A bearingless motor control system based on nine-phase inverter

Abstract

The present invention discloses a bearingless motor control system based on a nine-phase inverter, which mainly includes: a nine-phase inverter, a suspension winding flux observer, a torque winding flux observer, a space vector pulse width modulation module, a force-magnetic conversion module, a bearingless motor and a regulator. The signal of the bearingless motor detected by the sensor is compared with the original given signal in the PID controller, and then the difference signal and the signal observed by the observer are jointly transmitted to the conversion module, and then through space vector pulse width modulation, the signal is then processed, and through the design of the integrated control module of the nine-phase inverter, a set of control systems is graded and modulated, and finally the torque and suspension of the bearingless motor are controlled separately. While ensuring the torque and suspension control of the bearingless motor, the present invention also reduces the complexity of the bearingless motor control system, increases the flexibility and fault tolerance of the control system, and increases the space utilization rate.

Description

Technical Field

[0001] The invention belongs to the field of motor control, and in particular relates to a control system for a bearingless motor. Background Art

[0002] Bearingless motor technology has made significant progress in the past few decades. Currently, commercial bearingless motor products are available on the market, although they are generally used in specific high-performance applications such as high-speed motors, precision positioning systems, and specific industrial applications. The design and manufacture of bearingless motors require advanced materials and precision manufacturing techniques. As materials science and manufacturing processes advance, the cost and performance of bearingless motors are expected to be further improved.

[0003] Bearingless motor is an innovative motor design that supports and positions rotating parts by using electromagnetic force instead of traditional mechanical bearings. This design aims to improve the performance, reliability and life of the motor while reducing maintenance requirements. Bearingless motors have potential applications in many fields. Bearingless motors are mainly used in applications that require high-speed rotation and precision control, such as aircraft engines, precision machine tools, medical equipment, etc.

[0004] The control technology of bearingless motors is a core component, because these motors rely on precise control to maintain the suspension and positioning of the rotor. The existing control technologies for bearingless motors mainly include: PID control, adaptive control, sliding film control, self-suspension control, etc. However, due to the particularity of the bearingless control structure, the existing control systems all use dual inverters to connect the suspension winding and the torque winding respectively to control the suspension force and torque of the bearingless motor, which increases the complexity of the control, reduces the fault tolerance of the motor, and increases the cost and space. Summary of the invention

[0005] Purpose of the invention: In view of the deficiencies in the prior art, the present invention provides a bearingless motor control system based on a nine-phase inverter. Through the modular design of the nine-phase inverter, simultaneous control of the torque and suspension of the bearingless motor is achieved. Compared with the existing dual-inverter system for controlling bearingless motors, the present invention reduces the complexity of the bearingless motor control system, increases the flexibility and fault tolerance of the control system, and also increases space utilization.

[0006] Technical solution: The present invention discloses a bearingless motor control system based on a nine-phase inverter, which includes a suspension winding flux observer, a torque winding flux observer, a space vector pulse width modulation module, a force-magnetic conversion module, a nine-phase inverter integrated control module, a bearingless motor, a displacement regulator, and a speed regulator;

[0007] The position sensor detects the displacement signal x, y of the bearingless motor and the original given position signal x* ,y * 'Compare in the PID controller, then transmit the difference signal and the signal observed by the suspension winding flux observer to the force / magnetic conversion module for signal conversion, and then process the signal through space vector pulse width modulation, output a set of three-phase control current through the nine-phase inverter integrated control module, and realize the control of bearingless motor suspension through the displacement regulator;

[0008] The rotor position sensor detects the position signal w of the bearingless motor, which is different from the original speed signal w * , compared in the PID controller, and then the difference signal and the signal observed by the torque winding flux observer are transmitted to the reference flux generation module for signal conversion, and then the signal is processed through space vector pulse width modulation, and another set of three-phase control current is output through the nine-phase inverter integrated control module, and the speed of the bearingless motor is controlled through the speed regulator.

[0009] Further, the nine-phase inverter integrated control module includes a nine-phase inverter and an integrated control module;

[0010] The nine-phase inverter includes two three-phase two-level voltage source inverters with C phases connected and six H-bridges connected by floating capacitors, the A phase and the B phase of the two three-phase two-level voltage source inverters are respectively connected to an H-bridge connected by a floating capacitor, and the C phases of the two three-phase two-level voltage source inverters are connected and are respectively connected to an H-bridge connected by a floating capacitor;

[0011] The integrated control module analyzes the working state of the nine-phase inverter space voltage vector and the connected C phase according to the input space vector pulse width modulation signal, draws a voltage vector distribution diagram uniquely determined by the switching function, analyzes each group of effective voltage vectors to obtain and determine the switching cycle and power switch switching sequence of the nine-phase inverter, further predicts the state of the connected C phase, and finally outputs a three-phase control current.

