. To incorporate compensation into the controller, a non-singular fast terminal sliding mode controller with disturbance estimation term is designed.

[0054] .

[0055] When using a non-singular fast terminal sliding mode controller and a nonlinear disturbance observer for disturbance suppression control in an electromagnetic bearing control system, the axial magnetic bearing system is taken as the controlled object. By introducing linearized electromagnetic force and a sudden change in axial thrust load, a rotor dynamics model of the axial magnetic bearing with a sudden change in axial thrust load is established. If the magnetic bearing system is affected by the sudden change in axial thrust load, the disturbance value is estimated using a nonlinear disturbance observer. The compensation is then incorporated into the controller of the electromagnetic bearing control system to offset the sudden change in axial thrust load d under the current operating condition. The controller parameters are adjusted in real time to enhance the anti-interference capability and robustness of the electromagnetic bearing system.

[0056] This invention addresses axial magnetic bearing control systems, proposing a control system for electromagnetic bearings and a method to mitigate disturbances caused by sudden changes in axial thrust load. The system acquires the axial position feedback value of the magnetic bearing in real time through a displacement sampling circuit, calculates the difference between this feedback and the given position, and designs a non-singular fast terminal sliding mode surface based on this difference. This effectively accelerates the system's convergence speed and improves tracking accuracy. Simultaneously, a switching function is designed to avoid singularity problems that may occur in traditional terminal sliding mode control. Furthermore, an adaptive reaching law is designed using a hyperbolic tangent function, which can adaptively adjust the convergence rate according to the system's operating state, optimizing the system's dynamic response characteristics and reducing overshoot. In addition, this invention introduces a nonlinear disturbance observer to estimate the external disturbances experienced by the system in real time, and feeds the estimation results back to the controller for compensation, significantly enhancing the system's robustness and anti-interference capability.

[0057] In this invention, a sign function is introduced. For the input sliding surface Take the modulus value, and then obtain the result by taking the square coefficient of the modulus value. and with symbolic functions Multiplying the results, an adaptive reaching law is designed based on this, treating abrupt changes in axial thrust load and parameter perturbations as lumped disturbances. The difference between the output of the actual model and the ideal model is then equated to the control input. A nonlinear disturbance observer is designed, and the disturbance estimate is used to... Compensation is performed in the controller; the position z of the axial magnetic bearing system is fed back to the position... Given the difference, the error is obtained. Introducing a switching function And based on error The rotor dynamics model of the axial magnetic bearing system is used to design a non-singular fast-termining sliding surface. The adaptive reaching law and the non-singular fast-termining sliding surface are combined and substituted into the rotor dynamics model of the axial magnetic bearing system to derive the sliding mode control controller. Taking an axial magnetic bearing system as the controlled object, this invention establishes a rotor dynamics model of an axial magnetic bearing with a sudden change in axial thrust load by introducing linearized electromagnetic force and axial thrust load. The beneficial effects are: this invention incorporates the sudden change in axial thrust load into the dynamic analysis and modeling of the axial magnetic bearing, laying the foundation for achieving disturbance-resistant control of the magnetic bearing. Compared with general linear control strategies, by introducing a terminal attractor and designing a non-singular fast terminal sliding surface, the dynamic quality of the magnetic bearing is optimized, resulting in a faster rotor levitation response and improved position tracking accuracy. Simultaneously, the optimized design of the sliding surface structure avoids the singularity problems that may occur in traditional terminal sliding control, ensuring stable operation of the magnetic bearing under all operating conditions. Furthermore, the designed adaptive reaching law can adaptively adjust the convergence rate according to the system operating state, reducing the overshoot of the magnetic bearing during the levitation process. In addition, the present invention introduces a nonlinear disturbance observer to estimate the sudden change in axial thrust load of the magnetic bearing in real time, and feeds the estimation result back to the controller to adjust the configuration parameters of the controller in real time, which significantly enhances the robustness and anti-interference ability of the magnetic bearing control system, and can maintain the stable suspension of the rotor even under the condition of sudden change in axial load. Attached Figure Description

