Power electronic controller and control method for a five degree of freedom magnetic bearing

Abstract

This invention discloses a power electronic controller and control method for a five-degree-of-freedom magnetic levitation bearing, belonging to the field of magnetic levitation bearing control. It includes eight controllable switches and eight unidirectional conducting devices. Based on the connection method between the unidirectional conducting devices, controllable switches, and power supply, the eight bridge arms are divided into four forward bridge arms and four reverse bridge arms. Two forward bridge arms and two reverse bridge arms form a group of bridge arms. In each group, the two forward bridge arms and two reverse bridge arms are connected to five windings. By connecting the fifth winding of each group of bridge arms between every two windings of the first four windings, the current of each winding is controlled by changing the conduction time of each controllable switch. Only eight bridge arms are used to control ten windings. This invention reduces the complexity of the power electronic controller for a five-degree-of-freedom magnetic levitation bearing, while also reducing the controller's size and cost, thus possessing significant practical application value.

Description

Technical Field

[0001] This invention belongs to the field of magnetic levitation bearing control, and more specifically, relates to a power electronic controller and control method for a five-degree-of-freedom magnetic levitation bearing. Background Technology

[0002] Magnetic levitation bearings utilize electromagnetic force to levitate the rotor, achieving contactless operation between the rotor and stator. They are characterized by being frictionless, pollution-free, and having a long lifespan, making them suitable for high-speed, ultra-high-speed, and high-performance transmission applications requiring contactless, lubrication-free, and pollution-free operation. Foreign research on magnetic levitation bearings began earlier, entering practical application in the 1970s. Domestic research on magnetic levitation bearings started relatively late, but after decades of development by academia and industry, significant progress has been made, and products are gradually being applied, such as magnetic levitation bearing flywheel energy storage and magnetic levitation centrifugal blowers, showing promising application prospects.

[0003] For an active magnetic levitation bearing system, a control system is needed to regulate the magnitude of the electromagnetic force in each winding. The power amplifier, which receives control signals from the controller and converts the commanded current into actual current, is a crucial part of the control system. The rotor, which supports the magnetic levitation bearing, has five degrees of freedom, dictating that the magnetic levitation bearing system must be at least a five-degree-of-freedom system. This high degree of freedom results in a large number of controllable windings in the magnetic levitation bearing. Using traditional full-bridge topologies requires numerous power electronic devices and their drives, leading to a complex, large, and costly control system. Some researchers have proposed using a shared bridge arm to reduce the number of power electronic devices, requiring 24 devices to control 10 windings; or eliminating the shared bridge arm to control 8 windings with 16 devices, plus 6 more for the remaining 2, requiring a total of 22 devices. However, neither of these methods achieves a globally optimized device count; both still require a significant number of power electronic devices, further complicating the control system's structure, increasing its size and cost. Summary of the Invention

[0004] In view of the shortcomings of the existing technology and the need for improvement, the present invention provides a power electronic controller and control method for a five-degree-of-freedom magnetic levitation bearing. The purpose is to reduce the complexity of the power electronic controller for the five-degree-of-freedom magnetic levitation bearing, while reducing the size and cost of the controller.

[0005] To achieve the above objectives, according to one aspect of the present invention, a power electronic controller for a five-degree-of-freedom magnetic levitation bearing is provided. The five-degree-of-freedom magnetic levitation bearing includes ten windings, which are divided into two groups, with five windings in each group designated as the first to fifth windings. The controller includes:

[0006] Eight controllable switches and eight unidirectional conducting devices are provided. One controllable switch and one unidirectional conducting device are connected in series to form a bridge arm. The eight bridge arms are divided into two groups, and the four bridge arms in each group are referred to as the first to fourth bridge arms. Each winding, controllable switch and unidirectional conducting device includes a first end and a second end. The winding and the controllable switch use the end into which current flows as the first end and the end into which current flows as the second end. The unidirectional conducting device uses the end into which current flows as the first end and the end into which current flows as the second end.

[0007] In each group, the four bridge arms are connected in parallel across the power supply. In the first and second bridge arms, the first terminal of the controllable switch is connected to the positive terminal of the power supply, the second terminal is connected in series with the first terminal of the unidirectional conducting device, and the second terminal of the unidirectional conducting device is connected to the negative terminal of the power supply. In the third and fourth bridge arms, the first terminal of the unidirectional conducting device is connected to the positive terminal of the power supply, the second terminal is connected in series with the first terminal of the controllable switch, and the second terminal of the controllable switch is connected to the negative terminal of the power supply.