[0012] Furthermore, the space voltage vector analysis process of the nine-phase inverter of the integrated control module is as follows:

[0013] 1) The voltage of the nine-phase inverter is defined as a vector space, where the nine axes a, b, c, d, e, f, g, h, and i are spaced π / 9 apart from each other;

[0014] 2) Decompose the nine-phase system Park of the nine-phase inverter into (9-1) / 2 orthogonal planes. The α1-β1, α5-β5, and α7-β7 subspaces contain 2 9 =512 working states, including 2 zero voltage vectors and 510 non-zero voltage vectors, and the α3-β3 subspace has 36 non-zero voltage vectors;

[0015] 3) The spatial voltage vector synthesized by the four subspaces α1-β1, α3-β3, α5-β5, and α7-β7 is obtained by the following steps:

[0016] 3.1) The output phase voltage of the nine-phase inverter takes the neutral point of the DC bus as the reference point, so its nine-phase composite voltage vector is expressed as:

[0017]

[0018] Each axis corresponds to a voltage vector, which are U az , U bz , U cz , U dz , U ez , U fz , U gz , U hz , U iz ; The synthesized voltage vector of the nine-phase inverter, U az is the voltage vector of the nine-phase inverter in direction a, U bz is the voltage vector of the nine-phase inverter in direction b, and so on;

[0019] 3.2) The spatial voltage vector synthesized by the subspaces of α1-β1, α5-β5, and α7-β7 is expressed as:

[0020]

[0021] Among them, U dc is the power supply voltage of the nine-phase inverter, SW a is the a-phase switching signal of the nine-phase inverter, SW b is the b-phase switching signal of the nine-phase inverter, SW c is the c-phase switching signal of the nine-phase inverter, SW d is the d-phase switching signal of the nine-phase inverter, SW e is the e-phase switching signal of the nine-phase inverter, SW f is the f-phase switching signal of the nine-phase inverter, SW g is the g-phase switching signal of the nine-phase inverter, SW h is the h-phase switching signal of the nine-phase inverter, SW i is the i-phase switching signal of the nine-phase inverter;

[0022] 4) By drawing a voltage vector distribution diagram, the switching state change sequence of the final nine-phase inverter in different sectors is obtained.

[0023] Furthermore, the vectors of the 512 working states in the α1-β1, α5-β5, and α7-β7 subspaces are divided according to their amplitudes. kind, The vector ratios are as follows:

[0024]

[0025] So we can get:

[0026] Furthermore, the 512 working states of the α1-β1, α5-β5, and α7-β7 subspaces are divided into four groups: (1, 8), (2, 7), (3, 6), and (4, 5). The numbers in the brackets represent the number of bridge arms that are turned on or off. Then, based on the principle that the synthetic amplitude of adjacent turned-on bridge arms is the largest, several larger maximum voltage vectors are selected from each group as several working states. The working states corresponding to the several maximum voltage vectors selected in each group are analyzed each time.

[0027] Furthermore, the working state analysis of the interconnected C phase of the nine-phase inverter is as follows:

[0028] (1) The signals of the H-bridges SH1, SH2, and SH3 connected to the upper three floating capacitors of the nine-phase inverter are directly taken as the three signals PWM1, PWM2, and PWM3 of the suspension winding; the signals of the H-bridges SH4, SH5, and SH6 connected to the lower three floating capacitors of the nine-phase inverter are directly taken as the three signals PWM4, PWM5, and PWM6 of the torque winding;

[0029] (2) The working status of the common C phase of the nine-phase inverter is determined by the model prediction method.