[0058] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0059] Appendix Figure 1 This is a schematic diagram of the hardware structure of the control system for an electromagnetic bearing (axial magnetic bearing) in an embodiment of the present invention;

[0060] Appendix Figure 2 This is a schematic diagram of the electromagnetic bearing anti-disturbance control circuit structure in an embodiment of the present invention;

[0061] Appendix Figure 3 This is a schematic diagram of the structure of a non-singular fast terminal sliding surface in an embodiment of the present invention;

[0062] Appendix Figure 4 This is a schematic diagram of the adaptive reaching law in an embodiment of the present invention;

[0063] Appendix Figure 5 This is a schematic diagram of the nonlinear disturbance observer structure in an embodiment of the present invention. Detailed Implementation

[0064] As shown in the figure, a control system for an electromagnetic bearing employs non-singular fast terminal sliding mode control (NSLM) for both the outer position loop and the inner current loop of the electromagnetic bearing rotor to achieve dynamic levitation control. The outer position loop is controlled by the NLM controller of the control system. The input of the controller is the difference between the given position and the feedback position of the electromagnetic bearing rotor, and the output value is the reference value of the current loop control current. The inner loop of the electromagnetic bearing stator coil is controlled by the NLM controller. The input values ​​of the controller include the current bias value + the current reference value output by the position loop and the current bias value - the current reference value output by the position loop. The output is the duty cycle of the drive PWM signal for the electromagnetic bearing stator coil. The drive PWM signal is controlled and output by the CPU of the control system, and passes through a level conversion circuit and an optocoupler isolation circuit to a power amplifier. Under the action of the drive level, the power amplifier converts the DC power supply into a controllable current required for the operating conditions to power the stator coil of the electromagnetic bearing, enabling the electromagnetic bearing to operate under the required conditions.

[0065] The electromagnetic bearing is used in the magnetic bearing mechanism of a magnetic levitation centrifugal compressor. The control system of the electromagnetic bearing includes a CPU, a reset circuit, a clock configuration circuit, an A / D conversion circuit, a level conversion circuit, a signal processing circuit, an optocoupler isolation circuit, and a power amplifier. The signal processing circuit is connected to the displacement sampling circuit of the electromagnetic bearing. The displacement sampling circuit is used to monitor and sample the rotor and stator positions of the electromagnetic bearing. The control method is in software form and is run by the CPU controller. The A / D conversion circuit receives the signal from the signal processing circuit, processes it to obtain the magnetic bearing rotor position data and the bearing stator coil current signal, and then sends the processed signal to the CPU via the A / D conversion circuit.

[0066] An anti-disturbance method for an electromagnetic bearing control system is provided, specifically an axial thrust load mutation anti-disturbance method. First, the position feedback value in the axial direction of the magnetic bearing is obtained in real time through a displacement sampling circuit, and the difference between this value and the given position is calculated. A non-singular fast terminal sliding mode surface is formed based on this difference to accelerate the system's convergence speed and improve tracking accuracy. A switching function is used to avoid singularity problems that may occur in traditional terminal sliding mode control. Simultaneously, an adaptive reaching law is designed using a hyperbolic tangent function to adaptively adjust the convergence rate according to the system's operating state, optimizing the system's dynamic response characteristics and reducing overshoot. Then, a nonlinear disturbance observer is introduced to estimate the external disturbances experienced by the system in real time, and the estimation results are fed back to the controller for compensation, thereby enhancing the robustness and anti-interference capability of the control system.

