Zero common-mode voltage modulation method and device for magnetic suspension bearing

Abstract

The invention discloses a zero common-mode voltage modulation method and device for a magnetic suspension bearing, and belongs to the field of power electronic control. The modulation method comprises the following steps: acquiring reference voltages of midpoints of four bridge arms on a magnetic suspension bearing controller, and calculating normalized differential mode voltages and common mode voltages; judging the sector number N according to the differential mode voltage, and selecting a corresponding voltage vector from zero common mode voltage vectors according to the sector number; calculating the normalization action time of each voltage vector according to the sector number N, the differential mode voltage and the common mode voltage; according to the midpoint potential and the differential mode voltage, selecting a proper vector for splitting, and calculating the normalized action time and the corresponding duty ratio of each updated voltage vector; distributing the eight duty ratios to the four bridge arms according to the sector number N to generate corresponding modulation signals; pWM signals are generated and used for controlling switching devices of four bridge arms on the magnetic suspension bearing controller. Accurate control over the axis track of the magnetic suspension bearing rotor is achieved.

Description

Technical Field

[0001] This invention belongs to the field of power electronic control, and more specifically, relates to a method and apparatus for zero common-mode voltage modulation of magnetic levitation bearings. Background Technology

[0002] Magnetic levitation bearings are bearing devices that use electromagnetic force to levitate a rotor, thus replacing traditional mechanical bearings and achieving contactless operation between the rotor and stator. Because there is no mechanical contact between the rotor and stator, they offer advantages such as no need for lubrication, no mechanical friction, no pollution, high stability, and long service life. A magnetic levitation bearing system mainly consists of a rotor, sensors, a controller, and electromagnetic actuators; the design of its control system has a significant impact on the overall performance of the device.

[0003] The magnetic bearing controller primarily controls the winding current of the magnetic bearing through the switching action of the power electronic converter, thereby controlling the rotor position. The high-frequency switching action of the power electronic devices generates high-frequency common-mode voltage, which in turn produces high-frequency common-mode leakage current through the common-mode loop formed by the stray parameters of the magnetic bearing. In particular, in high-power magnetic bearing control systems, the electromagnetic interference of the magnetic bearing controller becomes increasingly severe as the voltage level increases.

[0004] In existing technologies, common-mode interference makes it difficult for magnetic levitation bearing controllers to meet electromagnetic compatibility standards; the resulting common-mode leakage current corrodes the protective bearing, threatening its safe operation; and high-frequency common-mode voltage also causes electromagnetic radiation in space, interfering with the position sensor signal and threatening the bearing's levitation control. Therefore, existing technologies present technical problems that hinder the precise and efficient control of magnetic levitation bearings. Summary of the Invention

[0005] In view of the deficiencies of related technologies, the purpose of this invention is to provide a zero common-mode voltage modulation method and device for magnetic levitation bearings, aiming to solve the technical problem that magnetic levitation bearings are difficult to control accurately and efficiently in the prior art.

[0006] To achieve the above objectives, the present invention provides a zero common-mode voltage modulation method for magnetic levitation bearings, comprising: S1. Obtain the reference voltages at the midpoints of the four bridge arms on the magnetic levitation bearing controller, and calculate the normalized differential-mode voltage and common-mode voltage based on the reference voltages; the differential-mode voltage includes... x Voltage difference between two windings with different degrees of freedom and in y Voltage difference between two windings with different degrees of freedom The common-mode voltage includes x The sum of the voltages of the two windings in the degree of freedom, or y The sum of the voltages of the two windings in the degree of freedom ; S2. Determine the sector number N based on the differential-mode voltage, and select the corresponding voltage vector from the zero common-mode voltage vectors based on the sector number; the zero common-mode voltage vectors used include two preset common-mode vectors, four large vectors, and eight small vectors; the voltage vectors include K preset large vectors and Q small vectors, where K is 0 or 2, and Q is 4; wherein, the large vector is the vector with the largest magnitude among the zero common-mode voltage vectors used, and the small vector is the vector with the smallest magnitude among the zero common-mode voltage vectors used. S3. Calculate the normalized duration of each voltage vector based on the sector number N, the differential-mode voltage, and the common-mode voltage; split the small vectors in the voltage vectors into common-mode vectors and large vectors based on the magnitude of the midpoint potential and the magnitude of the differential-mode voltage, and calculate the normalized duration and corresponding duty cycle of each updated voltage vector. S4. Assign the eight duty cycles to the four bridge arms according to the sector number N to generate corresponding modulation signals; S5: Compare the set carrier signal and the modulation signal to generate a PWM signal, which is used to control the switching devices of the four bridge arms on the magnetic levitation bearing controller.

