Senseless direct current motor control method and system based on sliding mode observer

Abstract

The invention provides a sensorless direct current motor rotating speed control method and system based on a sliding mode observer. The sliding mode control process comprises the steps that a sliding mode observer is established through a voltage mathematical model of the direct current motor, and a system sliding mode surface is designed according to the error between the estimated current and the actual current. And constructing a sliding mode control law based on the sign function, generating a high-frequency jitter signal, and carrying out filtering processing on the signal to obtain an estimated rotating speed of the motor. The estimated rotating speed serves as the feedback quantity of the double-closed-loop direct-current motor rotating speed control system, and non-sensing rotating speed control over the direct-current motor is achieved. Closed-loop control over the rotating speed of the direct-current motor can be completed under the working condition without a rotating speed sensor; the control performance of the direct current motor is effectively improved while the structure of the direct current motor is not changed.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensorless DC motor speed control based on sliding mode observer. Specifically, it relates to a method of establishing a sliding mode observer based on a mathematical model of a DC motor, estimating the motor speed by using the characteristics of sliding mode control, and using the estimated speed as the feedback of a dual closed-loop DC motor speed control system to achieve sensorless speed control of the DC motor. Background Art

[0002] DC motors are widely used in daily life, such as household appliances and power tools, and are also favored by industrial manufacturers due to their simple structure, large starting torque and good speed regulation performance. However, with the continuous progress of social production and science and technology, higher requirements are generally put forward for the control methods of DC motors. At the same time, the sensors used to obtain parameters such as motor speed, current and voltage also increase the cost of using the motor, affecting the economic benefits of enterprise production.

[0003] Sliding mode control is of great significance in sensorless DC motor control. It can effectively solve parameter uncertainty, environmental interference and achieve high-performance estimation. In sensorless motor control, it is necessary to estimate key state variables such as speed and position through sliding mode observers. Based on sliding mode control theory, sliding mode observers can achieve high-precision estimation through rapid convergence of measurement errors, while compensating for the problem of reduced accuracy caused by the lack of sensors and improving the performance of sensorless control systems. In terms of anti-interference ability, due to the high-frequency switching characteristics of sliding mode control, it has a natural suppression ability for interference, which can significantly reduce common interference in sensorless control, such as inaccurate estimation of back electromotive force and current measurement errors; even under complex working conditions, such as motor load fluctuations or changes in the external environment, the system can maintain stable operation.

[0004] An important goal of sensorless control is to reduce hardware costs. Sliding mode control reduces the use of sensors and uses cheap microprocessors to implement its control logic, which is suitable for low-cost, high-performance industrial or household motor control systems. Even without changing the structure of the DC motor, the closed-loop speed control performance of the DC motor can be improved without using a speed sensor, which is suitable for some resource-constrained scenarios. Summary of the invention

[0005] The present invention proposes a sensorless DC motor control method and system based on a sliding mode observer, which is characterized in that a sliding mode observer is established to estimate the motor speed, and the estimated speed is used as the feedback signal of a dual closed-loop DC motor speed control system; the method and system include the following steps: step one: establishing a sliding mode observer based on a voltage mathematical model of the DC motor; step two: establishing a system sliding mode surface according to the error between the actual current and the estimated current; step three: establishing a sliding mode control law, and obtaining a high-frequency jitter signal according to the sliding mode control law; step four: performing low-pass filtering on the high-frequency jitter signal to obtain a back electromotive force E; step five: calculating the motor speed n according to the linear relationship between the DC motor speed n and the back electromotive force E; step six: using the motor speed n as the actual feedback quantity of the dual closed-loop DC motor speed control system.

[0006] To achieve the above purpose, the technical solution provided by the present invention is:

[0007] A sensorless DC motor control method and system based on a sliding mode observer, characterized in that the voltage mathematical model expression of the DC motor in step 1 is:

[0008]

[0009] In the above formula, U is the input voltage of the motor, L is the armature inductance, i is the armature current; R is the armature resistance, and E is the back electromotive force; the sliding mode observer expression is established accordingly:

[0010]

[0011] in, is the estimated current, K is the sliding mode control law, is the calculated value of voltage.

[0012] Furthermore, the sensorless DC motor control method and system based on sliding mode observer is characterized in that the sliding mode surface e in step 2 is an estimated current The difference between the actual current i and the actual current i is expressed as:

[0013]

[0014] Furthermore, the sensorless DC motor control method and system based on sliding mode observer is characterized in that the sliding mode control law established in step three is:

[0015] K = η sgn (e)

[0016] In the above formula, η is a positive constant, and its constraints are: Where sgn(e) is the sign function of the sliding surface e, and its expression is:

[0017]

[0018] Through the sliding mode control law, the sliding surface e tends to 0, that is, the current estimation value Converges to the actual current i; according to the equivalent control principle of sliding mode control, a high-frequency jitter signal is obtained.

