Flying capacitor voltage control method and device for multi-level magnetic bearing driver

Abstract

The invention relates to a multi-level magnetic bearing driver flying capacitor voltage control method and device, and belongs to the technical field of magnetic suspension bearing power electronic control, and the method comprises the steps: calculating the voltage of a flying capacitor based on the number of windings, the connection mode of each winding and a power supply, the winding current and the duty ratio instruction value of each winding bridge arm; predicting the total current of the flying capacitor bridge arm in the next switching period; the connection mode is that the first end of the winding is connected with the positive pole of the power supply or the negative pole of the power supply through the switching device in the winding bridge arm; and controlling the midpoint voltage of the flying capacitor bridge arm based on the total current and the sampling voltage of the flying capacitor. According to the invention, the response speed of midpoint voltage control of the flying capacitor bridge arm can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics control for magnetic levitation bearings, and particularly to a method and device for controlling the flying capacitor voltage of a multilevel magnetic bearing driver. Background Art

[0002] A magnetic levitation bearing is a bearing device that uses electromagnetic force to levitate a rotor, replacing traditional mechanical bearings and achieving non-contact operation between the rotor and the stator. Since there is no mechanical contact between the rotor and the stator, it has the characteristics of not requiring lubrication, no mechanical friction, no pollution, good stability, and long working life. For the magnetic levitation bearing control system, its design has a huge impact on the performance of the entire bearing device. For example, the power amplifier in the magnetic levitation bearing control system converts the control signal into the current in the windings of the magnetic levitation bearing to control the electromagnetic force of the magnetic bearing, which is an important part of the magnetic levitation bearing system.

[0003] CN117040268A discloses a three-level power electronics controller and control method for a magnetic levitation bearing. The control method is a hysteresis control method for the midpoint voltage of the flying capacitor bridge arm. By setting the hysteresis width of the flying capacitor voltage and switching the charging and discharging states of the flying capacitor based on the change trend of the flying capacitor voltage, the midpoint voltage of the flying capacitor bridge arm is balanced. However, the winding current of the magnetic levitation bearing changes in real time and is non-periodic, and the adjustment speed of the hysteresis is much slower than the change speed of the winding current, so misjudgment will occur, resulting in the failure of the midpoint voltage control. Summary of the Invention

[0004] In view of this, it is necessary to provide a method and device for controlling the flying capacitor voltage of a multilevel magnetic bearing driver to solve the problem of poor real-time performance of the existing technology in controlling the midpoint voltage of the flying capacitor bridge arm.

[0005] To solve the above problems, in the first aspect, the present invention provides a method for controlling the flying capacitor voltage of a multilevel magnetic bearing driver, the method comprising: Predicting the total current of the flying capacitor bridge arm in the next switching period based on the number of windings, the connection mode of each winding to the power supply, the winding current, and the duty cycle command value of each winding bridge arm; wherein, the connection mode is that the first end of the winding is connected to the positive pole of the power supply or the negative pole of the power supply through the switching device in the winding bridge arm; Controlling the midpoint voltage of the flying capacitor bridge arm based on the total current and the sampled voltage of the flying capacitor.

[0006] In a possible implementation, the winding current includes a winding sampled current; predicting the total current of the flying capacitor arm in the next switching period based on the number of windings, the connection manner of each winding to the power supply, the winding current, and the duty ratio command value of each winding arm includes: Determining the total current through the following formula:

[0007] Wherein, represents the total current, N is the number of windings, represents the winding sampled current of the j-th winding, represents the duty ratio command value of the j-th winding arm connected to the j-th winding. When the first end of the j-th winding is connected to the positive pole of the power supply through the switching device in the j-th winding arm, , when the first end of the j-th winding is connected to the negative pole of the power supply through the switching device in the j-th winding arm, .

[0008] In a possible implementation, controlling the midpoint voltage of the flying capacitor arm based on the total current and the sampled voltage of the flying capacitor includes: Determining the charge / discharge state of the flying capacitor based on the total current and the sampled voltage of the flying capacitor; Controlling the midpoint voltage of the flying capacitor arm according to the charge / discharge state.

[0009] In a possible implementation, determining the charge / discharge state of the flying capacitor based on the total current and the sampled voltage of the flying capacitor includes: When the total current is greater than 0 and the sampled voltage of the flying capacitor is greater than a preset balance voltage, determining that the flying capacitor is in a discharge state; When the total current is greater than 0 and the sampled voltage of the flying capacitor is less than the preset balance voltage, determining that the flying capacitor is in a charging state.