[0008] In each bridge arm group, the midpoints of the first and second bridge arms are connected to the first ends of the first and second windings, respectively. The second ends of the first and second windings are connected together and then connected to the first end of the fifth winding. The midpoints of the third and fourth bridge arms are connected to the second ends of the third and fourth windings, respectively. The first ends of the third and fourth windings are connected together and then connected to the second end of the fifth winding.

[0009] Furthermore, all controllable switches are active switching transistors, and all unidirectional conducting devices are diodes.

[0010] Furthermore, the active switching transistor is an IGBT or a MOSFET.

[0011] Furthermore, the first terminal of the controllable switch is the collector of the IGBT, and the second terminal is the emitter of the IGBT;

[0012] The first terminal of the unidirectional conducting device is the negative terminal of the diode, and the second terminal is the positive terminal of the diode.

[0013] Furthermore, the current flowing through the winding is a unidirectional current.

[0014] According to a second aspect of the present invention, a control method is provided for implementing a power electronic controller for a five-degree-of-freedom magnetic levitation bearing as described in any one of the first aspects, comprising:

[0015] The duty cycle of the controllable switch is controlled to make the controller operate in one of five basic operating modes; for any one of the two sets of bridge arms, the five basic operating modes include:

[0016] First basic working mode: control the equivalent duty cycle of the midpoint of the four bridge arms to be equal, so that the current of the five windings remains unchanged;

[0017] Second basic working mode: control the equivalent duty cycle of the midpoint of the first and second bridge arms to be equal and higher than the equivalent duty cycle of the midpoint of the third and fourth bridge arms, so that the sum of the currents of the first and second windings and the sum of the currents of the third and fourth windings are both increased;

[0018] The third basic working mode: control the equivalent duty cycle of the midpoint of the third and fourth bridge arms to be equal and higher than the equivalent duty cycle of the midpoint of the first and second bridge arms, so that the sum of the currents of the first and second windings and the sum of the currents of the third and fourth windings are reduced.

[0019] Fourth basic operating mode: Control the equivalent duty cycle at the midpoint of the first and second bridge arms to change the difference in current between the first and second windings;

[0020] Fifth basic operating mode: Control the equivalent duty cycle of the third and fourth bridge arms to change the difference in current between the third and fourth windings;

[0021] The equivalent duty cycle at the midpoint of the first and second bridge arms is consistent with the duty cycle of the controllable switch in the first and second bridge arms, and the sum of the equivalent duty cycle at the midpoint of the third and fourth bridge arms and the duty cycle of the controllable switch in the third and fourth bridge arms is 1.

[0022] Furthermore, the fourth basic working mode includes:

[0023] The equivalent duty cycle at the midpoint of the first bridge arm is controlled to be higher than that at the midpoint of the second bridge arm, thereby increasing the difference in current between the first and second windings.

[0024] Alternatively, the equivalent duty cycle at the midpoint of the first and second bridge arms can be controlled to be equal, so that the difference in current between the first and second windings remains constant;

[0025] Alternatively, the equivalent duty cycle at the midpoint of the first bridge arm can be controlled to be lower than the equivalent duty cycle at the midpoint of the second bridge arm, thereby reducing the current difference between the first and second windings.

[0026] Furthermore, the fifth basic working mode includes:

[0027] The equivalent duty cycle at the midpoint of the third bridge arm is controlled to be higher than that at the midpoint of the fourth bridge arm, so that the difference in current between the third and fourth windings is reduced.

[0028] Alternatively, the equivalent duty cycle at the midpoint of the third and fourth bridge arms can be controlled to be equal, so that the difference in current between the third and fourth windings remains unchanged;

[0029] Alternatively, the equivalent duty cycle at the midpoint of the third bridge arm can be controlled to be lower than that at the midpoint of the fourth bridge arm, thereby increasing the current difference between the third and fourth windings.

[0030] Furthermore, it also includes controlling the duty cycle of the controllable switch so that the controller can operate simultaneously in two or more of the five basic operating modes, wherein the control between the two or more basic operating modes does not conflict.

[0031] Furthermore, the controller operates simultaneously in both the second and fifth basic operating modes;

[0032] Alternatively, the controller may operate simultaneously in both the third and fourth basic operating modes;

[0033] Alternatively, the controller may operate simultaneously in both the fourth and fifth basic operating modes.

