A bearingless motor suspension current control method based on two-stage execution mechanism

Abstract

The application discloses a bearingless motor suspension current control method based on a two-stage execution mechanism, in the face of high dynamic response control requirements of bearingless motor suspension current, combined with the high algorithm complexity characteristics of the bearingless motor, based on the idea of no dead time, using the symmetry of duty cycle in a control cycle of pulse width modulation technology, through double sampling of the current in a control cycle to complete current prediction and model parameter error compensation, and cooperating with a two-stage algorithm execution mechanism to ensure complete execution of the control algorithm, finally realizing high dynamic performance precise control of the bearingless motor suspension current. The application is simple, can complete current prediction and model parameter error identification without relying on any model parameters, the former can realize compensation of digital control delay effect, and the latter can realize compensation of model parameter error. The two-stage algorithm execution mechanism improves the execution efficiency of the control algorithm, ensures complete execution of the control algorithm, and the application has universality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bearingless motor drive, in particular to a bearingless motor suspension current control method based on two-stage execution mechanism. BACKGROUND

[0002] The advantage of bearingless motor without mechanical wear makes it widely used in aerospace, semiconductor manufacturing, life science and chemical process fields. The non-contact and non-wear characteristics of bearingless motor benefit from the introduction of its additional suspension control system, however, this also inevitably increases the algorithm complexity of bearingless motor control system. In addition, the existence of unknown external disturbance and non-ideal process factors requires the suspension control system of bearingless motor to have high dynamic response and strong robustness characteristics, especially for the suspension current control link of bearingless motor. As a more commonly used high dynamic performance control scheme, the deadbeat idea is applied to the suspension current control of bearingless motor, and its inherent digital control delay and model parameter error problem will seriously affect the suspension control performance. Therefore, for the aforementioned digital control delay and model parameter error problem, real-time compensating measures are needed to ensure the high-performance suspension control of bearingless motor, and combined with the characteristics of high algorithm complexity of its control system, the compensating measures taken must be simple and reliable, easy to implement. SUMMARY

[0003] In view of the defects of the prior art, the present application provides a bearingless motor suspension current control method based on two-stage execution mechanism. In the face of the high dynamic response control requirement of bearingless motor suspension current, combined with the high algorithm complexity characteristics of bearingless motor, based on the deadbeat idea, the symmetry of duty cycle within a control cycle is utilized by using pulse width modulation technology to complete current prediction and model parameter error compensation through double sampling of current within a control cycle, and at the same time, the two-stage algorithm execution mechanism is used to ensure the complete execution of the control algorithm, finally realizing the high dynamic performance precise control of bearingless motor suspension current.

[0004] The present application adopts the following technical solutions to solve the above technical problems:

[0005] A bearingless motor suspension current control method based on two-stage execution mechanism, combined with the high algorithm complexity characteristics of bearingless motor, based on the deadbeat idea, through double sampling of current within a control cycle to complete current prediction and model parameter error compensation, at the same time, the two-stage algorithm execution mechanism is used to ensure the complete execution of the control algorithm, finally realizing the high dynamic performance precise control of bearingless motor suspension current. The implementation steps of the method are as follows:

[0006] Step S1, at the initial moment of the first half of the control cycle, the suspension current i L(k) and other signals required for bearingless motor system closed-loop control are sampled;

[0007] Step S2, displacement outer loop control is completed, and a suspension current setting value is obtained;

[0008] Step S3, torque loop control is completed, and a torque winding end voltage setting value is obtained;

[0009] Step S4, the second sampling of the suspension current in a control period is performed at the initial moment of the latter half of the control period. L (k+0.5).

[0010] Step S5, the suspension current prediction at the next moment is performed in combination with the two suspension current sampling values in a control period. Lpre (k+1), and the specific formula is: i Lpre (k+1) = 2i L (k+0.5) - i L (k).

[0011] Step S6, the actual value of the suspension current sampled at the initial moment of the current control period is combined with the suspension current prediction value i L (k) in the last control period, real-time identification and correction of model parameter errors are performed in combination with the suspension current prediction value i Lpre (k), and suspension current loop control is completed.

[0012] Step S7, steps S1 to S6 are repeated to realize precise control of the high dynamic performance of the suspension current of the bearingless motor.

[0013] Further, the signals required for bearingless motor system closed-loop control in step S1 involve rotor angle signals, rotor speed signals, rotor radial displacement signals and stator current signals; and signal sampling is completed in the first half of the control period.