[0007] Optionally, the common-mode vector is represented as V17 and V18, which correspond to the switching states of the first to fourth bridge arms as PPNN and NNPP, respectively. The four large vectors are represented as V5, V6, V7 and V8, respectively, which correspond to the switching states of the first to fourth bridge arms as PNNP, PNPN, NPPN and NPNP; The eight small vectors are represented as V9, V10, V11, V12, V13, V14, V15 and V16, respectively, which correspond to the switching states of the first to fourth bridge arms as PONO, POON, OPON, OPNO, ONOP, ONPO, NOPO and NOOP; Wherein, P indicates that the midpoint of the bridge arm is connected to the positive DC bus, O indicates that the midpoint of the bridge arm is connected to the midpoint potential, and N indicates that the midpoint of the bridge arm is connected to the negative DC bus.

[0008] Optional, with x Degrees of freedom and y A coordinate system is constructed using the two differential-mode voltages and common-mode voltages of the two degrees of freedom as coordinate axes. All zero common-mode vectors used are mapped to the coordinate system, resulting in 8 sectors in the xy two-dimensional plane.

[0009] Optionally, in step S1: x The voltage difference between the two windings of the degree of freedom Represented as: ; y The voltage difference between the two windings of the degree of freedom Represented as: ; x The sum of the voltages of the two windings with the degree of freedom / y The sum of the voltages of the two windings with the degree of freedom Represented as: ; in, , for x The reference voltage of the bridge arm connected to the two windings in the direction. , for y The reference voltage of the bridge arm connected to the two windings in the direction. This is the DC bus voltage.

[0010] Optionally, in step S2, determining the sector number N based on the differential mode voltage includes: like ;but ; like 1; then ; like ;but ; like ;but ; like ;but ; like ;but ; like ;but ; like ;but ; The step of selecting the corresponding voltage vector from the zero common-mode voltage vector according to the sector number includes: when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is .

[0011] Optionally, in step S3, the normalized action time of each voltage vector is calculated based on the sector number N, the differential-mode voltage, and the common-mode voltage, including: Calculate the duration of action of the first major vector separately. Second largest vector action time Time of action of the first small vector The second smallest vector's duration of action The third smallest vector's duration of action and the time of action of the fourth smallest vector ;in, to The selected voltage vectors are selected sequentially; First major vector action time The calculation formula is:

[0012] The second largest vector action time The calculation formula is:

[0013] The first small vector's duration of action Second smallest vector action time The calculation formula is:

[0014] The time of action of the third small vector and the time of action of the fourth smallest vector The calculation formula is: .

[0015] Optionally, in step S3, the smaller vectors in the voltage vector are split into common-mode vectors and larger vectors according to the magnitude of the midpoint potential, and the normalized action time of each updated voltage vector is calculated, including: Based on the magnitudes of the differential-mode voltage, midpoint potential, and winding current, the duration of the smaller voltage vector is split into the duration of a common-mode vector and the duration of a larger voltage vector, and the normalized duration of the voltage vector is updated as follows: (1) When and Or 5 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (2) When and Or 5 o'clock: like and , ; like and , ; like and , ; like and , ; (3) When and Or 6 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (4) When and Or 6 o'clock: like and , ; like and , ; like and , ; like and , ; (5) When and Or 7 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (6) When and Or 7 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (7) When and Or 8 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (8) When and Or 8 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; in, It is the midpoint potential. The duration of the positive common-mode vector action. The duration of the reverse common-mode vector action; For the time of the first major vector action after the update, This is the updated second largest vector action time; 8 duty cycles The calculation formulas are as follows: ; ; ; ; ; ; ; .

[0016] Optionally, in step S4, the sector number N and eight duty cycles are assigned to the four bridge arms to generate corresponding modulation signals, including: when ; when ; when ; when ; Among them, letters D Indicates the bridge arm modulation signal. middle 'b' represents the switching device number, and 'b' represents the signal strength of the modulation signal. The value is a positive integer from 1 to 8, where b is 1 or 2, and .

[0017] Optionally, step S5 includes: For each bridge arm, when the triangular carrier signal is greater than the first modulation signal... And smaller than the second modulation signal When the signal is high, the generated PWM signal is high; otherwise, the generated PWM signal is low. The generated 8 PWM signals are distributed accordingly to x The upper tube drive of the bridge arm connected by the two windings in the direction and y The lower tube drive of the bridge arm connected by the two windings in the direction.

