CN113131806A

CN113131806A - Control device and method of brushless direct current motor

Info

Publication number: CN113131806A
Application number: CN201911419194.8A
Authority: CN
Inventors: 宾宏; 张筑亚; 孙小丽
Original assignee: Midea Group Co Ltd; Guangdong Welling Motor Manufacturing Co Ltd; Guangdong Midea White Goods Technology Innovation Center Co Ltd
Current assignee: Midea Group Co Ltd; Guangdong Welling Motor Manufacturing Co Ltd; Guangdong Midea White Goods Technology Innovation Center Co Ltd
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2021-07-16

Abstract

The application discloses brushless DC motor's controlling means and method, the device includes: the output three-phase bridge is connected with a three-phase input end of the brushless direct current motor; the input voltage detection circuit is connected with the output three-phase bridge in parallel between two poles of an input power supply; the input end of the microcontroller is connected with the input voltage detection circuit and the three-phase input end of the brushless direct current motor, the output end of the microcontroller is connected with the output three-phase bridge, the microcontroller sends a first driving signal to the output three-phase bridge in a 150-degree square wave driving mode, detects the terminal voltage of the three-phase input end of the brushless direct current motor, samples the zero crossing point of the terminal voltage, calculates to obtain a second driving signal of phase change in advance by combining with the power voltage sampled by the input voltage detection circuit, and sends the second driving signal to the output three-phase bridge. The current waveform is improved, the follow current state during phase change is improved, and the problem that the zero crossing point is submerged due to overlong follow current time in different loads is solved.

Description

Control device and method of brushless direct current motor

Technical Field

The application belongs to the technical field of brushless direct current motors, and particularly relates to a high-speed brushless direct current motor position sensorless control device and method adopting a 150-degree driving mode.

Background

Brushless direct current motors (BLDC) are increasingly widely used in the fields of small electric tools, hand-held vacuum cleaners, medical devices, and the like, due to their simple structure, high efficiency, and elimination of brushes and the like. The conventional BLDC adopts a 120-degree square wave mode for driving control, and this operation mode is colloquially called 6-beat control. The conduction mode of 6-beat control is simple, and mature driving circuits are the most mature and reliable technical scheme in BLDC application. However, the square wave control with the phase change of every 60 degrees forms a large harmonic current at the winding end, so that the harmonic loss and the iron loss of the motor are increased, and the efficiency of the motor is reduced. Meanwhile, the electromagnetic torque pulsation of the motor is large due to the conduction and the phase change of every 60 degrees, vibration and noise are generated due to the torque pulsation in the operation of the motor, the overall stability of the equipment is influenced, and the experience in use is poor.

By increasing the number of commutation times in the 360-degree electric cycle, the current waveform of the motor can be effectively improved, and the influence of torque pulsation is reduced while current harmonics are reduced. For example, if the number of phase changes in one electrical cycle is increased to 12, the angle of the original two-phase conduction is reduced to 30 °, and a 30 ° three-phase conduction process is inserted between each two-phase conduction, so that the 120 ° square wave control becomes 150 ° control, which is commonly referred to as 12-beat square wave control. The Hall position sensor can be used for simply and conveniently acquiring the position of the rotor to perform phase change operation, but the use of the Hall position sensor not only increases the volume and complexity of the system, but also increases the cost of the system, and simultaneously reduces the reliability of the system. Like the 120-degree square wave control, in the process of conducting each two phases, the suspended phase which is not electrified can be subjected to position judgment in a terminal voltage reading mode, and sensorless rotor position identification can still be realized in the mode. Slightly different from the 120 ° control, the 150 ° effective judgment interval is reduced from 60 ° to 30 °, especially for high-speed rotation applications, the simple use of 30 ° to judge the position may cause many problems, resulting in commutation failure.

Disclosure of Invention

The purpose of the application is achieved through the following technical scheme.

According to a first aspect of the present application, there is provided a control apparatus of a brushless dc motor, comprising: the output three-phase bridge is connected with a three-phase input end of the external brushless direct current motor; the input voltage detection circuit is connected with the output three-phase bridge in parallel between two poles of an input power supply; the input end of the microcontroller is connected with the input voltage detection circuit and the three-phase input end of the brushless direct current motor, the output end of the microcontroller is connected with the output three-phase bridge, the microcontroller sends a first driving signal to the output three-phase bridge in a 150-degree square wave driving mode, detects the terminal voltage of the three-phase input end of the brushless direct current motor, calculates a second driving signal with phase change in advance by combining the power voltage obtained by sampling of the input voltage detection circuit, and sends the second driving signal to the output three-phase bridge.

