A method for adaptively adjusting the speed of a brushless motor

Abstract

The present invention relates to the field of motor control technology, and in particular to a method for adaptively adjusting the speed of a brushless motor. The method collects the real-time speed of the motor in real time during the operation of the brushless motor and forms a sequence, and determines the adjustment amount required to increase the speed by analyzing the speed difference between the current speed and the speed to be adjusted at each moment. Further combined with the load mass of the motor, the load inertia of the motor at the current moment is determined and the motor duty cycle is determined. Power is distributed to the motor windings according to the relationship between the duty cycle and the current. After the power distribution is completed, the abnormal degree of the real-time speed of the motor is further analyzed and it is determined whether to re-distribute power. The present invention combines the load of the motor during operation, and through closed-loop control, increases the real-time response efficiency of the brushless motor and ensures the efficiency of improving the motor speed.

Description

Technical Field

[0001] The invention relates to the technical field of motor control, and in particular to a method for adaptively adjusting the rotation speed of a brushless motor. Background Art

[0002] Brushless motor is a type of motor widely used in modern automation control systems. Its rotor uses permanent magnets, the stator uses windings, and the motor's commutation is controlled by an electronic control system. Brushless motors usually use an electronic control system composed of Hall sensors to adjust the power-on state of the stator windings to produce continuous torque output. When the brushless motor performs speed increase, it will gradually increase the current according to the preset acceleration curve to increase the speed. However, during the actual operation of the motor, it is loaded. If the power supply to the motor windings is distributed without considering the load quality, the motor will stall or the direction will be confused. Summary of the invention

[0003] In order to solve the technical problem in the prior art that when the speed of a brushless motor is increased, the power supply to the motor winding is distributed without considering the load quality, resulting in motor stall or direction confusion, the purpose of the present invention is to provide a method for adaptively adjusting the speed of a brushless motor, and the technical solution adopted is as follows:

[0004] The present invention proposes a method for adaptively adjusting the speed of a brushless motor, the method comprising:

[0005] Get the real-time speed sequence and load quality of the motor during the operation of the brushless motor;

[0006] Obtaining the speed difference between the speed at each moment in the real-time speed sequence of the motor and the speed to be adjusted; obtaining the load inertia at the corresponding moment according to the speed difference and the load mass;

[0007] Determine the duty cycle of the motor according to the load inertia; distribute power to the motor windings according to the standard current value and the duty cycle;

[0008] After the motor winding power distribution is completed, it is determined whether the power distribution needs to be re-distributed according to the abnormal degree of the real-time motor speed.

[0009] Furthermore, the rotation speed difference acquisition method includes:

[0010] For any moment, a preset number of consecutive historical moments are searched in time sequence starting from the moment to form a time period to be analyzed at the corresponding moment; the difference between the average real-time motor speed in the time period to be analyzed and the speed to be adjusted is taken as the speed difference at the corresponding moment.

[0011] Furthermore, the load inertia is the product of the rotation speed difference and the load mass.

[0012] Furthermore, the method for obtaining the duty cycle includes:

[0013] The load inertia is normalized and rounded up, and then converted into a percentage to obtain a percentage result; the difference between the positive integer 1 and the percentage result is used as the duty cycle.

[0014] Furthermore, the load inertia is normalized by using the range normalization.

[0015] Furthermore, the power distribution method of the motor winding is:

[0016] The number of power supply windings in all motor windings is determined according to the duty cycle, and the motor windings are screened at intervals according to the number of power supply windings to determine the power supply windings.

[0017] Furthermore, the method for obtaining the value of the distributed power supply current of the power supply winding includes:

[0018] The standard current value of the motor winding coil during the process of providing electromagnetic force is multiplied by the duty cycle to obtain the power supply current value of each winding coil.

[0019] Furthermore, the method for obtaining the abnormality degree includes:

[0020] The Z-score normalization algorithm is used to detect abnormalities in the real-time speed sequence of the motor after the power supply distribution of the motor winding is completed, and the degree of abnormality at each moment is obtained.

[0021] Further, it is determined whether the abnormality level is greater than a preset abnormality threshold. If it is greater than the preset abnormality threshold, it is determined that power distribution needs to be re-distributed; otherwise, power distribution does not need to be re-distributed.

[0022] Furthermore, the motor speed information is obtained by detecting the signal of the Hall sensor.

