Fault-tolerant magnetic bearing control circuit, control method and controller

Abstract

The application discloses a magnetic suspension bearing control circuit with fault tolerance, a control method and a controller, and belongs to the field of magnetic suspension bearing control. The circuit comprises 2N windings in a magnetic suspension bearing, a direct-current power supply, two bipolar bridge arms and 2N-1 unipolar bridge arms. The two ends of each winding are connected to the midpoints of the two bridge arms. Each unipolar bridge arm is connected to two windings, and each bipolar bridge arm is connected to one winding. The upper and lower ends of each bridge arm are connected to the positive and negative poles of the direct-current power supply. The method comprises the following steps: judging the windings related to the faulty switch device in real time, blocking the switch device for controlling the winding, reversing the current in the winding, establishing a current constraint, recalculating the current command value of each winding under the current constraint, keeping the electromagnetic force consistent before and after the fault, and determining the switch signal of each switch device in the control circuit. The application can realize the switch circuit fault tolerance while reducing the number of switch devices.

Description

Technical Field

[0001] This invention belongs to the field of magnetic levitation bearing control, and more specifically, relates to a magnetic levitation bearing control circuit and control method with switch-off fault tolerance capability. Background Technology

[0002] Magnetic levitation bearings are mechatronic systems designed to replace traditional mechanical bearings, achieving contactless and stable operation between the rotor and magnetic poles. They are highly suitable for high-speed applications requiring clean environments and are widely used in industrial applications such as flywheel energy storage, compressors, and blowers. The working principle of a magnetic levitation bearing is to pass an electric current through the magnetic poles to generate electromagnetic force, thus leviting the rotor stably. An active magnetic levitation bearing system mainly includes a rotor, sensors, a controller, and electromagnetic actuators. Position sensors collect rotor position information, the controller receives the position information of each degree of freedom of the rotor and provides the necessary current to each winding, and the electromagnetic actuator converts the current in the coils into the electromagnetic force that achieves stable rotor levitation. The power amplifier, as a component of the controller, is the core of the mechatronic conversion and plays a crucial role in the entire system.

[0003] Patent application number 202010435591.0 discloses a series winding control device and method for magnetic levitation bearings, comprising five unidirectional conducting devices, five controllable switches, four windings, and a power supply. By changing the conduction time of each controllable switch within a switching cycle, the current through each winding is controlled. By dividing the four windings into two groups and controlling the common-mode and differential-mode currents within the windings, the current of the four windings controlling two degrees of freedom in the magnetic levitation bearing is controlled. This invention, with four windings connected in series, requires only five bridge arms to control the four windings of a single eight-pole radial magnetic bearing, compared to the two bridge arms required for a single coil in a conventional bridge circuit, effectively improving the utilization rate of the device.

[0004] However, power amplifiers contain numerous power electronic devices with many potential failure points. Under complex environments of high load, high dynamics, and strong interference, these devices are highly susceptible to open-circuit faults. In power amplifiers with magnetic levitation bearings, an open-circuit fault in the switching device can lead to voltage control failure, causing the winding current to deviate from the command value, rotor instability, and serious consequences such as high-speed rotor collisions with the protective bearing. The device provided in the aforementioned patent documents lacks fault tolerance for open-circuit faults. To address this issue, a series of patents, exemplified by application number CN202011605006.3, proposed power amplifiers with switch open-circuit fault tolerance. However, these amplifiers doubled the number of fully controlled switching devices for redundancy, resulting in an excessive number of devices and a large footprint. Summary of the Invention

[0005] To address the shortcomings and improvement needs of existing technologies, this invention provides a fault-tolerant magnetic levitation bearing control circuit, control method, and controller. The purpose is to optimize the topology of the magnetic levitation bearing control circuit, ensuring that the control circuit has fault-tolerant switching capability while reducing the number of fully controlled switching devices in the circuit.

[0006] To achieve the above objectives, according to one aspect of the present invention, a magnetic levitation bearing control circuit with switch-off fault tolerance is provided. The magnetic levitation bearing includes 2N windings and has N degrees of freedom, each degree of freedom being controlled by two windings, where N is a positive integer. The control circuit includes: the 2N windings in the magnetic levitation bearing, a DC power supply, and 2N+1 bridge arms; of the 2N+1 bridge arms, 2 are bipolar bridge arms and 2N-1 are unipolar bridge arms.

[0007] Each winding's two ends are connected to the midpoints of two bridge arms respectively; each unipolar bridge arm is connected to two windings simultaneously, and each bipolar bridge arm is connected to only one winding.

[0008] The upper and lower ends of each bridge arm are connected to the positive and negative terminals of the DC power supply, respectively.

[0009] According to another aspect of the present invention, a control method based on the above-described magnetic levitation bearing control circuit with switch-breaking fault tolerance is provided, comprising the following steps:

[0010] (S1) Real-time detection of the current of each winding to determine the degree of freedom of the fault in real time, which is taken as the degree of freedom of the fault. After the open circuit fault is detected, the winding related to the fully controlled switching device that caused the open circuit fault is determined among the two windings that control the degree of freedom of the fault, and is taken as the target winding.

[0011] (S2) Block the fully controlled switching device of the target winding; if there is a bipolar bridge arm connected to the target winding, open the fully controlled switching device in the lower bridge arm of the bipolar bridge arm.