[0018] In a second aspect, the present invention also provides a zero common-mode voltage modulation device for a magnetic levitation bearing, used to perform the zero common-mode voltage modulation method for a magnetic levitation bearing as described in any one of the first aspects, comprising: The voltage command calculation module is used to obtain the reference voltage at the midpoint of the four bridge arms on the magnetic levitation bearing controller, and calculate the normalized differential-mode voltage and common-mode voltage based on the reference voltage; the differential-mode voltage includes... x Voltage difference between two windings with different degrees of freedom and in y Voltage difference between two windings with different degrees of freedom The common-mode voltage includes x The sum of the voltages of the two windings in the degree of freedom, or y The sum of the voltages of the two windings in the degree of freedom ; The sector determination module is used to determine the sector number N based on the differential-mode voltage, and select the corresponding voltage vector from the zero common-mode voltage vectors according to the sector number. The zero common-mode voltage vectors used include two preset common-mode vectors, four large vectors, and eight small vectors. The voltage vectors include K preset large vectors and Q small vectors, where K is 0 or 2, and Q is 4. The large vectors are the vectors with the largest magnitude among the zero common-mode voltage vectors used, and the small vectors are the vectors with the smallest magnitude among the zero common-mode voltage vectors used. The action time calculation module is used to calculate the normalized action time of each voltage vector based on the sector number N, the differential mode voltage, and the common mode voltage; and to split the small vectors in the voltage vectors into common mode vectors and large vectors based on the magnitude of the midpoint potential and the magnitude of the differential mode voltage, and to calculate the normalized action time and corresponding duty cycle of each updated voltage vector. The duty cycle allocation module is used to allocate the four duty cycles to the four bridge arms according to the sector number N to generate corresponding modulation signals; The carrier comparison stage is used to compare the set carrier signal with the modulation signal to generate a PWM signal, which is used to control the switching devices of the four bridge arms on the magnetic levitation bearing controller.

[0019] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: 1. This invention provides a zero common-mode voltage modulation method for magnetic levitation bearings. It involves acquiring the reference voltage at the midpoint of the four bridge arms of the magnetic levitation bearing controller, calculating the normalized differential-mode voltage and common-mode voltage, determining the sector, and selecting the corresponding voltage vector. The voltage vector is then split based on the midpoint voltage. The normalized action time of each voltage vector is calculated based on the sector number, differential-mode voltage command, common-mode voltage command, and vector splitting method. Four duty cycles are calculated based on the normalized action time of each voltage vector and allocated to the four bridge arms to generate corresponding modulation signals. Finally, a PWM signal is generated to drive the magnetic bearing drive converter. This method achieves maximum DC voltage utilization in both differential-mode and common-mode voltage aspects without reducing the system's dynamic response speed, theoretically achieving zero common-mode interference voltage. It can significantly suppress common-mode electromagnetic interference from the magnetic levitation bearing controller at higher bus voltage levels without affecting the normal control of the magnetic levitation bearing, avoiding damage to the protected bearing and its impact on the displacement sensor. This solves the technical problem of difficult and inefficient control of magnetic levitation bearings in existing technologies, enabling precise control of the rotor shaft trajectory of the magnetic levitation bearing.

[0020] 2. This invention provides a zero common-mode voltage modulation method for magnetic levitation bearings. Theoretically, it achieves zero common-mode interference voltage without affecting normal current control and midpoint potential, significantly reducing common-mode interference in the system, avoiding the harmful effects of common-mode current on the bearing, reducing interference with displacement sensors, and increasing position control accuracy. Furthermore, it can be easily extended to axial magnetic levitation bearings with more degrees of freedom, suppressing common-mode interference from the entire control system while achieving multi-degree-of-freedom control. Attached Figure Description

[0021] Figure 1 This is a block diagram of the zero common-mode voltage modulation method provided by the present invention; Figure 2 A midpoint clamping three-level magnetic levitation bearing control device with common-mode interference suppression capability is provided as an example of the present invention. Figure 3 A vector diagram of the zero common-mode voltage modulation method proposed in this invention; Figure 4 This invention provides a common-mode vector sector determination diagram; Figure 5 Small vector decomposition diagram provided for this invention; Figure 6 This is a diagram showing the midpoint voltages of the four bridge arms output by the zero common-mode voltage modulation method proposed in this invention within one switching cycle. Figure 7 This is a comparison diagram of the common-mode leakage current of the device and method proposed in this invention with that of conventional carrier comparison PWM. Figure 8This is a comparison diagram of common-mode electromagnetic interference (EMI) between the device and method proposed in this invention and conventional carrier-based PWM. Detailed Implementation

[0022] 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.