[0030] Furthermore, a model prediction method is used to determine the state of the common C phase of the nine-phase inverter, which specifically includes the following steps:

[0031] (1) The stator current state equation of the bearingless motor in the rotating coordinate system dq is:

[0032]

[0033]

[0034] Among them, i d is the component of the stator current on the d-axis, i q is the component of the stator current on the q axis, w e is the angular velocity of the bearingless motor, f e is the power supply frequency of the bearingless motor, p is the number of pole pairs of the bearingless motor, L d is the inductance on the d-axis of the bearingless motor, L q is the inductance on the q axis of the bearingless motor, R is the stator resistance, u d is the component of the stator voltage on the d-axis, uq is the component of the stator voltage on the q axis, P e is the electromagnetic power of the bearingless motor;

[0035] (2) The stator current state equation is discretized using the first-order Euler method to obtain the stator current discrete state equation:

[0036]

[0037]

[0038] Among them, i d，k+1 is the stator current on the d-axis at the kth moment, i q，k+1 is the stator current on the q axis at the kth moment;

[0039] (3) The voltage vector that minimizes the error between the predicted current and the given current is selected as the optimal voltage vector through the value function. The value function is selected as:

[0040]

[0041] in, is the given value of the d-axis component of the stator current, is the given value of the q-axis component of the stator current, G i is the value function of the design.

[0042] Beneficial effects:

[0043] The present invention adopts a single nine-phase inverter to simultaneously control the suspension and torque control structure of the bearingless motor. The signal of the bearingless motor detected by the sensor is compared with the original given signal in the PID controller, and then the difference signal and the signal observed by the observer are jointly transmitted to the conversion module, and then through space vector pulse width modulation, the signal is processed, and through the design of the nine-phase inverter integrated control module, through the hierarchical modulation of a set of control systems, the torque and suspension of the bearingless motor are controlled separately. Through the design of the nine-phase inverter integrated control module, the present invention reduces the complexity of the bearingless motor control system while ensuring the torque and suspension control of the bearingless motor, increases the flexibility and fault tolerance of the control system, and also increases the space utilization.

[0044] The present invention realizes the simultaneous control of the torque and suspension of the bearingless motor by a single inverter through the analysis of the spatial voltage vector of the nine-phase inverter and the working state of the connected C phase and the design of the integrated control module. While ensuring the control requirements of the bearingless motor, the complexity of the bearingless motor control system is reduced, the use of components is reduced, the cost is reduced, and the space utilization is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a control block diagram of the torque and suspension of the bearingless motor of the present invention;

[0046] Figure 2 is a structural diagram of a nine-phase inverter of the present invention;

[0047] Figure 3 This is a schematic diagram of the spatial distribution of the nine-phase voltage vectors of the present invention;

[0048] Figure 4 It is the voltage vector distribution diagram of the present invention in the α1-β1, α5-β5, and α7-β7 subspaces. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings.

[0050] The present invention discloses a bearingless motor control system based on a nine-phase inverter, which specifically includes a suspension winding flux observer, a torque winding flux observer, a space vector pulse width modulation module, a force-magnetic conversion module, a nine-phase inverter integrated control module, a bearingless motor, a displacement regulator, and a speed regulator.

[0051] like Figure 1 This is a control block diagram of the torque and suspension of the bearingless motor of the present invention. The control method is:

[0052] (1) Suspension control:

[0053] First, the displacement signal x, y of the bearingless motor detected by the position sensor is compared with the original given position signal x * ,y * 'A comparison is made in the PID controller, and the difference signal and the signal observed by the suspension winding flux observer are then transmitted to the force / magnetic conversion module for signal conversion. The signal is then processed through space vector pulse width modulation, and a set of three-phase control currents are output through the nine-phase inverter integrated control module to achieve control of the bearingless motor suspension through the displacement regulator.

[0054] (2) Torque control:

[0055] First, the position signal w of the bearingless motor detected by the rotor position sensor is compared with the original speed signal w * , compared in the PID controller, and then the difference signal and the signal observed by the torque winding flux observer are sent to the reference flux generation module for signal conversion, and then through space vector pulse width modulation, the signal is processed and another set of three-phase control current is output through the nine-phase inverter integrated control module to control the speed of the bearingless motor through the speed regulator.

[0056] Among them, the force / magnetic conversion module converts the estimated value of the magnetic suspension force into the control signal of the motor, or converts the position feedback of the motor into a force signal, ensuring the stable operation of the system. The space vector pulse width modulation module is responsible for generating pulse width modulation signals suitable for bearingless motors, and can control the speed and direction of the motor by adjusting the direction and magnitude of the motor stator current. The reference flux generation module is used to generate an ideal flux reference value. This reference value, together with the actual observed flux value, is fed into the control system to adjust the operating state of the motor.