[0012] (S3) Reverse the current in the target winding and establish corresponding current constraints on the two bridge arms connected to the target winding.

[0013] For a bipolar bridge arm, the current constraint is: the current in the winding it is connected to is greater than 0;

[0014] For a unipolar bridge arm, the current constraint is: the currents of the two windings connected to it are equal in magnitude and the current flows into the bridge arm in one direction and out of the bridge arm in the other.

[0015] (S4) Under current constraints, recalculate the current command value of each winding so that the electromagnetic force generated by the two windings controlling each degree of freedom remains consistent before and after the circuit breaker fault.

[0016] (S5) Determine the switching signals of each fully controlled switching device in the control circuit based on the current command value calculated in step (S4).

[0017] Furthermore, in step (S1), determining the degree of freedom in which the fault occurred includes:

[0018] For each degree of freedom, determine whether the sum of the currents of the two windings controlling that degree of freedom is less than a preset bias threshold. If so, determine that the degree of freedom is a faulty degree of freedom.

[0019] Further, in step (S1), after detecting an open-circuit fault, the windings among the two windings controlling the fault degree of freedom that are related to the fully controlled switching device where the open-circuit fault occurred are determined, including:

[0020] The winding modulation waves of the two windings controlling the fault degree of freedom are obtained and compared. The winding with the larger winding modulation wave is identified as the winding associated with the fully controlled switching device that has experienced an open circuit fault.

[0021] Furthermore, in step (S4), for any degree of freedom, the current command values ​​of the two windings controlling that degree of freedom before and after the open-circuit fault satisfy:

[0022]

[0023] Among them, i aN and i cN i represents the magnitude of the current in the two windings before the open-circuit fault occurs. a and i c Let s1 and s2 represent the magnitude of the current in the two windings after an open circuit fault occurs, and let s1 and s2 represent the distances from the rotor to the two magnetic poles in that degree of freedom, respectively.

[0024] Further, step (S5) includes:

[0025] (S51) The current command value and current feedback value of each winding are subtracted and then PI control is performed to obtain the winding modulation wave of each winding.

[0026] (S52) Based on the winding modulation wave calculated in (S51) and Kirchhoff's voltage law, calculate the bridge arm modulation wave applied to the midpoint of each bridge arm.

[0027] (S53) Perform carrier comparison on the bridge arm modulation wave calculated in (S52) to obtain the expected PWM signal at the midpoint of each bridge arm;

[0028] (S54) Determine the drive signal of each fully controlled switching device in each bridge arm according to the expected PWM signal of each bridge arm; for any fully controlled switching device, if it is located in the upper bridge arm, its drive signal is consistent with the expected PWM signal of the bridge arm midpoint, and if it is located in the lower bridge arm, its drive signal is opposite to the expected PWM signal of the bridge arm midpoint.

[0029] According to another aspect of the present invention, a controller based on the above-described magnetic levitation bearing control circuit with switch-breaking fault tolerance is provided, comprising:

[0030] The current detection module is connected to each winding and is used to detect the current of each winding in real time.

[0031] The fault identification module, connected to the current detection module, is used to determine the degree of freedom of the fault based on the current detected by the current detection module, and to determine the fault degree of freedom. After detecting an open circuit fault, it determines the winding related to the fully controlled switching device that caused the open circuit fault among the two windings controlling the degree of freedom of the fault, and uses it as the target winding.

[0032] The variable bias current control module includes a constraint building unit and an electromagnetic force reconfiguration unit;

[0033] The constraint construction unit, connected to the fault identification module, is used to reverse the current in the target winding and establish corresponding current constraints for the two bridge arms connected to the target winding. For bipolar bridge arms, the current constraint is that the current in the windings they are connected to is greater than 0. For unipolar bridge arms, the current constraint is that the currents in the two windings they are connected to are equal in magnitude and opposite in direction.

[0034] The electromagnetic force reconfiguration unit, connected to the constraint construction unit, is used to recalculate the current command value of each winding under current constraints, so that the electromagnetic force generated by the two windings controlling each degree of freedom remains consistent before and after the open circuit fault.

[0035] The current control module is connected to the electromagnetic force reconstruction module and is used to determine the switching signals of each fully controlled switching device in the control circuit based on the current command value calculated by the electromagnetic force reconstruction module. The current control module is also connected to each fully controlled switching device and is used to enable or disable the fully controlled switching device.

[0036] Furthermore, the fault identification module determines the degrees of freedom of fault occurrence based on the current detected by the current detection module, including:

[0037] For each degree of freedom, determine whether the sum of the currents of the two windings controlling that degree of freedom is less than a preset bias threshold. If so, determine that the degree of freedom is a faulty degree of freedom.

[0038] Furthermore, after detecting an open-circuit fault, the fault identification module determines the winding among the two windings controlling the fault degree of freedom that is related to the fully controlled switching device where the open-circuit fault occurred, including:

[0039] The winding modulation waves of the two windings controlling the fault degree of freedom are obtained and compared. The winding with the larger winding modulation wave is identified as the winding associated with the fully controlled switching device that has experienced an open circuit fault.

[0040] Furthermore, the current control module includes:

[0041] The current comparison unit has a first input terminal for receiving the current command value and a second input terminal connected to the current detection module, which is used to calculate the difference between the current command value and the current feedback value of the winding.

[0042] The current control unit has its input terminal connected to the output terminal of the current comparison unit. It is used to perform PI control on the current difference output by the current comparison unit to obtain the winding modulation wave.