[0023] The present invention has the following beneficial effects:

[0024] The present invention collects the real-time speed of the motor in real time during the operation of the brushless motor and forms a sequence, and determines the adjustment amount that needs to be increased in speed by analyzing the speed difference between the current and the speed to be adjusted at each moment. Further combined with the load mass of the motor, the load inertia of the motor at the current moment is determined and the motor duty cycle is determined. The power distribution of the motor winding according to the relationship between the duty cycle and the current can control the electromagnetic force resultant value, ensure the controllability of the acceleration, and further eliminate the possibility of stalling. And after the power distribution is completed, the abnormal degree of the real-time speed of the motor is further analyzed and it is determined whether to re-distribute the power, which can realize closed-loop control, increase the real-time response efficiency of the brushless motor, and ensure the efficiency of improving the motor speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A method for adaptively adjusting the speed of a brushless motor provided by an embodiment of the present invention;

[0027] Figure 2 A brushless motor provided by one embodiment of the present invention does not consider the speed fluctuation caused by the load mass when increasing the speed;

[0028] Figure 3 A schematic diagram of internal windings of a brushless motor provided by an embodiment of the present invention;

[0029] Figure 4 A winding allocation schematic diagram provided by an embodiment of the present invention;

[0030] Figure 5 A schematic diagram of abnormality degree result distribution provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the specific implementation method, structure, features and effects of a brushless motor speed adaptive adjustment method proposed by the present invention in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0032] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0033] The embodiment of the present invention is directed to a brushless motor that uses a Hall sensor to detect the rotor position and an auxiliary controller to control the current direction to maintain stable rotation of the motor. This type of brushless motor is also called an inductive brushless motor. In order to obtain various parameters of the inductive brushless motor, the steps included in the experimental stage of the embodiment of the present invention include:

[0034] (1) Initialize hardware configuration.

[0035] (2) Connect the Hall sensor of the motor to the digital input pin of the microcontroller. The microcontroller used in the embodiment of the present invention is an Arduino control chip, and its corresponding input pins are D2, D3, and D4 pins.

[0036] (3) Connect the stator winding to the H-bridge or MOSFET drive circuit, and connect the control end of the drive circuit to the PWM output pin of the microcontroller. The corresponding output pins of the Arduino control chip are D5, D6, and D9 pins.

[0037] (4) Read the Hall sensor signal. Initialize the timer and use the internal timer of the microcontroller configured in high-speed counting mode. The resolution can be set to 1 microsecond.

[0038] (5) Detect the edge of the Hall sensor and configure external interrupts. When the Hall sensor signal rises or falls, the interrupt service program is triggered and the speed is calculated. In the interrupt service program, the time difference between the two rising edges is recorded, and the real-time speed of the motor can be calculated using the existing formula: ;in is the motor speed, Indicates the time difference between two rising edges. is the number of times the Hall sensor signal changes per revolution. For a three-phase motor, N is 6, and 1e6 represents 1 times 10 to the sixth power. The specific meaning of this formula is well known to those skilled in the art, and will not be elaborated here.

[0039] (6) Setting an initial duty cycle: According to the motor starting requirements, the initial duty cycle is set, which is set to 50% in the embodiment of the present invention.

[0040] (7) The adaptive control of the duty cycle of the motor can be achieved by a brushless motor speed adaptive control method proposed in an embodiment of the present invention. By obtaining the load mass of the motor and the real-time speed of the motor, the duty cycle is determined according to the speed to be adjusted and the power supply is distributed to the motor winding, so as to achieve adaptive real-time control of the torque. The duty cycle signal after adjustment controls the excitation of the stator winding through the output pin. At the same time, the embodiment of the present invention also sets a speed stability check, regularly checks the real-time speed, and fine-tunes the duty cycle if the speed fluctuation exceeds the set range. The setting range in the embodiment of the present invention is set to 5, that is, the duty cycle is fine-tuned when the speed fluctuation exceeds 5RPM. Further, overspeed or underspeed protection is configured, and the upper and lower limits of the speed are set. When the range is exceeded, the motor drive is automatically cut off or a warning signal is fed back. The upper and lower limits of the speed in the embodiment of the present invention are set to 300RPM to 3000RPM. In addition, in order to prevent the motor from overloading, the maximum and minimum values ​​of the duty cycle are set. In the embodiment of the present invention, the maximum value of the duty cycle is set to 90% and the minimum value is set to 10%.

[0041] (8) The speed update frequency can be set according to the motor application scenario. In the embodiment of the present invention, it is set to 10 times per second.