[0034] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0035] (1) The controller of the present invention divides the eight bridge arms into four forward bridge arms and four reverse bridge arms according to the connection method of the unidirectional conduction device and the controllable switch and the power supply. Two forward bridge arms and two reverse bridge arms form a group of bridge arms. In each group of bridge arms, the midpoint of the two forward bridge arms is connected to the first end of the first and second windings, and the midpoint of the two reverse bridge arms is connected to the second end of the third and fourth windings. The second ends of the first and second windings are connected together and then connected to the first end of the fifth winding. The first ends of the third and fourth windings are connected together and then connected to the second end of the fifth winding. By changing the conduction time of each controllable switch, the current of each winding connected to each bridge arm can be controlled. Based on the connection relationship of the fifth winding, by controlling the current flowing into each group of bridge arms, the current of the corresponding fifth winding in each group of bridge arms can be controlled, thereby realizing the control of the electromagnetic force generated by the 10 windings in the five-degree-of-freedom magnetic levitation bearing. This invention connects the fifth winding of each bridge arm between every two windings of the first four windings. Compared with existing five-degree-of-freedom magnetic levitation bearing controllers, this invention eliminates the bridge arm originally used to control the fifth winding of two windings, achieving control of 10 windings with only 8 bridge arms. This significantly reduces the number of power electronic devices in the five-degree-of-freedom magnetic levitation bearing controller, lowers the complexity of the power electronic controller, and reduces the size of the controller, thereby reducing costs and demonstrating significant practical application value.

[0036] (2) Further, based on the controller provided by this invention, this invention also provides a corresponding control method for the controller. By simultaneously controlling the duty cycle of the conduction time of the controllable switching device on each bridge arm, the controller can operate in different working modes. Each mode can work independently or cooperate with each other, thereby realizing the control of the charging and discharging time and freewheeling time of each winding, thus realizing the control of the current of each winding, and thus completing the control of the electromagnetic force in the five-degree-of-freedom magnetic levitation bearing, which meets the actual application requirements.

[0037] In summary, the power electronic controller and control method of the present invention can further reduce the number of power electronic devices in the magnetic levitation bearing controller, reduce the complexity of the power electronic controller for the five-degree-of-freedom magnetic levitation bearing, and reduce the size and cost of the controller. Attached Figure Description

[0038] Figure 1 A schematic diagram of the structure of a five-degree-of-freedom magnetic levitation bearing provided as an example of the present invention;

[0039] Figure 2 A schematic diagram of a single radial magnetic levitation bearing structure provided as an example of the present invention;

[0040] Figure 3 A topology diagram of a five-degree-of-freedom magnetic bearing power electronic controller provided as an example of the present invention;

[0041] Figure 4(a) shows the first basic operating mode of the controller provided in the example of the present invention;

[0042] Figure 4(b) shows the second basic operating mode of the controller provided in the example of the present invention;

[0043] Figure 4(c) shows the third basic operating mode of the controller provided in the example of the present invention;

[0044] Figure 4(d) shows one scenario of the fourth basic operating mode of the controller provided in the example of the present invention;

[0045] Figure 4(e) shows one scenario of the fifth basic operating mode of the controller provided in the example of the present invention;

[0046] Figure 5 A control schematic diagram showing that the current of a single sub-group winding remains constant, provided as an example of the present invention;

[0047] Figure 6 A schematic diagram illustrating the control of a single sub-group winding current rising in an embodiment of the present invention;

[0048] Figure 7 A schematic diagram illustrating the control of a single sub-group winding current decreasing as provided in an example of the present invention;

[0049] Figure 8(a) is a schematic diagram of the control of the current changes of the first to fourth windings corresponding to a set of bridge arms provided in an example of the present invention;

[0050] Figure 8(b) is a schematic diagram of the control of the current change of the first to fourth windings corresponding to a set of bridge arms to keep the current of the fifth winding constant, provided in an example of the present invention.

[0051] Figure 9This is a schematic diagram of control for stable levitation of a five-degree-of-freedom magnetic levitation bearing, provided as an example of the present invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0053] In this invention, the terms "first," "second," etc., used in the invention and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0054] like Figure 1 The diagram shown is a structural diagram of a five-degree-of-freedom magnetic levitation bearing. The five-degree-of-freedom magnetic levitation bearing system controls one rotor to achieve complete levitation. It requires two radial magnetic levitation bearings and one axial magnetic levitation bearing. It needs to control the forces of five degrees of freedom and the currents of ten windings. There is coupling between the degrees of freedom.

[0055] like Figure 2 The diagram shown is a structural diagram of a single radial magnetic levitation bearing. This radial magnetic levitation bearing structure has an electromagnetic force F in the x-direction. x Electromagnetic force F in the opposite direction to y y It needs to be controlled. The electromagnetic force F in the x-direction... x The electromagnetic force F in the y direction is determined by the difference in electromagnetic force generated by the two windings in the x-direction. y It is determined by the difference in electromagnetic force generated by the two windings in the y direction.

[0056] The magnitude F of the electromagnetic force on the rotor generated by each winding mag With the excitation current i of the winding s And the relative distance s between the winding and the rotor satisfies F mag =K i ×i s -K s s, where K i K is the electromagnetic force / current coefficient. s K is the electromagnetic force / displacement coefficient. i With K s It is determined by the structure of the radial winding of the magnetic levitation bearing.