[0043] The transformation matrix unit, whose input is connected to the output of the current control unit, is used to calculate the bridge arm modulation wave applied to the midpoint of each bridge arm based on the winding modulation wave output by the current controller and Kirchhoff's voltage law.

[0044] The switch drive unit is connected to each fully controllable switching device and is used to enable or block the switch;

[0045] The carrier comparison unit, whose input is connected to the output of the transformation matrix unit, is used to compare the carrier of the bridge arm modulation wave calculated by the transformation matrix to obtain the desired PWM signal at the midpoint of each bridge arm.

[0046] And a drive signal generation unit, whose input terminal is connected to the output terminal of the carrier comparison unit, and whose output terminal is connected to each fully controllable switching device, is used to determine the drive signal of each fully controllable switching device in each bridge arm according to the PWM signal expected at the midpoint of each bridge arm; for any fully controllable switching device, if it is located in the upper bridge arm, its drive signal is consistent with the PWM signal expected at the midpoint of the bridge arm, and if it is located in the lower bridge arm, its drive signal is opposite to the PWM signal expected at the midpoint of the bridge arm.

[0047] According to another aspect of the present invention, a magnetic levitation bearing system is provided, comprising a magnetic levitation bearing, the control circuit described above provided by the present invention, and the controller described above provided by the present invention.

[0048] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0049] (1) The magnetic levitation bearing control circuit with backup switch circuit breaking fault tolerance provided by the present invention requires only 2 redundant fully controlled switching devices while achieving circuit breaking fault tolerance.

[0050] (2) The control method provided by the present invention can determine whether a circuit break fault has occurred by real-time detection of the current of the controller and the operation of the modulation wave output of the current loop. It can accurately detect the circuit break fault of the switch and locate the relevant winding. On this basis, in the face of a circuit break fault, by blocking the relevant fully controlled switching devices and recalculating the current command value of each winding according to the current constraint of the circuit topology and the principle of electromagnetic force reconstruction, it can effectively prevent the magnetic levitation bearing system from becoming unstable after the switch has a circuit break fault, avoid the rotor from falling, effectively improve the system reliability, and has good practical application value.

[0051] In summary, for magnetic levitation bearing systems, the fault-tolerant operating mode can ensure uninterrupted operation when a switching device open circuit fault occurs, effectively improving the fault response capability of the magnetic levitation bearing system. Moreover, the number of redundant devices required is small, which will not impose a large hardware design burden on the controller. Attached Figure Description

[0052] Figure 1 A schematic diagram of an existing eight-pole radial (front and rear ends) magnetic levitation bearing structure;

[0053] Figure 2 A schematic diagram of the control circuit structure for an eight-pole radial (front and rear ends) magnetic levitation bearing provided in an embodiment of the present invention;

[0054] Figure 3 A flowchart of the control method provided in an embodiment of the present invention;

[0055] Figure 4 This is an overall control block diagram provided for embodiments of the present invention;

[0056] Figure 5 The diagrams provided in this embodiment of the invention illustrate the direction and path of winding current flow under different conditions; wherein, (a) is a diagram of the direction and path of winding current flow under normal operation; (b) to (e) are diagrams of the direction and path of winding current flow after each switch experiences a circuit breaker fault.

[0057] Figure 6 A block diagram of a current control module provided in an embodiment of the present invention. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0059] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0060] Before explaining the technical solution of the present invention in detail, the structure and control method of the magnetic levitation bearing are briefly introduced as follows:

[0061] For a magnetic levitation bearing with N degrees of freedom, each degree of freedom is controlled by two windings, resulting in 2N windings. According to existing technology, in order to achieve fault tolerance capability for switch circuit breaking, its control circuit requires 2N+1 bipolar bridge arms, which in turn requires 2×(2N+1) fully controlled switching devices.

[0062] by Figure 1 The example shown is an eight-pole radial (front and rear ends) magnetic levitation bearing. This bearing has four control degrees of freedom, each controlled by two windings. Specifically, the x1 direction is controlled by windings A1 and C1, the y1 direction by windings A2 and C2, the x2 direction by windings A3 and C3, and the y2 direction by windings A4 and C4. According to existing fault-tolerant schemes, its control circuit requires nine bipolar bridge arms, correspondingly requiring 18 fully controlled switching devices. Compared to control circuits without fault tolerance, the number of fully controlled switching devices is doubled, and the number of redundant devices is nine.

[0063] The components are redundant and occupy too much space.

[0064] To address the technical problem that existing magnetic levitation bearing control circuits require numerous redundant components and occupy excessive space while achieving fault tolerance for switch-circuit open-circuit faults, this invention provides a fault-tolerant magnetic levitation bearing control circuit, control method, and controller. The overall approach involves improving the topology of the magnetic levitation bearing control circuit based on the concept of electromagnetic force reconfiguration, thereby reducing the number of fully controlled switching devices in the control circuit while achieving fault tolerance for switch-circuit open-circuit faults. Without loss of generality, the following embodiments all use… Figure 1 The magnetic levitation bearing with four degrees of freedom shown is used as an example for illustration.

[0065] The following is an example.

[0066] Example 1:

[0067] A magnetic levitation bearing control circuit with switch-off fault tolerance, such as... Figure 1 As shown, the magnetic levitation bearing includes 8 windings and has 4 degrees of freedom, each of which is controlled by two windings.