[0057] The position sensor of this embodiment is used to detect the actual position or angle of the motor. Figure 3 The displacement signals x, y help the control system to accurately track the motion trajectory of the motor and perform precise position control through 2. The rotor position sensor is specially used to measure the current position of the rotor, which can help the system respond to external commands more quickly and accurately.

[0058] Figure 2 The structure diagram of the nine-phase inverter is shown in FIG. 1 , which is composed of two three-phase two-level voltage source inverters with C phases connected and six H-bridges connected by floating capacitors. The A and B phases of the two three-phase two-level voltage source inverters are respectively connected to an H-bridge connected by a floating capacitor, and the C phases of the two three-phase two-level voltage source inverters are connected and are respectively connected to an H-bridge connected by a floating capacitor.

[0059] The voltage of the nine-phase inverter is defined as a vector space, with nine axes spaced π / 9 apart from each other.

[0060] Figure 3 The figure is a schematic diagram of the spatial distribution of the nine-phase voltage vector of the present invention. As shown in the figure, the spatial vector of the nine-phase inverter is divided into 9 sectors by the axes a, b, c, d, e, f, g, h, i, and each axis corresponds to a voltage vector U az , U bz , U cz , U dz , U ez , U fz , U gz , U hz , U iz .

[0061] The nine-phase system can be decomposed into (9-1) / 2 orthogonal planes by Park. The four subspaces α1-β1, α5-β5, and α7-β7 contain 2 9 =512 working states, including 2 zero voltage vectors and 510 non-zero voltage vectors, and the α3-β3 subspace has 36 non-zero voltage vectors. The nine-phase inverter has two zero vector voltages: (0, 0, 0, 0, 0, 0, 0) and (1, 1, 1, 1, 1, 1, 1, 1).

[0062] The spatial voltage vector synthesized by the four subspaces α1-β1, α3-β3, α5-β5, and α7-β7 is obtained by the following steps:

[0063] (1) The output phase voltage of the nine-phase inverter takes the neutral point of the DC bus as the reference point, so its nine-phase composite voltage vector is expressed as:

[0064]

[0065] (2) The spatial voltage vector synthesized by the subspaces of α1-β1, α5-β5, and α7-β7 is expressed as:

[0066]

[0067] 2 9 The vectors are divided according to their magnitude. kind, The vector ratios are as follows:

[0068]

[0069] So we can get:

[0070] According to the vector ratio, the four layers of vectors in each subspace are drawn in a ratio of 1:1.5:1.75:1.875.

[0071] It is obviously unrealistic to draw out all 512 working states of the α1-β1, α5-β5, and α7-β7 subspaces. In the embodiment of the present invention, the 512 working states are divided into four groups: (1, 8), (2, 7), (3, 6), and (4, 5). The numbers in brackets represent the number of bridge arms that are turned on or off. Then, based on the principle that the synthetic amplitude of adjacent turned-on bridge arms is the largest, the 18 largest maximum voltage vectors are selected from each group as 18 working states, and the working states corresponding to the 18 maximum voltage vectors selected in each group are analyzed each time. Figure 4 The voltage vector distribution diagram of the present invention in the α1-β1, α5-β5, α7-β7 subspaces. As shown in the figure, the α1-β1, α5-β5, α7-β7 subspaces are divided into 18 sectors by the voltage vectors corresponding to 72 working states.

[0072] The switching state of the nine-phase inverter is closely related to the switching function. By drawing the voltage vector distribution diagram uniquely determined by the switching function, the switching state change sequence of the 512 working states of the nine-phase inverter in each sector is further obtained. In order to output a more standard sinusoidal voltage, the expected output voltage vector within α1-β1 is given priority, and the expected output voltage vector within α3-β3, α5-β5, and α7-β7 is set to 0. Therefore, the change sequence table of the first half cycle V1-V9 of the 72 working states in the α1-β1 subspace in 18 sectors is:

[0073]

[0074]

[0075] N i Indicates different sectors (i=1,2,…,18); V i (i=1,2,…,9) represents the working state of the nine-phase inverter after different phases are turned on. For example, when only one phase is turned on, the corresponding working states in the 18 sectors are V1 columns. Since the order of the working state changes in each switching cycle is symmetrical, the second half cycle V9-V1 is opposite to the above table.

[0076] The above table can be used to uniquely calculate the expected output voltage vector, and then determine the switching period of the inverter, and finally obtain the switching sequence of the power switches in different sectors, determine the final switching state of the nine-phase inverter, and realize the normal operation of the nine-phase inverter.