[0057] Taking a single degree of freedom as an example, its control typically employs a dual-loop control system: an outer position loop and an inner current loop. The relative position to the rotor obtained by the displacement sensor serves as feedback for the position loop. This position is compared with a given position, and the controller outputs a command signal for the excitation current of the inner winding. The actual current tracks the command current through the current loop, achieving effective control of the electromagnetic forces of each degree of freedom. The command current is distributed using differential control, with the command currents controlling a pair of windings for one degree of freedom being the addition and subtraction of the bias current and the control current, respectively.

[0058] like Figure 3 As shown in the schematic diagram of the power electronic controller structure for a five-degree-of-freedom magnetic levitation bearing provided in this embodiment of the invention, the five-degree-of-freedom magnetic levitation bearing includes ten windings, which are divided into two groups. The five windings in each group are respectively denoted as the first winding, the second winding, the third winding, the fourth winding, and the fifth winding. The current in the ten windings is unidirectional. Each winding includes a first end and a second end. The end into which the current flows is designated as the first end, and the end out of the winding is designated as the second end.

[0059] The power electronic controller for a five-degree-of-freedom magnetic levitation bearing mainly includes eight controllable switches and eight unidirectional conducting devices. Each controllable switch and each unidirectional conducting device are connected in series to form a bridge arm, resulting in eight bridge arms. These eight bridge arms are divided into two groups, and each group of bridge arms is connected to one of the two winding groups respectively. The connection point between each controllable switch and each unidirectional conducting device is defined as the midpoint of the corresponding bridge arm. Each controllable switch and each unidirectional conducting device includes a first terminal and a second terminal. For the windings and controllable switches, the terminal into which current flows is considered the first terminal, and the terminal out which current flows is considered the second terminal. For the unidirectional conducting devices, the terminal out which current flows is considered the first terminal, and the terminal into which current flows is considered the second terminal.

[0060] In each bridge arm group, four bridge arms are connected in parallel across the power supply. These four bridge arms are designated as the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm. In the first and second bridge arms, the first terminal of the controllable switch is connected to the positive terminal of the power supply, the second terminal of the controllable switch is connected in series with the first terminal of the unidirectional conducting device, and the second terminal of the unidirectional conducting device is connected to the negative terminal of the power supply. In the third and fourth bridge arms, the first terminal of the unidirectional conducting device is connected to the positive terminal of the power supply, the second terminal of the unidirectional conducting device is connected in series with the first terminal of the controllable switch, and the second terminal of the controllable switch is connected to the negative terminal of the power supply.

[0061] Through the above connection relationship, the first and second bridge arms are forward bridge arms, and the third and fourth bridge arms are reverse bridge arms.

[0062] The midpoint of the first bridge arm is connected to the first end of the first winding, the midpoint of the second bridge arm is connected to the first end of the second winding, and the second end of the first winding and the second end of the second winding are connected together and then connected to the first end of the fifth winding.

[0063] The midpoint of the third bridge arm is connected to the second end of the third winding, the midpoint of the fourth bridge arm is connected to the second end of the fourth winding, and the first end of the third winding and the first end of the fourth winding are connected together and then connected to the second end of the fifth winding.

[0064] The conduction time of the aforementioned controllable switch is controlled to ensure that the sum of the currents of the first and second windings connected to the midpoints of the first and second bridge arms is equal to the sum of the currents of the third and fourth windings connected to the midpoints of the third and fourth bridge arms.

[0065] To better illustrate the solution proposed in this invention, the following analysis focuses on the five-degree-of-freedom magnetic levitation bearing to which this invention applies, and an optimized winding layout for the five-degree-of-freedom magnetic levitation bearing. However, the controller proposed in this invention is not limited to the winding layout shown in the accompanying drawings of this embodiment. By reasonably adjusting the winding layout, different control requirements can be met among the controllable switches, unidirectional conduction devices, and winding connection methods determined in this invention.