[0068] like Figure 2 As shown, the control circuit includes: 8 windings in the magnetic levitation bearing, a DC power supply, and 9 bridge arms; of the 9 bridge arms, 2 are bipolar bridge arms and 7 are unipolar bridge arms.

[0069] Each winding's two ends are connected to the midpoints of two bridge arms respectively; each unipolar bridge arm is connected to two windings simultaneously, and each bipolar bridge arm is connected to only one winding.

[0070] The upper and lower ends of each bridge arm are connected to the positive and negative terminals of the DC power supply, respectively.

[0071] It is easy to understand, such as Figure 2 As shown, a unipolar bridge arm is defined as one and only one of the upper or lower bridge arms being a fully controlled switching device. In a bipolar bridge arm, both the upper and lower bridge arms are fully controlled devices, and each fully controlled switching device requires an anti-parallel connection of a unidirectional conducting device. Optionally, in this embodiment, the fully controlled switching device includes an insulated-gate bipolar transistor; the unidirectional conducting device is a diode.

[0072] Figure 2 In the control circuit shown, during normal operation, only the fully controlled switching device of the upper bridge arm participates in the winding control, while the fully controlled switching device of the lower bridge arm serves as a redundant backup, participating in winding control in the event of a switch open-circuit fault. Compared to control circuits without fault tolerance, this circuit only has two redundant switching devices, significantly reducing the number of redundant devices compared to existing fault-tolerant schemes.

[0073] It is easy to understand that as the control degrees of freedom of the magnetic levitation bearing increase, the number of unipolar bridge arms can be increased accordingly. Furthermore, it should be noted that when the control degrees of freedom of the magnetic levitation bearing increase, if existing fault-tolerant schemes are used, the number of redundant switching devices will increase accordingly. However, using the control circuit provided by this invention, the number of redundant switching devices remains at 2.

[0074] Example 2:

[0075] Based on the control method of the magnetic levitation bearing control circuit with switch-breaking fault tolerance provided in Embodiment 1 above, such as Figure 3 As shown, it includes the following steps:

[0076] (S1) Real-time detection of the current of each winding to determine the degree of freedom of the fault in real time, which is taken as the degree of freedom of the fault. After the open circuit fault is detected, the winding related to the fully controlled switching device that caused the open circuit fault is determined among the two windings that control the degree of freedom of the fault, and is taken as the target winding.

[0077] When the magnetic bearing is operating normally, the sum of the currents in the two windings is twice the preset bias current, i.e., 2I. bias0 Taking two windings with a certain degree of freedom as an example, the current i in these two windings... aN and i cN The sum satisfies: i aN +i cN =2I bias0 ;

[0078] After a switch-off fault occurs, the winding current controlled by the faulty fully controlled switching device will decrease significantly, and the sum of the currents in the two windings under the corresponding degree of freedom will decrease rapidly. A threshold I should be reasonably set based on the magnitude of the sum of the currents in the two windings under the same degree of freedom under normal and fault conditions. limit This threshold should be less than 2I. bias0 When the magnetic levitation bearing is working, the sum of the currents of the two windings controlling each degree of freedom is detected in real time and compared with a threshold. When the sum of the currents of the two windings corresponding to a certain degree of freedom is less than the set threshold, it can be determined that there is a problem with the current of the two windings corresponding to that degree of freedom. Furthermore, since the winding current controlled by the fully controlled switching device that has an open circuit fault will decrease rapidly, the difference between it and the current command value will increase, which will lead to an increase in the winding modulation wave of that winding. Therefore, after determining the two windings with current problems, by further comparing the winding modulation waves, the winding with the larger winding modulation wave can be identified, and the fault can be located to the switching device controlling a certain winding that has failed.

[0079] Based on this, in step (S1) of this embodiment, determining the degree of freedom in which a fault occurs includes:

[0080] For each degree of freedom, determine whether the sum of the currents of the two windings controlling that degree of freedom is less than the preset bias threshold. If so, it means that there is a fully controlled switching device with an open circuit fault in the bridge arm connected to the two windings controlling that degree of freedom, and then determine that the degree of freedom is the degree of freedom with a fault.

[0081] In step (S1) of this embodiment, after detecting an open-circuit fault, the winding related to the fully controlled switching device that experienced the open-circuit fault among the two windings controlling the degree of freedom of the fault is determined, including:

[0082] The winding modulation waves of the two windings controlling the fault degree of freedom are obtained and compared. The winding with the larger winding modulation wave is identified as the winding associated with the fully controlled switching device that has experienced an open circuit fault.

[0083] (S2) Block the fully controlled switching device of the target winding; if there is a bipolar bridge arm connected to the target winding, open the fully controlled switching device in the lower bridge arm of the bipolar bridge arm.

[0084] After locating the target winding associated with the fully controlled switching device that has experienced an open circuit fault, it is difficult to further determine the specific fully controlled switching device that has failed. In this embodiment, step (S2) directly blocks the fully controlled switching device of the current control target winding, which can disconnect the faulty device with lower control complexity.

[0085] (S3) Reverse the current in the target winding and establish corresponding current constraints on the two bridge arms connected to the target winding.