[0010] In a possible implementation, determining the charge / discharge state of the flying capacitor based on the total current and the sampled voltage of the flying capacitor includes: When the total current is less than 0 and the sampled voltage of the flying capacitor is greater than the preset balance voltage, determining that the flying capacitor is in a charging state; When the total current is less than 0 and the sampled voltage of the flying capacitor is less than the preset balance voltage, determining that the flying capacitor is in a discharge state.

[0011] In a possible implementation, the balance voltage is half of the bus voltage of the driver.

[0012] In a possible implementation, the flying capacitor leg includes a first switching device, a second switching device, a third switching device, and a fourth switching device; a first end of the first switching device is connected to the positive electrode of the power supply, and a second end of the first switching device is respectively connected to a first end of the flying capacitor and a first end of the second switching device; a second end of the second switching device is connected to a first end of the third switching device; a second end of the third switching device is respectively connected to a second end of the flying capacitor and a first end of the fourth switching device; and a second end of the fourth switching device is connected to the negative electrode of the power supply. Controlling the midpoint voltage of the flying capacitor leg according to the charge / discharge state includes: If it is in the charging state, control the first switching device and the third switching device to conduct, and control the second switching device and the fourth switching device to turn off; If it is in the discharging state, control the first switching device and the third switching device to turn off, and control the second switching device and the fourth switching device to conduct.

[0013] In a possible implementation, the multilevel magnetic bearing driver is a three-level magnetic bearing driver.

[0014] In a second aspect, the present invention further provides a multilevel magnetic bearing driver, including: A current prediction module, configured to predict the total current of the flying capacitor leg in the next switching period based on the number of windings, the connection manner of each winding to the power supply, the winding current, and the duty ratio command value of each winding leg; wherein, the connection manner is that a first end of the winding is connected to the positive electrode of the power supply or the negative electrode of the power supply through a switching device in the winding leg. A voltage control module, configured to control the midpoint voltage of the flying capacitor leg based on the total current and the sampled voltage of the flying capacitor.

[0015] In a third aspect, the present invention further provides a flying capacitor voltage control device for a multilevel magnetic bearing driver, including the above-mentioned multilevel magnetic bearing driver.

[0016] The beneficial effects of the present invention are: Based on the number of windings, the connection method of each winding to the power supply, the winding current, and the duty cycle command value of each winding arm, the present invention can predict the total current of the flying capacitor arm in the next switching cycle. Compared with real-time detection and then judgment, the prediction method can capture the influence of the winding current on the flying capacitor arm one step faster. Then, based on the predicted total current and the sampled voltage of the flying capacitor, the midpoint voltage of the flying capacitor arm is controlled, which can quickly make a midpoint voltage control response to the change trend of the winding current, improve the response speed of the midpoint voltage control, and avoid the occurrence of control failure situations. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 It is a topological structure diagram of a single-degree-of-freedom three-level magnetic bearing driver provided by the present invention; Figure 2 It is a schematic flowchart of an embodiment of the flying capacitor voltage control method for a multilevel magnetic bearing driver provided by the present invention; Figure 3 For the present invention Figure 2 It is a schematic flowchart of an embodiment of S202 in the present invention; Figure 4 For the present invention Figure 3 It is a schematic flowchart of an embodiment of S301 in the present invention; Figure 5 For the present invention Figure 3 It is a schematic flowchart of an embodiment of S302 in the present invention; Figure 6 It is a structure diagram of two modes of a flying capacitor arm provided by the present invention; Figure 7 It is a schematic structural diagram of an embodiment of a multilevel magnetic bearing driver provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0020] In the description of the embodiments of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more. In the embodiments of the present invention, "first", "second", etc. are used to distinguish similar objects, rather than to describe a specific order or sequence, nor to indicate or imply their relative importance or implicitly specify the quantity of the indicated technical features. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are usually of the same category, and the number of objects is not limited. For example, the first object can be one or more.

[0021] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present invention. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0022] The execution subject of the embodiments of the present invention can be a multilevel magnetic bearing driver, or a multilevel magnetic bearing controller. The driver can include N windings, N winding bridge arms, a flying capacitor bridge arm, and a flying capacitor; the first ends of the N windings are respectively connected to the midpoints of the N winding bridge arms, and the second ends of the N windings are connected to the midpoint of the flying capacitor bridge arm; both ends of the flying capacitor are connected to the flying capacitor bridge arm.