[0042] See also Figure 1 , which shows a flow chart of a method for adaptively adjusting the speed of a brushless motor provided by an embodiment of the present invention, the method comprising:

[0043] Step S1: Acquire the real-time speed sequence of the motor and the load mass during the operation of the brushless motor.

[0044] In an embodiment of the present invention, the real-time speed of the motor at each moment is determined by obtaining the real-time reading value of the Hall sensor. In an implementation of an embodiment of the present invention, the frequency of collecting the real-time speed of the motor is 50 times per second. Please refer to Table 1, which is a data set of the real-time speed of the motor collected in an embodiment of the present invention.

[0045]

[0046] Table 1

[0047] In the embodiment of the present invention, the motor real-time speed sequence can be obtained by sorting the acquired motor real-time speed according to the time sequence. The load mass can be directly acquired by data input or automatically acquired by a sensor, which will not be described in detail here.

[0048] Step S2: Obtain the speed difference between the speed at each moment in the real-time speed sequence of the motor and the speed to be adjusted; and obtain the load inertia at the corresponding moment according to the speed difference and the load mass.

[0049] The speed to be adjusted is the required speed for the speed adjustment to be performed. It is a priori value and can be directly obtained through data input. For example, the flight speed requirements of the aircraft are different at different times, and the propulsion speed is inconsistent, that is, the required speed of the motor is also different, thereby achieving stable flight in different environments. Therefore, the greater the speed difference between the speed at each moment and the speed to be adjusted, the greater the difference between the target speed index and the current speed, and the greater the acceleration required to make the speed efficiently reach the expected speed, and the higher the winding current power supply ratio should be. Therefore, the speed difference is accurately quantified for subsequent duty cycle determination.

[0050] Further considering that the larger the load, the greater the inertia effect on the motor during operation, the higher the electromagnetic force required during the startup process, and the motor speed needs to be reached within a certain period of time. If the speed reaches the required speed, but the load mass is large, the inertia will further affect the speed, causing the motor to stall. Please refer to Figure 2 , which shows a speed fluctuation diagram of a brushless motor provided by an embodiment of the present invention when increasing the speed without considering the load mass. Figure 2The horizontal axis is time, the vertical axis is speed, the time unit is seconds, and the speed unit is RPM. Figure 2 It can be seen that the speed changes little in the interval of 80 to 100 seconds, which can be regarded as stable; after more than 100 seconds, the speed fluctuation becomes larger and the speed change frequency becomes larger, indicating that the motor stalls. Motor stalling will affect the application of brushless motors in the scene and even cause safety hazards.

[0051] Therefore, the embodiment of the present invention combines the speed difference and the load mass to obtain the load inertia at the corresponding moment. When the load mass is high, if the speed difference is large, it means that the load inertia at this time is large, which means that the load responsible for the rotation of the brushless motor and the speed to be adjusted are high, the electromagnetic force required by the motor should be large, and a higher acceleration needs to be provided.

[0052] Preferably, in one embodiment of the present invention, the method for obtaining the rotation speed difference includes:

[0053] For any moment, take the moment as the starting point and find a preset number of consecutive historical moments in the time sequence to form the time period to be analyzed at the corresponding moment; the difference between the average motor real-time speed in the time period to be analyzed and the speed to be adjusted is taken as the speed difference at the corresponding moment. That is, it can be expressed as: ;in represents the speed difference at the ath moment, is the speed to be adjusted, is the number of moments in the time period to be analyzed corresponding to the a-th moment, is the real-time speed of the motor at the nth moment in the time period to be analyzed. The noise error caused by the Hall sensor in the speed calculation process can be eliminated by averaging. The noise here refers to the fact that the ratio between speed and torque is not linear within a certain speed range. The speed growth ratio needs to integrate the average value over a period of time to judge the difference between the speed and the speed to be adjusted.

[0054] In one embodiment of the present invention, the speed difference result obtained according to the data in Table 1 is shown in Table 2.

[0055]

[0056] Table 2

[0057] Preferably, in one embodiment of the present invention, the load inertia is the product of the rotation speed difference and the load mass.

[0058] Step S3: Determine the duty cycle of the motor according to the load inertia; distribute power to the motor windings according to the standard current value and the duty cycle.