In some embodiments of the present application, further comprising: and the current detection circuit is connected between the negative electrode of the input power supply and the output three-phase bridge in series and is connected with the microcontroller.

In some embodiments of the present application, further comprising: and the direct current bus supporting capacitor is connected between the two poles of the input power supply in parallel with the output three-phase bridge.

In some embodiments of the present application, the input voltage detection circuit is two serially connected first and second resistors, the first resistor is connected to the positive pole of the input power source, and the second resistor is connected to the negative pole of the input power source.

In some embodiments of the present application, the current detection circuit is a third resistor.

According to a second aspect of the present application, a method for controlling a brushless dc motor is provided, wherein a 150-degree square wave driving manner is adopted to send a first driving signal to the output three-phase bridge; detecting terminal voltages of three-phase input ends of the brushless direct current motor; calculating to obtain a second driving signal of the advanced commutation by combining the power supply voltage obtained by sampling the voltage of the input power supply; and sending the second driving signal to an output three-phase bridge.

In some embodiments of the present application, the calculating the second drive signal that is phase-shifted in advance comprises: and carrying out advanced commutation operation by a preset lead angle to obtain a second driving signal.

In some embodiments of the present application, the performing of the advance commutation operation at the preset lead angle comprises: and at the back edge of the terminal voltage, taking the moment when the detected terminal voltage is equal to one half of the power supply voltage plus a first constant when the pulse width modulation is started and the moment when the detected terminal voltage is equal to 0 plus the first constant when the pulse width modulation is stopped as commutation moments, and calculating the rest commutation moments according to the rotating speed of the motor.

In some embodiments of the present application, the calculating the remaining commutation time according to the rotation speed of the motor includes: and calculating the rotation speed of the motor according to the positions of the zero crossing points detected in two adjacent times, and calculating the time of 30-degree phase change for the other three times according to the rotation speed of the motor.

In some embodiments of the present application, the process of detecting a zero crossing point includes: starting terminal voltage AD scanning of a corresponding detection phase according to the fact that the sector is the fourth, eighth and twelfth sectors and the first time delay is finished; judging whether phase change occurs according to corresponding threshold values of front and rear edges of the terminal voltage, wherein the threshold value is a threshold value with an advance angle; and carrying out phase change operation according to the terminal voltage reaching the threshold value.

According to a third aspect of the present application, there is provided an electronic device comprising: a memory, a processor and a computer program stored on the memory and executable on the processor, the processor executing when executing the computer program to implement the method according to any of the second aspect.

According to a fourth aspect of the present application, a computer-readable medium is proposed, on which computer-readable instructions are stored, which are executable by a processor to implement the method according to any one of the second aspects.

The application has the advantages that:

1. compared with the original 120-degree driving scheme, the 150-degree driving control BLDC has the advantages that harmonic components in the current flowing into the motor end are greatly reduced, torque pulsation is reduced, and motor loss caused by current harmonics is reduced;

2. the current waveform when the power is switched on at 150 degrees can be improved by adopting 150-degree driving control and carrying out advanced phase conversion, so that the current harmonic wave is further reduced;

3. the 150-degree driving control is adopted for carrying out the advance control, the current waveform is improved, the follow current state during phase change is also improved, and the problem that the zero crossing point is submerged due to overlong follow current time in different loads is solved. The follow current time is shortened, the time for effectively detecting the position is further advanced, and the stability of phase change operation is improved;

4. the time for detecting the commutation point is further advanced by increasing or decreasing the zero crossing point judgment value by one increment, so that advanced commutation can be carried out at a new angle which is larger than the theoretical commutation angle of 15 degrees;

5. in the ultra-high speed application, the 15-degree commutation time corresponds to the time of only tens of microseconds, the time for effectively detecting the zero crossing point is prolonged by adding and subtracting increments, and the problem of commutation failure caused by single detection error is avoided;

6. the problem of untimely phase change caused by factors such as circuit and sampling delay during 150-degree ultrahigh-speed control is solved by a plus-minus increment advance phase change mode, and a low-cost MCU with a slow speed can also be adopted to obtain relatively sufficient processing time, so that the application cost is reduced;