[0067] The method includes the following steps;

[0068] Step 1: Taking the axial magnetic bearing system as the controlled object, establish a rotor dynamics model of the axial magnetic bearing with sudden changes in axial thrust load; Step 2: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] ,

[0069] Non-singular fast terminal sliding surface designed based on difference;

[0070]

[0071] Step 3: Based on the nonsingular fast terminal sliding surface and the hyperbolic tangent function, construct the required functional form and design an adaptive reaching law; [The text then abruptly shifts to a different topic:] ...the nonsingular fast terminal sliding surface... By combining the adaptive approach law with the rotor dynamics model of the axial magnetic bearing system, a non-singular fast terminal sliding mode controller is derived.

[0072] like Figure 4 As shown, to improve the anti-disturbance performance of the axial magnetic bearing control system under sudden changes in axial thrust load, an adaptive reaching law was designed. By adaptively increasing and decreasing the convergence speed based on the distance from the sliding surface, the speed and stability of the axial magnetic bearing control system under sudden changes in axial thrust load are effectively improved. Step four: The difference between the actual model and the ideal model output caused by sudden changes in axial thrust load and parameter perturbations is equivalent to the control input, and a nonlinear disturbance observer is designed.

[0073] like Figure 5 As shown, for the axial magnetic bearing control system, in order to solve the problem of reduced control performance caused by sudden changes in axial thrust load, the nonlinear disturbance observer treats the difference between the actual model and the ideal model output caused by the sudden change in axial thrust load as the control input, observes the disturbance, and compensates for it in the controller to achieve disturbance-resistant control.

[0074]

[0075] The electromagnetic bearing is an active magnetic bearing system, including a radial bearing, an axial thrust disk, a protective bearing, a sensor, and a rotor. The radial bearings are distributed at both ends of the rotor and have four degrees of freedom of radial displacement. It has a single degree of freedom displacement z in the axial direction.

[0076] Step one includes the following steps;

[0077] Step 1.1, according to Newton's second law, the basic dynamic equation of the magnetic bearing in the axial direction is as follows:

[0078]

[0079] Step 1.2: Under high-capacity operating conditions, if a sudden power outage or inverter alarm occurs while the compressor unit is running at high speed, the motor speed will drop instantly, causing a sudden change in axial thrust load. This will lead to the rotor's suspension position deviating from the set value, and in severe cases, rotor instability or even rotor fall may occur. Let the sudden change in axial thrust load be...

[0080] ;

[0081] Step 1.3, Electromagnetic force It is a nonlinear function of control current and deviation displacement; generally, when the rotor makes small displacement movements near the equilibrium position, it can be expressed by a Taylor expansion near the equilibrium position as follows:

[0082]

[0083]

[0084] Step 1.4, based on the above analysis, the dynamic equation of the axial magnetic bearing rotor with abrupt change in axial thrust load is:

[0085]

[0086] Step 1.5, let The dynamic equation of the axial magnetic bearing rotor with abrupt change in axial thrust load is expressed as follows:

[0087]

[0088] Step 1.6, let The standard form of the state-space model for an axial magnetic bearing control system with a sudden change in axial thrust load is:

[0089] .

[0090] In step two, a non-singular fast-end sliding surface is designed through the following steps to improve the robustness of the axial magnetic bearing control system;

[0091] Step 2.1, Define the output reference displacement value of the axial magnetic bearing system. The displacement error is ;

[0092]

[0093] Step 2.2 yields the following non-singular fast terminal sliding surface:

[0094]

[0095] Step 2.3, Switch Function Expressed as a formula

[0096]

[0097]

[0098]

[0100] Step three includes the following steps;

[0101] Step 3.1, first construct the first term of the adaptive reaching law, and then... The hyperbolic tangent function, followed by the coefficient Multiply;

[0102] Step 3.2, regarding The hyperbolic tangent function and the function term with respect to z Multiplication constructs the second term of the adaptive reaching law;

[0103] Step 3.3: Add the above two items together to design an adaptive reaching law, the specific construction of which is expressed by the following formula;

[0104]

[0105] Step 3.4: Combine the non-singular fast terminal sliding surface with the adaptive reaching law, and substitute it into the rotor dynamics model of the axial magnetic bearing system to derive the non-singular fast terminal sliding controller, which is expressed by the following formula;

[0106] .

