Magnetic fluid permanent magnet hybrid bearing

Abstract

The application relates to a magnetic fluid permanent magnetic hybrid bearing, which is mainly characterized in that magnetic fluid is added in a bearing gap, a permanent magnet is installed on a bearing rotating shaft, a controllable magnetic circuit is generated by controlling a coil through a power electronic circuit, the permanent magnet on the bearing rotating shaft is attracted, and the rotating shaft is suspended and rotates in a bearing inner cavity. The application also optimizes a control method of the hybrid bearing, improves effective stiffness and damping of high-frequency oscillation outside a controller bandwidth, and improves dynamic performance of the hybrid bearing. Meanwhile, the application solves the problems of high power consumption and high-frequency mode control of a traditional magnetic bearing through a magnetic fluid and permanent magnetic hybrid control scheme, and has good bearing capacity and dynamic performance.

Description

A magnetohydrodynamic permanent magnet hybrid bearing Technical Field

[0001] This invention relates to a novel magnetohydrodynamic permanent magnet hybrid bearing. Background Technology

[0002] Ordinary bearings have drawbacks in specific applications, such as friction and wear, leading to a shorter bearing life and requiring frequent replacement and maintenance. Due to friction and wear, ordinary bearings require regular inspection and maintenance to ensure proper operation. This also results in increased equipment downtime and higher maintenance costs.

[0003] Furthermore, due to the presence of friction, ordinary bearings will generate vibration and noise when rotating at high speeds, affecting the stability of the equipment and the working environment.

[0004] In addition, lubrication technology has been introduced to reduce friction and wear. Ordinary bearings require the use of lubricants to reduce friction and wear, thus necessitating the regular addition and replacement of lubricants, which increases maintenance costs and operational complexity.

[0005] To address the shortcomings of conventional bearings in specific applications, a new type of magnetic bearing has emerged. This type of bearing utilizes magnetic force to levitate the rotor in space and achieve high-speed rotation. Existing magnetic bearings generally use the magnetic field generated by the current in the conductor controlled by an electrical circuit to levitate the shaft. This is a method of achieving magnetic levitation using an active magnetic force generation device, i.e., an active magnetic bearing.

[0006] It is worth noting that magnetic bearings have relatively low stiffness and load-bearing capacity, which is determined by their reliance on pure magnetic force to drive levitation for system stability. Furthermore, because the motor rotor operates in a vacuum environment and carries a large load, traditional magnetic bearings use electromagnetic coils on both the stator and rotor sides. The rotor side, in particular, experiences significant heat generation due to eddy currents in the coils. Moreover, in a vacuum environment, heat dissipation can only be achieved through thermal radiation, resulting in extremely low heat dissipation efficiency and limiting the bearing's power output.

[0007] The magnetic bearing, which uses the active magnetic force generated by the electromagnetic coil to lift the rotor, has extremely high requirements for dynamic control under high-frequency modes. It is very easy for control instability, radial and nutation errors to occur, and failures to occur. Summary of the Invention

[0008] To address the aforementioned issues, the purpose of this invention is to overcome three major challenges in existing traditional active magnetic bearing technology: insufficient load-bearing capacity, high-frequency modal control, and power consumption and heat generation.

[0009] Adding passive magnetic force generating devices such as permanent magnets and magnetohydrodynamics to the traditional active magnetic bearing, and adapting them with a hybrid control method, is a novel design approach. This design can increase the bearing's stiffness and load-bearing capacity, while also improving the rotor's stability and precision, and solving the heat dissipation problem.

[0010] Magnetofluid, also known as magnetic liquid, ferrofluid, or magnetic fluid, is a novel functional material that combines the fluidity of a liquid with the magnetic properties of a solid magnetic material. It is a stable colloidal liquid composed of nanometer-sized magnetic solid particles (metal and alloy powders), a carrier liquid, and a surfactant. This fluid exhibits no magnetic attraction when static, but becomes magnetic when an external magnetic field is applied. Notably, magnetofluids are used in sealing, medical devices, sound modulation, optical displays, and magnetofluid mineral processing. Bearing sealing, in particular, is the most significant traditional application area for magnetofluids. Numerous patents and documents in the current technological field utilize magnetofluids for sealing. This design combines magnetofluid with a permanent magnet bearing, utilizing the magnetofluid to improve the control and heat dissipation performance of the bearing.

[0011] In terms of control systems, active magnetic bearings rely entirely on adjusting the current in the electromagnetic coil to change the magnetic field strength, thereby adjusting the bearing's supporting force on the rotor. Therefore, active magnetic bearings require complex control systems to adjust the current and maintain stable rotor operation. In contrast, magnetohydrodynamic (MHD) hybrid bearings utilize the magnetostrictive effect of magnetohydrodynamics and the magnetic force of permanent magnets to passively support the rotor. The external electrical control system of this type of MHD hybrid bearing is simpler than that of a purely active bearing.

[0012] Therefore, this invention combines the physical properties of magnetofluids and permanent magnets, and adds the electromagnetic force generated by an electromagnetic coil to form a magnetofluid-permanent magnet hybrid bearing.