[0014] Further, the purpose of the displacement outer loop control in step S2 is to obtain a suspension current setting value, and a PID regulator is adopted; and the displacement outer loop control is completed in the first half of the control period.

[0015] Further, the purpose of the torque loop control in step S3 is to obtain a torque winding end voltage setting value, and a PI regulator is adopted; and the torque loop control is completed in the first half of the control period.

[0016] As a bearingless motor suspension current control method based on a two-stage execution mechanism, the second sampling of the suspension current in step S4 is completed in the latter half of the control period.

[0017] As a bearingless motor suspension current control method based on a two-stage execution mechanism, the suspension current prediction in step S5 is completed in the latter half of the control period.

[0018] As the two-stage execution mechanism based bearingless motor suspension current control method of the application, the suspension current loop control scheme in the step S6 is designed based on the idea of no dead angle, the required instruction voltage at the current time is obtained through the system model, and the inverter switching signal is obtained through the corresponding modulation link to control the bearingless motor winding voltage and realize the closed-loop control of the suspension current.

[0019] As the two-stage execution mechanism based bearingless motor suspension current control method of the application, the model parameter error is identified and corrected in real time in the step S6, and the suspension current loop control is completed in the latter half of the control period.

[0020] Compared with the prior art, the above technical scheme of the application has the following technical effects:

[0021] 1. The current prediction can be completed without relying on any model parameters, and the compensation of the digital control delay effect is realized.

[0022] 2. The model parameter error identification and correction can be completed without relying on any model parameters, and the compensation of the model parameter error is realized.

[0023] 3. The two-stage algorithm execution mechanism improves the execution efficiency of the control algorithm and ensures the complete execution of the control algorithm.

[0024] 4. The algorithm is simple to implement, does not rely on any parameters, and has universality. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The flowchart of the two-stage execution mechanism based bearingless motor suspension current control method of the application is shown in the figure.

[0026] Figure 2 The current change rule in a control period of the pulse width modulation technology of the application is shown in the figure. DETAILED DESCRIPTION

[0027] The technical scheme of the application will be further described in detail below with reference to the accompanying drawings:

[0028] The application can be implemented in many different forms, and should not be considered limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the application thorough and complete, and to fully express the scope of the application to those skilled in the art.

[0029] The application discloses a bearingless motor suspension current control method based on a two-stage execution mechanism.

[0030] Step S1, sampling the suspension current i L (k) and other signals required by the closed-loop control of the bearingless motor system at the initial moment of the first half of the control period;

[0031] Step S2, completing displacement outer loop control to obtain a suspension current set value;

[0032] Step S3, completing torque loop control to obtain a torque winding end voltage set value;

[0033] Step S4, sampling the suspension current i L (k+0.5) for the second time in the control period at the initial moment of the second half of the control period;

[0034] Step S5, combining the two suspension current sampling values in the control period to predict the suspension current i Lpre (k+1) at the next moment, and the specific formula is as follows: i Lpre (k+1) = 2i L (k+0.5) - i L (k);

[0035] Step S6, combining the sampled suspension current actual value i L (k) at the initial moment of the current control period and the suspension current predicted value i Lpre (k) in the last control period to identify and correct the model parameter error in real time, and completing suspension current loop control;

[0036] Step S7, repeating steps S1 to S6 to realize high dynamic performance precise control of the bearingless motor suspension current.

[0037] Further, the signals required by the closed-loop control of the bearingless motor system in step S1 include but are not limited to rotor angle signals, rotor speed signals, rotor radial displacement signals and stator current signals.

[0038] Further, the signal sampling in step S1 is completed in the first half of the control period.

[0039] Further, the purpose of the displacement outer loop control in step S2 is to obtain a suspension current set value, and a PID regulator can be used but is not limited thereto.

[0040] Further, the displacement outer loop control in step S2 is completed in the first half of the control period.

[0041] Further, the purpose of the torque loop control in step S3 is to obtain a torque winding terminal voltage set value, and a PI regulator can be used but is not limited thereto.

[0042] Further, the torque loop control in step S3 is completed in the first half of the control period.

[0043] Further, the second sampling of the suspension current in step S4 is completed in the second half of the control period.

[0044] Further, the suspension current prediction in step S5 is completed in the second half of the control period.

[0045] Further, the suspension current loop control scheme in step S6 is designed based on the idea of zero error, the required command voltage at the current time is obtained through a system model, and the inverter switching signal is obtained through a corresponding modulation link to control the bearingless motor winding voltage, thereby realizing closed-loop control of the suspension current.