[0107] Step four, for the axial magnetic bearing control system, involves using a nonlinear disturbance observer to calculate sudden changes in axial thrust load and compensating for them in the controller to achieve disturbance-resistant control, thereby avoiding performance degradation caused by sudden changes in axial thrust load. This specifically includes the following steps:

[0108] Step 4.1, the matrix of nonlinear observer gain Expressed as a formula

[0109]

[0110] Step 4.2, through Estimates of the abrupt change in axial thrust load Exponential approach disturbance ,

[0111] ;

[0112] Step 4.3, the specific construction of the nonlinear disturbance observer is expressed by the following formula:

[0113]

[0114]

[0115]

[0116] Step 4.4, calculate the estimated fault value. To incorporate compensation into the controller, a non-singular fast terminal sliding mode controller with disturbance estimation term is designed.

[0117] .

[0118] When using a non-singular fast terminal sliding mode controller and a nonlinear disturbance observer for disturbance suppression control in an electromagnetic bearing control system, the axial magnetic bearing system is taken as the controlled object. By introducing linearized electromagnetic force and a sudden change in axial thrust load, a rotor dynamics model of the axial magnetic bearing with a sudden change in axial thrust load is established. If the magnetic bearing system is affected by the sudden change in axial thrust load, the disturbance value is estimated using a nonlinear disturbance observer. The compensation is then incorporated into the controller of the electromagnetic bearing control system to offset the sudden change in axial thrust load d under the current operating condition. The controller parameters are adjusted in real time to enhance the anti-interference capability and robustness of the electromagnetic bearing system.

[0119] Example:

[0120] like Figure 1 The hardware structure diagram of the axial magnetic bearing control system shown is the control system of the electromagnetic bearing described in this invention; it includes a CPU, reset circuit, clock configuration circuit, A / D conversion circuit, level conversion circuit, signal processing circuit, optocoupler isolation circuit, and power amplifier.

[0121] The A / D conversion circuit receives the signal from the signal processing circuit, which then processes the magnetic bearing rotor position and bearing stator coil current signals. These signals are sent to the CPU via the A / D conversion circuit. The CPU then controls and outputs a PWM signal, which passes through a level conversion circuit and an optocoupler isolation circuit before reaching the power amplifier.

[0122] The power amplifier, under the influence of the driving level, converts the input DC power supply into a controllable current to power the stator coil of the magnetic bearing.

[0123] This invention provides a control system and disturbance rejection method for an electromagnetic bearing. Both the outer loop of the electromagnetic bearing rotor position and the inner loop of the current utilize non-singular fast terminal sliding mode control to achieve dynamic levitation control. The control method runs as software within a CPU controller. Figure 2 (within the dashed box)

[0124] Figure 2The diagram shows the disturbance rejection control circuit structure for the magnetic bearing. The outer loop of the rotor position is controlled by a non-singular fast termination sliding mode controller. The input is the difference between the given position and the feedback position of the magnetic bearing rotor, and the output is the reference value of the current loop control current. The inner loop of the magnetic bearing stator coil is also controlled by a non-singular fast termination sliding mode controller. The inputs of the two controllers are the current bias value plus the current reference value output by the position loop and the current bias value minus the current reference value output by the position loop, respectively. The output is the duty cycle of the drive PWM signal for the magnetic bearing stator coil.

[0125] The implementation process of the disturbance rejection method is as follows: First, establish the dynamic model of the axial magnetic bearing rotor with a sudden change in axial thrust load; then design the non-singular fast terminal sliding surface; next, design the adaptive reaching law; derive the non-singular fast terminal sliding controller through the non-singular fast terminal sliding surface and the adaptive reaching law; finally, design the nonlinear disturbance observer.