[0013] The hybrid bearing includes: a bearing frame, a bearing core, a magnetohydrodynamic component, a permanent magnet, a housing, and an electrical control module;

[0014] The bearing outer frame has a cylindrical inner cavity and is a static component during bearing operation. It consists of a first magnetically conductive connecting part, a second magnetically conductive connecting part, an iron core, and windings.

[0015] The bearing inner core includes a rotating shaft body and a permanent magnet ring. The rotating shaft body is generally in the shape of an aerodynamic cylinder and is a dynamic component during bearing operation. It is installed in the cylindrical inner cavity of the bearing outer frame along the axial direction. The permanent magnet ring is installed on the cylindrical structure of the rotating shaft body.

[0016] The permanent magnet is designed as a cylindrical ring, which is fitted onto the rotating shaft body and located between the first magnetic connection part and the second magnetic connection part;

[0017] There is a gap between the bearing outer frame and the bearing inner core. This gap consists of two sections: one section corresponding to the first magnetically conductive connecting part is a magnetohydrodynamic chamber, and the other section corresponding to the second magnetically conductive connecting part is a gap chamber.

[0018] Magnetorheological fluid is filled into the magnetorheological fluid chamber. In a magnetorheological fluid permanent magnet hybrid bearing with the same mechanical structure design, different types of magnetorheological fluid can be injected to obtain different hybrid bearing operating load characteristics.

[0019] Magnetofluid and permanent magnet are passive magnetic force generators, which together provide passive magnetic force support. In this hybrid bearing, they play the role of passively generating magnetic force, providing basic magnetic force support for the entire bearing operation and damped load-bearing capacity to cope with high-speed and complex dynamic load changes.

[0020] The magnetic field lines pass sequentially along the magnetic circuit through the first magnetically conductive connecting part, the permanent magnet, and the second magnetically conductive connecting part, generating an attractive force with the permanent magnet ring;

[0021] The iron core and windings are installed in the gap chamber. The electrical control module, iron core, and windings together constitute an active magnetic force generating device. The electrical control module has a control unit, a drive execution unit, and a position sensor. The control unit receives the position offset signal transmitted from the position sensor and sends corresponding control commands to the drive execution unit. The power electronic devices in the drive execution unit send corresponding PWM waveforms to the windings, which generate a corresponding active control magnetic field, which is reinforced by the iron core to form a magnetic levitation support for the rotating shaft body of the hybrid bearing during operation.

[0022] During the operation of the hybrid bearing, the passive magnetic force generated by the permanent magnet and magnetohydrodynamic fluid, combined with the active magnetic force generated by the electrical control module, generates a magnetic force on the permanent magnet ring installed on the shaft body, causing the bearing core to levitate.

[0023] Preferably, the length of the rotating shaft occupied by the magnetofluid chamber and the length of the rotating shaft occupied by the void chamber are varied according to the application scenario required by the hybrid bearing, so that the volume of magnetofluid filled in can be variable, and the ratio of basic support force and dynamic support force can be relatively changed.

[0024] The relative lengths of the magnetohydrodynamic chamber and the void chamber are adjusted during the design process based on the actual ratio of high-speed dynamic response magnetic support and basic magnetic support in the actual bearing load characteristics.

[0025] Preferably, in order to make the force in the direction perpendicular to the axis of the rotating shaft relatively uniform, the relative ratio of the lengths of the magnetofluid chamber and the void chamber is set to between 1:1 and 1:3.

[0026] Preferably, the control unit of the electrical control module includes only one incomplete differential PID control module and one PI control module, which simplifies the complexity of control and improves the control response speed.

[0027] The control module receives the position feedback offset signal from the position sensor, processes it through the control unit, and sends it to the drive execution unit. The drive execution unit is a single H-bridge containing four controllable power transistors.

[0028] The winding of the electrical control module is a single set of coils, which are sent from the control unit of the electrical control module to the drive execution unit.

[0029] Preferably, in the control unit, the position sensor obtains and sends the current actual position feedback offset signal p_act, which is compared with the position control reference value p_ref to the incomplete derivative PID controller, and the comparison result is output to the PI controller;

[0030] The output calculation result of the incomplete differential PID controller is compared with the actual current sampling feedback value i_act in the H-bridge drive actuator;

[0031] The PI controller performs PI control on the output of the incomplete derivative PID controller and the actual current sampling feedback value i_act, and sends the output result to the H-bridge drive actuator to control the current of the power device in the H-bridge drive actuator, thereby outputting a PWM drive current waveform to the winding coil.

[0032] Preferably, the control flow logic from start-up to steady state is as follows:

[0033] (1) The hybrid bearing starts and enters the magnetic levitation control mode to control the shaft body of the hybrid bearing to enter the levitation rotation state. At this time, the model of the magnetic fluid that the hybrid bearing is compatible with needs to be loaded, and the different parameters of the compatible magnetic fluid, including the initial magnetic susceptibility and saturation magnetization.