[0023] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0024] Example 1 like Figure 1 As shown, the present invention provides a zero common-mode voltage modulation method for magnetic levitation bearings, comprising: S1. Obtain the reference voltages at the midpoints of the four bridge arms on the magnetic levitation bearing controller, and calculate the normalized differential-mode voltage and common-mode voltage based on the reference voltages; the differential-mode voltage includes... x Voltage difference between two windings with different degrees of freedom and in y Voltage difference between two windings with different degrees of freedom The common-mode voltage includes x The sum of the voltages of the two windings in the degree of freedom, or y The sum of the voltages of the two windings in the degree of freedom ; S2. Determine the sector number N based on the differential-mode voltage, and select the corresponding voltage vector from the zero common-mode voltage vectors based on the sector number; the zero common-mode voltage vectors used include two preset common-mode vectors, four large vectors, and eight small vectors; the voltage vectors include K preset large vectors and Q small vectors, where K is 0 or 2, and Q is 4; wherein, the large vector is the vector with the largest magnitude among the zero common-mode voltage vectors used, and the small vector is the vector with the smallest magnitude among the zero common-mode voltage vectors used. S3. Calculate the normalized duration of each voltage vector based on the sector number N, the differential-mode voltage, and the common-mode voltage; split the small vectors in the voltage vectors into common-mode vectors and large vectors based on the magnitude of the midpoint potential and the magnitude of the differential-mode voltage, and calculate the normalized duration and corresponding duty cycle of each updated voltage vector. S4. Assign the eight duty cycles to the four bridge arms according to the sector number N to generate corresponding modulation signals; S5: Compare the set carrier signal and the modulation signal to generate a PWM signal, which is used to control the switching devices of the four bridge arms on the magnetic levitation bearing controller.

[0025] The zero common-mode voltage modulation method for magnetic levitation bearings provided by this invention is implemented based on a magnetic levitation bearing controller. For example... Figure 2 As shown, a magnetic levitation bearing controller includes: a DC power supply 1, a bearing drive converter 2, a current control unit 3, a position control unit 4, a zero common-mode modulation unit 5, and a midpoint potential balancing unit 6. DC power supply 1 is used to power the entire magnetic levitation bearing control system. The magnetic bearing drive converter 2 is composed of power electronic devices and is used to amplify the power according to the gate drive signal to drive the two-degree-of-freedom magnetic levitation bearing. The current control unit 3 is used to receive current command values, acquire actual current values, execute current control algorithms, generate command voltages for the four bridge arms, and transmit them to the midpoint potential balancing unit.

[0026] The displacement control unit 4 is used to acquire the displacement deviation signal of the magnetic levitation bearing, execute the position control algorithm, and generate the current command value of the bearing winding, which is then transmitted to the current control unit. The zero common-mode voltage modulation unit 5 is used to receive the command voltage of the four bridge arms, execute the zero common-mode voltage modulation algorithm, and generate a gate drive signal to be transmitted to the magnetic bearing drive converter. The midpoint potential balancing unit 6 is used to split the voltage vector and adjust the midpoint potential balance according to the midpoint potential and the winding current during the modulation process.

[0027] Furthermore, the magnetic bearing drive converter uses a three-level topology with a four-bridge midpoint clamp to control the magnetic bearing within a single plane. x Two degrees of freedom and y The current in the four windings has two degrees of freedom; one end of the four windings is connected together and the other end is connected to the midpoint of the four bridge arms respectively.

[0028] x The difference in voltage between the two windings in the degree of freedom Represented as: ; y The difference in voltage between the two windings in the degree of freedom Represented as: ; x The sum of the voltages of the two windings in the degree of freedom or y The sum of the voltages of the two windings in the degree of freedom Represented as: ; in, , for x The reference voltage of the bridge arm connected to the two windings in the direction. , for y The reference voltage of the bridge arm connected to the two windings in the direction. The voltage at the star connection of the four windings, This is the DC bus voltage.

[0029] Figure 3 This is a vector diagram of the zero common-mode voltage modulation method proposed in this invention. According to... x Differential mode voltage V on the two windings in the direction DMx , y Differential mode voltage V on the two windings in the direction DMy , x The common-mode voltage V on the two windings in the direction CM Using three orthogonal coordinate axes, a vector diagram of all switch states can be drawn.

[0030] There are 18 zero common-mode voltage vectors in the magnetic levitation bearing controller, denoted as V1 to V18. V1-V4 do not participate in the zero common-mode voltage modulation method. In practice, the zero common-mode voltage modulation method used in magnetic levitation bearings includes two common-mode vectors V17 and V18, four large vectors V5, V6, V7, and V8, and eight small vectors V9, V10, V11, V12, V13, V14, V15, and V16. The corresponding switching states are shown in Table 1 below.

