Novel phase-locked loop stepping motor sensorless control strategy based on rotary integrator

Abstract

The invention provides a novel phase-locked loop stepping motor sensorless control strategy based on a rotary integrator. The method comprises the following steps: constructing a stepping motor model driven by a double-H-bridge inverter; rotating speed closed-loop and current closed-loop control is adopted, a rotating speed controller and a current controller both adopt proportional-integral controllers, and a modulation strategy is SVPWM (space vector pulse width modulation); building a disturbance observer model, estimating counter electromotive force by taking two opposite electromotive forces as disturbance quantities, then eliminating a coefficient for estimating the counter electromotive force, and ensuring that the performance of the stepping motor is consistent in a full-speed range; a novel phase-locked loop based on a rotation integrator is established, a sixth harmonic component is firstly filtered out, then a position estimation error of the phase-locked loop (PLL) is compensated, and finally rotor position information and rotation speed information of the stepping motor are obtained. The method can effectively solve the problem that a phase-locked loop has a large estimation error when the position of the rotor is estimated, reduces the higher harmonic component in the estimation of the back electromotive force, and improves the precision of a stepping motor control system.

Description

Technical Field

[0001] This invention relates to the field of power electronic system simulation, and mainly to a novel sensorless control of a phase-locked loop stepper motor based on a rotating integrator, which reduces the estimated back EMF harmonics and improves the position estimation accuracy. Background Technology

[0002] In recent years, stepper motors have been widely used in most industrial fields. However, with the continuous advancement of industry, many industries, such as robotics and 3D printing, have increasingly higher requirements for the high precision of stepper motors. Many advanced control algorithms have been proposed, and closed-loop servo control has become the mainstream control method. In general, the rotor position information in closed-loop servo control is obtained through feedback from an encoder. This method can obtain relatively accurate position information, but adding an external encoder increases system cost. Moreover, if the motor is in a harsh environment or experiences temperature changes, the encoder will be affected, reducing the stability of the motor control system and even causing the stepper motor to lose steps. Sensorless control methods can effectively avoid these problems. Traditional sensorless control strategies first estimate the back electromotive force (EMF) of the motor, and then use a phase-locked loop (PLL) or arctangent function method to extract the rotor position information from the back EMF. The back EMF obtained by this method has a large high-order harmonic content, resulting in errors between the obtained rotor position information and the actual rotor position information, leading to reduced position estimation accuracy. Summary of the Invention

[0003] This invention provides a novel sensorless control strategy for a phase-locked loop stepper motor based on a rotating integrator, which solves the problem of large estimation error in the phase-locked loop when estimating the rotor position, reduces the high-order harmonic components in the estimated back electromotive force, and improves the accuracy of the stepper motor control system.

[0004] To achieve the above objectives, the present invention adopts the following technical solution, including:

[0005] S1. Build a stepper motor (HSM) model driven by a dual H-bridge inverter;

[0006] S2. Speed ​​closed-loop and current closed-loop control are adopted. Both speed and current controllers use proportional-integral controllers, and the modulation strategy is SVPWM.

[0007] S3. Build a disturbance observer model, use the two opposite electromotive forces as disturbance quantities, and estimate the back electromotive force;

[0008] S4. Construct a novel phase-locked loop based on a rotating integrator. First, eliminate the back electromotive force coefficient, then compensate for the position estimation error of the phase-locked loop (PLL), and finally obtain the rotor position and speed information of the stepper motor.

[0009] This invention patent has the following advantages over the prior art:

[0010] Eliminating the back EMF coefficient ensures consistent performance of the stepper motor across its entire speed range, and compensates for errors in the rotor position estimated by the phase-locked loop.

[0011] By employing a multiple rotating integrator, the content of higher harmonics in the estimated back EMF is reduced, thereby improving the accuracy of rotor position estimation. Attached Figure Description

[0012] Figure 1 This is a block diagram of the vector control structure for a stepper motor.

[0013] Figure 2 Here is a block diagram of the disturbance observer structure;

[0014] Figure 3 Here is a block diagram of the rotating integrator structure;

[0015] Figure 4 Here is a block diagram of a phase-locked loop (PLL).

[0016] Figure 5 The diagram shows the harmonic content of the back electromotive force under a conventional phase-locked loop control strategy.

[0017] Figure 6 Figure showing the harmonic content of back electromotive force under a novel sensorless control strategy for a phase-locked loop stepper motor based on a rotating integrator.