7. meanwhile, the limitation problem that a Hall signal is needed to carry out phase change exceeding the theoretical 15 degrees is avoided, and the control of a 150-degree driving position-free sensor is realized;

8. by only detecting the process that the terminal voltage falls and passes zero and enters a negative value interval, the problem that the theoretical zero crossing point is detected in advance and only 3 states are effective is avoided, and the detection can be effectively performed in advance at the PWM switching-on and switching-off moments;

9. the controllable range of the rotating speed is improved through the advanced phase change mode of the addition and subtraction increment.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

FIG. 1 illustrates a functional block diagram of the system architecture described herein;

FIG. 2 shows a schematic diagram of a BLDC square wave drive theoretical waveform with 150 ° conduction control (no lead control);

FIG. 3 shows a schematic diagram of a commutation scheme described herein;

fig. 4 is a schematic diagram illustrating voltage zero crossing processing in software according to the present application;

FIG. 5 shows a timing logic diagram for look-ahead controlled commutation within one electrical cycle;

FIG. 6 shows a flow chart of the control software described in the present application;

FIG. 7 shows a current and voltage versus position diagram for a 150 square wave drive control ahead;

FIG. 8 shows a conventional 150 ° post control rotational speed diagram;

FIG. 9 is a schematic diagram illustrating rotational speed after leading commutation control according to an embodiment of the present application.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

Fig. 1 shows a schematic block diagram of the system architecture described in the present application. As shown in fig. 1, the reference numerals have the following meanings: 101 is a direct current bus current sampling resistor, 102 is an MCU, 103 is a direct current bus Vdc sampling resistor, 104 is a battery input, 105 is a motor terminal voltage sampling resistor, 106 is an output three-phase bridge, 107 is an MCU output driving signal corresponding to the output three-phase bridge, 108 is a BLDC motor and 109 is a direct current bus supporting capacitor. Where Vdc is the input supply voltage.

The main circuit includes an input power source, including a battery and other regulated power sources, a dc bus support capacitor 109 for bus voltage (i.e., the power source voltage) stabilization, and a three-phase full bridge 106 for controlling the input BLDC motor 108 voltage. And the MCU performs terminal voltage detection on the three-phase output voltage and is used for detecting a phase change point. And the MCU samples the bus voltage and the bus current to control the power. The driving signal 107 of the MCU drives the output three-phase bridge 106 via a driving means (not shown, well known in the art).

In the MCU control system in this application, be different from the 6 bat commutation phase of 120 degrees, 150 degrees commutation is on the basis that 6 bat double-phase switch on, inserts once three-phase conducting state between two bat intervals, changes former 6 bat to 12 bat commutation phases. The difficulty of system control is that the time interval between the timely detection of the zero crossing point and the phase change is short. The method is characterized by comprising the following two points:

in the ultra-high speed operation control, for example, 150000rpm, even if the motor only has a pair of polar frequencies as high as 2500Hz, the control time of 30-degree sector is only 33.3us, and the time of 15-degree commutation is only 16.7us for processing, the cost requirement of equipment similar to battery application is high, the calculation and sampling delay of MCU can affect the system control, the zero-crossing judgment and commutation time are prolonged by adopting a leading conduction mode, and the low-cost MCU application with limited calculation capability is facilitated. The operation of detecting only the falling edge makes the MCU calculate the pressure lower in 270 degrees in the whole electric cycle control, and other work can be carried out in the time. For the reasons, the zero crossing point is detected in time, and the phase change time is reasonably arranged.

The theoretical commutation switching on logic diagram for the BLDC square wave drive scheme with 150 ° conduction control is shown in fig. 2: in fig. 2, a thick line part is a theoretical waveform of a terminal voltage driven by a square wave, a thin line is a waveform of a three-phase current, a sequence number part in the figure indicates a phase change sector number driven by 150 degrees, and the time corresponding to 6 arrows in a ZCP part shown in the figure is a theoretical phase change position which can effectively detect a zero crossing point theoretically. The theoretical mode of delaying the phase change by 15 degrees after the zero crossing point is detected, and the current waveform and the terminal voltage waveform are theoretically superposed.