[0086] After blocking the relevant fully controlled switching devices, the unipolar bridge arm where the blocked switching device is located can neither absorb nor release current. Therefore, the current in the target winding needs to be reversed, and the two bridge arms connected to the target winding need to meet the corresponding current constraints to ensure the normal operation of the circuit. Specifically, for bipolar bridge arms, the current constraint is: the current of the windings connected to it is greater than 0, which is an inequality constraint. For unipolar bridge arms, the current constraint is: the currents of the two windings connected to it are equal in magnitude and the current flows into the bridge arm in one direction and out of the bridge arm in the other direction, which is an equality constraint.

[0087] (S4) Under current constraints, recalculate the current command value of each winding so that the electromagnetic force generated by the two windings controlling each degree of freedom remains consistent before and after the circuit breaker fault.

[0088] To ensure the control circuit has fault tolerance for switch-off faults, it is necessary to guarantee that after a switch-off fault occurs, the electromagnetic force generated by the windings controlling each degree of freedom is equal to the electromagnetic force under normal operating conditions. Taking one degree of freedom as an example, under normal conditions, the current in the two windings is i. aN and i cN Under normal operating conditions, the sum of the two currents is twice the system's preset bias current, i.e., i aN +i cN =2I bias The corresponding electromagnetic force is Where s1 and s2 are the distances from the rotor to the two magnetic poles in this degree of freedom, respectively, which can be obtained by a position sensor, k mag The coefficient that generates electromagnetic force can be considered a constant;

[0089] To ensure the current i of the two windings in fault-tolerant mode after an open-circuit fault occurs.a with i c The magnitude of the generated electromagnetic force should be the same as that under normal mode conditions, i.e. Right now

[0090]

[0091] For each degree of freedom, according to the above current relationship, establish the corresponding equations and solve them under the constraints to obtain the new current command value for each winding;

[0092] (S5) Determine the switching signals of each fully controlled switching device in the control circuit based on the current command value calculated in step (S4);

[0093] Step (S5) of this embodiment includes:

[0094] (S51) The current command value and current feedback value of each winding are subtracted and then PI control is performed to obtain the winding modulation wave of each winding.

[0095] (S52) Based on the winding modulation wave calculated in (S51) and Kirchhoff's voltage law, calculate the bridge arm modulation wave applied to the midpoint of each bridge arm.

[0096] It is easy to understand that, in order to avoid overmodulation, the modulated wave of each bridge arm needs to be limited to [0, V]. dc Within the range of ], where V dc This is the DC bus voltage;

[0097] (S53) Perform carrier comparison on the bridge arm modulation wave calculated in (S52) to obtain the expected PWM signal at the midpoint of each bridge arm;

[0098] (S54) Determine the drive signal of each fully controlled switching device in each bridge arm according to the expected PWM signal of each bridge arm; for any fully controlled switching device, if it is located in the upper bridge arm, its drive signal is consistent with the expected PWM signal of the bridge arm midpoint, and if it is located in the lower bridge arm, its drive signal is opposite to the expected PWM signal of the bridge arm midpoint.

[0099] The control method provided in this embodiment can accurately detect switch open circuit faults and locate the relevant windings. Based on this, by blocking the relevant fully controlled switching devices, establishing corresponding current constraints, and recalculating the current command values ​​of each winding based on the principle of electromagnetic force reconstruction, it can effectively prevent the magnetic levitation bearing system from becoming unstable after a switch open circuit fault, avoid rotor drop, effectively improve system reliability, and has good practical application value.

[0100] It is easy to understand that when the magnetic levitation winding is working normally, it is controlled according to the current command value given to each winding, and the drive signal of each switching device is determined. The method of determining the drive switching signal is similar to the above step (S5). The difference is that, since there is no reverse winding current, the mathematical relationship between the winding modulation wave and the bridge arm modulation wave established based on Kirchhoff's voltage law (KVL) is different.

[0101] Figure 4 This is a block diagram of normal control and fault-tolerant control provided by the present invention. Under normal operation, each shaft winding is in a current differential control mode, that is, the current on one winding is the bias current plus the output value of the position controller, and the current on the opposite winding is the bias current minus the output value of the position controller. The sum of the two currents of the shaft is kept constant in real time, that is, constant bias current control. However, in the fault-tolerant operation mode after a fault, due to the constraints in the circuit topology, there are inequalities or equality constraints between the winding currents. This causes the control of the winding current of each shaft to not fully realize the constant bias current control strategy. Therefore, the current control strategy applied at this time is a variable bias current control strategy.

[0102] The control method provided in this embodiment will be further explained below in conjunction with specific fault scenarios.

[0103] Figure 5 This is a schematic diagram showing the direction and path of current flow in the magnetic levitation winding under normal operating conditions and after each switch experiences a circuit breaker fault. Figure 5 In diagram (a), the current flow direction and path of the winding under normal operating conditions are shown. The modulation wave of the winding from left to right is u... A1 ,u A2 ,u A3 ,u A4 ,u C1 ,u C2 ,u C3 ,u C4 The modulation waves of the bridge arms from left to right are u1, u2, u3, u4, u5, u6, u7, u8, u9. The conversion from winding modulation waves to bridge arm modulation waves must follow Kirchhoff's voltage law, i.e.,

[0104]

[0105] If an open-circuit fault occurs in the switch of the first bridge arm, the current in winding A1 will drop significantly. Based on the fault detection described above, the fault is determined to be an open-circuit fault in the switch of control winding A1. The switches of control winding A1, i.e., the switches of the first and second bridge arms, are blocked. At this time, the current in winding A1 needs to be reversed while satisfying the current constraint i. a1 =i a2The variable bias control, which is equivalent to electromagnetic force, is implemented below. Under normal mode, the currents of windings A1, C1, A2, and C2 are i a1N i c1N i a2N i c2N Therefore, it exists. and

