CN115173752A - Accurate commutation control method for brushless direct current motor without position sensing - Google Patents

Abstract

The invention discloses a precise phase-changing control method of a brushless direct current motor without position sensing, which comprises the following steps: s1, a timing value of a timer module is used for calculating the speed of a motor rotor to complete a timing function; s2, the A/D module samples the terminal voltage and the phase current of the motor, and then converts the terminal voltage and the phase current into corresponding line values for calculating the position of the rotor; s3, the PWM module obtains a commutation logic signal according to the detected rotor position signal, sends out a corresponding driving signal and controls the motor to commutate to realize the control function of the commutation driving signal; in a certain time, the motor rotating speed is obtained by dividing the counting value of the counter potential zero crossing point number by the pole number, and the ideal no-load rotating speed point of the motor can be flexibly adjusted. When the motor is under a load condition, the purpose of controlling the output torque of the motor can be achieved by adjusting the rotating speed, and the phase change accuracy is improved.

Description

A precise commutation control method for a position-sensing brushless DC motor

technical field

The invention belongs to the technical field of motors, and in particular relates to a precise commutation control method for a position-sensing brushless DC motor.

Background technique

Brushless DC motors have been widely used in aerospace, process control, electronic equipment, underground mine operations, household appliances, etc. due to their high operating efficiency, good speed regulation performance, simple structure, and easy maintenance. The commutation is affected by the commutation delay and whether the motor is working or not, so the motor speed cannot be accurately obtained within a certain period of time, and the real-time position of the rotor is difficult to determine, and the next commutation point cannot be accurately obtained, which affects the accuracy of commutation. . To this end, we propose a precise commutation control method for a position sensorless brushless DC motor to solve the problems mentioned in the above background art.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a precise commutation control method for a position-sensing brushless DC motor, so as to solve the above-mentioned problems in the background art.

In order to achieve the above purpose, the present invention provides the following technical solutions: a method for precise commutation control of a position-sensing brushless DC motor, comprising the following steps:

S1. The timing value of the timer module is used to calculate the rotor speed of the motor to complete the timing function;

S2. The A/D module samples the motor terminal voltage and phase current, and then converts them into corresponding line values for rotor position calculation;

S3. The PWM module obtains the commutation logic signal according to the detected rotor position signal, sends out the corresponding driving signal, and controls the motor commutation to realize the control function of the commutation driving signal;

S4. The start function makes up for the disadvantage that no position sensor can detect the zero-crossing point of the back electromotive force when it is stationary or at low speed, and realizes the soft start of the motor.

The precise commutation control system of the position sensorless brushless DC motor includes a brushless DC motor body, a rotor position detection unit, a controller, an inverter and a DC power supply;

The DC power supply is electrically connected to the brushless DC motor body through the inverter, the brushless DC motor body is connected to the controller through the rotor position detection unit, and the controller is electrically connected to the inverter;

The rotor position signal of the brushless DC motor body is transmitted to the controller through the rotor position detection unit, and the controller outputs trigger pulses to drive the inverter, so that the windings of the brushless DC motor body are energized regularly, and the magnetic field of the rotor of the brushless DC motor body is And the magnetic field generated by the current passes through the synthetic electromagnetic torque, thereby driving the normal operation of the brushless DC motor body.

In the step S1, the calculation of the rotor speed of the motor includes the following steps:

The time for the rotor to rotate through 60 electrical degrees corresponds to the interval between two adjacent back-EMF zero-crossing points, and the timer module is used to determine the time between two adjacent back-EMF zero-crossing points to calculate the rotor speed;

(转/分钟)，其中，f_PWM表示PWM信号的频率；p表示极对数；COUNT表示一个60度电角度内PWM定时计数器的计数值；The motor speed is calculated as:

(revolution/minute), where f _PWM represents the frequency of the PWM signal; p represents the number of pole pairs; COUNT represents the count value of the PWM timer counter within a 60-degree electrical angle;

When two adjacent back-EMF zero-crossing points are detected, the count value of COUNT is read and cleared, and COUNT is counted again.

In the step S3, the commutation logic signal is obtained by logical processing of the back EMF zero-crossing signal, which specifically includes: after the rotational speed is compared with a given rotational speed through negative feedback, the rotational speed PI is adjusted;

The output is used as the given value of the current loop, and after comparing with the output phase current, the output is adjusted by PI through the current loop. After the amplitude limiting and rectification processing, the duty cycle of the PWM can be adjusted. The logic switch signal is processed and processed, and the gate signal input of the inverter bridge module is obtained to act on the inverter, which indirectly controls the average voltage that the motor can obtain.