[0023] Refer to Figure 1 , which shows a topological structure diagram of a single-degree-of-freedom three-level magnetic bearing driver provided by the present invention. The single degree of freedom means N = 2, that is, the driver includes 2 windings and 2 winding bridge arms. The driver also includes a flying capacitor bridge arm and a flying capacitor. The flying capacitor bridge arm includes a first switching device S1, a second switching device S2, a third switching device S3, and a fourth switching device S4; the first end of the first switching device S1 is connected to the positive pole of the power supply, and the second end of the first switching device S1 is respectively connected to the first end of the flying capacitor and the first end of the second switching device S2; the second end of the second switching device S2 is connected to the first end of the third switching device S3; the second end of the third switching device S3 is respectively connected to the second end of the flying capacitor and the first end of the fourth switching device S4; the second end of the fourth switching device S4 is connected to the negative pole of the power supply.

[0024] The winding bridge arm can be a three-level bridge arm. The first winding bridge arm of the 2 winding bridge arms includes switching devices Sa1 and Sa2, and also includes 2 conducting devices. The second winding bridge arm includes switching devices Sc1 and Sc2, and also includes another 2 conducting devices.

[0025] The first end of the first winding in the two windings is connected to the midpoint of the first winding leg, and the second end is respectively connected to the midpoint O of the flying capacitor leg, and the midpoints of the switching devices Sa1 and Sa2. The first end of the second winding is connected to the midpoint of the second winding leg, and the second end is respectively connected to the midpoint O of the flying capacitor leg, and the midpoints of the switching devices Sc1 and Sc2.

[0026] Figure 1 In d 1 and d 2 respectively represent the duty ratio command values of the first winding leg and the second winding leg, I 1 and I 2 respectively represent the winding sampled currents of the first winding and the second winding, Vdc represents the power supply voltage, and Vcap represents the flying capacitor voltage.

[0027] Referring to Figure 2 , a flowchart of an embodiment of the flying capacitor voltage control method for a multilevel magnetic bearing driver provided by the present invention is shown. The method includes: S201, predicting the total current of the flying capacitor leg in the next switching period based on the number of windings, the connection manner of each winding to the power supply, the winding current, and the duty ratio command value of each winding leg; wherein, the connection manner is that the first end of the winding is connected to the positive pole of the power supply or the negative pole of the power supply through the switching device in the winding leg.

[0028] The duty ratio command value of the winding leg can be obtained by the modulation method based on carrier stacking comparison. The duty ratio command value refers to the target value of the duty ratio calculated by the driver according to the target requirements (such as voltage, current, or speed). Based on the number of windings in the previous switching period, the connection manner of each winding to the power supply, the winding current of each winding, and the duty ratio command value of the switching device in each winding leg connected to the winding, the total current flowing into or out of the flying capacitor leg in the next switching period can be predicted. The switching period can refer to the control period of the switching device in the flying capacitor leg.

[0029] In some embodiments of the present invention, the winding current can include the winding sampled current; the total current can be calculated by the following formula:

[0030] Wherein, represents the total current, N is the number of windings, represents the winding sampled current of the jth winding, denotes the duty ratio command value of the j-th winding bridge arm connected to the j-th winding. When the first end of the j-th winding is connected to the positive pole of the power supply through the switching device in the j-th winding bridge arm, when the first end of the j-th winding is connected to the negative pole of the power supply through the switching device in the j-th winding bridge arm, .

[0031] According to the positive and negative values of the total current, the direction of the total current can be judged, that is, it can be judged whether the winding current flows into or out of the flying capacitor bridge arm in the next switching period.

[0032] S202, control the midpoint voltage of the flying capacitor bridge arm based on the total current and the sampled voltage of the flying capacitor.

[0033] The driver may also include a voltage sensor. The voltage of the flying capacitor can be collected through the voltage sensor, and then based on the predicted total current of the winding current flowing into or out of the flying capacitor bridge arm in the next switching period and the sampled voltage currently sampled from the flying capacitor, the midpoint voltage of the flying capacitor bridge arm can be regulated to achieve the balance of the midpoint voltage of the flying capacitor bridge arm.

[0034] In summary, based on the number of windings, the connection method of each winding to the power supply, the winding current of each winding, and the duty ratio command value of each winding bridge arm, the present invention can predict the total current of the flying capacitor bridge arm in the next switching period. Compared with real-time detection and then judgment, the prediction method can capture the influence of the winding current on the flying capacitor bridge arm one step faster. Then, based on the predicted total current and the sampled voltage of the flying capacitor, the midpoint voltage of the flying capacitor bridge arm is controlled, which can quickly make a midpoint voltage control response to the change trend of the winding current, improve the response speed of the midpoint voltage control, and avoid the occurrence of control failure.