[0018] Figure 7 Estimating rotor position diagram under conventional phase-locked loop control strategy;

[0019] Figure 8 Estimating rotor position diagrams for a novel sensorless control strategy for a phase-locked loop stepper motor based on a rotating integrator; Detailed Implementation

[0020] To make the features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] A novel sensorless control structure block diagram for a phase-locked loop stepper motor based on a rotating integrator is shown below. Figure 1 As shown, it includes:

[0022] S1. Build a stepper motor model driven by a dual H-bridge inverter;

[0023] In practical implementation, the proposed model consists of a 24V DC power supply, a dual H-bridge inverter, and a stepper motor, with the stepper motor driven by the dual H-bridge inverter. In the stationary coordinate system (a, β axis), the mathematical model of the stepper motor is as follows:

[0024]

[0025] In the formula, u a and u β These are the a-axis and β-axis voltages, and R and L, respectively. s These are the stator resistance and stator inductance of a stepper motor, i a i β It is the a-axis and beta-axis current, k m ω is the motor torque coefficient, w is the rotor electrical angular velocity, and θ is the motor rotor electrical angle.

[0026] S2. Speed ​​closed-loop and current closed-loop control are adopted. Both speed and current controllers use proportional-integral controllers, and the modulation strategy is SVPWM.

[0027] In practice, its control strategy is as follows: Figure 1 As shown, the rotor position information of the motor is obtained by the disturbance observer and the voltage and current of the motor. After passing through the speed loop and the current loop, the reference voltage vector is obtained. Both the speed loop and the current loop adopt proportional-integral controllers. The switching signal of the dual H-bridge inverter is generated by SVPWM modulation to drive the stepper motor.

[0028] S3. Build a disturbance observer model, use two opposite electromotive forces as disturbance quantities, estimate the back electromotive force, and then eliminate the coefficient of the estimated back electromotive force to ensure consistent performance of the stepper motor across the entire speed range.

[0029] In practical implementation, its structural block diagram is as follows: Figure 2 As shown, the voltage and current of the stepper motor are collected, and then a disturbance observer is built to estimate the back electromotive force. The disturbance observer model is as follows:

[0030]

[0031] The estimated back electromotive force is:

[0032]

[0033] In equations (2) and (3), z = [z1 z2] T l is an intermediate variable. e For back electromotive force gain, The two opposite electromotive forces are estimated.

[0034] Transfer function of the back EMF observer:

[0035]

[0036] e a e β This is the actual back electromotive force (EMF). The estimated back EMF can be obtained from the transfer function of the back EMF observer:

[0037]

[0038] p is the number of teeth on the stepper motor rotor, w r It is the angular velocity of the motor rotor, ψ f θ is the motor flux linkage, and θ is the motor rotor electrical angle.

[0039] To eliminate the back electromotive force coefficient and ensure consistent performance of the stepper motor across its entire speed range, the formula is:

[0040]

[0041] The back electromotive force obtained after eliminating the coefficients from the estimated back electromotive force.

[0042] S4. Construct a novel phase-locked loop based on a rotating integrator. First, filter out the sixth harmonic component, then compensate for the position estimation error of the phase-locked loop (PLL), and finally obtain the rotor position and speed information of the stepper motor.

[0043] In practical implementation, the structural block diagram of the novel phase-locked loop based on the rotating integrator is as follows: Figure 3 and Figure 4 As shown, a rotating integrator cascaded with a proportional-integral controller, the transfer function of the rotating integrator in the discrete domain is:

[0044]

[0045] In the formula, T is the sampling period and w0 is the resonant frequency. When the resonant frequency w0 of the rotating integrator is equal to the angular frequency w of the input signal, the gain of the rotating integrator is infinite and the phase shift is 0, which can achieve zero steady-state error tracking of a specific sub-frequency.

[0046] The estimated back electromotive force (EMF) contains higher harmonics, with the 5th and 7th harmonics being the main components. The back EMF can be rewritten as:

[0047] e = e b +e h (8)

[0048]

[0049]

[0050] In the formula, e b e h These are the fundamental wave and the 6k±1st harmonic in the extended back electromotive force, E1 and E2, respectively. 6k±1 These represent the amplitudes of the fundamental wave and the 6k±1st harmonic, respectively. After obtaining the estimated back electromotive force, a phase-locked loop (PLL) is used to acquire position information. The position error ΔE in the PLL is:

[0051]

[0052] In equation (10), and These are the 1st and 6k±1st order observation angles. When the phase-locked loop converges, the 6k±1st harmonic error of the estimated back electromotive force becomes the 6kth harmonic error in ΔE, leading to a decrease in rotor position estimation accuracy. Therefore, a novel sensorless control strategy for a phase-locked loop stepper motor based on a rotating integrator is proposed to suppress the 6kth harmonic.

[0053] The rotor position estimated by the phase-locked loop (PLL) has a fixed error, and the rotor position compensation formula is:

[0054]

[0055] The rotor position is estimated by the phase-locked loop (PLL), and θ is the final estimated motor rotor angle.

