Brushless direct current motor control method based on improved PID

Abstract

The invention discloses a brushless direct current motor control method based on improved PID, and relates to the field of motor control. The method comprises the following steps: establishing an SPID controller which introduces an error square term; determining a symbol of an error square item gain coefficient in the SPID controller according to an error between the actual rotating speed and the target rotating speed of the brushless direct current motor; judging whether a differential item of the SPID controller is started or not according to whether the actual rotating speed reaches the target rotating speed or not; the error between the actual rotating speed and the target rotating speed serves as the input quantity of an SPID controller, and the current control quantity is output; controlling the rotating speed of the direct current brushless motor according to the current control quantity until the error meets the precision requirement; a brushless direct current motor system can reach a target value faster and more stably, system overshoot is reduced, and the anti-interference capability of the system is improved.

Description

Technical Field

[0001] The present application relates to the technical field of motor control, and in particular to a brushless DC motor control method based on improved PID. Background Art

[0002] Brushless direct current (BLDC) motors have been successfully applied to robotics, textiles, electric vehicles and other fields due to their simple structure, high efficiency, low maintenance cost and fast dynamic response. High-performance BLDC control systems have also become a hot topic for many scholars. In BLDC control systems, proportional-integral-differential (PID) controllers are often used for speed regulation. PID controllers calculate the output signal through a combination of proportional gain, integral gain and differential gain to achieve precise control of the controlled object. PID controllers have the advantages of simple structure, easy implementation and good robustness, but there are some problems in technical applications. For example, PID control is highly dependent on the selection of gain parameters, which may lead to a decrease in the performance of brushless DC motors. Summary of the invention

[0003] In order to solve the problems mentioned in the background technology, the present application provides a brushless DC motor control method based on improved PID, so that the brushless DC motor system can reach the target value faster and more stably and reduce system overshoot, thereby improving the system's anti-interference ability.

[0004] To achieve the above objectives, this application provides the following solutions.

[0005] The present application provides a brushless DC motor control method based on improved PID, comprising:

[0006] S1: Establish a SPID controller that introduces the squared error term; the expression of the established SPID controller is Where e(t) is the error between the actual speed and the target speed of the brushless DC motor; e 2 (t) is the square error term; K S is the error square gain coefficient; t represents time; K P is the proportional gain; K I is the integral gain; K D is the differential gain; u(t) is the current control quantity output by the SPID controller;

[0007] S2: Determine the sign of the error square gain coefficient in the SPID controller according to the error between the actual speed and the target speed of the brushless DC motor;

[0008] S3: Determine whether to enable the differential item of the SPID controller based on whether the actual speed has reached the target speed;

[0009] S4: Take the error between the actual speed and the target speed as the input of the SPID controller and output the current control amount;

[0010] S5: Control the speed of the brushless DC motor according to the current control value until the error meets the accuracy requirement.

[0011] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0012] The present application provides a brushless DC motor control method based on improved PID, which introduces the square error term into the traditional PID controller, and adopts the differential term threshold to construct a SPID controller; the sign of the square error term gain coefficient is judged according to the positive or negative difference e(t) between the actual speed of the motor and the target speed, and whether to enable the differential term is judged according to whether the current speed has reached the target speed value; the current error e(t) is used as the input of the SPID controller, the current control quantity u(t) is output, and the above steps are repeated until e(t) meets the accuracy requirements, thereby realizing the speed control of the DC brushless motor. The SPID controller provided by the present invention significantly improves the response speed of the motor system, and can avoid excessive overshoot, enhance the anti-interference ability of the system, and shorten the stabilization time. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 It is a flow chart of a brushless DC motor control method based on improved PID;

[0015] Figure 2 It is the structural block diagram of SPID controller;

[0016] Figure 3 It is the working process diagram of SPID controller;

[0017] Figure 4 This is the block diagram of the BLDCM speed regulation system used to verify the control effect of the SPID controller;

[0018] Figure 5 This is a comparison chart of the effects of brushless DC motor under SPID control and traditional PID control. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be described clearly and completely below, so that those skilled in the art can better understand the technical details of the present application and its advantages and features, and thus make a clearer definition of the protection scope of the present application. The embodiments described in this application are only part of the embodiments of the present application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] In some embodiments, the present application provides a brushless DC motor control method based on improved PID, comprising: Figure 1 The steps S1 to S5 shown are described in detail as follows.

