Position control method of permanent magnet synchronous motor with predictive control mode self-switching

Abstract

The present invention discloses a method for position control of a permanent magnet synchronous motor with self-switching of a predictive control mode, the method comprising the following contents: 1. dividing the motor position control process and adopting the corresponding mode for control; 2. establishing a cost function; 3. switching from the acceleration stage of predictive current control to the uniform speed stage of predictive speed control; 4. switching from the uniform speed stage of predictive speed control to the deceleration stage of predictive current control; 5. switching from the deceleration stage of predictive current control to the low speed approach stage of predictive position control. The invention has the beneficial effects of improving the dynamic response speed, reducing the tracking error, and being applicable to the case of different position setting values.

Description

Technical Field

[0001] The invention relates to the technical field of permanent magnet synchronous motor position control, and in particular to a permanent magnet synchronous motor position control method with predictive control mode self-switching. Background Art

[0002] Permanent Magnet Synchronous Motor (PMSM) has the advantages of high power factor, simple structure, wide speed regulation range, etc., and has been widely used in high-performance position control occasions. PMSM control systems generally adopt vector control strategies based on PI controllers, but due to the limitations of PI controllers, it is difficult to take into account both the speed and stability of the system. Model Predictive Control (MPC) has the advantages of fast dynamic response, simple modeling, excellent control effect, and easy handling of multi-objective control, and has attracted widespread attention from many scholars.

[0003] In the field of motor control, model predictive control can be divided into three control modes according to different control objectives: predictive current control, predictive speed control and predictive position control. In motor position control systems, model predictive control is widely used, but most of them only use a single predictive control mode. The motor position control process includes different stages such as startup acceleration, constant speed, deceleration and position approach. A single control mode cannot meet the control requirements of different stages at the same time, nor can it take into account both rapidity and stability, making it difficult to achieve the optimal control effect.

[0004] In order to simultaneously meet the requirements of the position control system for rapidity and accuracy, the motor position control process is divided into acceleration stage, uniform speed stage, deceleration stage and low speed approach stage, such as Figure 2 As shown. The acceleration and deceleration stages require the motor to respond quickly, so the predictive current control mode is adopted; the uniform speed stage mainly focuses on reducing torque and speed fluctuations to ensure system stability, so the predictive speed control mode is adopted; the low-speed approach stage needs to avoid position oscillation while ensuring control accuracy to ensure position control accuracy, so the predictive position control mode is adopted. However, in the existing control methods, if different control modes are switched directly, it will affect the system control effect and even cause system instability, so a method that can smoothly switch between different control modes is needed. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and to design a position control method for a permanent magnet synchronous motor with predictive control mode self-switching.

[0006] To achieve the above object, the technical solution of the present invention is a position control method for a permanent magnet synchronous motor with predictive control mode self-switching, the method comprising the following steps:

[0007] Step 1: The motor position control process is divided into an acceleration stage, a uniform speed stage, a deceleration stage and a low speed approach stage, wherein the acceleration stage and the deceleration stage adopt a predicted current control mode, the uniform speed stage adopts a predicted speed control mode, and the low speed approach stage adopts a predicted position control mode;

[0008] Step 2: Establish a cost function and change the predictive control mode by adjusting the weight coefficients in the cost function. The formula of the cost function is as follows:

[0009]

[0010] Where: λ1 is the weight coefficient of the current part, λ2 is the weight coefficient of the speed part, λ3 is the weight coefficient of the position part, i q * is the set value of the q-axis component of the stator current, is the predicted value of the d-axis component of the stator current; is the predicted value of the q-axis component of the stator current, is the predicted value of rotor speed, ω r * is the speed setting value, θ p (k+1) is the predicted value of the rotor position angle, θ * Set a value for the position;

[0011] Step 3: Switch from the acceleration phase of predicted current control to the uniform speed phase of predicted speed control, and adjust the weight coefficient λ2 in the cost function according to the motor speed:

[0012]

[0013] Where: 2max is the maximum value of the weight coefficient of the speed part in the cost function, ω is the actual speed of the motor, ω max To set the maximum speed; when the actual motor speed ω is equal to ω0, it enters the transition process. During the transition process, the speed weight coefficient λ2 increases from zero according to formula (2), and the speed part of the cost function gradually increases, which can ensure the fast response of the motor while suppressing overshoot;

[0014] Step 4: Switch from the uniform speed stage of predicted speed control to the deceleration stage of predicted current control. Since the speed is high in the uniform speed stage, the motor needs a certain amount of time to decelerate. Therefore, it is necessary to decelerate in advance before reaching the set position and switch to current control. At this time, there is no need to consider overshoot and other issues, and λ2 is directly set to 0;

[0015] Step 5: Switch from the deceleration phase of the predicted current control to the low-speed approach phase of the predicted position control, and set λ2 to λ 2max . Adjust the weight coefficient λ3 according to the position information:

[0016]

[0017] Where: 3max is the maximum value of the weight coefficient of the position part in the cost function, θ is the actual position of the motor. When the actual position θ of the motor is equal to θ2, the transition process begins. During the transition process, the weight coefficient λ3 of the position part increases from zero according to formula (3). The proportion of the position part in the cost function gradually increases, which improves the motor position control accuracy and suppresses oscillation.