[0031] Table 1

[0032] Wherein, P indicates that the midpoint of the bridge arm is connected to the positive DC bus, O indicates that the midpoint of the bridge arm is connected to the midpoint potential, and N indicates that the midpoint of the bridge arm is connected to the negative DC bus.

[0033] Furthermore, x The switching transistors S1, S2, S3, and S4 corresponding to the bridge arms connected by the two windings in the direction; for example, for S1 and S2, P means that both S1 and S2 are on, O means that S1 is off and S2 is on, N means that both S1 and S2 are off, and S3 and S4 are the same as S1 and S2. y The switching transistors S5, S6, S7, and S8 corresponding to the bridge arms connected by the two windings in the direction; for example, for S5 and S6, P means that both S5 and S6 are off, O means that S6 is off and S5 is on, N means that both S5 and S6 are on, and S7 and S8 are the same as S5 and S6.

[0034] Furthermore, V1 and V3 respectively represent... x Voltage difference between two windings with different degrees of freedom These are the positive and negative vectors of the coordinate axes; V4 and V2 are respectively... y Voltage difference between two windings with different degrees of freedom These are the positive and negative vectors of the coordinate axes.

[0035] Furthermore, with x Degrees of freedom and y A coordinate system is constructed using the two differential-mode voltages and common-mode voltages of the two degrees of freedom as coordinate axes. All zero common-mode vectors used are mapped to the coordinate system, resulting in 8 sectors in the xy two-dimensional plane.

[0036] Figure 4 This invention provides a common-mode vector sector determination diagram. V DMx -V DMy The plane is divided into eight sectors.

[0037] Optionally, in step S2, determining the sector number N based on the differential mode voltage includes: like ;but ; like 1; then ; like ;but ; like ;but ; like ;but ; like ;but ; like ;but ; like ;but ; The step of selecting the corresponding voltage vector from the zero common-mode voltage vector according to the sector number includes: when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is ; when When, the selected voltage vector is .

[0038] Figure 5 The small vector decomposition diagram provided by this invention achieves midpoint potential adjustment by splitting the corresponding small vector into adjacent common-mode voltage vectors and large vectors. Specifically, it includes the following steps: The vector action time calculation step is used to calculate the normalized action time of each voltage vector based on the sector number N, the differential mode voltage, and the common mode voltage. Specifically, calculate the duration of the first major vector action. Second largest vector action time Time of action of the first small vector The second smallest vector's duration of action The third smallest vector's duration of action and the time of action of the fourth smallest vector ;in, to The selected voltage vectors are sequentially matched; for example, when When, the selected voltage vector is , Corresponding to the control time of V6, Corresponding to the control time of V5, Corresponding to the control time of V10, Corresponding to the control time of V14, Corresponding to the control time of V9, The corresponding control time for V13.

[0039] First major vector action time The calculation formula is:

[0040] The second largest vector action time The calculation formula is:

[0041] The first small vector's duration of action Second smallest vector action time The calculation formula is:

[0042] The time of action of the third small vector and the time of action of the fourth smallest vector The calculation formula is: .

[0043] The duty cycle allocation step is used to split the small vector in the voltage vector into a common-mode vector and a large vector according to the magnitude of the midpoint potential and the magnitude of the differential-mode voltage, and to calculate the normalized action time and corresponding duty cycle of each updated voltage vector. Specifically, based on the magnitudes of the differential-mode voltage, midpoint potential, and winding current, the duration of the smaller voltage vector is split into the duration of a common-mode vector and the duration of a larger voltage vector, and the normalized duration of the voltage vector is updated as follows: (1) When and Or 5 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (2) When and Or 5 o'clock: like and , ; like and , ; like and , ; like and , ; (3) When and Or 6 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (4) When and Or 6 o'clock: like and , ; like and , ; like and , ; like and , ; (5) When and Or 7 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (6) When and Or 7 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (7) When and Or 8 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; (8) When and Or 8 o'clock: like and ,but ; like and ,but ; like and ,but ; like and ,but ; in, It is the midpoint potential. The duration of the positive common-mode vector action. The duration of the reverse common-mode vector action; For the time of the first major vector action after the update, This is the updated second largest vector action time; 8 duty cycles The calculation formulas are as follows: ; ; ; ; ; ; ; .

[0044] Then, according to the sector number N, the eight duty cycles are allocated to the four bridge arms to generate corresponding modulation signals; Specifically, in step S4, the sector number N and eight duty cycles are allocated to the four bridge arms to generate corresponding modulation signals, including: when ; when ; when ; when ; Among them, letters D Indicates the bridge arm modulation signal. middle 'b' represents the switching device number, and 'b' represents the signal strength of the modulation signal. The value is a positive integer from 1 to 8, where b is 1 or 2, and .