[0035] In some embodiments of the present invention, as Figure 3 shown, step S202 includes: S301, determine the charge / discharge state of the flying capacitor based on the total current and the sampled voltage of the flying capacitor; S302, control the midpoint voltage of the flying capacitor bridge arm according to the charge / discharge state.

[0036] Based on the current sampled voltage of the flying capacitor and the positive and negative conditions of the predicted total current of the flying capacitor bridge arm in the next switching period, it can be determined whether the flying capacitor needs to be charged or discharged in the next switching period. Further, according to the determined charge / discharge process, the flying capacitor is charged or discharged accordingly, so as to control the midpoint voltage of the flying capacitor bridge arm.

[0037] In summary, by calculating the total current and judging the charge / discharge state once in each period, the self-balancing of the midpoint voltage of the flying capacitor leg can be achieved.

[0038] In some embodiments of the present invention, as Figure 4 shown, step S301 includes: S401, when the total current is greater than 0 and the sampled voltage of the flying capacitor is greater than the preset balance voltage, it is determined that the flying capacitor is in a discharging state; the balance voltage can be half of the driver bus voltage; S402, when the total current is greater than 0 and the sampled voltage of the flying capacitor is less than the preset balance voltage, it is determined that the flying capacitor is in a charging state; S403, when the total current is less than 0 and the sampled voltage of the flying capacitor is greater than the preset balance voltage, it is determined that the flying capacitor is in a charging state; S404, when the total current is less than 0 and the sampled voltage of the flying capacitor is less than the preset balance voltage, it is determined that the flying capacitor is in a discharging state.

[0039] In some embodiments of the present invention, when the topology of the driver is Figure 1 the topology shown, as Figure 5 shown, step S302 includes: S501, if it is in a charging state, control the first switch device and the third switch device to conduct, and control the second switch device and the fourth switch device to turn off; S502, if it is in a discharging state, control the first switch device and the third switch device to turn off, and control the second switch device and the fourth switch device to conduct.

[0040] When it is determined that the flying capacitor needs to be charged in the next switching period, S1 and S3 can be controlled to conduct, and S2 and S4 can be controlled to turn off; when it is determined that the flying capacitor needs to be discharged in the next switching period, S1 and S3 can be controlled to turn off, and S2 and S4 can be controlled to conduct.

[0041] The embodiments of the present invention utilize information such as winding current to predict the change of the winding current in the flying capacitor leg, so as to accurately select the charge / discharge state of the flying capacitor, realize the balance of the midpoint voltage of the flying capacitor leg, and have the characteristics of high control accuracy, good stability and real-time performance.

[0042] Referring to Figure 6 , two modal structure diagrams of a flying capacitor leg provided by the present invention are shown. The first mode is: S1 and S3 conduct, and S2 and S4 turn off. In the first mode, the midpoint voltage of the flying capacitor leg is Vdc - Vcap. The second mode is: S1 and S3 turn off, and S2 and S4 conduct. In the second mode, the midpoint voltage of the flying capacitor leg is Vcap.

[0043] Reference Figure 7 shows a schematic structural diagram of an embodiment of the multilevel magnetic bearing driver provided by the present invention. The driver 70 includes: A current prediction module 701, configured to predict the total current in the flying capacitor bridge arm in the next switching period based on the number of windings, the connection mode of each winding to the power supply, the winding current, and the duty ratio command value of each winding bridge arm; wherein, the connection mode is that the first end of the winding is connected to the positive pole of the power supply or the negative pole of the power supply through the switching device in the winding bridge arm; A voltage control module 702, configured to control the midpoint voltage of the flying capacitor bridge arm based on the total current and the sampled voltage of the flying capacitor.

[0044] It should be noted that: the implementation principle or implementation process of the above modules can refer to the embodiments of the flying capacitor voltage control method of the foregoing multilevel magnetic bearing driver, and will not be elaborated here one by one.

[0045] The present invention also provides a flying capacitor voltage control device for a multilevel magnetic bearing driver, and the device includes the above-mentioned multilevel magnetic bearing driver.

[0046] Those skilled in the art can understand that all or part of the processes for implementing the methods of the above embodiments can be completed by instructing relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. Among them, the computer-readable storage medium is a magnetic disk, an optical disk, a read-only memory, or a random access memory, etc.

