Control method for improving precision of position sensor of permanent magnet synchronous motor

Abstract

The invention relates to the field of motor control, in particular to a control method for improving the precision of a position sensor of a permanent magnet synchronous motor, which comprises the following steps of: establishing an actual physical system for motor operation and an estimator which operates in a microcontroller; when the motor runs, inductive control is started, a deflection angle estimated by an estimator of the motor and a position deflection angle obtained by an actual physical sensor are obtained, and the difference value of the deflection angle and the position deflection angle is calculated; and when the difference value is smaller than the error between the used sensor and the observation model, inputting the difference value into the estimation compensator PI to correct the final output angle. According to the control method, the output position precision of the low-cost physical position sensor is improved, the cost of the whole system is also remarkably reduced, and the error of the physical position sensor is compensated by using the estimator, so that the dependence on the mounting position precision of the sensor is reduced.

Description

Technical Field

[0001] The present invention relates to the field of motor control, and in particular to a control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor. Background Art

[0002] In the control design of the motor, position sensors such as magnetic encoders, rotary encoders, and Hall sensors are usually used to detect the deflection angle of the motor. These sensors have advantages in accurately measuring position and angle. However, their cost is relatively high, and in some application environments, stability may be affected. For example, magnetic encoders may be interfered in a strong magnetic field environment, and rotary encoders may have wear problems when rotating at high speeds. Although the Hall sensor is low in cost, its performance may degrade in a high temperature environment. The sensorless control method achieves control by estimating the state of the motor, avoiding dependence on position sensors. The main advantage of this method is that it is low cost and does not require expensive sensors. However, the control accuracy of the sensorless control method is usually poor, especially at low speed or startup stage, it is difficult to achieve accurate positioning, and the load capacity of this method is also limited. In the case of large load changes, the control effect may not be as good as the method using position sensors. Summary of the invention

[0003] The present invention aims at the deficiencies in the prior art and provides the following technical solutions:

[0004] A control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor comprises the following steps:

[0005] S10: Establishing the actual physical system of the motor operation and the estimator, which runs in the microcontroller;

[0006] S20: When the motor is running, it enters sensory control, obtains the deflection angle estimated by the motor estimator and the position deflection angle obtained by the actual physical sensor, and calculates the difference between the two;

[0007] S30: When the difference is smaller than the error between the sensor and the estimator, the difference is input into a PI controller of the estimator to correct the final output angle.

[0008] As an improvement of the above technical solution, the actual physical system includes a motor and a physical position sensor connected to the motor, and the estimator includes a motor model, a motor speed loop model, a sensorless position sensor model and a PI controller.

[0009] As an improvement of the above technical solution, the position sensorless model is equivalent to a first-order low-pass filter.

[0010] As an improvement of the above technical solution, the acquisition of the motor speed loop model depends on the following formula:

[0011]

[0012] Among them, T e is the electromagnetic torque, T L is the load torque, w is the mechanical speed of the motor, B is the friction coefficient, and J is the moment of inertia of the motor.

[0013] As an improvement of the above technical solution, the acquisition of the estimated compensator PI depends on the following formula:

[0014] T d_total =T curr +T c +T senor

[0015]

[0016] Among them, T d_total is the total delay time, T curr is the current loop delay time, T c Calculate the delay time, T senor is the delay time of the physical position sensor, k p is the proportional coefficient of the PI controller, and ki is the integral gain coefficient of the PI controller

[0017] As an improvement of the above technical solution, the parameter design of the estimation compensator PI relies on a symmetric optimal method.

[0018] As an improvement of the above technical solution, when step S20 is executed, the difference between the deflection angle in the motor startup phase and the deflection angle in the physical position does not participate in correcting the final output angle, and the time interval of the motor startup phase is a preset parameter.

[0019] Beneficial effects of the present invention:

[0020] The control method of the present invention not only improves the position accuracy of the output of the low-cost physical position sensor, but also significantly reduces the cost of the overall system. By using an estimator to compensate for the error of the physical position sensor, the dependence on the accuracy of the sensor installation position is reduced. The estimator can calculate the accurate position estimate in real time based on the operating parameters and historical data of the motor, and compare and correct it with the output of the physical sensor. This process can effectively eliminate the error caused by the sensor position offset and improve the robustness of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The schematic diagram of the mutual correction control between the actual physical system and the estimator;

[0022] Figure 2 is a flow chart of the control method of the present invention;

[0023] Figure 3 It is a comparison diagram of the simulation framework of the present invention;

[0024] Figure 4 It is a comparison diagram of the simulation experiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] In the control design of the motor, position sensors such as magnetic encoders, rotary encoders, and Hall sensors are usually used to detect the deflection angle of the motor. However, in actual application environments, various sensors used in existing technologies may have the following problems:

[0027] Magnetic encoders may interfere in strong magnetic fields, while rotary encoders may wear out at high speeds. Although Hall sensors are low-cost, their performance may degrade in high-temperature environments. The sensorless control method estimates the state of the motor to achieve control, avoiding the reliance on position sensors. The main advantage of this method is that it is low-cost and does not require expensive sensors.