[0066] Figure 3 This invention provides a topology diagram of a power electronic controller for a five-degree-of-freedom magnetic levitation bearing, and marks the winding distribution and the reference direction of the winding current, corresponding to... Figure 1 The winding distribution is as follows. In the first bridge arm, the first winding corresponds to the winding L in the positive x-direction of the front radial magnetic bearing. a1 The second winding corresponds to the winding L in the negative x direction of the front radial magnetic bearing. c1 The third winding corresponds to the winding L in the positive y-direction of the front radial magnetic bearing. a2 The fourth winding corresponds to the winding L in the negative y-direction of the front radial magnetic bearing. c2 The fifth winding corresponds to the winding L in the positive z direction of the axial magnetic bearing. a5 In the second set of bridge arms, the first winding corresponds to the winding L in the positive x-direction of the rear radial magnetic bearing. a3 The second winding corresponds to the winding L in the negative x direction of the rear radial magnetic bearing. c3 The third winding corresponds to the winding L in the positive y-direction of the rear radial magnetic bearing. a4 The fourth winding corresponds to the winding L in the negative y-direction of the rear radial magnetic bearing. c4 The fifth winding corresponds to the winding L in the negative z direction of the axial magnetic bearing. c5 .

[0067] Specifically, in the first group of bridge arms, the first end of the controllable switch S11 is connected to the positive terminal of the power supply, the second end is connected to the first end of the unidirectional conducting device D11, and the second end of the unidirectional conducting device D11 is connected to the negative terminal of the power supply, forming a positive bridge arm.

[0068] In the first group of bridge arms, the first end of the controllable switch S12 is connected to the positive terminal of the power supply, the second end is connected to the first end of the unidirectional conducting device D12, and the second end of the unidirectional conducting device D12 is connected to the negative terminal of the power supply, forming a positive bridge arm.

[0069] In the first group of bridge arms, the first end of the unidirectional conducting device D13 is connected to the positive terminal of the power supply, the second end is connected to the first end of the controllable switch S13, and the second end of the controllable switch S13 is connected to the negative terminal of the power supply, forming a reverse bridge arm.

[0070] In the first group of bridge arms, the first end of the unidirectional conducting device D14 is connected to the positive terminal of the power supply, the second end is connected to the first end of the controllable switch S14, and the second end of the controllable switch S14 is connected to the negative terminal of the power supply, forming a reverse bridge arm.

[0071] In the first bridge arm, the first winding L a1 The first end is connected to the midpoint of the first bridge arm, and the second winding L c1 The first end is connected to the midpoint of the second bridge arm, and the first winding L a1 Second winding L c1 The second ends are connected together and connected to the fifth winding L a5 The first end; the third winding L a2 The second end is connected to the midpoint of the third bridge arm, and the fourth winding L c2 The second end is connected to the midpoint of the fourth bridge arm, and the third winding L a2 and the fourth winding L c2 The first ends are connected together and connected to the fifth winding L a5 The second end.

[0072] The power electronic devices in the second bridge arm, namely controllable switches S21, S22, S23, and S24, unidirectional conducting devices D21, D22, D23, and D24, and the other five windings L a3 L c3 L a4 L c4 L c5 The connection method is the same as that in the first group of bridge arms.

[0073] In addition to the power electronic controller for the five-degree-of-freedom magnetic levitation bearing provided by this invention, this invention also provides a corresponding control method. By controlling the conduction time of the controllable switch in each bridge arm, the current of the corresponding winding can be controlled. By controlling the current flowing into the first and second bridge arms, the current of the fifth winding in each group of windings can be controlled, thereby realizing the control of the electromagnetic force generated by the ten windings in the five-degree-of-freedom magnetic levitation bearing.

[0074] The control methods of the first group of bridge arms and the second group of bridge arms are completely the same. This embodiment will be used to illustrate the control between the two forward bridge arms and the two reverse bridge arms in the first group of bridge arms and the corresponding five windings.

[0075] The first winding L is controlled by the switching transistor S11. a1 The voltage level at the first terminal: When S11 is on, the voltage level of the first winding L... a1 The first terminal is connected to the positive terminal of the power supply; when S11 is turned off, winding L a1 The first end is connected to the negative terminal of the power supply. The second winding L c1 With the first winding L a1 The control principles are the same.

[0076] The third winding L is controlled by the switching transistor S13. a2 The voltage level at the first terminal: When S13 is on, the voltage level of the third winding L... a2 The first terminal is connected to the positive terminal of the power supply; when S13 is turned off, the third winding L a2 The first terminal is connected to the negative terminal of the power supply. The fourth winding L... c2 With the third winding L a2 The control principles are the same.

[0077] By controlling the duty cycle of the conduction times of S11, S12, S13, and S14, the circuit can operate in different modes. The equivalent circuits under different modes are as follows: Figures 4(a)-4(e) As shown, the equivalent duty cycle at the midpoint of the forward bridge arm is consistent with the duty cycle of the switching device in the forward bridge arm, and the sum of the equivalent duty cycle at the midpoint of the reverse bridge arm and the duty cycle of the switching device in the reverse bridge arm is 1.

