Method for giving direct torque of brushless direct current motor

Abstract

The invention discloses a brushless direct current motor direct torque setting method. The method comprises the following steps: step 1, constructing a basic brushless direct current motor direct torque setting system; 2, constructing a sliding mode variable speed controller, and replacing a speed controller in a basic brushless direct current motor direct torque given system with the sliding mode variable speed controller; step 3, optimizing a sliding mode surface in the sliding mode variable speed controller; 4, optimizing the reaching law in the sliding mode variable speed controller; and 5, giving the direct current torque of the brushless direct current motor by using the optimized brushless direct current motor direct torque giving system based on the sliding mode variable speed controller. According to the method, the torque ripple of the brushless direct current motor in direct torque control is effectively reduced, and the running smoothness of the motor is improved.

Description

Technical Field

[0001] The invention relates to the technical field of brushless DC motor control, and in particular to a method for direct torque setting of a brushless DC motor. Background Art

[0002] With the development of the motor industry, brushless DC motors have been widely used in aerospace, industrial automation, medical equipment, computer peripherals, etc. due to their small size, light weight, easy maintenance, high efficiency and energy saving, and easy control.

[0003] However, the torque pulsation problem of the brushless DC motor control system directly affects the control characteristics of the power transmission system and the reliability of the drive system, and brings about vibration, resonance, noise and other problems. Therefore, studying the control technology of the brushless DC motor control system, how to solve the more prominent problems such as torque pulsation of the brushless DC motor, how to maximize the accuracy and reliability of the brushless motor system on the basis of fully reducing its size and cost, so that it can be more widely used while giving full play to its own advantages, has important theoretical and practical significance for the development of social economy. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for directly setting the torque of a brushless DC motor to solve the technical problem of torque pulsation in the prior art.

[0005] The present invention provides a method for direct torque setting of a brushless DC motor, comprising the following steps:

[0006] Step 1: Build a basic brushless DC motor direct torque setting system;

[0007] Step 2: Construct a sliding mode variable speed controller and use the sliding mode variable speed controller to replace the speed controller in the basic brushless DC motor direct torque given system;

[0008] Step 3: Optimize the sliding surface in the sliding mode variable speed controller;

[0009] Step 4: Optimize the reaching law in the sliding mode variable speed controller;

[0010] Step 5: Use the optimized brushless DC motor direct torque setting system based on sliding mode variable speed controller to set the DC torque of the brushless DC motor.

[0011] Furthermore, in step 3, the sliding surface in the sliding mode variable speed controller is optimized by replacing the linear sliding surface in the sliding mode variable speed controller with a nonlinear integral sliding surface.

[0012] Furthermore, the optimization method in step 4 is:

[0013] The power reaching rate and the exponential reaching rate are combined to form a hybrid reaching law, and the hybrid reaching law is used to replace the reaching law in the sliding mode variable speed controller to optimize the reaching law in the sliding mode variable speed controller.

[0014] Furthermore, the nonlinear integral sliding surface optimized in step 3 is:

[0015]

[0016] In the formula, x1 is the speed error value; x2 is its corresponding integral; k is the coefficient, which is a positive constant.

[0017] Furthermore, in step 4, the mixed reaching law is:

[0018]

[0019] In the formula, s 2 |s| is the power term of the approach rate; βs is the exponential term of the approach rate; α is a positive constant; s is the distance between the moving point and the switching surface.

[0020] Beneficial effects of the present invention:

[0021] The present invention effectively reduces the torque pulsation of the brushless DC motor in direct torque control and improves the smoothness of the motor operation;

[0022] The given method of the present invention has a faster dynamic response speed and can quickly respond to load changes and speed adjustments, thereby improving the response performance of the system;

[0023] The present invention utilizes the hybrid reaching law to reduce the jitter and torque pulsation of the system, improve the control accuracy, and make the speed and torque control of the motor more precise; at the same time, it correspondingly reduces the energy loss and improves the efficiency of the motor, thereby achieving energy saving effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0025] Figure 1 is a flow chart of a specific embodiment of the present invention;

[0026] Figure 2 is a rotation speed waveform of a given method of the present invention in a specific embodiment of the present invention;

[0027] Figure 3 is an electromagnetic waveform of a given method of the present invention in a specific embodiment of the present invention;

[0028] Figure 4is the torque waveform of the given method of the present invention in a specific embodiment of the present invention;

[0029] Figure 5 is the speed waveform of the conventional PI-based given method in the specific embodiment of the present invention;

[0030] Figure 6 is the reference current of the given method of the present invention in a specific embodiment of the present invention;

[0031] Figure 7 It is the reference current of the given method based on PI in the specific embodiment of the present invention. DETAILED DESCRIPTION

[0032] 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 conjunction with the drawings in the embodiments of the present invention. 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 those skilled in the art without creative work are within the scope of protection of the present invention.

[0033] The present invention is further illustrated below in conjunction with specific embodiments. Those skilled in the art should understand that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention, and modifications to various equivalent forms of the present invention fall within the scope defined by the appended claims of this application.