[0059] The higher the load inertia, the higher the electromagnetic force required by the motor in a certain period of time. Therefore, the load inertia and the motor duty cycle show an obvious negative correlation. The duty cycle can be determined based on the load inertia. The smaller the duty cycle, the more windings in the motor participate in power distribution and the more windings are activated. Figure 3 , which shows a schematic diagram of the internal winding of a brushless motor provided by an embodiment of the present invention. The rotor is a rotatable magnet inside the motor, and the winding is a stator coil fixed around it. Figure 3 The figure shows the interface of a three-phase brushless motor with 6 windings. When the number of windings turned on is 3, the duty cycle is 50%.

[0060] Preferably, in one embodiment of the present invention, a method for obtaining a duty cycle includes:

[0061] After the load inertia is normalized and rounded up, it is converted into a percentage to obtain a percentage result; the difference between the positive integer 1 and the percentage result is used as the duty cycle. The purpose of rounding up is to avoid the phenomenon that the speed acceleration does not reach the standard value due to the small number of windings energized and the low noise electromagnetic force, which in turn causes the motor to stall.

[0062] Furthermore, the normalization method adopts range normalization, that is, by counting the values ​​of multiple groups of load inertia under different speeds to be adjusted and different load requirements, the maximum and minimum values ​​are determined, and then normalization is achieved. The calculation formula of range normalization is a technical means well known to those skilled in the art, and will not be elaborated here.

[0063] After the duty cycle is obtained, the power supply to the motor winding can be distributed in real time. Figure 3 Taking the three winding groups ABC in the figure as an example, the duty cycle is 66%, which means that two-thirds of the winding coils provide the corresponding electromagnetic force during the acceleration process. That is, one of the three winding groups is not energized, please refer to Figure 4 , which shows a winding allocation schematic diagram provided by an embodiment of the present invention, wherein both winding groups AB are activated, and winding group C is not activated due to duty cycle limitation.

[0064] Furthermore, after determining the windings that need to be activated, it is necessary to allocate power to each activated winding according to the standard current value and duty cycle. When the duty cycle is lower, more windings are involved in providing electromagnetic force, and the power supply current value of each winding should be smaller, because there are more units providing electromagnetic force, and a reasonable higher current value does not require excessive power supply to achieve motor speed acceleration.

[0065] Preferably, in one embodiment of the present invention, the power distribution method of the motor winding is:

[0066] The number of power supply windings among all motor windings is determined based on the duty cycle, and the motor windings are screened based on the number of power supply windings to determine the power supply windings. Figure 4 As shown, by interval screening, the C group winding is set not to participate in the power supply, so that the coils at relative angles can be powered at the same time, providing electromagnetic thrust on the left side of the rotor and electromagnetic attraction on the right side, further improving the speed acceleration.

[0067] Furthermore, in the embodiment of the present invention, the standard current value of the motor winding coil in the process of providing electromagnetic force is multiplied by the duty cycle to obtain the power supply current value of each winding coil. That is, the power supply current value is set to a percentage of the standard current value using the duty cycle, which can eliminate the stall phenomenon caused by excessive instantaneous torque, so that the motor can accelerate stably, ensure reasonable fixation, and avoid stalling.

[0068] Step S4: After the motor winding power distribution is completed, it is determined whether the power distribution needs to be re-distributed according to the abnormal degree of the real-time motor speed.

[0069] In order to realize the closed-loop control of the brushless motor, the embodiment of the present invention further realizes that after the power supply distribution of the motor winding is completed, the real-time speed reaches the speed to be adjusted, and the motor maintains a constant speed. The real-time speed of the electrode is further continuously collected to obtain the real-time speed of the motor after adjustment, and the real-time speed sequence of the motor is formed. The data information in the real-time speed sequence of the motor can be used to further determine the abnormality of the speed data at each moment, and then determine whether the power supply distribution needs to be re-performed.

[0070] Preferably, in one embodiment of the present invention, the method for obtaining the abnormality degree includes:

[0071] The Z-score standardization algorithm is used to detect abnormalities in the real-time speed sequence of the motor after the power supply distribution of the motor winding is completed, and the degree of abnormality at each moment is obtained. It should be noted that the Z-score standardization algorithm is a technical means well known to those skilled in the art. The degree of abnormality is obtained by obtaining the difference between the data value and the average value, and further dividing it by the variance. The greater the degree of abnormality, the more abnormal the speed data at the current moment is, and the more likely it is to stall. Therefore, the embodiment of the present invention further determines whether the degree of abnormality is greater than the preset abnormal threshold. If it is greater than the preset abnormal threshold, it is determined that power distribution needs to be re-allocated, and the duty cycle can be re-acquired according to the above steps, or the duty cycle can be fine-tuned. Otherwise, there is no need to re-allocate power and maintain uniform speed operation until the next adjustment demand for the speed to be adjusted arrives. In an embodiment of the present invention, the abnormality threshold is set to 0.8. If Figure 5 As shown, it shows a schematic diagram of abnormal degree result distribution provided by an embodiment of the present invention, Figure 5 The horizontal axis is time, and the vertical axis is the degree of abnormality. Figure 5In the above data, data points above 0.8 are considered to be data points with stall risk.