The specific PWM driving and detection relationship list is shown in table 1 below:

TABLE 1, 150 ° commutation PWM driving method and position detection relation table

The theoretical 150 commutation control can be achieved according to the sequential control logic of table 1 and fig. 2. The theoretical 150 degree driving control BLDC is suitable for a low-speed motor, and the MCU has enough time to detect a zero crossing point and perform 15 degree delayed commutation control. In the practical use process, particularly the application of the high-speed motor is realized under the condition that the commutation logic of the table 1 is kept unchanged, and the performance of the ultra-high-speed motor can be improved by carrying out the following measures.

In the present application, a scheme of performing 150 ° commutation control using an AD sampling voltage is specifically shown in fig. 3. Where 201 is a preceding stream time, 202 is a following stream time, 204 is a zero-crossing point of a preceding PWM on time, 203 is a zero-crossing point of a preceding PWM off time, 205 is a zero-crossing point of a following PWM on time, 206 is a zero-crossing point of a following PWM off time, 209 is a lead detection position (hereinafter also referred to as an action point) of a following PWM on time, 210 is a lead detection position of a following PWM off time, 208 is a lead detection position (hereinafter also referred to as an action point) of a preceding PWM on time, 207 is a lead detection position of a preceding PWM off time, which is undetectable, and 211 is a lead detected voltage AD value increment set for leading commutation.

As can be seen from fig. 3, the initial control scheme is to detect Vdc/2 at PWM On and 0 at PWM Off, determine the rotor position as the terminal voltage zero crossing, and then advance the commutation. To perform the phase advance commutation with the lead angle θ, the detection point is changed to the following point: PWM On ═ Vdc/2+ m; PWM Off is 0+ m. And for terminal voltage fronts: PWM On time is equal to Vdc/2-m; PWM Off is 0-m. Since the terminal voltage AD sampling cannot detect a negative value, the operation point cannot be detected in advance at the PWM Off of the leading edge. This results in inconsistent advance of the operating point, uneven commutation, speed fluctuation, and loss of synchronism at high speed.

Aiming at the detection problem of the front edge of the terminal voltage, only the front action point of the rear edge is detected, and the rest phase change time is calculated according to the speed. This ensures consistency of each detection lead.

And the time of terminal voltage trailing edge detection is respectively the three times with the sequence numbers of 4(W- > V), 8 (V- > U) and 12(U- > W) according to the commutation logic table. When the action point is detected, the time interval between the current time and the previous action point is recorded as T120, and then the time interval is divided by 4 to obtain the estimated time T30 of the remaining commutation time as T120/4. The specific implementation logic is shown in fig. 4.

As shown in fig. 4, 301 is a theoretical terminal voltage waveform, 302 is a shielding time for avoiding a phase-change follow current at t1 time, 303 is a zero-crossing processing time for AD detection at t2 time for advance detection, 304 is a software zero-crossing processing procedure, 305 is a lead detection time (advance angle θ) set by t3 software, 306 is a theoretical terminal voltage zero-crossing point, 307 is an actually set advance detection point (0+ m), 308 is a maximum advance-possible angle at the time of theoretical detection, and 309 is a maximum advance-possible control angle using advance detection.

When entering the

sector

4, 8 or 12 which can detect the terminal voltage falling edge, firstly, the delay of t1 time is completed, and the interval in which the terminal voltage judgment is invalid due to the follow current state of the switching tube caused by inductance factors caused by the change of the current direction in the winding when the last phase change is completed is mainly avoided in the time period, which is called follow current shielding time or undetectable time. Starting AD sampling (4 → U, 8 → W, 12 → V) of the corresponding phase after the delay of the time t1 is finished, and then starting AD to continuously scan the terminal voltage value of the corresponding phase, wherein when the terminal voltage judgment standard is PWM On, the terminal voltage value is Vdc/2+ m; PWM Off is 0+ m. The interval time available for checking is t2, and t2 is a random time, the length of which depends on when the appropriate voltage value is sampled. And after the AD scans to a proper voltage value, carrying out phase change according to the optimal advance angle value. The advance angle θ may be determined by the t3 setting as the t2 time ends. The advancing angle can theoretically span the range of 15 degrees and be increased from theta to theta' by adopting the scheme different from the traditional scheme.

While commutation is proceeding, the motor speed is calculated from the positions where the zero-crossing points were captured the last two times (T120), and the time for another 30 ° commutation is estimated from this speed. Since 3 effective positions can be obtained by rotating one electric cycle, the electric cycle of 360 degrees is divided into 3 120-degree intervals by the 3 effective positions, 1 sector position of 30 degrees in each 120-degree interval is determined, the other 3 30-degree intervals realize automatic phase commutation by the time delay of a timer, and the determination of each 30-degree interval is realized by T30-T120/4. The timing diagram is shown in fig. 5.