[0028] In addition to the above-mentioned sensor detection, a sensorless control method can also be used. Although the sensorless control method can realize the control function, the control accuracy of this scheme is usually poor, especially in the low speed or startup stage, it is difficult to achieve accurate positioning, and the load capacity of this method is also limited. In the case of large load changes, the control effect may not be as good as the method using a position sensor.

[0029] To solve the above problems, see Figure 1 , where the dotted box at the top of the figure is the actual running physical system, which is composed of a motor and a physical position sensor, and the dotted box at the bottom of the figure is the estimator, which contains a digital simulation module of the actual physical system, that is, Figure 1 Motor model G in p_est (s) and sensor model G s_est (s), this digital simulation module will run in the microcontroller, the purpose is to make the output of the estimator close to or even equal to the output of the actual physical system. To achieve this goal, the motor model G in the estimator p_est (s) and sensor model G s_est(s) must be close to the real physical system. When the output of the estimator is equal to the output of the actual physical system, the estimation error E0(s) is zero. However, in reality, due to modeling errors, noise and disturbances, there must be an estimation error E0(s). Therefore, a PI controller of a digital system estimator is needed to construct a closed-loop control loop to control the estimation error E0(s) to zero.

[0030] Based on the above theory, please refer to Figures 1 to 4 , this embodiment provides a control method for improving the accuracy of a permanent magnet synchronous motor position sensor, comprising the following steps:

[0031] S10: Establish the actual physical system of the motor operation and the estimator of the digital system, which runs in the microcontroller.

[0032] When constructing the physical system and the estimator, the specific construction framework is: the actual physical system includes a motor and a physical position sensor connected to the motor, and the estimator includes a motor model, a motor speed loop model, a sensorless position sensor model and a PI controller.

[0033] The acquisition of the motor speed loop model depends on the following formula:

[0034]

[0035]

[0036] Among them, T e is the electromagnetic torque, T L is the load torque, w is the mechanical speed of the motor, B is the friction coefficient, and J is the moment of inertia of the motor.

[0037] From the above formula, we can know that the electromagnetic torque T e Overcoming load torque T L Then input it into the motor model After that, the motor mechanical speed w can be obtained. For the convenience of modeling, the friction coefficient B is used as the load torque, and the motor model can be simplified as follows:

[0038] The acquisition of the estimated compensator PI depends on the following formula:

[0039] T d_total =T curr +T c +T senor

[0040]

[0041] Among them, T d_total is the total delay time, Tcurr is the current loop delay time, T c Calculate the delay time, T senor is the delay time of the physical position sensor, k p is the proportional coefficient of the PI controller, and ki is the integral gain coefficient of the PI controller.

[0042] S20: When the motor is running, it enters sensory control, obtains the deflection angle estimated by the motor estimator and the position deflection angle obtained by the actual physical sensor, and calculates the difference between the two.

[0043] When the motor is just starting up, the speed is low, the current is small and the fluctuation is large. If this data is used for estimation, the final result will be quite different from the ideal situation. Therefore, when step S20 is executed, the difference between the deflection angle in the motor starting phase and the deflection angle in the physical position is not used to correct the final output angle, and the time interval in the motor starting phase is a parameter pre-entered during the design.

[0044] As the speed continues to increase, the current fluctuation becomes smaller and smaller, and the overall operating state of the motor tends to be stable. The estimation result at this time is more accurate. The difference between the output angle of the physical position sensor and the output angle of the estimator is continuously detected. When the angle difference between the two is less than a certain set value, it can be considered that both the physical system and the digital system are in a stable operating state. At this time, the difference between the two can be sent to the PI controller of the estimator as a correction item to complete the mutual correction of the two systems and improve the output accuracy of the physical position sensor.

[0045] S30: When the difference is smaller than the error between the sensor and the estimator, the difference is input into a PI controller of the estimator to correct the final output angle.

[0046] In this embodiment, the error between the sensor and the observation model is about 0.1°. Therefore, when performing detection, if it is determined that the error is less than 0.1°, the difference is input into the PI controller of the estimator for correction.