Claims

1. A control system for an electromagnetic bearing, characterized in that: Both the outer position loop and the inner current loop of the electromagnetic bearing rotor employ non-singular fast termination sliding mode control to achieve dynamic levitation control. The outer position loop is controlled by a non-singular fast termination sliding mode controller of the control system. The input of this controller is the difference between the given position and the feedback position of the electromagnetic bearing rotor, and the output value is the reference value of the current loop control current. The inner current loop of the electromagnetic bearing stator coil is controlled by a non-singular fast termination sliding mode controller. The input values ​​of the controller include the current bias value + the current reference value output by the position loop and the current bias value - the current reference value output by the position loop. The output is the duty cycle of the drive PWM signal of the electromagnetic bearing stator coil. The drive PWM signal is controlled and output by the CPU of the control system, and passes through a level conversion circuit and an optocoupler isolation circuit to the power amplifier. Under the action of the drive level, the power amplifier converts the DC power supply into a controllable current required for the operating conditions to power the stator coil of the electromagnetic bearing, so that the electromagnetic bearing operates under the required conditions.

2. The control system for an electromagnetic bearing according to claim 1, characterized in that: The electromagnetic bearing is used in the magnetic bearing mechanism of a magnetic levitation centrifugal compressor. The control system of the electromagnetic bearing includes a CPU, a reset circuit, a clock configuration circuit, an A / D conversion circuit, a level conversion circuit, a signal processing circuit, an optocoupler isolation circuit, and a power amplifier. The signal processing circuit is connected to the displacement sampling circuit of the electromagnetic bearing. The displacement sampling circuit is used to monitor and sample the rotor and stator positions of the electromagnetic bearing. The control method is in software form and is run by the CPU controller. The A / D conversion circuit receives the signal from the signal processing circuit, processes it to obtain the magnetic bearing rotor position data and the bearing stator coil current signal, and then sends the processed signal to the CPU via the A / D conversion circuit.

3. A disturbance rejection method for an electromagnetic bearing control system, used in the control system of the electromagnetic bearing as described in claim 1, characterized in that: The disturbance rejection method is an axial thrust load change disturbance rejection method; firstly, the position feedback value in the axial direction of the magnetic bearing is obtained in real time through the displacement sampling circuit and the position setpoint is subtracted; based on the calculated difference, a non-singular fast terminal sliding surface is formed to accelerate the convergence speed of the system and improve the tracking accuracy. A switching function is used to avoid singularity problems. An adaptive reaching law is designed using a hyperbolic tangent function to adaptively adjust the convergence rate according to the system's operating state, optimize the system's dynamic response characteristics, and reduce overshoot. Then, a nonlinear disturbance observer is introduced to estimate the external disturbances to the system in real time, and the estimation results are fed back to the controller for compensation to enhance the robustness and anti-interference ability of the control system.

4. The anti-disturbance method for the electromagnetic bearing control system according to claim 3, characterized in that: The method includes the following steps; Step 1: Taking the axial magnetic bearing system as the controlled object, establish a rotor dynamics model of the axial magnetic bearing with sudden changes in axial thrust load; Step 2: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] , Step 3: Based on the non-singular fast terminal sliding surface and the hyperbolic tangent function, construct the required function form and design an adaptive reaching law; The non-singular fast terminal sliding surface... Combined with the adaptive approach law, the non-singular fast terminal sliding mode controller is derived by substituting it into the rotor dynamics model of the axial magnetic bearing system; Step 4: The difference between the output of the actual model and the ideal model caused by the sudden change in axial thrust load and parameter perturbation is equivalent to the control input, and a nonlinear disturbance observer is designed.

5. The anti-disturbance method for the electromagnetic bearing control system according to claim 4, characterized in that: The electromagnetic bearing is an active magnetic bearing system, including a radial bearing, an axial thrust disk, a protective bearing, a sensor, and a rotor. The radial bearings are distributed at both ends of the rotor and have four degrees of freedom of radial displacement. It has a single degree of freedom displacement z in the axial direction.