[0034] (2) After the magnetic levitation control mode has been running for a period of time, determine whether the levitation operation state of the rotating shaft body has entered a steady state;

[0035] (3) If the judgment result of step (2) is negative, the suspension control state will continue until the next judgment cycle;

[0036] (4) If the judgment result of step (2) is yes, then control the rotating shaft body to enter the eccentric control state, adjust the center position of the rotating shaft body, make the rotating shaft body eccentric and enter the magnetic levitation light load control state.

[0037] (5) When the hybrid bearing is in a light load control state of magnetic levitation, it is determined whether the load has reached the threshold.

[0038] (6) If the judgment result of step (5) is yes, then the control state of the hybrid bearing returns to the suspension control state;

[0039] (7) If the judgment result of step (5) is negative, then continue to run and determine whether to accept the shutdown command every control cycle;

[0040] (8) If the judgment result of step (7) is no, it is determined that no stop command has been received, and the magnetic levitation light load control state is maintained.

[0041] (9) If the judgment result of step (7) is yes, then enter the shutdown state, reduce the speed of the hybrid bearing and stop the machine, and wait for the next start command.

[0042] Preferably, in the control flow logic from start to steady state, the parameter for step (2) to determine whether the suspension operation state of the rotating shaft body has entered a steady state is whether the speed fluctuation value is less than 0.2% of the rated speed.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) Enhanced stiffness and load-bearing capacity: Permanent magnets and magnetohydrodynamic structures can provide stronger magnetic force, enabling the rotor to be better suspended and kept stable. This can improve the stiffness and load-bearing capacity of the bearing, thus adapting to a wider range of application scenarios.

[0045] (2) Improve the stability of shaft rotation. By adding a magnetofluid structure and using proprietary adaptive control methods and parameters, the problem of high-frequency mode control of traditional magnetic bearings is solved, and the dynamic performance of the bearing is improved.

[0046] (3) Adding magnetic fluid forms a stable liquid film between the rotor and the bearing, which improves the heat dissipation capacity of the bearing and reduces the vibration and noise of the rotor during rotation.

[0047] (4) Due to the introduction of permanent magnets and magnetofluids, the components of this hybrid magnetic bearing are simple and compact, effectively reducing steady-state power consumption without increasing the overall volume, and reducing the dependence on power supply compared to active magnetic bearings.

[0048] (5) The simpler control system of the magnetohydrodynamic permanent magnet hybrid bearing uses fewer components, reducing costs and the probability of later failures, and improving the operation and maintenance performance of the equipment. Passive magnetic force control utilizes the inherent magnetism of the magnetic material itself. Compared with the pure active magnetic bearing, which relies entirely on electricity to provide magnetic force, this hybrid bearing reduces the power requirement for magnetic bearing drive, and thus can achieve the same load-bearing capacity with less power consumption. Attached Figure Description

[0049] Figure 1 is a three-dimensional diagram of an embodiment of a magnetohydrodynamic permanent magnet hybrid magnetic bearing.

[0050] Figure 2 is a three-dimensional cross-sectional view of an embodiment of a magnetohydrodynamic permanent magnet hybrid magnetic bearing.

[0051] Figure 3 is a cross-sectional view of an embodiment of a magnetohydrodynamic permanent magnet hybrid magnetic bearing.

[0052] Figure 4 is a topology diagram of the electrical control section of a traditional active magnetic bearing.

[0053] Figure 5 is a topology diagram of the electrical control section of a magnetohydrodynamic permanent magnet hybrid magnetic bearing.

[0054] Figure 6 is a flowchart of the start-up to steady-state control cycle of the magnetohydrodynamic permanent magnet hybrid magnetic bearing.

[0055] In the figure: 11, First magnetically conductive connecting part; 12, Second magnetically conductive connecting part; 13, Iron core; 14, Winding; 21, Rotating shaft body; 22, Permanent magnet ring; 23, Spacer strip; 24, Gap chamber; 25, Magnetorheological fluid chamber; 31, Magnetorheological fluid; 32, Permanent magnet; 40, Housing; 101, Control unit; 102, Drive execution unit; 103, Position sensor. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0057] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0058] Figure 1 is a three-dimensional view of one embodiment of the magnetohydrodynamic permanent magnet hybrid magnetic bearing, and Figure 2 is a three-dimensional cross-sectional view of the embodiment of the magnetohydrodynamic permanent magnet hybrid magnetic bearing. As can be seen from the overall three-dimensional view, the bearing has a ring-shaped structure, which conforms to the principle of rotational dynamics. The bearing components are located around the cylindrical rotor, including the bearing outer frame, bearing inner core, magnetohydrodynamic fluid 31, permanent magnet 32, and housing 40.

[0059] Figure 3 is a cross-sectional view of a typical embodiment of the magnetohydrodynamic permanent magnet hybrid magnetic bearing. As shown in the figure, the bearing outer frame has a cylindrical inner cavity and is a static component during bearing operation. It consists of a first magnetically conductive connecting part 11, a second magnetically conductive connecting part 12, an iron core 13, and a winding 14. The bearing inner core includes a shaft body 21 and a permanent magnet ring 22. The shaft body 21 is generally aerodynamically shaped and is a dynamic component during bearing operation. It is installed in the cylindrical inner cavity of the bearing outer frame along the axial direction. The permanent magnet ring 22 is installed on the cylindrical structure of the shaft body 21.