[0021] S1: Establish a SPID controller that introduces the squared error term.

[0022] The present application establishes an improved PID controller by introducing a squared error term into a traditional PID controller and adopting a differential term threshold. The improved PID controller is called a SPID controller. The structure of the SPID controller is as follows: Figure 2 As shown, it includes the error square term, the proportional part, the integral part and the differential part. Specifically, the expression of the SPID controller is:

[0023]

[0024] Where e(t) is the error between the actual speed y(t) of the brushless DC motor and the target speed r(t); 2 (t) is the square error term, K S is the error square gain coefficient. K P is the proportional gain; K I is the integral gain; K D is the differential gain; the proportional gain K P To enhance the system's sensitivity to errors, the integral gain K I Eliminate the steady-state error of the system, the differential gain K D Suppress the oscillation of the system. t represents time; u(t) is the current control quantity output by the SPID controller. The controlled object in this application is a brushless DC motor. Of course, in practical applications, the invention of this application can also be used for other forms of motors.

[0025] S2: Determine the sign of the square error gain coefficient in the SPID controller according to the error between the actual speed and the target speed of the brushless DC motor.

[0026] K SThe sign of the error square term determines whether it increases or decreases the system input, and K S The choice of sign will be determined based on the error e(t). The expression of e(t) is:

[0027] e(t)=r(t)-y(t) (2)

[0028] In the formula, r(t) is the target value, that is, the target speed of the brushless DC motor; y(t) is the actual output value, that is, the actual speed of the brushless DC motor. Then K S The symbolic expression is:

[0029] sgn(K S )=sgn(e(t)) (3)

[0030] K S The expression for evaluating is:

[0031]

[0032] In the formula, K S ′∈[0,1], that is, K S ′ is a set value in the range of 0 to 1.

[0033] From formula (3), we can see that if e(t)>0, K S Take a positive value; otherwise, if e(t)<0, K S Takes negative value.

[0034] S3: Determine whether to enable the differential item of the SPID controller based on whether the actual speed has reached the target speed.

[0035] Considering that if the differential term starts braking in advance when the system starts from rest, the system response speed will be slowed down. Therefore, in order to speed up the system response, this application adopts the differential term threshold start based on the establishment of SPID controller, that is, when the system output does not reach the target value or the target value changes, K D =0, after the system reaches the target value, K D is the set value.

[0036] Specifically, after the brushless DC motor is started, if the actual speed does not reach the target speed, the differential term of the SPID controller is disabled and K D =0, then the expression of the SPID controller is On the contrary, if the actual speed reaches the target speed, the differential item is enabled, K D is the set value, then the expression of the SPID controller is

[0037] S4: Use the error between the actual speed and the target speed as the input of the SPID controller and output the current control quantity.

[0038] Set the target speed value for the brushless DC motor, collect the actual speed data output by the brushless DC motor in real time through the Hall sensor, and input it into the brushless DC motor controller. Calculate the current error e(t) between the actual speed and the target speed as the input of the SPID controller, and calculate the system input required for the target value, that is, the current control quantity u(t). The SPID control will calculate the input u(t) to the system once in each cycle.

[0039] S5: Control the speed of the brushless DC motor according to the current control value until the error meets the accuracy requirement.

[0040] The PWM signal corresponding to the current control quantity u(t) is amplified by the three-phase inverter and input to the brushless DC motor for driving. The actual speed of the brushless DC motor is collected by the Hall sensor, and steps S2 to S5 are repeated until the error e(t) meets the accuracy requirements.

[0041] The present application provides a brushless DC motor control method based on improved PID, which increases the system's sensitivity to error by introducing the squared error term; uses a differential term threshold to enable the differential term only after the system reaches the target value for the first time; inputs the error into the SPID controller, and inputs the output value into the DC brushless motor to achieve motor speed control. The present application enables the system to reach the target value faster and more stably without generating excessive overshoot, and at the same time further improves the system's sensitivity to error and improves the system's anti-interference ability.