[0046] Further, the model parameter error is identified and corrected in real time, and the suspension current loop control is completed in the second half of the control period.

[0047] Further, in combination with Figure 1 and Figure 2 , the specific process of the bearingless motor suspension current control method based on the two-stage execution mechanism is described in detail. The current commonly used pulse width modulation techniques, such as sine pulse width modulation, space vector pulse width modulation, etc., all use the form of “carrier intersection” to realize the control of the duty cycle, and the carrier is mostly a central symmetric triangular wave, such as the carrier shown in Figure 2 . The symmetry of the duty cycle of the power device switching signal in a control period can be used to predict the current, so as to compensate for the digital control delay. By double sampling the suspension current values at the starting point and the midpoint of the carrier, the suspension current value at the starting point of the next control period is predicted in real time and sent as feedback to the current regulator to compensate for the digital control delay. Figure 2 Taking a three-phase suspension winding as an example, S A , S B , S C are the upper tube switching signals of the A, B, and C three-phase bridge arms, respectively, and i A is the A-phase suspension winding current; taking the A-phase suspension current i AFor example, the duty cycle of the first half of a control cycle is the same as the duty cycle of the second half of the control cycle, ignoring the resistance voltage drop, and there is no back electromotive force in the suspension winding of the bearingless motor, Δi A1 = Δi A2 . By double sampling the current in a control cycle, the current at the initial time of the next control cycle can be predicted:

[0048] i A (k+1) = 2i A (k+0.5) - i A (k) (1)

[0049] Further, the current prediction scheme based on formula (1) does not depend on any model parameters, compared with the traditional scheme, eliminating the parameter dependence of the current prediction link, and being easy to implement. Based on this, only the multi-sampling technology is needed, and the suspension current is double sampled at the carrier midpoint, that is, at the middle time of the control cycle, to realize the model-independent suspension current prediction. At the same time, combined with the actual value of the suspension current i L (k) sampled at the initial time of the current control cycle, combined with the predicted value of the suspension current i Lpre (k) of the last control cycle, the model parameter error is identified and corrected in real time. Taking the bearingless motor suspension control scheme based on flux-oriented control technology as an example, the discrete voltage vector equation of the bearingless motor is:

[0050]

[0051] Where T s is the control cycle, α = R s T s / L s , β = T s / L s , R s and L s are the equivalent resistance and equivalent inductance of the suspension winding of the bearingless motor, ω e is the motor electrical angular velocity, formula (2) considers the digital control delay effect, and the command voltage calculated by sampling the current at time k will act on the bearingless motor at time k+1.

[0052] Further, based on the foregoing double-sampling current prediction technology of the suspension current, the deviation between the actual current vector and the estimated current vector at time k+0.5 can be obtained:

[0053]

[0054] Where, and represent the estimated values of the equivalent resistance and equivalent inductance of the motor winding,

[0055] Further, the model parameter error can be calculated and identified in real time:

[0056]

[0057] wherein, represents the conjugate value of the corresponding vector It is worth mentioning that, since the suspension winding of the bearingless motor has no back electromotive force, the permanent magnet flux linkage parameter term in the traditional motor does not need to be considered, which also makes the real-time model parameter error be solved and identified. If there is an additional permanent magnet flux linkage term in the traditional permanent magnet motor, the number of unknowns is greater than the number of effective equation groups, and formula (4) cannot obtain a unique solution.

[0058] Further, the suspension command voltage vector considering the model parameter error identification and correction in the application can be expressed as:

[0059]

[0060] wherein, represents the reference current vector at k time. The real-time model parameter identification and correction scheme of the bearingless motor suspension current control in the application has a simple structure and is easy to implement.

[0061] At the same time, in order to ensure that the algorithm can be completely executed within a control period and make the algorithm have the highest execution efficiency, the proposed control algorithm is divided into two segments, as shown in Figure 1 The first half of the period realizes the sampling of the suspension current at k time, and samples other signals required for the control of the bearingless motor, such as rotor angle and radial displacement signals, to complete the control of the displacement outer ring of the suspension system and the control of the torque system. The second half of the period samples the suspension current at k+0.5 time and predicts the suspension current value at the initial time (carrier starting point) of the next control period, and completes the control of the current loop of the suspension system. If the double-sampling current prediction scheme is used, all algorithms must be completely executed within half a period using the traditional algorithm execution mechanism. The two-segment algorithm execution mechanism in the application ingeniously divides the bearingless motor algorithm into two segments for execution, executes the suspension control displacement outer ring and torque control that are irrelevant to the double-sampling current prediction scheme in the first half of the period, and executes the double-sampling current prediction scheme and completes the suspension current inner loop control in the second half of the period, without the need to reduce the system control frequency, so as to ensure the complete execution of the algorithm.