[0060] The magnetofluid 31 and the permanent magnet 32 ​​are passive magnetic force generators, jointly providing passive magnetic force support. In this hybrid bearing, they passively generate magnetic force, providing basic magnetic force support for the entire bearing operation and damped load-bearing capacity to cope with high-speed and complex dynamic load changes. The permanent magnet 32 ​​is designed as a ring-shaped cylinder, fitted onto the shaft body 21, and located between the first magnetic conductive connection part 11 and the second magnetic conductive connection part 12.

[0061] To enable the bearing to levitate, a gap is left between the bearing outer frame and the bearing inner core. This gap consists of two sections: one section corresponding to the first magnetically conductive connecting part 11 is a magnetofluid chamber 25, and the other section corresponding to the second magnetically conductive connecting part 12 is a gap chamber 24.

[0062] Magnetofluid 31 is filled into the magnetofluid chamber 25. In a magnetofluid-permanent magnet hybrid bearing with the same mechanical structure design, different types of magnetofluid can be injected to obtain different hybrid bearing operating load effects. The magnetofluid 31 in the magnetofluid chamber 25 has adaptive characteristics, and the magnetic particles located in the special liquid medium can automatically adjust the magnitude and distribution of the magnetic force according to the bearing's operating state and load changes. This is because the magnetofluid is composed of micron-sized magnetic particles and a special liquid medium with lubricating effects. In the absence of an external magnetic field, the magnetic particles are in a disordered distribution state, and the magnetic forces cancel each other out, resulting in no significant magnetic effect. However, when an external magnetic field is applied to the magnetofluid chamber, the magnetic particles are affected by the magnetic field, causing them to align in the magnetofluid. Due to the interaction between the magnetic particles, a stable magnetic chain is formed, which enhances the magnetic force throughout the magnetofluid chamber. At the same time, the directional alignment of the magnetic particles also affects the flow characteristics of the magnetofluid. When the bearing is subjected to external forces or its motion state changes, the magnetic particles will change their alignment, thereby changing the viscosity characteristics of the magnetofluid. This change in viscosity allows the magnetic force within the magnetohydrodynamic chamber to be adjusted.

[0063] By adjusting the strength and direction of the external magnetic field applied to the magnetohydrodynamic (MHD) chamber, the orientation and distribution of magnetic particles can be altered. When the external magnetic field changes, the magnetic particles automatically rearrange to form new magnetic chains, thereby adjusting the magnitude and distribution of the magnetic force. Therefore, this self-adjusting capability allows hybrid bearings to adapt to different operating conditions, providing stable magnetic support and load-bearing capacity. This characteristic enables hybrid bearings to adapt to different operating conditions, providing stable support and load-bearing capacity.

[0064] Furthermore, the magnetofluid 31 in the magnetofluid chamber 25 possesses certain viscosity and damping characteristics. When the bearing vibrates or is subjected to impact, the viscosity of the magnetofluid 31 can absorb energy, reducing the impact of vibration and impact on the bearing and improving the stability of the shaft system. Traditional active magnetic bearings rely on a cooling system where the shaft body and bearing housing do not directly contact each other during operation. The gap between the bearing housing and the shaft body is either filled with an air gap chamber (air or a protective inert gas such as helium) or a vacuum chamber (the gap is evacuated using a molecular pump). The heat generated during bearing operation is transferred to the surrounding environment through thermal radiation and heat conduction via the gas (air or a protective inert gas such as helium), resulting in low heat dissipation efficiency. This often triggers overheat protection and causes the magnetic bearing to shut down under frequent operation. Hybrid bearings using magnetofluid 31 have a separate space between the bearing housing and the shaft body: part of the gap is a magnetofluid chamber 25 filled with magnetofluid 31, and the other part is an empty space chamber 24, which can be filled with vacuum, air, or an inert protective gas depending on the design requirements.

[0065] Magnetofluid, as a liquid medium, can effectively help dissipate heat from the shaft body. Therefore, the heat dissipation efficiency of the magnetofluid permanent magnet hybrid bearing is much higher than that of an active magnetic bearing completely enclosed in vacuum or gas, making it suitable for more application scenarios and operating conditions. The relative length ratio of the magnetofluid chamber 25 and the void chamber 24 can be designed according to changes in application scenarios and operating conditions. However, due to the heat dissipation advantages of the hybrid bearing, the relative length ratio of the magnetofluid chamber and the void chamber should not be too low (i.e., the magnetofluid chamber should occupy at least a considerable proportion of the hybrid bearing shaft length, such as more than 25%). Otherwise, the heat dissipation efficiency of the hybrid bearing will be too similar to that of the traditional active magnetic bearing, failing to reflect the design advantages of the hybrid bearing in thermal effect management.

[0066] Meanwhile, the magnetofluid 31 in the magnetofluid chamber 25 has the characteristic of rapid response. When the bearing operating state changes, the magnetofluid can quickly adapt to changes in the operating load of the hybrid bearing, changes in the hybrid bearing clearance, and changes in the magnetic force generated by the winding coil in the active magnetic force generator, thereby changing the distribution of magnetic particles and rapidly adjusting the distribution of magnetic force.