In the step S5, the soft start of the motor specifically includes: first, after positioning by the rotor pre-positioning method, then sealing all the driving signals, so that the motor is in a power-off state;

Then use the same method to pre-position the rotor to realize the accurate positioning of the motor. The pre-positioning position is based on the positioning of the first pre-positioning, and the conduction step is forwarded or backward. A commutation occurs;

Position the motor rotor to a specific position, and then commutate the motor according to the commutation sequence of the brushless DC motor. This is the second stage of the three-stage starting method, that is, the external synchronous acceleration method;

When the rotor positioning is completed, according to the rotation direction of the motor, the long pulse is used to accelerate the motor, and the short pulse is used to detect the rotor position signal;

When the commutation signal is applied to the stator winding of the motor, on the one hand, the commutation signal should apply the drive signal to the inverter tube according to the six-step energization commutation sequence, and the duty cycle of the PWM signal should be gradually increased, continuously increasing by six. The commutation frequency of the power-on sequence is adjusted step by step, so that the stator winding voltage can be increased to the expected frequency, so that the motor can reach a certain speed, and the back EMF signal in it can be increased enough to be detected.

Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a precise commutation control method for a brushless DC motor without position sensing. Divide the count value by the number of poles to get the motor speed. The output of speed PI is fed back to the input terminal of current PI, and then the detected phase current output value is converted by the A/D module of STM32, and then compared with the output value, and then the current loop control is formed through the current PI in the form of deviation. . The current PI module outputs a signal that can control the PWM duty cycle, and then enters the drive circuit to control the on-off of the power tube to adjust the rotor voltage, which can flexibly adjust the ideal no-load speed point of the motor. When the motor is under load, the relationship between voltage and current, current and output torque can also be adjusted by adjusting the speed, so as to achieve the purpose of controlling the output torque of the motor and complete double closed-loop control.

The control implementation process of the brushless DC motor control system, the introduction of the experimental platform, and the design of the functional unit circuits respectively, taking into account the rated operating voltage and output current indicators. The invention draws on the open-loop operation mode of the stepping motor to start the motor, then accelerates, and then smoothly switches to the closed-loop operation of zero-crossing detection. The other part is the most important part of the whole algorithm, that is, after the zero-crossing detection is started, the single-chip microcomputer must correctly detect the zero-crossing point, which is the basis of the commutation, and the real-time position of the rotor can be obtained, and then after the delay calculation, the next commutation can be obtained. Phase point, drive commutation, improve the accuracy of commutation.

Description of drawings

Fig. 1 is the flow chart of rotational speed calculation procedure;

Figure 2 is a schematic diagram of a precise commutation control system for a position-sensing brushless DC motor;

Fig. 3 is the mechanical characteristic curve diagram of the brushless DC motor;

Fig. 4 is the block diagram of BLDCM double closed-loop control system;

Figure 5 is a hardware diagram of the BLDCM drive circuit;

Figure 6 is a schematic diagram of the characteristic parameters of IRF540NS;

Figure 7 is a design diagram of a power supply circuit;

8 is a schematic diagram of a bus voltage and ambient temperature detection circuit;

9 is a schematic diagram of a back EMF zero-crossing position detection circuit;

Figure 10 is a flow chart of a software system program;

Figure 11 is the main program flow chart;

Figure 12 is a flowchart of the A/D interrupt program;

Fig. 13 is a flow chart of motor start-up control;

Figure 14 is a flow chart of motor commutation;

Figure 15 is a flowchart of a closed-loop operation program;

Figure 16 is a flow chart of the motor PWM driver.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The brushless DC motor has the same mechanical characteristics as the brushed DC motor, that is, the load torque decreases with the increase of the speed under a certain DC voltage, and the two are inversely proportional. Among them, its characteristic curve is shown in Fig. 3.

The ideal no-load speed will increase with the increase of the supply voltage under a certain load, and the two are in the same proportional relationship. Therefore, the main method of speed regulation of the brushless DC motor is to adjust the voltage applied to the motor. The size, in this way, is realized by using a voltage regulator source for pulse width modulation control.