[0062] Further, in combination with Figure 1 The bearingless motor suspension current control method based on the two-segment execution mechanism in the application has the following process:

[0063] First, the suspension current and other signals required for closed-loop control of the bearingless motor system are sampled at the beginning of the first half of the control period.

[0064] Next, displacement outer loop control and torque loop control are completed in the first half of the control period, and the suspension current and torque current set values are obtained. The control part unrelated to the suspension current is completed in the first half of the control period. The second sampling of the suspension current in one control period is performed at the beginning of the second half of the control period, and the suspension current prediction at the next moment is performed in combination with the two suspension current sampling values in one control period.

[0065] Subsequently, the model parameter error is identified and corrected in real time in combination with the actual value of the suspension current sampled at the beginning of the current control period and the suspension current prediction value of the last control period, and the suspension current loop control is completed.

[0066] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the prior art, and should not be interpreted in an idealized or overly formal sense unless otherwise defined.

[0067] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for bearingless motor levitation current control based on two-stage execution mechanism, characterized in that, Based on the idea of no dead zone, using pulse width modulation technology, the symmetry of duty cycle in a control cycle, through the double sampling of current in a control cycle to complete the current prediction and model parameter error compensation, while cooperating with two-stage algorithm execution mechanism to ensure the complete execution of the control algorithm, finally realize the high dynamic performance precision control of bearingless motor suspension current; The implementation steps of the method are as follows: Step S1, sampling the suspension current i at the initial moment of the first half of the control period L (k) and other signals required for closed-loop control of the bearingless motor system Step S2, complete displacement outer ring control, get the suspension current set value; Step S3, complete torque loop control, get the torque winding end voltage set value; Step S4, at the initial moment of the second half of the control period, a second sampling of the suspension current i within the control period is performed L (k + 0.5); Step S5, combining the two suspension current sampling values in a control period, the next moment suspension current prediction i Lpre (k+1), the specific formula is: Lpre (k+1) = 2i L (k+0.5) - i L (k) Step S6, combine the current control cycle initial time sampling suspension current actual value i L (k), combined with the last control cycle suspension current prediction value i Lpre (k), real-time identification and correction of model parameter error, complete the suspension current loop control; Step S7, repeat step S1 to step S6, realize the high dynamic performance precision control of bearingless motor suspension current.

2. The bearingless machine suspension current control method based on two-stage execution mechanism according to claim 1, characterized in that, The signals required for closed-loop control of the bearingless motor system in step S1 involve rotor angle signal, rotor speed signal, rotor radial displacement signal, stator current signal; The sampling of the signal is completed in the first half of the control cycle.

3. The bearingless machine suspension current control method based on two-stage execution mechanism according to claim 1, characterized in that, The displacement outer ring in step S2 adopts PID regulator; The displacement outer ring control is completed in the first half of the control cycle.

4. The bearingless machine suspension current control method based on two-stage execution mechanism according to claim 1, characterized in that, The torque loop control in step S3 adopts PI regulator.

5. The bearingless machine suspension current control method based on two-stage execution mechanism according to claim 1, characterized in that, The torque loop control in step S3 is completed in the first half of the control cycle.

6. The bearingless machine levitation current control method based on two-stage execution mechanism according to claim 1, characterized in that, The second sampling of the suspension current in step S4 is completed in the second half of the control cycle.

7. The bearingless machine levitation current control method based on two-stage execution mechanism according to claim 1, characterized in that, The suspension current prediction in step S5 is completed in the second half of the control cycle.

8. The bearingless machine levitation current control method based on two-stage execution mechanism according to claim 1, characterized in that, The suspension current loop control scheme in step S6 is designed based on the idea of no dead zone, the required command voltage at the current time is obtained through the system model, and the inverter switching signal is obtained through the corresponding modulation link to control the bearingless motor winding voltage, thereby realizing the closed-loop control of the suspension current.

9. The bearingless machine levitation current control method based on two-stage execution mechanism according to claim 1, characterized in that, The real-time identification and correction of model parameter error and the suspension current loop control in step S6 are completed in the second half of the control cycle.

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