[0077] An integrated control method is used to realize segmented control of the speed and suspension of the bearingless motor. In this embodiment:

[0078] (1) The signals of the upper 3H bridges SH1, SH2, and SH3 of the nine-phase inverter are directly taken from the three signals PWM1, PWM2, and PWM3 of the suspension winding; the signals of the lower 3H bridges SH4, SH5, and SH6 of the nine-phase inverter are directly taken from the three signals PWM4, PWM5, and PWM6 of the torque winding.

[0079] (2) Determine the working status of the common C phase through model prediction.

[0080] Since the nine-phase inverter has a common C phase problem, the model prediction method is used to analyze the state of the common C phase of the nine-phase inverter, which is carried out by the following steps:

[0081] (2.1) The stator current state equation of the bearingless motor in the rotating coordinate system (dq) is:

[0082]

[0083]

[0084] i d is the component of the stator current on the d-axis, i q is the component of the stator current on the q axis, w e is the angular velocity of the motor, f e is the power supply frequency of the motor, p is the number of pole pairs of the motor, L d is the inductance on the d-axis of the motor, L q is the inductance on the q axis of the motor, R is the stator resistance, u d is the component of the stator voltage on the d-axis, u q is the component of the stator voltage on the q axis, P e is the electromagnetic power of the motor.

[0085] (2.2) The stator current state equation is discretized using the first-order Euler method to obtain the stator current discrete state equation:

[0086]

[0087]

[0088] i d，k+1 is the stator current on the d-axis at the kth moment, L q，k+1 is the stator current on the q-axis at the kth moment.

[0089] (3) The core idea of ​​the improved model prediction is to select the voltage vector that minimizes the error between the predicted current and the given current as the optimal voltage vector through the value function. The value function is selected as:

[0090]

[0091] is the given value of the d-axis component of the stator current, is the given value of the q-axis component of the stator current, G i is the value function of the design.

[0092] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A bearingless motor control system based on a nine-phase inverter, characterized in that: It includes a suspension winding flux observer, a torque winding flux observer, a space vector pulse width modulation module, a force-magnetic conversion module, a nine-phase inverter integrated control module, a bearingless motor, a displacement regulator, and a speed regulator; The position sensor detects the displacement signal x, y of the bearingless motor and the original given position signal x * ,y * , and then compare them in the PID controller, and then transmit the difference signal and the signal observed by the suspension winding flux observer to the force / magnetic conversion module for signal conversion, and then process the signal through space vector pulse width modulation, and output a set of three-phase control current through the nine-phase inverter integrated control module, and realize the control of bearingless motor suspension through the displacement regulator; The rotor position sensor detects the position signal w of the bearingless motor, which is different from the original speed signal w * , compared in the PID controller, and then the difference signal and the signal observed by the torque winding flux observer are sent to the reference flux generation module for signal conversion, and then the signal is processed through space vector pulse width modulation, and another set of three-phase control current is output through the nine-phase inverter integrated control module, and the speed of the bearingless motor is controlled through the speed regulator; The nine-phase inverter integrated control module includes a nine-phase inverter and an integrated control module; The nine-phase inverter includes two three-phase two-level voltage source inverters with C phases connected and six H-bridges connected by floating capacitors, the A phase and the B phase of the two three-phase two-level voltage source inverters are respectively connected to an H-bridge connected by a floating capacitor, and the C phases of the two three-phase two-level voltage source inverters are connected and are respectively connected to an H-bridge connected by a floating capacitor; The integrated control module analyzes the working state of the nine-phase inverter space voltage vector and the connected C phase according to the input space vector pulse width modulation signal, draws a voltage vector distribution diagram uniquely determined by the switching function, analyzes each group of effective voltage vectors to obtain and determine the switching cycle and power switch switching sequence of the nine-phase inverter, further predicts the state of the connected C phase, and finally outputs a three-phase control current.