[0067] The permanent magnet 32 ​​is located between the first magnetically conductive connecting part 11 and the second magnetically conductive connecting part 12. Magnetic lines of force sequentially pass through the first magnetically conductive connecting part 11, the permanent magnet 32, and the second magnetically conductive connecting part 12 along the magnetic path, generating an attractive force with the permanent magnet ring 22 in the bearing core. The material selection for the permanent magnet 32 ​​is crucial. Commonly used permanent magnet materials include neodymium iron boron and cobalt magnets. Different materials have different magnetic properties, and the appropriate material needs to be selected based on the specific application scenario of this hybrid bearing, i.e., the predicted base load and variable load.

[0068] The length of the magnetofluid chamber 25 relative to the length of the shaft body 21 occupied by the void chamber 24 can be varied depending on the application scenario required by the hybrid bearing. This allows for a change in the relative ratio of basic support force to dynamic support force. The relative ratio of the lengths of the magnetofluid chamber 25 and the void chamber 24 can be adjusted during the design phase based on the actual ratio of high-speed dynamic response magnetic support to basic magnetic support in the actual bearing load characteristics. Experimental verification shows that if the ratio of the void chamber 24 to the magnetofluid chamber 25 is too large, i.e., the relative ratio of the passive support magnetic force generated by the filled magnetofluid to the active electromagnetic force in the winding coil is too low, it cannot effectively provide the adaptive and damping support provided by the magnetofluid in the hybrid bearing, thus losing the advantages of the hybrid bearing. Furthermore, since the characteristics of the active electromagnetic force generated in the winding coil and the passive magnetic force of the magnetic particles in the magnetofluid differ significantly, if the ratio of the active electromagnetic force in the winding coil to the passive supporting magnetic force generated by the magnetofluid is too large, the absolute value and rate of change of the force on the side of the shaft body in the gap chamber will be significantly higher than that on the side of the shaft body in the magnetofluid chamber. To ensure that the force on the shaft body 21 in the direction perpendicular to the axis is relatively uniform, the relative ratio of the lengths of the magnetofluid chamber 25 and the gap chamber 24 is preferably set between 1:1 and 1:3.

[0069] Figure 4 shows the topology of the electrical control section of a traditional active magnetic bearing. The electrical control module, iron core 13, and winding 14 together constitute the active magnetic force generating device. The electrical control module includes a control unit 101, a drive execution unit 102, and a position sensor 103. The control unit 101 receives the position offset signal transmitted from the position sensor 103 and sends corresponding control commands to the drive execution unit 102. The power electronic devices in the drive execution unit 102 send corresponding PWM waveforms to the windings, which generate a corresponding active control magnetic field. This field is reinforced by the iron core 13, forming an active magnetic levitation support for the rotating shaft of the active magnetic bearing. When the bearing starts operating, the current applied by the external power supply system excites the windings to generate a magnetic field. This magnetic field interacts with the magnetic field of the permanent magnet ring 22 on the shaft body 21, thereby forming a magnetic force in the bearing. This magnetic force, combined with the magnetic force provided by the magnetohydrodynamics, levitates the bearing core, realizing the levitation operation of the active magnetic bearing.

[0070] The control unit of the electrical control module includes one incomplete differential PID control module and two PI control modules. The control module receives position feedback offset signals from the position sensor, processes them through the control unit, and sends them to the drive execution unit 102. The drive execution unit 102 consists of two sets of H-bridges sharing one bridge arm. The windings of the electrical control module are driven by the control signals from the control unit to the drive execution unit, corresponding to two sets of coils driven by the two H-bridges. The two H-bridges together include two controllable power transistors (such as MOSFETs or IGBTs) and two uncontrollable power transistors (such as diodes) on two independent bridge arms, and one controllable power transistor and one uncontrollable power transistor on one shared bridge arm. Defining the two sets of H-bridges as p and n respectively, the current in the two coil windings driven by the two H-bridges is... and When the active magnetic bearing is running, the position sensor acquires and sends a feedback offset signal of the current actual position. , and position control reference value The comparison is performed using a common-to-incomplete-differential PID controller, and the comparison result is then compared with the currents in the two coil windings obtained from sampling. and The values ​​are compared to generate two corresponding control reference values ​​for the H-bridge current. and Then and The results are output to two PI controllers respectively. The calculated result is compared with the actual sampled feedback value of the actual current in the H-bridge driven actuator. and The two comparisons are then input into two separate PI controllers, which in turn control the calculated results. and The output is sent to the drive actuator unit, namely the power drive devices on the two H-bridges, to control the current of the power devices in the H-bridge drive actuator, thereby outputting an effective PWM drive current waveform to the winding coil.