[0078] Figure 4(a) shows the equivalent circuit of the first basic working mode, which is used to keep the current in all windings constant: the equivalent duty cycle of the midpoint of all bridge arms is equal. At this time, there is no potential difference between the first end of the first and second windings and the second end of the third and fourth windings, and the current in the five windings is almost constant.

[0079] Figure 4(b) shows the equivalent circuit of the second basic working mode: the equivalent duty cycle of the midpoint of the two positive bridge arms is equal and higher than the equivalent duty cycle of the midpoint of the two negative bridge arms. Relative to the current direction, the two windings (i.e. the first and second windings) of the positive bridge arm are positive voltages at this time. At this time, the sum of the currents of the first and second windings increases, and the sum of the currents of the third and fourth windings increases.

[0080] Figure 4(c) shows the equivalent circuit of the third basic working mode: the equivalent duty cycle of the midpoint of the two reverse bridge arms is equal and higher than the equivalent duty cycle of the midpoint of the two positive bridge arms. Relative to the current direction, the two windings (i.e. the third and fourth windings) of the reverse bridge arms are both negative voltages. At this time, the sum of the currents of the first and second windings decreases, and the sum of the currents of the third and fourth windings decreases.

[0081] Figure 4(d) shows the equivalent circuit for one case in the fourth basic operating mode, where the equivalent duty cycle of the midpoint of one positive bridge arm is higher than that of the midpoint of another positive bridge arm. Relative to the winding current direction, the voltage across the winding connected to the midpoint of the positive bridge arm with the higher equivalent duty cycle is higher than the voltage across the winding connected to the midpoint of the other positive bridge arm. In this case, the current difference between the winding connected to the midpoint of the positive bridge arm with the higher equivalent duty cycle and the winding connected to the midpoint of the positive bridge arm with the lower equivalent duty cycle increases. Taking the equivalent duty cycle of the first bridge arm midpoint being higher than that of the second bridge arm midpoint as an example, relative to the winding current direction, the voltage across the first winding is higher than that across the second winding. In this case, the current difference between the first and second windings increases. In practical applications, the equivalent duty cycle at the midpoint of one positive bridge arm can be controlled to be equal to the equivalent duty cycle at the midpoint of another positive bridge arm, so that the difference in current between the first and second windings remains unchanged; or the equivalent duty cycle at the midpoint of one positive bridge arm can be controlled to be lower than the equivalent duty cycle at the midpoint of another positive bridge arm, so that the difference in current between the first and second windings decreases.

[0082] Figure 4(e) shows the equivalent circuit for one case in the fifth basic operating mode. The equivalent duty cycle of the midpoint of one reverse bridge arm is higher than that of the midpoint of another reverse bridge arm. Relative to the winding current direction, the voltage across the winding connected to the midpoint of the reverse bridge arm with the higher equivalent duty cycle is lower than the voltage across the winding connected to the midpoint of the other reverse bridge arm. At this time, the difference in current between the winding connected to the midpoint of the reverse bridge arm with the higher equivalent duty cycle and the winding connected to the midpoint of the reverse bridge arm with the lower equivalent duty cycle decreases. Taking the equivalent duty cycle of the third bridge arm midpoint being higher than that of the fourth bridge arm midpoint as an example, relative to the winding current direction, the voltage across the third winding is lower than the voltage across the fourth winding. At this time, the difference in current between the third and fourth windings decreases. In practical applications, the equivalent duty cycle of the midpoint of one reverse bridge arm can be controlled to be equal to that of the midpoint of the other reverse bridge arm, so that the current difference between the third and fourth windings remains unchanged; or the equivalent duty cycle of the midpoint of one reverse bridge arm can be controlled to be lower than that of the midpoint of the other reverse bridge arm, so that the current difference between the third and fourth windings increases.

[0083] In any of the five basic operating modes mentioned above, the current in the fifth winding is always equal to the sum of the currents in the first and second windings, as well as the sum of the currents in the third and fourth windings. That is, the sum of the currents in the two windings connected to the midpoint of the positive bridge arm is always equal to the sum of the currents in the two windings connected to the midpoint of the negative bridge arm, and is also equal to the current flowing through the fifth winding. This current value changes in real time during operation, and its magnitude is determined by the control requirements of the fifth winding.

[0084] This control method ensures that the current flowing through the five-degree-of-freedom magnetic levitation bearing winding is unidirectional.

[0085] Depending on the actual control requirements, the above five basic operating modes can work independently or be combined in combination without conflict to achieve more complex control requirements. For example, the second and fifth basic operating modes can be combined with each other, the third and fourth basic operating modes can be combined with each other, and the fourth and fifth basic operating modes can be combined with each other to apply the required voltage to the two ends of the corresponding windings, thereby controlling the magnitude of the winding current.