[0047] When designing the parameters of the PI controller of the estimator, the symmetric optimal method can be used. In order to verify the specific effect of this embodiment, the following test method is provided:

[0048] When designing, you can use the motor's rotational inertia parameters. For example, if J is set to 0.00016, then T curr =0.0008, T c =0.0010, T senor =0.0016, using a first-order low-pass filter To approximate T d_tatal delayed effect.

[0049] Based on the above parameters, when using the symmetric optimal method for parameter design, the parameters can be set as follows:

[0050] T d_total =0.0034(s)

[0051]

[0052] PM=2tan -1 α-90°

[0053] PM is the phase margin of the control system. When the phase margin is greater than 0, the system is stable. The larger the value, the higher the system stability. When α is 3, PM=53.1>0, which meets the stability condition. Lc is the speed loop bandwidth.

[0054] like Figure 3 As shown, mark 201 represents the simulation block diagram of an ideal physical position sensor, mark 202 represents the simulation block diagram of an actual physical position sensor, and mark 203 represents the mutual correction simulation block diagram of the actual physical position sensor and the estimator of the digital system, wherein mark 2031 represents the actual physical position sensor system, and mark 2032 is the estimator system of the digital system.

[0055] Ideally, the physical position sensor has no phase lag, that is, its model output at mark 201 is 1. In reality, a cheaper sensor may be used to save costs, and cheaper sensors often have lower bandwidths, which may cause the final system phase delay to increase. If the bandwidth of the physical position sensor is 628 (rad / s).

[0056] Since the actual physical position sensor has a hysteresis in the output of the signal, and the first-order low-pass filter also has a similar input signal hysteresis, in this case the two can be approximated, so this sensor is equivalent to a first-order low-pass filter ( ), we can know that the delay time is:

[0057] The non-sensing position sensor in the estimator system in mark 203 should be quite close to the physical system sensor system, and can also be equivalent to a first-order low-pass filter.

[0058] Therefore, after correction by the solution of this embodiment, the parameters of the estimated compensator PI are modified as follows:

[0059]

[0060] PM=2tan -1 α-90°

[0061] PM is the phase margin of the control system. When the phase margin is greater than 0, the system is stable. The larger the value, the higher the system stability. When α is 2, PM=36.86>0, which meets the stability condition. senor is the delay time of the physical position sensor, ω Lc is the bandwidth of the correction loop.

[0062] After the simulation experiment, the results are as follows Figure 4 As shown in the figure, it can be seen that the mutual correction model simulation results are closer to the output results of the ideal physical position sensor. Therefore, the scheme recorded in this embodiment has a smaller error, is more consistent with the detection accuracy under the ideal state, and provides a more precise control effect.

[0063] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them.

Claims

1. A control method for improving the accuracy of a permanent magnet synchronous motor position sensor, characterized in that: The steps include: S10: Establishing the actual physical system of the motor operation and the estimator, which runs in the microcontroller; S20: When the motor is running, it enters sensory control, obtains the deflection angle estimated by the motor estimator and the position deflection angle obtained by the actual physical sensor, and calculates the difference between the two; S30: When the difference is smaller than the error between the sensor and the estimator, the difference is input into a PI controller of the estimator to correct the final output angle.

2. A control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor according to claim 1, characterized in that: The actual physical system includes a motor and a physical position sensor connected to the motor, and the estimator includes a motor model, a motor speed loop model, a sensorless position sensor model and a PI controller.

3. A control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor according to claim 2, characterized in that: The position sensorless model is equivalent to a first-order low-pass filter.

4. A control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor according to claim 2, characterized in that: The motor speed loop model is obtained based on the following formula: Among them, T e is the electromagnetic torque, T L is the load torque, w is the mechanical speed of the motor, B is the friction coefficient, and J is the moment of inertia of the motor.

5. A control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor according to claim 2, characterized in that: The acquisition of the estimated compensator PI depends on the following formula: T d_total =T curr +T c +T senor Among them, T d_total is the total delay time, T curr is the current loop delay time, T c Calculate the delay time, T senor is the delay time of the physical position sensor, k p is the proportional coefficient of the PI controller, and ki is the integral gain coefficient of the PI controller.

6. A control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor according to claim 5, characterized in that: The parameter design of the estimation compensator PI relies on a symmetric optimization method.

7. A control method for improving the accuracy of a position sensor of a permanent magnet synchronous motor according to claim 1, characterized in that: When step S20 is executed, the difference between the deflection angle in the motor startup phase and the deflection angle in the physical position does not participate in correcting the final output angle, and the time interval in the motor startup phase is a preset parameter.

Images