[0034] The present invention provides a method for direct torque setting of a brushless DC motor, comprising the following steps:

[0035] Step 1: Build a basic brushless DC motor direct torque setting system;

[0036] Step 2: Construct a sliding mode variable speed controller and use the sliding mode variable speed controller to replace the speed controller in the basic brushless DC motor direct torque given system;

[0037] Step 3: Optimize the sliding surface in the sliding mode variable speed controller, specifically:

[0038] The sliding surface in the sliding mode variable speed controller is optimized by replacing the linear sliding surface in the sliding mode variable speed controller with a nonlinear integral sliding surface. The nonlinear integral sliding surface is:

[0039]

[0040] In the formula, x1 is the speed error value; x2 is its corresponding integral; k is the coefficient, which is a positive constant;

[0041] The coefficient k is a positive constant, and its value determines the speed at which the system approaches a stable state. The larger the k, the faster the corresponding speed, and the shorter the time required for speed regulation. However, a too large k value will cause the system to have integral saturation, which will increase the time required for the system to finally stabilize.

[0042] Step 4: Optimize the reaching law in the sliding mode variable speed controller, specifically:

[0043] The power reaching rate and the exponential reaching rate are combined to form a hybrid reaching law, and the hybrid reaching law is used to replace the reaching law in the sliding mode variable speed controller to optimize the reaching law in the sliding mode variable speed controller.

[0044] Among them, the mixed reaching law is:

[0045]

[0046] In the formula, s 2 |s| is the power term of the approach rate; βs is the exponential term of the approach rate; α is a positive constant; s is the distance from the moving point to the switching surface;

[0047] When the system moves far away from the sliding surface, the corresponding s is very large. The values ​​of the power part and the exponential part corresponding to the above formula are both large, so the approaching speed of the two parts superimposed is also relatively large. When the moving point almost reaches the switching surface, s approaches 0. The power term not only improves the chattering problem caused by the sudden change when the function of the medium-speed approaching part in the exponential approaching rate switches, making the dynamic response of the system more stable, but also ensures the approaching speed. The exponential approaching part maintains the rapidity of the original exponential approaching rate.

[0048] Step 5: Use the optimized brushless DC motor direct torque setting system based on sliding mode variable speed controller to set the DC torque of the brushless DC motor.

[0049] The stability and chattering analysis of the designed sliding mode control system is carried out. In order to determine the stability of the controlled system, the Lyapunov function is selected:

[0050]

[0051] Taking its derivative we get:

[0052]

[0053] Analysis shows that for any range of s, The system is stable if the Lyapunov stability condition is satisfied.

[0054] Discretizing the mixed approach rate used yields:

[0055]

[0056] When s(n)=0, due to the smoothing effect of the function and the saturation function within the range of δ, s(n+1) is still 0 in the next cycle. Therefore, without considering the influence of other factors, the ideal jitter amplitude under the mixed approach rate is zero.

[0057] The given method of the brushless DC motor direct torque given system is modeled and analyzed by MATLAB / SIMULINK. The analysis results are as follows: Figure 2-7 As shown, it can be seen from the smoothness of the flat top of the reference current waveform under various control modes that, based on the torque given mode of the present invention, the given reference current rectangular wave is smoother, and combined with the proportional relationship between the given and given reference currents, it is not difficult to find that the given torque obtained under the torque given mode of the present invention is the most stable, while the given torque pulsation under PI control is larger, and it can be seen from the speed torque response curve shown that, compared with the PI control mode, under the improved control mode of the present invention, the speed response curve is smoother, showing better static response performance.

[0058] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for direct torque setting of a brushless DC motor, characterized in that: The steps include: Step 1: Build a basic brushless DC motor direct torque setting system; Step 2: Construct a sliding mode variable speed controller and use the sliding mode variable speed controller to replace the speed controller in the basic brushless DC motor direct torque given system; Step 3: Optimize the sliding surface in the sliding mode variable speed controller; Step 4: Optimize the reaching law in the sliding mode variable speed controller; Step 5: Use the optimized brushless DC motor direct torque setting system based on sliding mode variable speed controller to set the DC torque of the brushless DC motor.

2. The method for direct torque setting of a brushless DC motor according to claim 1, characterized in that: In step 3, the sliding surface in the sliding mode variable speed controller is optimized by replacing the linear sliding surface in the sliding mode variable speed controller with a nonlinear integral sliding surface.

3. The method for direct torque setting of a brushless DC motor as claimed in claim 1, characterized in that: The optimization method in step 4 is: The power reaching rate and the exponential reaching rate are combined to form a hybrid reaching law, and the hybrid reaching law is used to replace the reaching law in the sliding mode variable speed controller to optimize the reaching law in the sliding mode variable speed controller.

4. The method for direct torque setting of a brushless DC motor as claimed in claim 2, characterized in that: The nonlinear integral sliding surface optimized in step 3 is: In the formula, x1 is the speed error value; x2 is its corresponding integral; k is the coefficient, which is a positive constant.

5. The method for direct torque setting of a brushless DC motor as claimed in claim 3, characterized in that: In step 4, the mixed reaching law is: In the formula, s 2 |s| is the power term of the approach rate; βs is the exponential term of the approach rate; α is a positive constant; s is the distance between the moving point and the switching surface.

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