[0071] Figure 5 is a topology diagram of the electrical control section of the hybrid bearing of the present invention. The electrical control module, iron core 13, and winding 14 together constitute an active magnetic force generating device. The electrical control module has a control unit 101, a drive execution unit 102, and a position sensor 103. The control unit receives the position offset signal transmitted from the position sensor and issues corresponding control commands to the drive execution unit. The power electronic devices in the drive execution unit send corresponding PWM waveforms to the windings, which generate a corresponding active control magnetic field, which is reinforced by the iron core to form a magnetic levitation support for the rotating shaft of the hybrid bearing during operation. When the bearing starts to operate, the current applied by the external power supply system excites the windings to generate a magnetic field. This magnetic field interacts with the magnetic field of the permanent magnet ring on the shaft body, thereby forming a magnetic force in the bearing. This magnetic force, combined with the magnetic force provided by the magnetohydrodynamic fluid, levitates the inner core of the bearing, realizing the levitation operation of the active magnetic bearing. Therefore, during the operation of the hybrid bearing, the passive magnetic force generated by the permanent magnet and the magnetohydrodynamic fluid, combined with the active magnetic force generated by the electrical control module, jointly generate magnetic force on the permanent magnet ring installed on the shaft body, causing the bearing core to levitate.

[0072] The control unit of the electrical control module contains only one incomplete differential PID control module and one PI control module, simplifying the control complexity and improving the control response speed. The control module receives position feedback offset signals from the position sensor, processes them through the control unit, and sends them to the drive actuator, which is a single set of H-bridges. The windings of the electrical control module, which transmit control signals from the control unit to the drive actuator, consist of a single set of coils.

[0073] The aforementioned single H-bridge contains a total of 4 controllable power transistors (such as MOSFETs or IGBTs).

[0074] The control unit's center position sensor acquires and sends a feedback offset signal of the current actual position. , and position control reference value The output of the PID controller is compared with that of the incomplete derivative PID controller, and the comparison result is output to the PI controller. The output calculation result of the incomplete derivative PID controller is compared with the actual current sampling feedback value in the H-bridge drive actuator. The comparison is performed. The PI controller will take the output of the incompletely differentiable PID controller and the actual current sample feedback value. The result is used for PI control, and the output result is sent to the H-bridge driver actuator to control the current of the power device in the H-bridge driver actuator, thereby outputting a PWM drive current waveform to the winding coil.

[0075] Comparing the electrical control topology of traditional active magnetic bearings and the magnetic fluid permanent magnet hybrid bearing of this invention, the number of PI controllers is reduced from 2 to 1, the number of comparison calculation stages is reduced from 5 to 2, the number of H-bridges driving actuators is reduced from 2 to 1, the number of required power electronic devices is reduced from 6 to 4, and the number of windings is reduced from 2 to 1. Compared to traditional active magnetic bearings, the electrical control hardware structure and control logic of the magnetic fluid permanent magnet hybrid bearing of this invention are significantly simplified, resulting in faster control response and a lower failure rate.

[0076] A PI controller is a commonly used type of controller, consisting of proportional (P) and integral (I) parts. The PI controller adjusts the output signal based on the magnitude of the control error to make the system's output value approximate the desired value. The proportional (P) part generates the output signal based on the magnitude of the control error. It adjusts the output signal magnitude by multiplying the control error by a proportional gain. The proportional gain determines the sensitivity of the output signal to the control error; increasing the proportional gain can speed up the system's response but may introduce oscillations and instability. The integral (I) part generates the output signal based on the integral of the control error. It adjusts the output signal magnitude by multiplying the control error by an integral gain. The integral gain can eliminate the system's static error and improve system stability. However, if the integral gain is too large, it may introduce oscillations and instability. The output signal of a PI controller is the superposition of the proportional and integral parts. By adjusting the proportional and integral gains, the system's response speed, stability, and static error can be controlled. Typically, the appropriate gain parameter for a PI controller can be determined through trial and error, empirical methods, or system modeling.

[0077] PI controllers are widely used in industrial control systems, especially for systems with high requirements for static error. They provide stable control performance and are relatively simple to use. However, for complex systems with high response speed requirements, the selection and tuning of the PI gain parameters are very demanding; even slight errors in parameter selection can lead to non-convergence and control errors. Therefore, hybrid bearings, through the passive magnetic support provided by magnetohydrodynamics and permanent magnets, reduce the speed requirements for the system's dynamic response and decrease system complexity. By eliminating one PI controller, the resulting system simplification significantly reduces the difficulty of parameter tuning and tuning, increasing the overall stability of the hybrid bearing system.

[0078] Furthermore, H-bridge circuits with shared arms inherently suffer from drawbacks such as complex control and low system stability. Since the two arms share a single current loop, more complex control strategies are needed to ensure mutual exclusion between the two arms, thus avoiding short-circuit problems in the loop. This significantly increases the complexity and design difficulty of the control system. Reducing the number of H-bridges driving the actuator from two to one reduces system complexity, lowers the failure rate, simplifies components, and lowers hardware costs for manufacturing.

[0079] Figure 6 is a flowchart of the start-up to steady-state control cycle of the magnetohydrodynamic (MHD) permanent magnet hybrid bearing. The MHD permanent magnet hybrid bearing of this invention has a smaller range of conditions for entering steady-state control compared to typical active magnetic levitation bearings. Because the hybrid bearing provides additional passive magnetic support through the combination of permanent magnets and magnetohydrodynamics, its adaptive and damping capabilities against load changes are higher than those of typical active magnetic levitation bearings, enabling more stable levitation and positioning. Typical active magnetic levitation bearings require the amplitude and rate of change of the driving current, combined with the rotational speed fluctuation range of the shaft body, to determine when the shaft body has entered a steady state.