[0018] Beneficial Effects

[0019] The position control method of a permanent magnet synchronous motor with self-switching of a predictive control mode produced by the technical solution of the present invention has the following advantages:

[0020] 1. This method effectively improves the dynamic response speed and steady-state control accuracy of the PMSM position control system. According to the motor control target, the position control process is divided into different stages and corresponding control modes are adopted respectively. The smooth self-switching of the control mode is achieved by adjusting the weight coefficient of the cost function online in real time.

[0021] 2. The predictive control mode self-switching method proposed in this method can improve the dynamic response speed, reduce the tracking error, and is suitable for situations with different position setting values. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a flow chart of the position control method of a permanent magnet synchronous motor with self-switching of a predictive control mode according to the present invention;

[0023] Figure 2 It is the control process division diagram of the present invention;

[0024] Figure 3 is a cost function weight coefficient table under different predictive control modes of the present invention;

[0025] Figure 4 is a parameter table of the motor system of the present invention;

[0026] Figure 5 It is an experimental waveform diagram of the motor under no-load condition of the present invention;

[0027] Figure 6 It is an experimental waveform diagram of the motor under loading condition of the present invention;

[0028] Figure 7This is a waveform diagram of the direct switching and self-switching comparison experiment of the motor under no-load condition of the present invention;

[0029] Figure 8 It is a waveform diagram of the direct switching and self-switching comparison experiment under motor loading of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below in conjunction with the accompanying drawings. Figure 1-8 As shown;

[0031] The cost function adopted by the position control method for predictive mode self-switching proposed in this application is as follows.

[0032] cost = λ1([i d p (k+1)] 2 +[i q * -i q p (k+1)] 2 )+λ2[ω r * -ω r p (k+1)] 2 +λ3[θ * -θ p (k+1)] 2 (1)

[0033] Where: λ1 is the weight coefficient of the current part, λ2 is the weight coefficient of the speed part, and λ3 is the weight coefficient of the position part. The predictive control mode is changed by adjusting the weight coefficients in the cost function. The weight coefficients of the cost function corresponding to each control mode are as follows: Figure 3 shown.

[0034] If different control modes are switched directly, the system control effect will be affected and even the system will become unstable. This application designs a control mode switching method based on the motor speed and position information to achieve smooth self-switching of different control modes.

[0035] Switch from predicted current control (acceleration phase) to predicted speed control (constant speed phase), and adjust the weight coefficient λ2 in the cost function according to the motor speed:

[0036]

[0037] Where: 2max is the maximum value of the weight coefficient of the speed part in the cost function, ω is the actual speed of the motor, ω maxTo set the maximum speed. If the motor switches directly from predicted current control to predicted speed control, speed overshoot and fluctuation will occur. This application introduces a transition process. When the speed is equal to ω0, the transition process is entered. During the transition process, the speed weight coefficient λ2 increases from zero according to formula (2), and the proportion of the speed part in the cost function gradually increases, which can ensure the rapid response of the motor while suppressing overshoot.

[0038] Switch from predicted speed control (constant speed stage) to predicted current control (deceleration stage). Since the speed is high in the uniform speed stage, the motor needs a certain amount of time to decelerate. Therefore, it is necessary to decelerate in advance before reaching the set position and switch to current control. At this time, there is no need to consider overshoot and other issues, and λ2 is directly set to 0.

[0039] Switching from predictive current control (deceleration phase) to predictive position control (low speed approach phase), in order to suppress overshoot, the proportion of the speed part in the cost function should be increased, and λ2 should be set to λ 2max . Adjust the weight coefficient λ3 according to the position information:

[0040]

[0041] Where: 3max is the maximum value of the weight coefficient of the position part in the cost function. If the motor switches directly from predicted current control to predicted position control, oscillation will occur and affect the control accuracy. This application introduces a transition process. When the actual position is equal to θ2, the transition process begins. During the transition process, the weight coefficient λ3 of the position part increases from zero according to formula (11), and the proportion of the position part in the cost function gradually increases, which can improve the motor position control accuracy while suppressing oscillation.