[0019] Furthermore, the sensorless DC motor control method and system based on sliding mode observer is characterized in that the high-frequency jitter signal is subjected to low-pass filtering in step 4, and the transfer function of the classic first-order low-pass filter is:

[0020]

[0021] In the above formula, s is the Laplace operator, τ is the filtering time constant; the signal after filtering is the back electromotive force E.

[0022] Furthermore, the sensorless DC motor control method and system based on sliding mode observer is characterized in that the linear relationship between the DC motor speed n and the back electromotive force E in step 5 is expressed as follows:

[0023]

[0024] In the above formula, K e is the back EMF constant, n is the actual motor speed; according to the filtered back EMF E, the motor speed is further obtained from the above formula.

[0025] Furthermore, the sensorless DC motor control method and system based on sliding mode observer is characterized in that in step 6, the motor speed n is used as the actual feedback quantity for the motor speed PI control; the classic PI controller is designed as follows:

[0026]

[0027] Among them, K p is the proportional coefficient, e(t) is the error at the current moment, that is, the difference between the target speed and the actual speed. K i is the integral coefficient, which determines the strength of the integral term; the speed error is calculated by comparing the current motor speed n with the set motor target speed; based on the error, the PI controller calculates the output of the proportion and the integral to obtain the final control quantity; further, based on the calculated control quantity, the input voltage or current of the motor is adjusted to accelerate or decelerate the motor, thereby reducing the error.

[0028] Furthermore, the sensorless DC motor control method and system based on sliding mode observer is characterized in that the dual closed-loop DC motor speed control system comprises the following steps:

[0029] Step 1: The actual speed n obtained by the sliding mode observer is used as the speed feedback signal and input into the speed PI controller.

[0030] Step 2: The speed PI controller is based on the given speed n * The error with the actual speed n is calculated by PI to output the corresponding given current i * .

[0031] Step 3: Measure the actual motor current i through the Hall element, filter and amplify the signal, and input the actual motor current i as the current feedback signal to the current PI controller.

[0032] Step 4: The current PI controller is based on the given current i * The error between the actual current i and the output PWM control signal U after PI operation c .

[0033] Step 5: Order in is the calculated voltage value, K PWM is the amplification factor of the PWM amplifier. Further, the PWM amplifier is connected to an H-bridge driving circuit, and the H-bridge driving circuit modulates the output voltage according to the duty cycle of the PWM signal to drive the DC motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a block diagram of a dual closed-loop DC motor speed control system of a sensorless DC motor control method and system based on a sliding mode observer.

[0035] Figure 2 The present invention is a flow chart of a method for calculating the motor speed n of a sensorless DC motor control method and system based on a sliding mode observer.

[0036] Figure 3 The present invention is a schematic diagram of actual current, estimated current and sliding mode control law K in a sensorless DC motor control method and system based on a sliding mode observer. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] like Figure 1 The present invention provides a sensorless DC motor control method and system based on a sliding mode observer.

[0039] Step 1: Establish a sliding mode observer based on the voltage mathematical model of the DC motor. The expression of the sliding mode observer is:

[0040]

[0041] in is the calculated voltage, L is the armature inductance; R is the armature resistance, and E is the back EMF; is the estimated current, and K is the sliding mode control law.

[0042] Step 2: Based on the estimated current The difference between the actual current i establishes the system sliding surface e, which is expressed as:

[0043]

[0044] Step 3: Establish the sliding mode control law, which is expressed as:

[0045] K = η sgn (e)

[0046] Where sgn(e) is the sign function of the sliding surface e, and its expression is:

[0047]

[0048] Step 4: Obtain the high-frequency jitter signal according to the sliding mode control law, and perform low-pass filtering on the high-frequency jitter signal. The transfer function of the classic first-order low-pass filter is:

[0049]

[0050] In the above formula, s is the Laplace operator, τ is the filtering time constant; the signal after filtering is the back electromotive force E.

[0051] Step 5: According to the linear relationship between the DC motor speed n and the back electromotive force E, the motor speed n is obtained. The linear relationship expression is:

[0052]

[0053] In the above formula, K e is the back EMF constant, n is the actual motor speed;

[0054] Step 6: Input the actual speed n as the speed feedback signal to the speed PI controller; the speed PI controller is based on the given speed n * The error with the actual speed n is calculated by PI to output the corresponding given current i * .

[0055] Step 7: Input the actual motor current i as the current feedback signal to the current PI controller. The current PI controller is based on the given current i * The error with the actual current i is output through PI operation to generate the corresponding duty cycle signal which enters the PWM controller.

[0056] Step 8: Connect the PWM controller to the H-bridge drive circuit, and the PWM controller generates a PWM signal; the H-bridge drive circuit outputs a voltage control signal U to drive the DC motor according to the PWM signal.

[0057] The embodiment of the present invention provides a sensorless DC motor control method and system based on a sliding mode observer.