In a certain period of time, the motor speed is obtained by dividing the count value of the number of back EMF zero-crossing points by the number of poles. The output of speed PI is fed back to the input terminal of current PI, and then the detected phase current output value is converted by the A/D module of STM32, and then compared with the output value, and then the current loop control is formed through the current PI in the form of deviation. .

The current PI module outputs a signal that can control the PWM duty cycle, and then enters the drive circuit to control the on-off of the power tube to adjust the rotor voltage, which can flexibly adjust the ideal no-load speed point of the motor.

When the motor is under load, the relationship between voltage and current, current and output torque can also be adjusted by adjusting the speed, so as to achieve the purpose of controlling the output torque of the motor and complete double closed-loop control. The double closed-loop system control system composed of the BLDCM speed main loop and the current sub-loop is shown in Figure 4.

The design and realization of the position sensorless control system of the brushless DC motor consists of the following parts of the hardware circuit: the main control circuit MCU, the main circuit and driver chip circuit composed of power tubes, and the auxiliary unit with detection and protection functions. Among them, the main control circuit selects STM32F103ZETT6 as the MCU, and compiles and debugs the program in the compilation environment MDK5.

Generally, the driving voltage of the power device unit is usually +10~20V, but in this design, we use the IR2110S chip as the conversion chip of the power driving part due to the use of +3.3V power supply microcontroller chip and high requirements. The IRF540NS is used to separate the power section of the MOSFET power inverter. The detection circuit can use resistive voltage divider to reduce system cost.

(1) Drive circuit design:

The hardware diagram of the BLDCM drive circuit is shown in Figure 5. The first is the drive of the six bridge arms. The MOS tube model selected by the driver board is: IRF540NS, SMD package, and a heat sink can be added if necessary. The characteristic parameters of IRF540NS are shown in Figure 6.

IR's HEXFET power field effect transistor IRF540NS is manufactured with advanced process technology and has extremely low on-resistance. This feature of the IRF540NS, combined with its fast slew rate and its well-known rugged HEXFET design, makes the IRF540NS an extremely efficient and reliable device for a wide range of applications. Simply put, the IRF540NS is superior.

(2) Power circuit design:

For simple and convenient power supply and enhanced versatility, as the only source of energy for the entire control system, the power supply circuit should have as few external interfaces as possible in the entire control system, and the power supply is obtained directly or indirectly from the DC bus power supply of the inverter. 15V and 5V power supplies are used here. Considering the drive of the PMSM motor, we also designed a 3.3V power supply part here. The 15V power supply is obtained by using the linear voltage regulator chip LM317. The maximum input voltage of the chip is 37V. It is normal for the chip to heat up during normal operation. If necessary, you can add a radiator to assist heat dissipation. The 5V power supply is obtained by the LM2596-5.0 chip, and the 3.3V is obtained by the AMS1117-3.3. The power circuit design diagram is shown in Figure 7.

(3) Design of bus voltage and temperature sensor circuit:

Its purpose is to reduce or avoid these events that will make the system not work properly or even damage the circuit. The protection of the system can be classified into hardware protection and software protection. Hardware protection is to block the running output of the drive system by directly generating the protection action by the hardware, without the need to go through the program judgment link to achieve the purpose of protection. However, the system generally occurs software protection first, and only starts hardware protection when the software protection is invalid. A high-quality control system, even if software protection and hardware protection cooperate and coordinate with each other, cannot make it immune to the damaging consequences of any event.

The bus voltage and ambient temperature detection circuit is shown in Figure 8. It can perform over-voltage protection, under-voltage protection and high-temperature protection, etc. Of course, these all require program programming support.

(4) Design of the back EMF zero-crossing detection circuit:

The back EMF zero-crossing position detection circuit is shown in Figure 9. The circuit is mainly divided into three parts: PWM pulse comparator reference voltage setting, reverse voltage comparison, and pull-up circuit. When the power tube of the upper bridge arm is PWM-ON, the single-chip microcomputer opens the back EMF zero-crossing capture port. At this time, the PWM terminal outputs a high level, the transistors Q1 and Q2 are saturated and turned on, and R3 is approximately grounded. Since R2=R3, the voltage value of the reference terminal of the reverse voltage comparator is set to be one-half of the power supply voltage. The terminal voltage and the reference voltage are compared. When the two are equal, the output level of the comparator is reversed and input to the microcontroller through the capture port, and then a delay of 30 electrical degrees is performed to obtain the ready commutation position of the rotor. The rotor position detection analysis is similar when the power switch is PWM-OFF.