[0106] Figure 5 (b) shows the direction and path of winding current flow in fault-tolerant mode. The conversion from winding modulation wave to bridge arm modulation wave must follow Kirchhoff's voltage law, i.e.,

[0107]

[0108] If an open-circuit fault occurs in the lower transistor of the second bridge arm, this fault will cause a significant drop in the current of windings A1 and A2. If, based on the above fault detection, the fault is determined to be an open-circuit fault in the switch of control winding A1, then the switches of control winding A1 (i.e., the switches of the first and second bridge arms) must be blocked. In this case, the current in winding A1 must be reversed and the current constraint i must be satisfied. a1 =i a2 The variable bias control, which achieves electromagnetic force equivalent, is described below. The winding current flow direction and path in fault-tolerant mode are as follows: Figure 5 As shown in (b) above. If the fault detection indicates an open-circuit fault in the switch of control winding A2, then the switches of control winding A2, i.e., the switches of the second and third bridge arms, should be blocked. In this case, the current in winding A2 needs to be reversed and the current constraint i must be satisfied. a1 =i a2 =i a3 The variable bias control, which achieves electromagnetic force equivalent, is described below. The winding current flow direction and path in fault-tolerant mode are as follows: Figure 5 As shown in (c) in the figure.

[0109] If an open-circuit fault occurs in the upper transistor of the third bridge arm, this fault will cause a significant drop in the current of windings A2 and A3. If, based on the above fault detection, the fault is determined to be an open-circuit fault in the switch of control winding A2, then the switches of control winding A2 (i.e., the switches of the second and third bridge arms) must be blocked. In this case, the current in winding A2 must be reversed and the current constraint i must be satisfied. a1 =i a2 =i a3 The variable bias control, which achieves electromagnetic force equivalent, is described below. The winding current flow direction and path in fault-tolerant mode are as follows: Figure 5 As shown in (c). If the fault detection above indicates that the switch of control winding A3 has an open circuit fault, then the switch of control winding A3, i.e., the switches of the third and fourth bridge arms, should be blocked. At this time, the current of winding A3 needs to be reversed and the current constraint i must be satisfied. a2=i a3 =i a4 The variable bias control, which achieves electromagnetic force equivalent, is described below. The winding current flow direction and path in fault-tolerant mode are as follows: Figure 5 As shown in (d) in the figure.

[0110] If an open-circuit fault occurs in the lower transistor of the fourth bridge arm, this fault will cause a significant drop in the current of windings A3 and A4. If, based on the above fault detection, the fault is determined to be an open-circuit fault in the switch of control winding A3, then the switch of control winding A3 (i.e., the switches of the third and fourth bridge arms) must be blocked. In this case, the current in winding A3 must be reversed and the current constraint i must be satisfied. a2 =i a3 =i a4 The variable bias control, which achieves electromagnetic force equivalent, is described below. The winding current flow direction and path in fault-tolerant mode are as follows: Figure 5 As shown in (d). If the fault detection above indicates that the switch of control winding A4 has an open circuit fault, then the switch of control winding A4, i.e., the switches of the fourth and fifth bridge arms, should be blocked. At this time, the current of winding A4 needs to be reversed and the current constraint i must be satisfied. a3 =i a4 =i c1 The variable bias control, which achieves electromagnetic force equivalent, is described below. The winding current flow direction and path in fault-tolerant mode are as follows: Figure 5 As shown in (e).

[0111] When other switching transistors experience open-circuit faults, the specific control methods can be referred to the above description, and will not be listed one by one here.

[0112] Example 3:

[0113] A controller based on the aforementioned magnetic levitation bearing control circuit with switching and fault-tolerant capability, such as... Figure 6 As shown, it includes:

[0114] The current detection module is connected to each winding and is used to detect the current of each winding in real time.

[0115] The fault identification module, connected to the current detection module, is used to determine the degree of freedom of the fault based on the current detected by the current detection module, and to determine the fault degree of freedom. After detecting an open circuit fault, it determines the winding related to the fully controlled switching device that caused the open circuit fault among the two windings controlling the degree of freedom of the fault, and uses it as the target winding.

[0116] The variable bias current control module includes a constraint building unit and an electromagnetic force reconfiguration unit;

[0117] The constraint construction unit, connected to the fault identification module, is used to reverse the current in the target winding and establish corresponding current constraints for the two bridge arms connected to the target winding. For bipolar bridge arms, the current constraint is that the current in the windings they are connected to is greater than 0. For unipolar bridge arms, the current constraint is that the currents in the two windings they are connected to are equal in magnitude and opposite in direction.

[0118] The electromagnetic force reconfiguration unit, connected to the constraint construction unit, is used to recalculate the current command value of each winding under current constraints, so that the electromagnetic force generated by the two windings controlling each degree of freedom remains consistent before and after the open circuit fault.

[0119] The current control module is connected to the electromagnetic force reconstruction module and is used to determine the switching signals of each fully controlled switching device in the control circuit based on the current command value calculated by the electromagnetic force reconstruction module. The current control module is also connected to each fully controlled switching device and is used to enable or disable the fully controlled switching device.