[0042] In order to verify the effectiveness of the above control method, a permanent magnet synchronous motor system is tested. The motor system parameters are as follows: Figure 4 shown.

[0043] Control performance of predictive control mode self-switching method

[0044] Under no-load conditions, the motor position control experiment was carried out based on the predictive control mode self-switching method at the set positions θ*=10rad, θ*=50rad and θ*=100rad, and the maximum speed was 1000rpm. Figure 5 The speed and position experimental waveforms under different position setting values. Figure 5 It can be found that under no-load conditions, for different position setting values, the predictive control mode self-switching method proposed in the present application has a fast response speed, small overshoot and basically no oscillation phenomenon, and the position can also follow the setting value well.

[0045] The applied load is the rated load of 1.27N·m. When the set positions are θ*=10rad, θ*=50rad and θ*=100rad and the maximum speed is 1000rpm, the motor position control experiment is carried out based on the predictive control mode self-switching method. Figure 6 The speed and position experimental waveforms at different position setting values ​​under loading conditions. Figure 6 It can be found that, during loading, the predictive control mode self-switching method proposed in the present application can also adapt to situations with different position setting values, and the position can also follow the setting value well.

[0046] Comparison between direct control mode switching and automatic control mode switching

[0047] The control mode self-switching method and the control mode direct switching method are compared in the experiment.When the setting position θ*=200rad and the maximum speed is 1000rpm, the motor position control comparison experiment is carried out. Figure 7 The speed and position experimental waveforms of the two control methods under no-load conditions are shown in Figure 2. Figure 8 The speed and position experimental waveforms of the two control methods under the rated load of 1.27N·m. Figure 7 and Figure 8 It can be found that compared with the direct control mode switching method, the control mode self-switching method can effectively reduce the speed overshoot, suppress position oscillation when approaching the set position, and improve the control accuracy.

[0048] The method adopted in this application mainly solves the problem that the single position control mode of the motor system cannot take into account both rapidity and accuracy, and realizes smooth self-switching of three predictive control modes through the control mode self-switching method. Experimental results show that the predictive control mode self-switching method proposed in this method can improve the dynamic response speed, reduce the tracking error, and is suitable for different position setting values.

[0049] In the process of implementing this application, the principles for determining the switching points between different stages of the motor control process are as follows:

[0050] Switching point A: Switching from the acceleration phase (predicted current control) to the constant speed phase (predicted speed control). In order to reduce speed overshoot, the switch needs to be made in advance. Speed ​​ω0 = l*ω max When the switching condition is met, l is the adjustment coefficient. If l is too large, obvious overshoot will occur. If l is too small, it will switch to the speed control mode too early, affecting the rapidity of the system. In this application, l is set to 0.9 in combination with experimental tests.

[0051] Switching point B: Switching from the uniform speed stage (predicted speed control) to the deceleration stage (predicted current control). If the deceleration is too early, the time required for the motor to reach the reference position will increase; if the deceleration is too late, the motor may enter the low-speed approach stage at a higher speed, resulting in position overshoot and oscillation. Therefore, deceleration too early or too late will affect the motor control performance, and choosing the appropriate deceleration point is very critical. According to formula (8), this application sets the actual motor position θ1 = θ0 / 2 to meet the switching condition.

[0052] Switching point C and switching point E: Both are switching from the deceleration stage (predicted current control) to the low-speed approach stage (predicted position control). Position oscillation should be avoided while improving control accuracy. The switching point position is set to: θ2 = θ * -β, this application combines experimental tests and selects β=0.2rad.

[0053] Switching point D: Switching from the acceleration phase (predicted current control) to the deceleration phase (predicted current control), at this time the position setting value is less than θ0, excluding the uniform speed phase, setting the actual motor position θ3 = θ * / 2 satisfies the switching condition.

[0054] In the dq coordinate system, the mathematical model of the permanent magnet synchronous motor is:

[0055]

[0056] Where: i d 、i q are the d-axis and q-axis components of the stator current, u d 、u q are the d-axis and q-axis components of the stator voltage, L d , L q are the d-axis and q-axis inductances respectively. For a surface-mounted permanent magnet synchronous motor, L d =L q , R s , f are stator resistance and permanent magnet flux, ω e is the electrical angular velocity, ω r is the mechanical angular velocity, ω r =ω e / p, p is the number of pole pairs, T e is the electromagnetic torque, T l is the load torque, J is the moment of inertia, B is the friction coefficient, and θ is the actual position of the motor rotor.