(5) Layout design:

Since this driver integrates a high-current drive circuit and a high-speed single-chip digital circuit, the parasitic parameters in it will have a great impact on the power supply circuit, and even the power supply spikes caused by it may destroy the circuit. Therefore, in the layout design, it is necessary to minimize the The effect of parasitic parameters on the power loop.

The layout design shall comply with the following rules:

1. In order to effectively reduce the influence of parasitic parameters on the capacitor, the capacitor filter circuit should be as close as possible to the device pins to shorten the distance from the capacitor to the pins.

2. In order to avoid the peak voltage generated by the parasitic inductance when the power MOS tube switching device outputs a large current, the star grounding must be used. The star grounding is based on the ground of the power MOS tube loop, and all ground wires are used as a reference.

3. Since the resistance has a certain inductance and the influence of the loop parasitic inductance, on the sampling resistance, the switching current may generate a large induced voltage, which will cause the logic disorder of the small signal loop. Therefore, the current sampling resistance should be as close as possible to the low-side MOS tube. source and reference ground.

4. Because of the parasitic capacitance between two adjacent traces or traces between layers, the signal line may be unstable. Pay attention to the direction of the traces and avoid the influence of parasitic capacitance as much as possible. For example, the traces of the small signal loop should be separated from the traces of the power supply loop.

5. The power supply circuit is equivalent to a coil, and its area should be as small as possible. Because the area contained in the power supply loop will generate an electromagnetic field that may affect the small signal loop, the area of the power supply loop should be designed as small as possible so as not to cross the small signal loop.

The present invention provides a precise commutation control method for a position-sensing brushless DC motor as shown in Figures 1-16, including the following steps:

S1. The timing value of the timer module is used to calculate the rotor speed of the motor to complete the timing function;

S2. The A/D module samples the motor terminal voltage and phase current, and then converts them into corresponding line values for rotor position calculation;

S3. The PWM module obtains the commutation logic signal according to the detected rotor position signal, sends out the corresponding driving signal, and controls the motor commutation to realize the control function of the commutation driving signal;

S4. The start function makes up for the disadvantage that no position sensor can detect the zero-crossing point of the back electromotive force when it is stationary or at low speed, and realizes the soft start of the motor.

The precise commutation control system of the position sensorless brushless DC motor includes a brushless DC motor body, a rotor position detection unit, a controller, an inverter and a DC power supply;

The DC power supply is electrically connected to the brushless DC motor body through the inverter, the brushless DC motor body is connected to the controller through the rotor position detection unit, and the controller is electrically connected to the inverter;

The rotor position signal of the brushless DC motor body is transmitted to the controller through the rotor position detection unit, and the controller outputs trigger pulses to drive the inverter, so that the windings of the brushless DC motor body are energized regularly, and the magnetic field of the rotor of the brushless DC motor body is And the magnetic field generated by the current passes through the synthetic electromagnetic torque, thereby driving the normal operation of the brushless DC motor body.

In the step S1, the calculation of the rotor speed of the motor includes the following steps:

The time for the rotor to rotate through 60 electrical degrees corresponds to the interval between two adjacent back-EMF zero-crossing points, and the timer module is used to determine the time between two adjacent back-EMF zero-crossing points to calculate the rotor speed;

(转/分钟)，其中，f_PWM表示PWM信号的频率；p表示极对数；COUNT表示一个60度电角度内PWM定时计数器的计数值；The motor speed is calculated as:

(revolution/minute), where f _PWM represents the frequency of the PWM signal; p represents the number of pole pairs; COUNT represents the count value of the PWM timer counter within a 60-degree electrical angle;

When two adjacent back-EMF zero-crossing points are detected, the count value of COUNT is read and cleared, and COUNT is counted again.

In the step S3, the commutation logic signal is obtained by logical processing of the back EMF zero-crossing signal, which specifically includes: after the rotational speed is compared with a given rotational speed through negative feedback, the rotational speed PI is adjusted;

The output is used as the given value of the current loop, and after comparing with the output phase current, the output is adjusted by PI through the current loop. After the amplitude limiting and rectification processing, the duty cycle of the PWM can be adjusted. The logic switch signal is processed and processed, and the gate signal input of the inverter bridge module is obtained to act on the inverter, which indirectly controls the average voltage that the motor can obtain.