[0042] like Figure 3 As shown, for a specific brushless DC motor system and a specific target value r(t), the working process of the SPID controller of the present application is as follows:

[0043] i. Initialize SPID controller parameters. Set K S , K P , K I , K D and r(t) and input them into the brushless DC motor control system.

[0044] The brushless DC motor control system used in this embodiment is composed of a brushless DC motor, a motor driver board, a Hall sensor, a power supply, a motor controller, a hysteresis brake and a hysteresis controller. All control and regulation of the system are completed by the motor controller. The controller directly outputs a PWM signal, and the PWM signal is amplified by the motor driver board to drive the DC brushless motor. The Hall sensor is used to collect the actual motor speed y(t). The DC brushless motor and the hysteresis brake are connected through a coupling. The load size of the hysteresis brake is set by the hysteresis controller. The SPID controller is equivalent to a part of the motor controller. The motor controller completes the actual speed acquisition, PWM signal output and other tasks. The SPID controller calculates the u(t) required for the system input, and u(t) refers to the PWM signal.

[0045] Where K S The initial value of is calculated according to formula (4), K P , K I , K D The initial value of is mainly set according to the needs of the controlled system. When the motor speed needs to change, the target value will be updated. For example, when the speed changes from 500r / min to 1000r / min, the target value will be updated.

[0046] ii. The actual speed y(t) output by the brushless DC motor is collected through the Hall sensor and transmitted to the motor controller. The motor speed error e(t) = r(t)-y(t) is calculated based on the set target value r(t).

[0047] iii. The SPID controller determines K according to formula (3) S Symbol. If e(t)>0, K S Take a positive value; otherwise, e(t)<0, K S Takes negative value.

[0048] iv. If the system output has not reached the target value or the target value is updated, K D = 0, disable the derivative term. At this time, the SPID controller expression is: On the contrary, if the system output reaches the target value, K D is the set value, and the differential term is enabled. The expression is: Calculate the controller output u(t). Return to step ii until the system output y(t) stabilizes within the target range.

[0049] Figure 4The block diagram of the BLDCM speed control system for verifying the performance of the SPID controller of this application is shown in the figure. The speed control system first sets the target value r(t), and then subtracts it from the actual speed y(t) collected by the Hall sensor. The error e(t) obtained is used for calculation by the SPID controller. The input u(t) required by the calculation system is calculated. This u(t) refers to the PWM signal. The PWM signal needs to be amplified by the three-phase inverter before it can be input to the motor for driving. The way to verify SPID is mainly to judge by the actual speed of the motor. If the actual motor speed can reach the target value in a short time and without generating a large overshoot, it means that the SPID controller is effective. The specific verification process is provided below.

[0050] 1) Set the controller parameters. Set the target value r(t) = 1800rpm and the load to 0.2N·m. In order to compare the advantages and disadvantages of the SPID controller and the traditional PID controller, four different control schemes are used. The PID1 controller parameters are: K P =0.30703, K I =0.05602, K D =0.48138; PID2 controller parameters are: K P =1.55703, K I =0.05602, K D =0.48138; PID3 controller parameters are: K P =0.30703, K I =0.15213, K D =0.48138; SPID controller parameters are: K P =0.30703, K I =0.15213, K D =0.48138, K S ′=0.70000,

[0051] 2) The real-time speed y(t) of the brushless DC motor is collected through the Hall sensor and transmitted to the SPID controller. The motor speed error e(t) = r(t)-y(t) is calculated according to the set target value r(t).

[0052] 3) For SPID controller: When e(t)>0, K S Take a positive value; otherwise, when e(t)<0, K S Takes negative value.

[0053] 4) For SPID controller, if the system output has not reached the target value, K D =0, the expression is: On the contrary, if the system output reaches the target value for the first time, K D is the set value, the expression is: Calculate the system input u(t) required to obtain the target value. Return to step 2) until the system stabilizes to the target range.