[0045] The carrier comparison stage is used to compare the set carrier signal with the modulation signal to generate a PWM signal, which is used to control the switching devices of the four bridge arms on the magnetic levitation bearing controller.

[0046] In the carrier comparison stage, the carrier is a triangular carrier; specifically, for each bridge arm, when the triangular carrier signal is greater than the first modulation signal... And smaller than the second modulation signal When the signal is high, the generated PWM signal is high; otherwise, the generated PWM signal is low. The generated 8 PWM signals are distributed accordingly to x The upper tube drive of the bridge arm connected by the two windings in the direction and y The lower tube drive of the bridge arm connected by the two windings in the direction.

[0047] Figure 6 This is a diagram showing the midpoint voltages of the four bridge arms output by the zero common-mode voltage modulation method proposed in this invention within one switching cycle. By selecting the zero common-mode voltage vector to synthesize the reference voltage, high-frequency common-mode voltage elimination is achieved.

[0048] Figure 7 This is a comparison diagram of the common-mode leakage current of the device and method proposed in this invention with that of conventional carrier comparison PWM. By adopting the zero common-mode modulation method proposed in this invention, the common-mode leakage current can be significantly reduced.

[0049] Figure 8 This is a comparison chart of common-mode electromagnetic interference (EMI) between the device and method proposed in this invention and conventional carrier-based comparative PWM. By adopting the zero common-mode modulation method proposed in this invention, EMI spikes are significantly suppressed.

[0050] This invention provides a zero common-mode voltage modulation method for magnetic levitation bearings. It involves acquiring the reference voltage at the midpoint of the four bridge arms of the magnetic levitation bearing controller, calculating the normalized differential-mode voltage and common-mode voltage, determining the sector, and selecting the corresponding voltage vector. The voltage vector is then split based on the midpoint voltage. The normalized duration of each voltage vector is calculated based on the sector number, differential-mode voltage command, common-mode voltage command, and vector splitting method. Four duty cycles are calculated based on the normalized duration of each voltage vector and allocated to the four bridge arms to generate corresponding modulation signals. Finally, a PWM signal is generated to drive the magnetic bearing drive converter. Since the midpoint clamping three-level topology has the highest DC voltage utilization in both differential-mode and common-mode voltage aspects, it does not reduce the dynamic response speed of the system, theoretically achieving zero common-mode interference voltage. It can significantly suppress common-mode electromagnetic interference from the magnetic levitation bearing controller at higher bus voltage levels without affecting the normal control of the magnetic levitation bearing, avoiding damage to the protected bearing and impact on the displacement sensor. This solves the technical problem of difficult and inefficient control of magnetic levitation bearings in existing technologies, achieving precise control of the rotor shaft trajectory of the magnetic levitation bearing.

[0051] Furthermore, based on the above embodiments, the above method can control a single plane. x and y For a magnetic levitation bearing with two degrees of freedom in one direction, and a magnetic levitation bearing with M planes, 2M degrees of freedom can be extended using M associated control devices. Therefore, the above method can be easily extended to magnetic levitation bearings with more degrees of freedom in the axial direction, achieving multi-degree-of-freedom control while suppressing common-mode interference from the entire control system.

[0052] Example 2 The present invention also provides a zero common-mode voltage modulation device for a magnetic levitation bearing, used to perform the zero common-mode voltage modulation method for a magnetic levitation bearing as described in any one of Embodiment 1, comprising: The voltage command calculation module is used to obtain the reference voltage at the midpoint of the four bridge arms on the magnetic levitation bearing controller, and calculate the normalized differential-mode voltage and common-mode voltage based on the reference voltage; the differential-mode voltage includes... x Voltage difference between two windings with different degrees of freedom and in y Voltage difference between two windings with different degrees of freedom The common-mode voltage includes x The sum of the voltages of the two windings in the degree of freedom, or y The sum of the voltages of the two windings in the degree of freedom ; The sector determination module is used to determine the sector number N based on the differential-mode voltage, and select the corresponding voltage vector from the zero common-mode voltage vectors according to the sector number. The zero common-mode voltage vectors used include two preset common-mode vectors, four large vectors, and eight small vectors. The voltage vectors include K preset large vectors and Q small vectors, where K is 0 or 2, and Q is 4. The large vectors are the vectors with the largest magnitude among the zero common-mode voltage vectors used, and the small vectors are the vectors with the smallest magnitude among the zero common-mode voltage vectors used. The action time calculation module is used to calculate the normalized action time of each voltage vector based on the sector number N, the differential mode voltage, and the common mode voltage; and to split the small vectors in the voltage vectors into common mode vectors and large vectors based on the magnitude of the midpoint potential and the magnitude of the differential mode voltage, and to calculate the normalized action time and corresponding duty cycle of each updated voltage vector. The duty cycle allocation module is used to allocate the four duty cycles to the four bridge arms according to the sector number N to generate corresponding modulation signals; The carrier comparison stage is used to compare the set carrier signal with the modulation signal to generate a PWM signal, which is used to control the switching devices of the four bridge arms on the magnetic levitation bearing controller.