[0120] In this embodiment, the fault identification module determines the degree of freedom of fault occurrence based on the current detected by the current detection module, including:

[0121] For each degree of freedom, determine whether the sum of the currents of the two windings controlling that degree of freedom is less than a preset bias threshold. If so, determine that the degree of freedom is a faulty degree of freedom.

[0122] Furthermore, after detecting an open-circuit fault, the fault identification module determines the winding among the two windings controlling the fault degree of freedom that is related to the fully controlled switching device where the open-circuit fault occurred, including:

[0123] The winding modulation waves of the two windings controlling the fault degree of freedom are obtained and compared. The winding with the larger winding modulation wave is identified as the winding associated with the fully controlled switching device that has experienced an open circuit fault.

[0124] For specific judgment criteria, please refer to the description in Example 2 above.

[0125] like Figure 6 As shown, in this embodiment, the current control module includes:

[0126] The current comparison unit has a first input terminal for receiving the current command value and a second input terminal connected to the current detection module, which is used to calculate the difference between the current command value and the current feedback value of the winding.

[0127] The current control unit has its input terminal connected to the output terminal of the current comparison unit. It is used to perform PI control on the current difference output by the current comparison unit to obtain the winding modulation wave.

[0128] The transformation matrix unit, whose input is connected to the output of the current control unit, is used to calculate the bridge arm modulation wave applied to the midpoint of each bridge arm based on the winding modulation wave output by the current controller and Kirchhoff's voltage law.

[0129] The carrier comparison unit, whose input is connected to the output of the transformation matrix unit, is used to compare the carrier of the bridge arm modulation wave calculated by the transformation matrix to obtain the desired PWM signal at the midpoint of each bridge arm.

[0130] The switch drive unit is connected to each fully controllable switching device and is used to enable or block the switch;

[0131] And a drive signal generation unit, whose input terminal is connected to the output terminal of the carrier comparison unit, and whose output terminal is connected to each fully controllable switching device, is used to determine the drive signal of each fully controllable switching device in each bridge arm according to the PWM signal expected at the midpoint of each bridge arm; for any fully controllable switching device, if it is located in the upper bridge arm, its drive signal is consistent with the PWM signal expected at the midpoint of the bridge arm, and if it is located in the lower bridge arm, its drive signal is opposite to the PWM signal expected at the midpoint of the bridge arm.

[0132] Example 4:

[0133] A magnetic levitation bearing system includes a magnetic levitation bearing, a control circuit provided in Embodiment 1 above, and a controller provided in Embodiment 3 above.

[0134] 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 control method of a control circuit of a magnetic bearing with switch-off fault-tolerant capability, the magnetic bearing comprising 2N windings and having N degrees of freedom, each degree of freedom being controlled by two windings, N being a positive integer; the control circuit comprising: 2N windings, a DC power supply and 2N+1 bridge arms; Among the 2N+1 bridge arms, 2 are bipolar bridge arms and 2N-1 are unipolar bridge arms; Two ends of each winding are connected to the midpoints of two bridge arms; each unipolar bridge arm is connected to two windings, and each bipolar bridge arm is connected to one winding; Upper ends and lower ends of each bridge arm are connected to the positive and negative poles of the DC power supply, respectively; The control method comprises the following steps: (S1) Real-time detection of the current of each winding to determine the freedom degree of failure in real time, as the fault freedom degree, and after detecting the open circuit fault, determining the winding related to the open circuit fault of the fault freedom degree, as the target winding; (S2) Blocking the current of the target winding; if there is a bipolar bridge arm connected to the target winding, opening the full-controlled switch device in the lower bridge arm of the bipolar bridge arm; (S3) Reversing the current in the target winding and establishing the corresponding current constraint for the two bridge arms connected to the target winding; For the bipolar bridge arm, the current constraint is that the current of the connected winding is greater than 0; For the unipolar bridge arm, the current constraint is that the currents of the two connected windings are equal in size and the current directions are one flowing into the bridge arm and the other flowing out of the bridge arm; (S4) Under the current constraint, recalculating the current command value of each winding so that the electromagnetic force generated by the two windings controlling each freedom degree remains consistent before and after the open circuit fault; (S5) Determining the switching signal of each full-controlled switch device in the control circuit according to the current command value calculated in step (S4).

2. The control method according to claim 1, characterized by, In step (S1), the determination of the freedom degree of failure comprises: For each freedom degree, determining whether the sum of the currents of the two windings controlling the freedom degree is less than a preset bias threshold value, and if so, determining that the freedom degree is the freedom degree of failure.

3. The control method according to claim 2, characterized by, In step (S1), after detecting the open circuit fault, the winding related to the open circuit fault of the full-controlled switch device in the two windings controlling the fault freedom degree comprises: Obtaining the winding modulation waves of the two windings controlling the fault freedom degree and comparing them to determine the winding with a larger winding modulation wave as the winding related to the open circuit fault of the full-controlled switch device.

4. The control method according to any one of claims 1 to 3, characterized by, In step (S4), for any freedom degree, the current command values of the two windings controlling the freedom degree before and after the open circuit fault satisfy: wherein i aN and i cN is the current in the two windings before the circuit breaking fault, i a and i c is the current in the two windings after the circuit breaking fault, s 1 and s 2 are the distances of the rotor to the two magnetic poles in this degree of freedom, respectively.