[0072] It should be noted that, because the embodiment of the present invention is intended to update the motor speed in real time, only the abnormality degree at the latest moment is determined and a threshold judgment is performed when determining the abnormality degree. In other embodiments of the present invention, after obtaining a motor real-time speed sequence, all data points greater than the abnormality threshold in the entire sequence are counted, and whether there is a stall risk at the latest moment is determined by the number of data points greater than the abnormality threshold.

[0073] In summary, the present invention collects the real-time speed of the motor in real time during the operation of the brushless motor and forms a sequence, and determines the adjustment amount that needs to be increased in speed by analyzing the speed difference between the current speed and the speed to be adjusted at each moment. Further combined with the load mass of the motor, the load inertia of the motor at the current moment is determined and the motor duty cycle is determined. Power is distributed to the motor windings according to the relationship between the duty cycle and the current. After the power distribution is completed, the abnormality of the real-time speed of the motor is further analyzed and it is determined whether to re-distribute power. The present invention combines the load of the motor during operation and increases the real-time response efficiency of the brushless motor through closed-loop control to ensure the efficiency of improving the motor speed.

[0074] It should be noted that the sequence of the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0075] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A method for adaptively adjusting the speed of a brushless motor, characterized in that: The method comprises: Get the real-time speed sequence and load quality of the motor during the operation of the brushless motor; Obtaining the speed difference between the speed at each moment in the real-time speed sequence of the motor and the speed to be adjusted; obtaining the load inertia at the corresponding moment according to the speed difference and the load mass; Determine the duty cycle of the motor according to the load inertia; distribute power to the motor windings according to the standard current value and the duty cycle; After the motor winding power distribution is completed, it is determined whether the power distribution needs to be re-distributed according to the abnormal degree of the real-time motor speed; The load inertia is the product of the rotation speed difference and the load mass; The method for obtaining the duty cycle includes: The load inertia is normalized and rounded up, and then converted into a percentage to obtain a percentage result; the difference between the positive integer 1 and the percentage result is used as the duty cycle.

2. A brushless motor speed adaptive adjustment method according to claim 1, characterized in that: The rotation speed difference acquisition method comprises: For any moment, a preset number of consecutive historical moments are searched in time sequence starting from the moment to form a time period to be analyzed at the corresponding moment; the difference between the average real-time motor speed in the time period to be analyzed and the speed to be adjusted is taken as the speed difference at the corresponding moment.

3. The method for adaptively adjusting the speed of a brushless motor according to claim 1, characterized in that: The load inertia is normalized using range standardization.

4. The method for adaptively adjusting the speed of a brushless motor according to claim 1, characterized in that: The power distribution method for the motor windings is: The number of power supply windings in all motor windings is determined according to the duty cycle, and the motor windings are screened at intervals according to the number of power supply windings to determine the power supply windings.

5. A brushless motor speed adaptive adjustment method according to claim 4, characterized in that: The method for obtaining the value of the distributed supply current of the supply winding includes: The standard current value of the motor winding coil during the process of providing electromagnetic force is multiplied by the duty cycle to obtain the power supply current value of each winding coil.

6. The method for adaptively adjusting the speed of a brushless motor according to claim 1, characterized in that: The method for obtaining the abnormality degree includes: The Z-score normalization algorithm is used to detect abnormalities in the real-time speed sequence of the motor after the power supply distribution of the motor winding is completed, and the degree of abnormality at each moment is obtained.

7. A brushless motor speed adaptive adjustment method according to claim 6, characterized in that: Determine whether the abnormality is greater than a preset abnormality threshold, and if so, determine that power supply distribution needs to be re-distributed; Otherwise no re-power distribution is required.

8. The method for adaptively adjusting the speed of a brushless motor according to claim 1, characterized in that: The motor speed information is obtained by detecting the signal of the Hall sensor.

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