[0057] Predictive Current Control

[0058] According to the mathematical model of permanent magnet synchronous motor, the current prediction model can be obtained as follows:

[0059]

[0060] Where: T s is the control period and prediction step size, are the predicted values ​​of the d-axis and q-axis components of the stator current respectively. The cost function of the predicted current control is:

[0061] cost = [i d p (k+1)] 2 +[i q * -i q p (k+1)] 2

[0062] Where: i q * Set the value for the q-axis component of the stator current. The cost function can make the actual current follow the set value and reduce current and torque ripple.

[0063] Predictive speed control

[0064] According to the motor mathematical model, the speed prediction model can be obtained as follows:

[0065]

[0066] Where: r p (k+1) is the predicted value of the rotor speed. The cost function of the predicted speed control is:

[0067] cost = λ1([i d p (k+1)] 2 +[i q * -i q p (k+1)] 2 )+λ2[ω r * -ω r p (k+1)] 2

[0068] Where: r * is the speed setting value. The first part of the cost function can make the actual current follow the setting value, prevent the starting current from being too large, and ensure the normal starting of the motor; the second part can make the actual speed follow the setting value and reduce the speed fluctuation.

[0069] Predictive Position Control

[0070] According to the motor mathematical model, the position prediction model can be obtained:

[0071]

[0072] Where: θ p (k+1) is the predicted value of the rotor position angle. The cost function of the predicted position control is:

[0073] cost = λ1([i d p (k+1)] 2 +[i q * -i q p (k+1)] 2 )+λ2[ω r * -ω r p (k+1)] 2 +λ3[θ * -θ p (k+1)] 2

[0074] Where: θ * is the position set value. The first two parts of the cost function have the same effect as the predicted speed control, and the third part can make the actual position follow the set value and improve the position control accuracy.

[0075] It should be noted that, in this application, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions. The sentence "includes an element defined by ... does not exclude the existence of other identical elements in the process, method, article or device including the element".

[0076] The above technical solutions only reflect the preferred technical solutions of the technical solutions of the present invention. Some changes that may be made to certain parts thereof by technicians in this technical field all reflect the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for position control of a permanent magnet synchronous motor with predictive control mode self-switching, characterized in that: The method comprises the following steps: Step 1: The motor position control process is divided into an acceleration stage, a uniform speed stage, a deceleration stage and a low speed approach stage, wherein the acceleration stage and the deceleration stage adopt a predicted current control mode, the uniform speed stage adopts a predicted speed control mode, and the low speed approach stage adopts a predicted position control mode; Step 2: Establish a cost function and change the predictive control mode by adjusting the weight coefficients in the cost function. The formula of the cost function is as follows: Where: λ1 is the weight coefficient of the current part, λ2 is the weight coefficient of the speed part, λ3 is the weight coefficient of the position part, i q * is the set value of the q-axis component of the stator current, is the predicted value of the d-axis component of the stator current; i q p (k+1) is the predicted value of the q-axis component of the stator current, ω r p (k+1) is the predicted value of rotor speed, ω r * is the speed setting value, θ p (k+1) is the predicted value of the rotor position angle, θ * Set a value for the position; Step 3: Switch from the acceleration phase of predicted current control to the uniform speed phase of predicted speed control, and adjust the weight coefficient λ2 in the cost function according to the motor speed: Where: 2max is the maximum value of the weight coefficient of the speed part in the cost function, ω is the actual speed of the motor, ω max To set the maximum speed; when the actual motor speed ω is equal to ω0, it enters the transition process. During the transition process, the speed weight coefficient λ2 increases from zero according to formula (2), and the speed part of the cost function gradually increases, which can ensure the fast response of the motor while suppressing overshoot; Step 4: Switch from the uniform speed stage of predicted speed control to the deceleration stage of predicted current control. Since the speed is high in the uniform speed stage, the motor needs a certain amount of time to decelerate. Therefore, it is necessary to decelerate in advance before reaching the set position and switch to current control. At this time, there is no need to consider overshoot and other issues, and λ2 is directly set to 0; Step 5: Switch from the deceleration phase of the predicted current control to the low-speed approach phase of the predicted position control, and set λ2 to λ 2max . Adjust the weight coefficient λ3 according to the position information: Where: 3max is the maximum value of the weight coefficient of the position part in the cost function, θ is the actual position of the motor. When the actual position θ of the motor is equal to θ2, the transition process begins. During the transition process, the weight coefficient λ3 of the position part increases from zero according to formula (3). The proportion of the position part in the cost function gradually increases, which improves the motor position control accuracy and suppresses oscillation.

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