[0086] The operating modes and control principles of the second bridge arm are completely consistent with those of the first bridge arm. According to actual control requirements, the corresponding basic operating mode can be selected or different basic operating modes can be combined without conflict to achieve control over the magnitude of the current in all windings.

[0087] Figure 5The diagram illustrates the case where the current remains almost constant under the first basic operating mode. In this mode, the equivalent duty cycle at the midpoint of each bridge arm is consistent. The current in the fifth winding is equal to the sum of the currents in the first and second windings, and therefore remains constant. In the diagram, g11, g12, g13, and g14 represent the on and off states of the switching transistors S11, S12, S13, and S14, respectively. A high level indicates that the corresponding switching transistor is on, and a low level indicates that the corresponding switching transistor is off. i11, i12, i13, and i14 represent the current passing through the corresponding winding.

[0088] Figure 6 This demonstrates the situation where all winding currents increase under the second basic operating mode, where the current in the fifth winding is equal to the sum of the currents in the first and second windings, and therefore also increases.

[0089] Figure 7 This demonstrates the situation where all winding currents decrease under the third basic operating mode, where the current in the fifth winding is equal to the sum of the currents in the first and second windings, and therefore also decreases.

[0090] Figure 8(a) shows the situation where, under the superposition of the fourth and fifth basic operating modes, the winding current connected to the midpoint of the positive bridge arm increases, the winding current connected to the midpoint of the other positive bridge arm decreases, the winding current connected to the midpoint of the reverse bridge arm increases, and the winding current connected to the midpoint of the other reverse bridge arm decreases.

[0091] Figure 8(b) shows the case where the current in the fifth winding of this subgroup remains unchanged under the superposition of the fourth and fifth basic operating modes.

[0092] For a five-degree-of-freedom magnetic levitation bearing, the control method of this invention is a novel differential control approach. The sum of the currents in the two windings of the front magnetic bearing in the x-direction is equal to the sum of the currents in the two windings of the front magnetic bearing in the y-direction, and the sum of the currents in the two windings of the rear magnetic bearing in the x-direction is equal to the sum of the currents in the two windings of the rear magnetic bearing in the y-direction. The sum of the currents in the two windings of the axial magnetic bearing is a constant value. Therefore, the power electronic controller proposed in this invention for a five-degree-of-freedom magnetic levitation bearing fully meets the control requirements of such bearings. Furthermore, the control method of this invention allows the sum of the currents in a pair of windings controlling the same degree of freedom to be determined as needed, and the difference in current magnitude determines the magnitude of the electromagnetic force in that degree of freedom. This ensures that in each bridge arm, the sum of the currents in the first and second windings is equal to the sum of the currents in the third and fourth windings, and the sum of the currents in the first and second windings in both bridge arms can be determined according to actual needs.

[0093] Using the control method described above, the power electronic controller for a five-degree-of-freedom magnetic levitation bearing proposed in this invention can achieve stable levitation of the five-degree-of-freedom magnetic levitation bearing. Figure 9 The results demonstrate stable suspension.

[0094] All of the above controllable switches are active switching transistors, the unidirectional conducting devices are diodes, and the control signals for the active switching transistors are pulse modulation signals with adjustable duty cycles.

[0095] By adjusting the conduction time of each active switching transistor, the magnitude of the winding current can be controlled, thereby controlling the electromagnetic force.

[0096] Preferably, the active switching transistor is an IGBT or a MOSFET. In this embodiment, all eight controllable switches are insulated gate bipolar transistors (IGBTs), and all eight unidirectional conducting devices are diodes. The first terminal of the controllable switch is the collector of the IGBT, and the second terminal of the controllable switch is the emitter of the IGBT. The first terminal of the unidirectional conducting device is the cathode of the diode, and the second terminal of the unidirectional conducting device is the anode of the diode.

[0097] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A power electronic controller for a five-degree-of-freedom magnetic levitation bearing, wherein the five-degree-of-freedom magnetic levitation bearing comprises ten windings, the ten windings are divided into two groups, and five windings in each group are designated as the first to fifth windings, characterized in that, The controller includes: Eight controllable switches and eight unidirectional conducting devices are provided. One controllable switch and one unidirectional conducting device are connected in series to form a bridge arm. The eight bridge arms are divided into two groups, and the four bridge arms in each group are referred to as the first to fourth bridge arms. Each winding, controllable switch and unidirectional conducting device includes a first end and a second end. The winding and the controllable switch use the end into which current flows as the first end and the end into which current flows as the second end. The unidirectional conducting device uses the end into which current flows as the first end and the end into which current flows as the second end. In each group, the four bridge arms are connected in parallel across the power supply. In the first and second bridge arms, the first terminal of the controllable switch is connected to the positive terminal of the power supply, the second terminal is connected in series with the first terminal of the unidirectional conducting device, and the second terminal of the unidirectional conducting device is connected to the negative terminal of the power supply. In the third and fourth bridge arms, the first terminal of the unidirectional conducting device is connected to the positive terminal of the power supply, the second terminal is connected in series with the first terminal of the controllable switch, and the second terminal of the controllable switch is connected to the negative terminal of the power supply. In each bridge arm group, the midpoints of the first and second bridge arms are connected to the first ends of the first and second windings, respectively. The second ends of the first and second windings are connected together and then connected to the first end of the fifth winding. The midpoints of the third and fourth bridge arms are connected to the second ends of the third and fourth windings, respectively. The first ends of the third and fourth windings are connected together and then connected to the second end of the fifth winding.