[0053] The present invention provides a zero common-mode voltage modulation device for a magnetic levitation bearing that performs a zero common-mode voltage modulation method for a magnetic levitation bearing and has the same beneficial effects.

[0054] 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 zero common mode voltage modulation method for a magnetic bearing, characterized by, Comprise: S1, obtaining reference voltages of the midpoints of the four bridge arms of the magnetic suspension bearing controller, calculating normalized differential mode voltage and common mode voltage based on the reference voltages; the differential mode voltage includes the difference between the voltages of two windings of a degree of freedom x voltage difference of two windings of a degree of freedom and in y voltage difference of two windings of a degree of freedom ; the common mode voltage includes the sum of the voltages of two windings of a degree of freedom, or in x sum of the voltages of two windings of a degree of freedom y sum of the voltages of two windings of a degree of freedom ; S2, according to the sector number N of the difference mode voltage, according to the sector number from the zero common mode voltage vector to select the corresponding voltage vector; The adopted zero common mode voltage vector includes two preset common mode vectors, four large vectors and eight small vectors; The voltage vector includes preset K large vectors and Q small vectors, wherein K is 0 or 2, Q is 4; Wherein, the large vector is the largest vector in the length of the adopted zero common mode voltage vector, and the small vector is the smallest vector in the length of the adopted zero common mode voltage vector; S3, according to the sector number N, the difference mode voltage and the common mode voltage, the normalized action time of each voltage vector is calculated; According to the size of the midpoint potential and the size of the difference mode voltage, the small vector in the voltage vector is split into common mode vector and large vector, and the normalized action time of each voltage vector after updating is calculated and the corresponding duty cycle is calculated; S4, according to the sector number N, the eight duty cycles are distributed to four bridge arms to generate corresponding modulation signals; S5: compare the set carrier signal with the modulation signal to generate PWM signal, which is used to control the switching device of four bridge arms on the magnetic suspension bearing controller.

2. The method of claim 1, wherein, The common mode vector is represented as V17 and V18, which corresponds to the switching tube state of the first to fourth bridge arms as PPNN and NNPP in turn; Four large vectors are represented as V5, V6, V7 and V8, which correspond to the switching tube state of the first to fourth bridge arms as PNNP, PNPN, NPPN and NPNP in turn; Eight small vectors are represented as V9, V10, V11, V12, V13, V14, V15 and V16, which correspond to the switching tube state of the first to fourth bridge arms as PONO, POON, OPON, OPNO, ONOP, ONPO, NOPO and NOOP in turn; Wherein, P represents that the bridge arm midpoint is connected with the positive DC bus, O represents that the bridge arm midpoint is connected with the midpoint potential, and N represents that the bridge arm midpoint is connected with the negative DC bus.

3. The method of claim 2, wherein, With x Degrees of freedom and y Two differential-mode voltages and common-mode voltage of the degrees of freedom are used as coordinate axes to construct a coordinate system, and all zero common-mode vectors used are mapped to the coordinate system to obtain 8 sectors in the x-y two-dimensional plane.

4. The method of claim 3, wherein, In step S1: x the difference between the voltages of the two windings of the degree of freedom is represented as: ； y Difference between the voltages of two windings of a degree of freedom is expressed as: ； x Sum of voltages of two windings of a degree of freedom y Sum of voltages of two windings of a degree of freedom is expressed as: ； wherein , is x a reference voltage of the bridge arm to which the two windings are connected, , is y a reference voltage of the bridge arm to which the two windings are connected, is a DC bus voltage.

5. The method of claim 2, wherein, In step S2, according to the sector number N of the difference mode voltage, comprising: If ; then ; If 1 ; then ; If ; then ; If ; then ; If ; then ; If ; then ; If ; then ; If ; then ; The corresponding voltage vector is selected from the zero common mode voltage vector according to the sector number, comprising: When the selected voltage vector is ; When the selected voltage vector is ; When the selected voltage vector is ; When the selected voltage vector is ; When the selected voltage vector is ; When the selected voltage vector is ; When the selected voltage vector is ; When the selected voltage vector is .