[0056] The invention is further illustrated below with specific implementation results diagrams:

[0057] In the specific implementation of this invention, compared with conventional phase-locked loop (PLL) control strategies, a novel sensorless PLL control strategy for a stepper motor based on a rotating integrator is first built in MATLAB / SIMULINK and simulated for comparison with conventional control methods. The reference speed of the stepper motor is set to 200 rpm. Under the conventional PLL control strategy, the harmonic content of the stepper motor's back electromotive force is shown in the figure below. Figure 5 The harmonic content is 2.30%, which is relatively high. Figure 6 The diagram shows the back EMF harmonic content under the novel sensorless control strategy for a phase-locked loop stepper motor based on a rotating integrator. The harmonic content is 0.11%, which is a significant reduction, and the sixth harmonic content is suppressed. Figure 7 This is the rotor position estimation diagram under a conventional control strategy. Figure 8 This is a rotor position estimation diagram under a novel sensorless control strategy for a phase-locked loop stepper motor based on a rotating integrator. It can be seen that... Figure 7 The estimated rotor position has a significant positional error. Figure 8 The estimated rotor position is more accurate, with no significant position error. In summary, the above analysis demonstrates that using the novel sensorless control strategy for the stepper motor based on a rotating integrator proposed in this paper can reduce the back EMF harmonic content, suppress the sixth harmonic, and improve the accuracy of rotor position estimation.

[0058] Finally, the method described in this application is merely a preferred embodiment and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. The present invention provides a new type of phase-locked loop stepper motor sensorless control strategy based on a rotating integrator, characterized in that, Comprise: S1. Build a model of a stepping motor (HSM) driven by a double H-bridge inverter; S2. Use speed closed loop, current closed loop control, speed and current controller are proportional integral controller, modulation strategy for SVPWM; S3. Build a disturbance observer model, the two-phase back EMF as a disturbance, estimate the back EMF, and then eliminate the estimated back EMF coefficient to ensure the performance of the stepper motor in the full speed range; S4. Build a new phase-locked loop based on the rotating integrator, first filter out the six harmonic components, then compensate for the position estimation error of the phase-locked loop (PLL), and finally get the stepper motor rotor position information and speed information.

2. A novel phase locked loop stepper motor sensorless control strategy based on a rotating integrator as claimed in claim 1, wherein The model described in S1 consists of a 24V DC power supply, a double H-bridge inverter, and a stepper motor, which drives the stepper motor to work. In the stationary coordinate system, the mathematical model of the stepper motor is represented as: where u a and u β are the a, β-axis voltages, R, L s are the stator resistance and inductance of the stepper motor, i a , i β are the a, β-axis currents, k m is the motor torque coefficient, w is the rotor electrical angular velocity, and θ is the motor rotor electrical angle.

3. A novel phase locked loop stepper motor sensorless control strategy based on a rotating integrator as claimed in claim 1, wherein The control strategy described in S2 drives the stepper motor, obtains the rotor position information of the motor through the disturbance observer and the voltage and current of the motor, and obtains the reference voltage vector after the speed loop and the current loop. The speed loop and the current loop are proportional integral controllers, and the double H-bridge inverter switching signal is generated by SVPWM modulation to drive the stepper motor to work.

4. A novel phase locked loop stepper motor sensorless control strategy based on a rotating integrator as claimed in claim 1, wherein The disturbance observer model described in S3 is: The estimated back EMF is: where z = [z1 z2] T is an intermediate variable, l e is the back EMF gain, is the estimated two-phase back EMF. The transfer function of the back EMF observer is: e a 、e β is the actual back EMF. The back EMF estimate is derived from the back EMF observer transfer function: p is the number of steps of the motor rotor, w r is the angular velocity of the motor rotor, ψ f is the motor flux, θ is the motor rotor electrical angle. Eliminate the back EMF coefficient to ensure the performance of the stepper motor in the full speed range, the formula is: Back emf after cancellation factor for estimated back emf.

5. A novel phase locked loop stepper motor sensorless control strategy based on a rotating integrator as claimed in claim 1, wherein The rotating integrator described in S4 cascades a proportional integral controller, and the transfer function of the rotating integrator in the discrete domain is: Where T is the sampling period, and w0 is the resonant frequency. When the resonant frequency w0 of the rotating integrator is equal to the angular frequency w of the input signal, the gain of the rotating integrator is infinite, and the phase angle displacement is 0, which can realize the zero static error tracking of the specific frequency. The estimated back EMF contains high-order harmonics, among which the 5th and 7th harmonics are the main components. Rewrite the back EMF as: e = e b +e h (8) where e f , e h are the fundamental and 6k±1 harmonic of the extended back EMF, respectively, and E1and E 6k±1 are the amplitudes of the fundamental and 6k±1 harmonic, respectively. After obtaining the estimated back EMF, a phase locked loop is employed to obtain the position information, in which the position error AEis: In formula (10), and are 1st and 6k±1st order observation angles. When the phase-locked loop converges, the 6k±1st order harmonic error of the estimated back-EMF becomes the 6kth order harmonic error in ΔE, resulting in a decrease in the accuracy of the rotor position estimation. Therefore, a new phase-locked loop control strategy using a rotating integrator cascaded with a proportional integral controller is proposed. The rotor position estimated by the phase-locked loop (PLL) has a fixed error, and the rotor position compensation formula is: The rotor position estimated by the phase-locked loop (PLL) is θ, which is the final estimated motor rotor angle.

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