[0080] Furthermore, different types of magnetofluids possess different properties, such as viscosity and permeability. Hybrid bearings require design and manufacturing based on the properties of the magnetofluid used to ensure proper bearing operation. As mentioned earlier, the bearing's dimensions and structural design vary depending on the load type characteristics, especially the relative design ratio of the lengths of the magnetofluid chamber and the void chamber, which affects the relative ratio of passive and active magnetic forces during operation. Inappropriate magnetofluid parameter settings can lead to instability during hybrid bearing operation and control, and even bearing damage. Therefore, when a magnetic bearing starts and enters the magnetic levitation control mode, it is necessary to load the magnetofluid type and corresponding parameters suitable for the current application scenario, such as initial magnetization and saturation magnetization. For hybrid bearings designed for a specific type of load characteristics (i.e., the relative design ratio of the lengths of the magnetofluid chamber and the void chamber is determined during design), different types of magnetofluids can be injected to obtain magnetofluid permanent magnet hybrid bearings with slightly different load characteristics. For example, in turbo blowers and turbo compressors, high-speed selective magnetohydrodynamic (MHD) permanent magnet hybrid bearings are used. Different turbine blade profiles result in different bearing load characteristics. Therefore, by injecting different types of magnetohydrodynamic fluid into the magnetohydrodynamic cavity and matching different hybrid bearing control parameters, optimal control performance under specific load conditions can be obtained.

[0081] The operating control loop logic of the hybrid bearing from startup to steady-state operation is as follows:

[0082] (1) The hybrid bearing starts and enters the magnetic levitation control mode to control the shaft body of the hybrid bearing to enter the levitation rotation state. At this time, the model of the magnetic fluid that the hybrid bearing is compatible with needs to be loaded, and the different parameters of the compatible magnetic fluid, such as the initial magnetic susceptibility and saturation magnetization intensity.

[0083] (2) After the magnetic levitation control mode has been running for a period of time, determine whether the levitation operation state of the rotating shaft body has entered a steady state.

[0084] (3) If the judgment result of step (2) is negative, the suspension control state will continue until the next judgment cycle.

[0085] (4) If the judgment result of step (2) is yes, then the control shaft body enters the eccentric control state, adjusts the center position of the control shaft body, makes the shaft body eccentric and enters the magnetic levitation light load control state.

[0086] (5) When the hybrid bearing is in the light load control state of magnetic levitation, it is determined whether the load has reached the threshold.

[0087] (6) If the judgment result of step (5) is yes, the control state of the hybrid bearing returns to the suspension control state.

[0088] (7) If the judgment result of step (5) is negative, continue to run and determine whether to accept the shutdown command every control cycle.

[0089] (8) If the judgment result of step (7) is negative, it is determined that no stop command has been received, and the magnetic levitation light load control state is maintained.

[0090] (9) If the judgment result of step (7) is yes, then enter the shutdown state, reduce the speed of the hybrid bearing and stop the machine, and wait for the next start command.

[0091] Because magnetohydrodynamics and permanent magnets are introduced as passive magnetic support for the hybrid bearing, its operation stability is higher than that of the active magnetic bearing, meaning the rotational speed fluctuation is lower. In the control parameters of the magnetohydrodynamic-permanent magnet hybrid bearing, a lower rotational speed fluctuation ratio can be used to determine whether the shaft has entered a steady-state levitation operation, thus achieving better operational control accuracy. In the control flow logic from start-up to steady state of the hybrid bearing, step (2) determines whether the levitation operation state of the shaft body has entered a steady state by whether the rotational speed fluctuation value is less than 0.2% of the rated speed.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A magnetohydrodynamic permanent magnet hybrid bearing, characterized in that, include: The bearing assembly comprises a bearing outer frame, a bearing inner core, a magnetic fluid, a permanent magnet, a housing, and an electrical control module. The bearing outer frame has a cylindrical inner cavity and is a static component during bearing operation, consisting of a first magnetically conductive connecting part, a second magnetically conductive connecting part, an iron core, and windings. The bearing inner core includes a rotating shaft body and a permanent magnet ring. The rotating shaft body is generally aerodynamically shaped and is a dynamic component during bearing operation, installed along the axial direction within the cylindrical inner cavity of the bearing outer frame. The permanent magnet ring is mounted on the cylindrical structure of the rotating shaft body. The permanent magnet is designed as a ring-shaped cylinder, fitted onto the rotating shaft body, and located between the first and second magnetically conductive connecting parts. A gap exists between the bearing outer frame and the bearing inner core, comprising two sections: one corresponding to the first magnetically conductive connecting part is a magnetic fluid chamber, and the other corresponding to the second magnetically conductive connecting part is a gap chamber. Magnetic fluid is filled into the magnetic fluid chamber, and a magnetic fluid permanent magnet with the same mechanical structure is... In hybrid bearings, different types of magnetorheological fluids can be injected to achieve different operating load characteristics. The magnetorheological fluid and permanent magnets act as passive magnetic force generators, jointly providing passive magnetic support. In this hybrid bearing, they passively generate magnetic force, providing fundamental magnetic support for the entire bearing operation and damped load-bearing capacity to cope with high-speed, complex, and dynamic load changes. Magnetic lines of force sequentially pass through the first magnetically conductive connecting part, the permanent magnet, and the second magnetically conductive connecting part along the magnetic circuit, generating an attractive force with the permanent magnet's magnetic ring. The iron core and windings are installed in a cavity. The electrical control module, iron core, and windings together constitute an active magnetic force generating device. The electrical control module has a control unit, a drive execution unit, and a position sensor. The control unit receives the position offset signal transmitted from the position sensor and issues corresponding control commands to the drive execution unit. The power electronic devices in the drive execution unit emit corresponding PWM signals. The waveform is transmitted to the winding, which generates a corresponding active control magnetic field, which is reinforced by the iron core to form a magnetic levitation support for the rotating shaft of the hybrid bearing during operation. During the operation of the hybrid bearing, the passive magnetic force generated by the permanent magnet and the magnetohydrodynamic fluid, combined with the active magnetic force generated by the electrical control module, generates a magnetic force on the permanent magnet ring installed on the shaft body, causing the bearing core to levitate.