2. According to claim 1, a bearingless motor control system based on a nine-phase inverter is characterized in that: The spatial voltage vector analysis process of the nine-phase inverter of the integrated control module is as follows: 1) The voltage of the nine-phase inverter is defined as a vector space, where the nine axes a, b, c, d, e, f, g, h, and i are spaced π / 9 apart from each other; 2) Decompose the nine-phase system Park of the nine-phase inverter into (9-1) / 2 orthogonal planes. The α1-β1, α5-β5, and α7-β7 subspaces contain 2 9 =512 working states, including 2 zero voltage vectors and 510 non-zero voltage vectors, and the α3-β3 subspace has 36 non-zero voltage vectors; 3) The spatial voltage vector synthesized by the four subspaces α1-β1, α3-β3, α5-β5, and α7-β7 is obtained by the following steps: 3.1) The output phase voltage of the nine-phase inverter takes the neutral point of the DC bus as the reference point, so its nine-phase composite voltage vector is expressed as: Each axis corresponds to a voltage vector, which are U az , U bz , U cz , U dz , U ez , U fz , U gz , U hz , U iz ; The synthesized voltage vector of the nine-phase inverter, U az is the voltage vector of the nine-phase inverter in direction a, U bz is the voltage vector of the nine-phase inverter in direction b, and so on; 3.2) The spatial voltage vector synthesized by the subspaces of α1-β1, α5-β5, and α7-β7 is expressed as: Among them, U dc is the power supply voltage of the nine-phase inverter, SW a is the a-phase switching signal of the nine-phase inverter, SW b is the b-phase switching signal of the nine-phase inverter, SW c is the c-phase switching signal of the nine-phase inverter, SW d is the d-phase switching signal of the nine-phase inverter, SW e is the e-phase switching signal of the nine-phase inverter, SW f is the f-phase switching signal of the nine-phase inverter, SW g is the g-phase switching signal of the nine-phase inverter, SW h is the h-phase switching signal of the nine-phase inverter, SW i is the i-phase switching signal of the nine-phase inverter; 4) By drawing a voltage vector distribution diagram, the switching state change sequence of the final nine-phase inverter in different sectors is obtained.

3. The bearingless motor control system based on the nine-phase inverter according to claim 2 is characterized in that: The vectors of the 512 working states in the α1-β1, α5-β5, and α7-β7 subspaces are divided according to their amplitudes. 4 categories, The vector ratios are as follows: So we can get:

4. The bearingless motor control system based on the nine-phase inverter according to claim 2 is characterized in that: The 512 working states of the α1-β1, α5-β5, and α7-β7 subspaces are divided into four groups: (1, 8), (2, 7), (3, 6), and (4, 5). The numbers in the brackets represent the number of bridge arms that are turned on or off. Then, based on the principle that the synthetic amplitude of adjacent turned-on bridge arms is the largest, several larger maximum voltage vectors are selected from each group as several working states. The working states corresponding to the several maximum voltage vectors selected in each group are analyzed each time.

5. The bearingless motor control system based on a nine-phase inverter according to claim 1 is characterized in that: The working state analysis of the interconnected C phase of the nine-phase inverter is as follows: (1) The signals of the H-bridges SH1, SH2, and SH3 connected to the upper three floating capacitors of the nine-phase inverter are directly taken as the three signals PWM1, PWM2, and PWM3 of the suspension winding; the signals of the H-bridges SH4, SH5, and SH6 connected to the lower three floating capacitors of the nine-phase inverter are directly taken as the three signals PWM4, PWM5, and PWM6 of the torque winding; (2) The working status of the common C phase of the nine-phase inverter is determined by the model prediction method.

6. The bearingless motor control system based on the nine-phase inverter according to claim 5 is characterized in that: The state of the common C phase of the nine-phase inverter is determined by using a model prediction method, which specifically includes the following steps: (1) The stator current state equation of the bearingless motor in the rotating coordinate system dq is: Among them, i d is the component of the stator current on the d-axis, i q is the component of the stator current on the q axis, w e is the angular velocity of the bearingless motor, f e is the power supply frequency of the bearingless motor, L d is the inductance on the d-axis of the bearingless motor, L q is the inductance on the q axis of the bearingless motor, R is the stator resistance, u d is the component of the stator voltage on the d-axis, u q is the component of the stator voltage on the q axis, P e is the electromagnetic power of the bearingless motor; (2) The stator current state equation is discretized using the first-order Euler method to obtain the stator current discrete state equation: Among them, i d，k+1 is the stator current on the d-axis at the kth moment, i q，k+1 is the stator current on the q axis at the kth moment; (3) The voltage vector that minimizes the error between the predicted current and the given current is selected as the optimal voltage vector through the value function. The value function is selected as: in, is the given value of the d-axis component of the stator current, is the given value of the q-axis component of the stator current, G i is the value function of the design.

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