As shown in fig. 5, 401 is a sector number, 402 is an electrical angle corresponding to a sector, 403 is a non-zero-crossing detection region estimated from the time of T30 two commutation, 404 is a time interval of T120 two effective zero-crossing determinations, 405 is a freewheel masking time which is time T1, and 406 is zero-crossing detection (ZC) and advanced commutation processing.

The control flow chart of the zero-crossing processing software is shown in fig. 6, the zero-crossing judgment process is carried out in

sectors

4, 8 and 12, and before the zero-crossing judgment, the time delayed by t1 is ensured to avoid continuous flow. Starting the terminal voltage AD scanning of the corresponding phase after t1 is delayed, and setting the terminal voltage AD scanning as Vdc/2+ m when the terminal voltage AD scanning passes through PWM On; and when the PWM is Off, the two branches are 0+ m to judge whether to change the phase. The delay time corresponding to the angle value is related to the running speed of the motor and is determined by a look-up table. The time is long when the motor runs at a slow speed, and the time is short when the motor runs at a fast speed, and is inversely proportional to the speed. And after the phase change is finished, measuring the speed through the count value of a specific timer to determine the time interval between the current phase change and the last phase change, wherein the interval is T120. The time for the next commutation is calculated according to the formula T30-T120/4 and the timing function is then started.

The theoretical current position and the terminal voltage position will have a tendency to advance after processing according to the above-described scheme, which is referred to as advance control in the present application, and the waveform behavior thereof will change as shown in fig. 7. Here, 501 is a sector number, 502 is an electrical angle corresponding to a sector, 503 is a U-phase terminal voltage waveform, 504 is a U-phase current waveform, 505 is a V-phase terminal voltage waveform, 506 is a V-phase current waveform, 507 is a W-phase terminal voltage waveform, and 508 is a W-phase current waveform. The arrow in fig. 7 indicates the leading commutation processing timing actually performed in the present application.

This application adopts 150 drive control BLDC to compare in former 120 drive scheme, owing to insert the three-phase and switch on the process, the electric current step number increases, and the electric current wave form more approaches to the sine wave, the harmonic composition greatly reduced in the electric current that flows into the motor end. The zero crossing point is judged by a method for detecting the end voltage of the suspended phase in the two-phase conduction process, so that the position of the rotor is obtained, the position-sensor-free control of 150-degree driving is realized, and the system cost is reduced. During the phase change process of obtaining the rotor position by detecting the zero crossing point, the position of the phase change point is changed to move back and forth by a certain angle (called as leading phase change or lagging phase change) to obtain different control effects, and especially the waveform of the current flowing into the motor is further changed. The current waveform can be further improved and the harmonic wave can be reduced by adopting a leading phase conversion mode on the basis of the original current waveform improvement. And the more lead angles, the shorter the freewheel time of the current. Therefore, by adopting the advanced commutation, the current harmonic can be effectively reduced, the motor efficiency is improved, the risk that the zero crossing point is submerged due to the overlong follow current time can be reduced, and the commutation stability is greatly improved.

Particularly in low-voltage high-current BLDC high-speed applications, the freewheel time increases with increasing current, which eventually results in the zero crossing being buried. As shown in fig. 8, the control was performed in a conventional manner at 150 ° and 114780 rpm. For ultrahigh-speed application, due to the problems of terminal voltage detection hardware delay, the running speed of a low-price MCU and the like, when advanced control is not performed, the time for entering 12-thousand-turn left and right controllable position detection becomes very short, and then the speed-up system is out of control.

When a high-speed BLDC motor runs, 150-degree driving is adopted, the difference between the terminal voltage zero-crossing position and the phase-change point is only 15 degrees, and particularly for an ultra-high-speed motor, the 15 degrees are often only ten or more microseconds. Too short a response time to detect motion results in insufficient lead time after terminal voltage detection to perform a leading commutation. According to the method provided by the embodiment, on the premise of not increasing any hardware cost, the advance judgment of the zero crossing point is realized by a mode of detecting the terminal voltage falling edge (a detection scheme of the terminal voltage zero crossing position of 180 degrees) and adding zero crossing prediction, the advance judgment time is applied to the advanced commutation, the harmonic quality of the current waveform is further improved, and the efficiency of the high-speed BLDC motor is further improved. FIG. 9 shows the result of the control according to the proposed method of this embodiment, with a rotational speed of 149220 rpm.