2. The magnetohydrodynamic permanent magnet hybrid bearing according to claim 1, characterized in that, The length of the magnetic fluid chamber and the length of the void chamber on the shaft can be varied according to the application scenario required by the hybrid bearing, so that the volume of magnetic fluid filled can be changed, and the ratio of basic support force and dynamic support force can be changed relatively. The relative ratio of the length of the magnetic fluid chamber and the void chamber is adjusted during the design according to the actual ratio of high-speed dynamic response magnetic support and basic magnetic support in the actual bearing load characteristics.

3. A magnetohydrodynamic permanent magnet hybrid bearing according to claim 2, characterized in that, To ensure that the force is relatively uniform in the direction perpendicular to the axis of the rotating shaft body, the relative ratio of the lengths of the magnetofluid chamber and the void chamber is set between 1:1 and 1:

3.

4. A magnetohydrodynamic permanent magnet hybrid bearing according to any one of claims 1-3, characterized in that, The control unit of the electrical control module contains only one incomplete differential PID control module and one PI control module, which simplifies the complexity of control and improves the control response speed. The control module receives the position feedback offset signal from the position sensor, processes it through the control unit, and sends it to the drive execution unit. The drive execution unit is a single H-bridge containing four controllable power transistors. The winding of the electrical control module is a single set of coils, which are the control signals sent from the control unit of the electrical control module to the drive execution unit.

5. A magnetohydrodynamic permanent magnet hybrid bearing according to claim 4, characterized in that, In the control unit, the position sensor acquires and sends a feedback offset signal of the current actual position. , and position control reference value The comparison is performed between the common-to-incomplete-differential PID controller and the incomplete-differential PID controller, and the comparison result is output to the PI controller. The output calculation result of the incomplete-differential PID controller is compared with the actual current sampling feedback value in the H-bridge drive actuator. The comparison involves the PI controller inputting the incompletely differentiable PID controller output and the actual current sample feedback value. The result is used for PI control, and the output result is sent to the H-bridge driver actuator to control the current of the power device in the H-bridge driver actuator, thereby outputting a PWM drive current waveform to the winding coil.

6. A magnetohydrodynamic permanent magnet hybrid bearing according to claim 5, characterized in that, The control flow logic from start-up to steady state is as follows: (1) The hybrid bearing starts and enters the magnetic levitation control mode to control the shaft body of the hybrid bearing to enter the levitation rotation state. At this time, the model of the magnetic fluid that the hybrid bearing is adapted to and the different parameters of the magnetic fluid, including the initial magnetization and saturation magnetization, need to be loaded; (2) After the magnetic levitation control mode runs for a period of time, it is determined whether the levitation running state of the shaft body has entered the steady state; (3) If the judgment result of step (2) is no, the levitation control state is maintained until the next judgment cycle; (4) If the judgment result of step (2) is yes, the shaft body is controlled to enter the eccentric control state and the center position of the shaft body is adjusted. (5) When the hybrid bearing is in the magnetic levitation light load control state, it determines whether the load has reached the threshold. (6) If the result of step (5) is yes, the control state of the hybrid bearing returns to the levitation control state. (7) If the result of step (5) is no, it continues to run and determines whether to accept the stop command every control cycle. (8) If the result of step (7) is no, it is determined that no stop command has been received and the magnetic levitation light load control state continues to be maintained. (9) If the result of step (7) is yes, it enters the stop state, the hybrid bearing is slowed down and stopped, and waits for the next start command.

7. A magnetohydrodynamic permanent magnet hybrid bearing according to claim 6, characterized in that, In the control flow logic from start to steady state, the parameter for step (2) to determine whether the suspension running state of the shaft body has entered a steady state is whether the speed fluctuation value is less than 0.2% of the rated speed.

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