6. The anti-disturbance method for the electromagnetic bearing control system according to claim 5, characterized in that: Step one includes the following steps; Step 1.1, the basic dynamic equation of the magnetic bearing in the axial direction is as follows: Step 1.2: Under high-capacity operating conditions, if the compressor unit experiences a sudden power outage or inverter alarm while the rotor is running at high speed, assume the axial thrust load changes abruptly. ； Step 1.3, Electromagnetic force It is a nonlinear function of control current and deviation displacement; when the rotor makes a small displacement near the equilibrium position, the Taylor expansion near the equilibrium position is expressed by the following formula: Step 1.4, based on the above analysis, the dynamic equation of the axial magnetic bearing rotor with abrupt change in axial thrust load is: Step 1.5, let The dynamic equation of the axial magnetic bearing rotor with abrupt change in axial thrust load is expressed as follows: Step 1.6, let The standard form of the state-space model for an axial magnetic bearing control system with a sudden change in axial thrust load is: 。 7. The anti-disturbance method for the electromagnetic bearing control system according to claim 4, characterized in that: In step two, a non-singular fast-end sliding surface is designed through the following steps to improve the robustness of the axial magnetic bearing control system; Step 2.1, Define the output reference displacement value of the axial magnetic bearing system. The displacement error is ; Step 2.2 yields the following non-singular fast terminal sliding surface: Step 2.3, Switch Functions Expressed as a formula 。 8. The anti-disturbance method for the electromagnetic bearing control system according to claim 4, characterized in that: Step three includes the following steps; Step 3.1, first construct the first term of the adaptive reaching law, and then... The hyperbolic tangent function, followed by the coefficient Multiply; Step 3.2, regarding The hyperbolic tangent function and the function term with respect to z Multiplication constructs the second term of the adaptive reaching law; Step 3.3: Add the above two items together to design an adaptive reaching law, the specific construction of which is expressed by the following formula; Step 3.4: Combine the non-singular fast terminal sliding surface with the adaptive reaching law, and substitute it into the rotor dynamics model of the axial magnetic bearing system to derive the non-singular fast terminal sliding controller, which is expressed by the following formula; 。 9. The anti-disturbance method for the electromagnetic bearing control system according to claim 4, characterized in that: Step four, for the axial magnetic bearing control system, uses a nonlinear disturbance observer to calculate sudden changes in axial thrust load and compensates for them in the controller to achieve disturbance-resistant control, thus avoiding the degradation of control performance caused by sudden changes in axial thrust load. Specifically, this includes the following steps: Step 4.1, the matrix of nonlinear observer gain Expressed as a formula Step 4.2, through Estimates of the abrupt change in axial thrust load Exponential approach disturbance , ； Step 4.3, the specific construction of the nonlinear disturbance observer is expressed by the following formula: Step 4.4, calculate the estimated fault value. To incorporate compensation into the controller, a non-singular fast terminal sliding mode controller with disturbance estimation term is designed. 。 10. The anti-disturbance method for the electromagnetic bearing control system according to claim 9, characterized in that: When using a non-singular fast terminal sliding mode controller and a nonlinear disturbance observer for disturbance suppression control in an electromagnetic bearing control system, the axial magnetic bearing system is taken as the controlled object. By introducing linearized electromagnetic force and a sudden change in axial thrust load, a rotor dynamics model of the axial magnetic bearing with a sudden change in axial thrust load is established. If the magnetic bearing system is affected by the sudden change in axial thrust load, the disturbance value is estimated using a nonlinear disturbance observer. The compensation is then incorporated into the controller of the electromagnetic bearing control system to offset the sudden change in axial thrust load d under the current operating condition. The controller parameters are adjusted in real time to enhance the anti-interference capability and robustness of the electromagnetic bearing system.

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