2. The controller according to claim 1, characterized in that, All controllable switches are active switching transistors, and all unidirectional conducting devices are diodes.

3. The controller according to claim 2, characterized in that, The active switching transistor is an IGBT or a MOSFET.

4. The controller according to claim 3, characterized in that, The first terminal of the controllable switch is the collector of the IGBT, and the second terminal is the emitter of the IGBT. The first terminal of the unidirectional conducting device is the negative terminal of the diode, and the second terminal is the positive terminal of the diode.

5. The controller according to claim 1, characterized in that, The current flowing through the winding is a unidirectional current.

6. A control method for implementing a power electronic controller for a five-degree-of-freedom magnetic levitation bearing as described in any one of claims 1-5, characterized in that, include: The duty cycle of the controllable switch is controlled so that the controller operates in one of the five basic operating modes; For any one of the two sets of bridge arms, the five basic operating modes include: First basic working mode: control the equivalent duty cycle of the midpoint of the four bridge arms to be equal, so that the current of the five windings remains unchanged; Second basic working mode: control the equivalent duty cycle of the midpoint of the first and second bridge arms to be equal and higher than the equivalent duty cycle of the midpoint of the third and fourth bridge arms, so that the sum of the currents of the first and second windings and the sum of the currents of the third and fourth windings are both increased; The third basic working mode: control the equivalent duty cycle of the midpoint of the third and fourth bridge arms to be equal and higher than the equivalent duty cycle of the midpoint of the first and second bridge arms, so that the sum of the currents of the first and second windings and the sum of the currents of the third and fourth windings are reduced. Fourth basic operating mode: Control the equivalent duty cycle at the midpoint of the first and second bridge arms to change the difference in current between the first and second windings; Fifth basic operating mode: Control the equivalent duty cycle of the third and fourth bridge arms to change the difference in current between the third and fourth windings; The equivalent duty cycle at the midpoint of the first and second bridge arms is consistent with the duty cycle of the controllable switch in the first and second bridge arms, and the sum of the equivalent duty cycle at the midpoint of the third and fourth bridge arms and the duty cycle of the controllable switch in the third and fourth bridge arms is 1.

7. The control method according to claim 6, characterized in that, The fourth basic working mode includes: The equivalent duty cycle at the midpoint of the first bridge arm is controlled to be higher than that at the midpoint of the second bridge arm, thereby increasing the difference in current between the first and second windings. Alternatively, the equivalent duty cycle at the midpoint of the first and second bridge arms can be controlled to be equal, so that the difference in current between the first and second windings remains constant; Alternatively, the equivalent duty cycle at the midpoint of the first bridge arm can be controlled to be lower than the equivalent duty cycle at the midpoint of the second bridge arm, thereby reducing the current difference between the first and second windings.

8. The control method according to claim 6, characterized in that, The fifth basic working mode includes: The equivalent duty cycle at the midpoint of the third bridge arm is controlled to be higher than that at the midpoint of the fourth bridge arm, so that the difference in current between the third and fourth windings is reduced. Alternatively, the equivalent duty cycle at the midpoint of the third and fourth bridge arms can be controlled to be equal, so that the difference in current between the third and fourth windings remains unchanged; Alternatively, the equivalent duty cycle at the midpoint of the third bridge arm can be controlled to be lower than that at the midpoint of the fourth bridge arm, thereby increasing the current difference between the third and fourth windings.

9. The control method according to claim 6, characterized in that, It also includes controlling the duty cycle of the controllable switch so that the controller can operate simultaneously in two or more of the five basic operating modes, wherein the control between the two or more basic operating modes does not conflict.

10. The control method according to claim 9, characterized in that, The controller operates simultaneously in the second basic operating mode and the fifth basic operating mode; Alternatively, the controller may operate simultaneously in both the third and fourth basic operating modes; Alternatively, the controller may operate simultaneously in both the fourth and fifth basic operating modes.

Images