5. The control method according to claim 4, characterized by, The step (S5) comprises: (S51) PI control is performed on the difference between the current command value and the current feedback value of each winding to obtain the winding modulation wave of each winding; (S52) According to the winding modulation wave calculated in (S51) and Kirchhoff's voltage law, the bridge arm modulation wave applied to the midpoint of each bridge arm is calculated; (S53) Carrier comparison is performed on the bridge arm modulation wave calculated in (S52) to obtain the expected PWM signal of the midpoint of each bridge arm; (S54) determining the driving signals of each of the full-controlled switching devices in each of the bridge arms according to the PWM signal expected by the midpoint of each of the bridge arms; for any one full-controlled switching device, if it is located in the upper bridge arm, its driving signal is consistent with the PWM signal expected by the midpoint of the bridge arm, if it is located in the lower bridge arm, its driving signal is opposite to the PWM signal expected by the midpoint of the bridge arm.

6. A controller of a control circuit of a magnetic bearing with switch-off fault-tolerant capability, the magnetic bearing comprising 2N windings and having N degrees of freedom, each degree of freedom being controlled by two windings, N being a positive integer; the control circuit comprising: The 2N windings, the DC power supply and the 2N+1 bridge arms; Among the 2N+1 bridge arms, 2 are bipolar bridge arms and 2N-1 are unipolar bridge arms; The two ends of each winding are connected to the midpoints of two bridge arms respectively; each unipolar bridge arm is connected to two windings simultaneously, and each bipolar bridge arm is connected to only one winding; The upper end and the lower end of each bridge arm are connected to the positive electrode and the negative electrode of the DC power supply respectively; The controller comprises: A current detection module connected to each winding for detecting the current of each winding in real time; A fault identification module connected to the current detection module for judging the freedom degree that has occurred a fault according to the current detected by the current detection module, taking the freedom degree as a fault freedom degree, and judging the winding related to the full-controlled switching device that has occurred a circuit breaking fault among the two windings that control the fault freedom degree as a target winding after detecting the circuit breaking fault; A variable bias current control module comprising a constraint construction unit and an electromagnetic force reconstruction unit; The constraint construction unit is connected to the fault identification module for reversing the current in the target winding and establishing corresponding current constraints for the two bridge arms connected to the target winding; for a bipolar bridge arm, the current constraint is that the current of the winding connected thereto is greater than 0; for a unipolar bridge arm, the current constraint is that the currents of the two windings connected thereto are equal in magnitude and opposite in direction; The electromagnetic force reconstruction unit is connected to the constraint construction unit for recalculating the current command values of the windings under the current constraints so that the electromagnetic forces generated by the two windings that control each freedom degree remain consistent before and after the circuit breaking fault; A current control module connected to the electromagnetic force reconstruction module for determining the switching signals of each full-controlled switching device in the control circuit according to the current command values calculated by the electromagnetic force reconstruction module; the current control module is also connected to each full-controlled switching device for enabling or blocking the full-controlled switching device.

7. The controller of claim 6, wherein, The fault identification module judges the freedom degree that has occurred a fault according to the current detected by the current detection module, comprising: For each freedom degree, judging whether the sum of the currents of the two windings that control the freedom degree is less than a preset bias threshold, if yes, judging that the freedom degree is the freedom degree that has occurred a fault; And the fault identification module judges the winding related to the full-controlled switching device that has occurred a circuit breaking fault among the two windings that control the fault freedom degree after detecting the circuit breaking fault, comprising: Obtaining the winding modulation waves of the two windings that control the fault freedom degree and comparing them, and determining the winding with the larger winding modulation wave as the winding related to the full-controlled switching device that has occurred a circuit breaking fault.

8. A controller as claimed in claim 6 or 7, wherein, The current control module comprises: a current comparison unit, a first input terminal of which is used for receiving the current command value, and a second input terminal of which is connected with the current detection module, and which is used for subtracting the current feedback value from the current command value of the winding; a current control unit, an input terminal of which is connected with an output terminal of the current comparison unit, and which is used for performing PI control on the current difference value outputted by the current comparison unit, to obtain a winding modulation wave; a transformation matrix unit, an input terminal of which is connected with an output terminal of the current control unit, and which is used for calculating a bridge arm modulation wave applied to a midpoint of each bridge arm according to the winding modulation wave outputted by the current control unit and the Kirchhoff voltage law; a carrier comparison unit, an input terminal of which is connected with an output terminal of the transformation matrix unit, and which is used for performing carrier comparison on the bridge arm modulation wave calculated by the transformation matrix unit, to obtain a PWM signal expected by the midpoint of each bridge arm; a switch driving unit, which is connected with each of the controllable switching devices, and which is used for enabling or blocking the controllable switching devices; and a driving signal generating unit, an input terminal of which is connected with an output terminal of the carrier comparison unit, and an output terminal of which is connected with each of the controllable switching devices, and which is used for determining the driving signal of each controllable switching device in each bridge arm according to the PWM signal expected by the midpoint of each bridge arm; for any one controllable switching device, if it is located in an upper bridge arm, its driving signal is consistent with the PWM signal expected by the midpoint of the bridge arm, and if it is located in a lower bridge arm, its driving signal is opposite to the PWM signal expected by the midpoint of the bridge arm.

9. A magnetic bearing system, characterized by, The magnetic bearing system comprises a magnetic bearing, a control circuit, and the controller according to any one of claims 6-8.

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