[0054] Figure 5 This is a comparison chart of the effects of brushless DC motor under traditional PID control and SPID control, and the speed target value is 1800rpm. Figure 5 As shown in the figure, there is almost no overshoot in the PID1 controller system, but the speed rises too slowly and the stabilization time is long; in order to solve the problem of PID1 speed rising too slowly, the proportional gain is increased in the PID2 controller. Although the response is extremely fast and the initial rise time is shortened, the speed not only rises slowly but also oscillates in the later stage, and the stabilization time is also longer; in view of this, the integral gain is increased in the PID3 controller. Although the response is fast and the rise time is significantly shortened, the system has large overshoot and oscillation, so the stabilization time is also longer. In contrast, after adopting the SPID controller, the square error term is introduced, and the differential term threshold is used. Under the same parameter conditions as PID3, it can not only greatly improve the system response speed and greatly shorten the stabilization time, but also significantly reduce the system overshoot, and the advantages are very obvious.

[0055] This application introduces an error square term on the basis of PID control, which increases the system's sensitivity to error and shortens the system's response time; secondly, the introduction of the error square term can effectively suppress large errors and enhance the system's anti-interference ability; finally, the differential term threshold is adopted, and the differential term is not enabled when the system has not reached the target value or the target value is updated, and the differential term is enabled only when the system reaches the target value for the first time, thereby further improving the system's response speed and stability.

[0056] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A brushless DC motor control method based on improved PID, characterized in that: include: S1: Establish a SPID controller that introduces the squared error term; S2: Determine the sign of the error square gain coefficient in the SPID controller according to the error between the actual speed and the target speed of the brushless DC motor; S3: Determine whether to enable the differential item of the SPID controller based on whether the actual speed has reached the target speed; S4: Take the error between the actual speed and the target speed as the input of the SPID controller and output the current control amount; S5: Control the speed of the brushless DC motor according to the current control value until the error meets the accuracy requirement.

2. The brushless DC motor control method based on improved PID according to claim 1, characterized in that: The SPID controller introduced with the square error term is established, specifically comprising: The expression of the established SPID controller is: Where e(t) is the error between the actual speed and the target speed of the brushless DC motor; e 2 (t) is the square error term; K S is the error square gain coefficient; t represents time; K P is the proportional gain; K I is the integral gain; K D is the differential gain; u(t) is the current control quantity output by the SPID controller.

3. The brushless DC motor control method based on improved PID according to claim 2, characterized in that: The step of determining the sign of the error square term gain coefficient in the SPID controller according to the error between the actual speed of the brushless DC motor and the target speed specifically includes: The error e(t) between the actual speed y(t) of the brushless DC motor and the target speed r(t) is calculated using the formula e(t)=r(t)-y(t); According to the formula sgn(K S )=sgn(e(t))Determine the error square gain coefficient K S symbol.

4. The brushless DC motor control method based on improved PID according to claim 3 is characterized in that: The step of determining whether to enable the differential item of the SPID controller according to whether the actual speed has reached the target speed specifically includes: After the brushless DC motor is started, if the actual speed does not reach the target speed, disable the differential term of the SPID controller and set K D =0, then the expression of the SPID controller is On the contrary, if the actual speed reaches the target speed, the differential term is enabled, K D is the set value, then the expression of the SPID controller is 5. The brushless DC motor control method based on improved PID according to claim 4, characterized in that: The error between the actual speed and the target speed is used as the input of the SPID controller to output the current control amount, specifically including: The error e(t) between the actual speed and the target speed is used as the input of the SPID controller, and the current control quantity u(t) is output; the square error gain coefficient K S The value of K S ′∈[0,1].

6. The brushless DC motor control method based on improved PID according to claim 5, characterized in that: The speed control of the brushless DC motor is performed according to the current control amount until the error meets the accuracy requirement, specifically including: The PWM signal corresponding to the current control quantity u(t) is amplified by the three-phase inverter and then input to the brushless DC motor for driving; The actual speed of the brushless DC motor is collected through the Hall sensor, and steps S2 to S5 are repeatedly executed until the error e(t) meets the accuracy requirement.

Images