There is also provided, in accordance with some embodiments of the present application, electronic apparatus comprising: the control system comprises a memory, a processor and a computer program which is stored on the memory and can run on the processor, wherein the processor executes when running the computer program to realize the control method.

There is also provided, in accordance with some embodiments of the present application, a computer-readable medium having computer-readable instructions stored thereon, the computer-readable instructions being executable by a processor to implement the control method described above.

The above description is only for the preferred embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A control device for a brushless dc motor, comprising:

the output three-phase bridge is connected with a three-phase input end of the external brushless direct current motor;

the input voltage detection circuit is connected with the output three-phase bridge in parallel between two poles of an input power supply;

the input end of the microcontroller is connected with the input voltage detection circuit and the three-phase input end of the brushless direct current motor, the output end of the microcontroller is connected with the output three-phase bridge, the microcontroller sends a first driving signal to the output three-phase bridge in a 150-degree square wave driving mode, detects the terminal voltage of the three-phase input end of the brushless direct current motor, and calculates a second driving signal with phase conversion in advance by combining the terminal voltage with the power voltage sampled by the input voltage detection circuit, and sends the second driving signal to the output three-phase bridge.

2. The control apparatus of a brushless DC motor according to claim 1,

the input voltage detection circuit comprises a first resistor and a second resistor which are connected in series, the first resistor is connected with the anode of the input power supply, and the second resistor is connected with the cathode of the input power supply.

3. The control device of a brushless dc motor according to claim 1, further comprising:

and the current detection circuit is connected between the negative electrode of the input power supply and the output three-phase bridge in series and is connected with the microcontroller.

4. A control apparatus of a brushless DC motor according to claim 3,

the current detection circuit is a third resistor.

5. The control device of a brushless dc motor according to claim 1, further comprising:

and the direct current bus supporting capacitor is connected between the two poles of the input power supply in parallel with the output three-phase bridge.

6. A control method of a brushless DC motor is characterized in that,

sending a first driving signal to an output three-phase bridge in a 150-degree square wave driving mode;

detecting terminal voltages of three-phase input ends of the brushless direct current motor;

sampling the terminal voltage, and calculating to obtain a second driving signal of the advanced commutation by combining the power supply voltage obtained by sampling the voltage of the input power supply;

and sending the second driving signal to an output three-phase bridge.

7. The control method of a brushless DC motor according to claim 6,

the sampling and calculating to obtain a second driving signal with advanced commutation comprises the following steps:

and carrying out advanced commutation operation by a preset lead angle to obtain a second driving signal.

8. The control method of a brushless DC motor according to claim 7,

the phase advance commutation operation with a preset lead angle comprises:

and at the back edge of the terminal voltage, taking the moment when the detected terminal voltage is equal to one half of the power supply voltage plus a first constant when the pulse width modulation is started and the moment when the detected terminal voltage is equal to 0 plus the first constant when the pulse width modulation is stopped as commutation moments, and calculating the rest commutation moments according to the rotating speed of the motor.

9. The control method of a brushless DC motor according to claim 8,

the step of calculating the other commutation moments according to the rotating speed of the motor comprises the following steps:

and calculating the rotating speed of the motor according to the positions of the zero crossing points detected in two adjacent times, and calculating the time of 30-degree phase change for the other three times according to the rotating speed of the motor.

10. The control method of a brushless DC motor according to claim 9,

the process of detecting zero crossings includes:

starting terminal voltage AD scanning of a corresponding detection phase according to the fact that the sector is the fourth, eighth and twelfth sectors and the first time delay is finished;

judging whether phase change occurs according to corresponding threshold values of front and rear edges of the terminal voltage, wherein the threshold value is a threshold value with an advance angle;

and carrying out phase change operation according to the terminal voltage reaching the threshold value.

11. An electronic device, comprising: memory, processor and computer program stored on the memory and executable on the processor, characterized in that the processor executes when executing the computer program to implement the method according to any of claims 6-10.

12. A computer readable medium having computer readable instructions stored thereon which are executable by a processor to implement the method of any one of claims 6 to 10.