[0058] Reference Figure 1 The sensorless DC motor control method and system based on sliding mode observer described in the system block diagram are suitable for DC brush motors; for working conditions without speed sensors, the use of sliding mode control can effectively improve the accuracy and robustness of the DC motor speed control system, especially in reducing costs and increasing economic benefits.

[0059] Embodiment 1, the present invention can be applied to sensorless DC motor control, by sampling the voltage and current of the DC motor, and combining the mathematical model of the DC motor to establish a sliding mode observer; at the same time, the system sliding surface is designed, and the motor speed is further estimated online by establishing the sliding mode control law, and the speed information is used as feedback to act on the dual closed-loop DC motor speed control system. Finally, the control signal adjusts the duty cycle of the PWM controller, driving the H-bridge circuit to output a corresponding voltage signal to drive the DC motor.

[0060] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A sensorless DC motor control method and system based on sliding mode observer, characterized in that Establish a sliding mode observer to estimate the motor speed, and use the estimated speed as the speed feedback signal of the dual closed-loop DC motor speed control system; the specific working process The method comprises the following steps: step 1: establishing a sliding mode observer based on a voltage mathematical model of a DC motor; step 2: establishing a system sliding mode surface according to an error between an actual current and an estimated current; step 3: establishing a sliding mode control law, and obtaining a high-frequency jitter signal according to the sliding mode control law; step 4: performing low-pass filtering on the high-frequency jitter signal to obtain a back electromotive force E; step 5: calculating a motor speed n according to a linear relationship between a DC motor speed n and the back electromotive force E; step 6: using the motor speed n as an actual feedback quantity for a dual closed-loop DC motor speed control system.

2. The sensorless DC motor control method and system based on sliding mode observer according to claim 1, characterized in that: In step 1, the voltage mathematical model expression of the DC motor is: In the above formula, U is the input voltage of the motor, L is the armature inductance, i is the armature current; R is the armature resistance, and E is the back electromotive force; the sliding mode observer expression is established accordingly: in, is the estimated current, K is the sliding mode control law, is the calculated value of voltage.

3. The sensorless DC motor control method and system based on sliding mode observer according to claim 1, characterized in that: In step 2, the sliding surface e is the estimated current The difference between the actual current i and the actual current i is expressed as:

4. The sensorless DC motor control method and system based on sliding mode observer according to claim 1, characterized in that: The sliding mode control law established in step 3 is: K = η sgn (e) In the above formula, η is a positive constant, and its constraints are: Where sgn(e) is the sign function of the sliding surface e, and its expression is: Through the sliding mode control law, the sliding surface e tends to 0, that is, the current estimation value Converge to the actual current i; obtain a high-frequency jitter signal according to the sliding mode control law.

5. The sensorless DC motor control method and system based on sliding mode observer according to claim 1, characterized in that: In step 4, the high-frequency jitter signal is subjected to low-pass filtering, and the transfer function of the classic first-order low-pass filter is: In the above formula, s is the Laplace operator, τ is the filtering time constant; the signal after filtering is the back electromotive force E.

6. The sensorless DC motor control method and system based on sliding mode observer according to claim 1, characterized in that: In step 5, the linear relationship between the DC motor speed n and the back electromotive force E is expressed as: In the above formula, K e is the back EMF constant, n is the actual motor speed; according to the filtered back EMF E, the motor speed is further obtained from the above formula.

7. The sensorless DC motor control method and system based on sliding mode observer according to claim 1, characterized in that: In step 6, the motor speed n is used as the actual feedback quantity for the motor speed PI control; the classic PI controller is designed as follows: Among them, K p is the proportional coefficient, e(t) is the error at the current moment, that is, the difference between the target speed and the actual speed. K i is the integral coefficient, which determines the strength of the integral term; the speed error is calculated by comparing the current motor speed n with the set motor target speed; based on the error, the PI controller calculates the output of the proportion and the integral to obtain the final control quantity; further, based on the calculated control quantity, the input voltage or current of the motor is adjusted to accelerate or decelerate the motor, thereby reducing the error.

8. A dual closed-loop DC motor speed control system according to any one of claims 1 to 6, based on a sensorless DC motor control method using a sliding mode observer, comprising the following steps: Step 1: The actual speed n obtained by the sliding mode observer is used as the speed feedback signal and input into the speed PI controller. Step 2: The speed PI controller is based on the given speed n * The error with the actual speed n is calculated by PI to output the corresponding given current i * . Step 3: Measure the actual motor current i through the Hall element, filter and amplify the signal, and input the actual motor current i as the current feedback signal to the current PI controller. Step 4: The current PI controller is based on the given current i * The error between the actual current i and the output PWM control signal U after PI operation c . Step 5: Order in is the calculated voltage value, K PWM is the amplification factor of the PWM amplifier. Further, the PWM amplifier is connected to an H-bridge driving circuit, and the H-bridge driving circuit modulates the output voltage according to the duty cycle of the PWM signal to drive the DC motor.

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