[0047] The above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A flying capacitor voltage control method for a multi-level magnetic bearing driver, characterized in that: include: Based on the number of windings, the connection mode of each winding and the power supply, the winding current and the duty cycle command value of each winding bridge arm, the total current of the flying capacitor bridge arm in the next switching cycle is predicted; wherein the connection mode is that the first end of the winding is connected to the positive electrode of the power supply through the switching device in the winding bridge arm, or is connected to the negative electrode of the power supply; The midpoint voltage of the flying capacitor bridge arm is controlled based on the total current and the sampled voltage of the flying capacitor.

2. The flying capacitor voltage control method of a multi-level magnetic bearing driver according to claim 1, characterized in that: The winding current includes a winding sampling current; the total current of the flying capacitor bridge arm in the next switching cycle is predicted based on the number of windings, the connection mode of each winding and the power supply, the winding current and the duty cycle command value of each winding bridge arm, including: The total current is determined by the following formula: in, Represents the total current, N is the number of windings, represents the winding sampling current of the jth winding, represents the duty cycle command value of the jth winding bridge arm connected to the jth winding. When the first end of the jth winding is connected to the positive electrode of the power supply through the switching device in the jth winding bridge arm, , when the first end of the jth winding is connected to the negative pole of the power supply through the switching device in the jth winding bridge arm, .

3. The flying capacitor voltage control method of a multi-level magnetic bearing driver according to claim 2, characterized in that: The controlling the midpoint voltage of the flying capacitor bridge arm based on the total current and the sampled voltage of the flying capacitor comprises: Determining a charge / discharge state of the flying capacitor based on the total current and a sampled voltage of the flying capacitor; According to the charge / discharge state, the midpoint voltage of the flying capacitor bridge arm is controlled.

4. The flying capacitor voltage control method of a multi-level magnetic bearing driver according to claim 3, characterized in that: The determining the charge / discharge state of the flying capacitor based on the total current and the sampled voltage of the flying capacitor comprises: When the total current is greater than 0 and the sampling voltage of the flying capacitor is greater than a preset equilibrium voltage, determining that the flying capacitor is in a discharge state; When the total current is greater than 0 and the sampling voltage of the flying capacitor is less than a preset equilibrium voltage, it is determined that the flying capacitor is in a charging state.

5. The flying capacitor voltage control method of a multi-level magnetic bearing driver according to claim 3, characterized in that: The determining the charge / discharge state of the flying capacitor based on the total current and the sampled voltage of the flying capacitor comprises: When the total current is less than 0 and the sampling voltage of the flying capacitor is greater than a preset equilibrium voltage, determining that the flying capacitor is in a charging state; When the total current is less than 0 and the sampling voltage of the flying capacitor is less than a preset equilibrium voltage, it is determined that the flying capacitor is in a discharge state.

6. The flying capacitor voltage control method for a multi-level magnetic bearing driver according to any one of claims 4 or 5, characterized in that: The balance voltage is half of the bus voltage of the driver.

7. The flying capacitor voltage control method of a multi-level magnetic bearing driver according to claim 3, characterized in that: The flying capacitor bridge arm includes a first switch device, a second switch device, a third switch device and a fourth switch device; the first end of the first switch device is connected to the positive electrode of the power supply, and the second end of the first switch device is respectively connected to the first end of the flying capacitor and the first end of the second switch device; the second end of the second switch device is connected to the first end of the third switch device; the second end of the third switch device is respectively connected to the second end of the flying capacitor and the first end of the fourth switch device; the second end of the fourth switch device is connected to the negative electrode of the power supply; The step of controlling the midpoint voltage of the flying capacitor bridge arm according to the charge / discharge state comprises: If it is in the charging state, controlling the first switch device and the third switch device to be turned on, and controlling the second switch device and the fourth switch device to be turned off; When in the discharging state, the first switching device and the third switching device are controlled to be turned off, and the second switching device and the fourth switching device are controlled to be turned on.

8. The flying capacitor voltage control method of a multi-level magnetic bearing driver according to claim 1, characterized in that: The multi-level magnetic bearing driver is a three-level magnetic bearing driver.

9. A multi-level magnetic bearing drive, characterized in that: include: A current prediction module, used to predict the total current of the flying capacitor bridge arm in the next switching cycle based on the number of windings, the connection mode of each winding and the power supply, the winding current and the duty cycle command value of each winding bridge arm; wherein the connection mode is that the first end of the winding is connected to the positive electrode of the power supply through the switching device in the winding bridge arm, or is connected to the negative electrode of the power supply; A voltage control module is used to control the midpoint voltage of the flying capacitor bridge arm based on the total current and the sampled voltage of the flying capacitor.

10. A flying capacitor voltage control device for a multi-level magnetic bearing driver, characterized in that: Comprising the multi-level magnetic bearing drive as claimed in claim 9.

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