6. The method of claim 1, wherein, In step S3, according to the sector number N, the difference mode voltage and the common mode voltage, the normalized action time of each voltage vector is calculated, comprising: The first large vector acting time , the second large vector acting time , the first small vector acting time , the second small vector acting time , the third small vector acting time , and the fourth small vector acting time are calculated respectively; wherein, to correspond to the selected voltage vectors in sequence; First large vector action time The formula for calculating is: Second major vector action time The formula for calculating is: The first small vector action time And the second small vector action time The calculation formula is: Third small vector action time And fourth small vector action time The calculation formula is: 。 7. The method of claim 6, wherein, In step S3, according to the size of the midpoint potential, the small vector in the voltage vector is split into common mode vector and large vector, and the normalized action time of each voltage vector after updating is calculated, comprising: According to the size of the difference mode voltage, the midpoint potential and the winding current, the action time of the small vector in the voltage vector is split into the action time of a common mode vector and the action time of a large vector, and the normalized action time of the voltage vector is updated as follows: (1) when and or 5: If and then ; If and then ; If and then ; If and then ; (2) when and or 5: If and , ; If and , ; If and , ; If and , ; (3) when and or 6: If and then ; If and then ; If and then ; If and then ; (4) when and or 6: If and , ; If and , ; If and , ; If and , ; (5) when and or 7: If and then ; If and then ; If and then ; If and then ; (6) when and or 7: If and then ; If and then ; If and then ; If and then ; (7) when and or 8: If and then ; If and then ; If and then ; If and then ; (8) when and or 8: If and then ; If and then ; If and then ; If and then ; wherein, is the midpoint potential, is the positive common mode vector acting time, is the negative common mode vector acting time; is the updated first large vector acting time, is the updated second large vector acting time; 8 duty cycles The calculation formulas are respectively: ; ; ; ; ; ; ; .

8. The method of claim 7, wherein, In step S4, according to the sector number N and eight duty cycles distributed to four bridge arms, corresponding modulation signals are generated, comprising: When ; When ; When ; When ; Wherein, the letter D represents a bridge arm modulation signal, in represents the number of switching devices, b represents the signal strength of the modulation signal, is a positive integer with a value of 1-8, b is 1 or 2, and .

9. The method of claim 1, wherein, Step S5 comprises: For each bridge leg, the generated PWM signal is high when the triangular carrier signal is greater than the first modulation signal and less than the second modulation signal and low otherwise. The generated 8-way PWM signal is assigned accordingly to x the upper transistor drive of the bridge arm to which the two windings of the direction are connected and y the lower transistor drive of the bridge arm to which the two windings of the direction are connected.

10. A zero common mode voltage modulation arrangement for a magnetic bearing, characterized by The zero common mode voltage modulation method for magnetic suspension bearing according to any one of claims 1-9, comprising: a voltage command calculation module configured to obtain reference voltages for the midpoints of four bridge arms of a magnetic bearing controller, and to calculate a normalized differential mode voltage and a common mode voltage based on the reference voltages; the differential mode voltage comprising a difference between the voltages of two windings of a degree of freedom x the voltage difference of two windings of a degree of freedom and the sum of the voltages of two windings of a degree of freedom y the voltage difference of two windings of a degree of freedom ; the common mode voltage comprising the sum of the voltages of two windings of a degree of freedom x the sum of the voltages of two windings of a degree of freedom y the sum of the voltages of two windings of a degree of freedom ; A sector judgment module is configured to determine a sector number N according to the differential mode voltage, and select a corresponding voltage vector from zero common mode voltage vectors according to the sector number. The zero common mode voltage vectors include two preset common mode vectors, four large vectors and eight small vectors. The voltage vector includes K preset large vectors and Q preset small vectors, where K is 0 or 2, and Q is 4. The large vector is the largest vector in the zero common mode voltage vectors, and the small vector is the smallest vector in the zero common mode voltage vectors. An action time calculation module is configured to calculate normalized action times of the voltage vectors according to the sector number N, the differential mode voltage and the common mode voltage. The small vectors in the voltage vectors are split into common mode vectors and large vectors according to the size of the midpoint potential and the size of the differential mode voltage, and the normalized action times and corresponding duty cycles of the updated voltage vectors are calculated. A duty cycle distribution module is configured to distribute the four duty cycles to four bridge arms according to the sector number N to generate corresponding modulation signals. A carrier comparison link is configured to compare a set carrier signal with the modulation signals to generate a PWM signal, which is used to control switching devices of the four bridge arms on the magnetic suspension bearing controller.

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