In the step S5, the soft start of the motor specifically includes: first, after positioning by the rotor pre-positioning method, then sealing all the driving signals, so that the motor is in a power-off state;

Then use the same method to pre-position the rotor to realize the accurate positioning of the motor. The pre-positioning position is based on the positioning of the first pre-positioning, and the conduction step is forwarded or backward. A commutation occurs;

Position the motor rotor to a specific position, and then commutate the motor according to the commutation sequence of the brushless DC motor. This is the second stage of the three-stage starting method, that is, the external synchronous acceleration method;

When the rotor positioning is completed, according to the rotation direction of the motor, the long pulse is used to accelerate the motor, and the short pulse is used to detect the rotor position signal;

When the commutation signal is applied to the stator winding of the motor, on the one hand, the commutation signal should apply the drive signal to the inverter tube according to the six-step energization commutation sequence, and the duty cycle of the PWM signal should be gradually increased, continuously increasing by six. The commutation frequency of the power-on sequence is adjusted step by step, so that the stator winding voltage can be increased to the expected frequency, so that the motor can reach a certain speed, and the back EMF signal in it can be increased enough to be detected.

Software design of control system:

After the control system design is completed, the software needs to be designed. In this paper, the single chip microcomputer is mainly used to realize the function of the position sensor. The software design of the single chip computer is the core of the overall design. Therefore, whether the algorithm of the single chip computer is effective and whether it can work stably is the key to whether the system can work normally.

In the software control system, including the main program, startup program, closed-loop operation program, interrupt service program, etc. Among them, to realize the normal start of the motor, the entire control program is divided into two parts. In this design, the open-loop operation mode of the stepping motor is used to start the motor, then accelerate, and then smoothly switch to the closed-loop operation of zero-crossing detection. The closed-loop operation program is divided into: back-EMF zero-crossing detection, speed calculation and other parts. The other part is the most important part of the whole algorithm, that is, after the zero-crossing detection is started, the single-chip microcomputer must correctly detect the zero-crossing point, which is the basis of the commutation, and the real-time position of the rotor can be obtained, and then after the delay calculation, the next commutation can be obtained. Phase point, drive commutation. The flow chart of the software system program is shown in Figure 10.

Main program design:

The main program design mainly completes the initialization configuration of the STM32 microprocessor and the realization of the self-starting of the motor. The initialization configuration includes system working clock configuration, I/O port configuration, initial value assignment of global variables, configuration of timer module, configuration of A/D module, configuration of motor drive PWM generation module, and implementation of software protection. In the module configuration, there are also corresponding interrupt service routine configurations such as timer interrupt switch and priority setting, A/D sampling interrupt priority configuration, etc. The timing value of the timer module is used to calculate the rotor speed of the motor to complete the timing function; the A/D module samples the motor terminal voltage and phase current, and then converts them into corresponding line values for rotor position calculation; the PWM module According to the detected rotor position signal, the commutation logic is obtained, the corresponding driving signal is sent out, and the motor commutation is controlled to realize the control function of the commutation driving signal. The starting function is mainly to make up for the shortcoming that no position sensor cannot detect the zero-crossing point of the back electromotive force at a standstill or at low speed, so as to realize the soft start of the motor.

The main program flow is mainly to complete the initialization, and is responsible for the initialization of each program and register. After the microcontroller is powered on, the main program is used as the entry program. First, the register resources must be allocated. After the program starts, this program mainly configures the PWM module and the ADC module. In addition, each variable and initializer must be declared. After initialization, the six operating states of the motor are sequenced, and the current state is loaded into the PWM output register. The program enters a loop and waits until the sampling and PWM modulation trigger an interrupt before changing the output state. The program flow chart is shown in Figure 11.

The main initialization procedure is as follows:

TIMx outputs PWM signal initialization, among which, as long as this function is called, the four channels of TIMx will have PWM signal output:

Turn on the clocks of the GPIO, DMA, and ADC involved in the initialization:

/*Open ADC IO port clock*/

ADC_GPIO_APBxClock_FUN(ADC_GPIO_CLK,ENABLE);

/* Turn on the DMA clock */

RCC_AHBPeriphClockCmd(ADC_DMA_CLK,ENABLE);

/* Turn on ADC clock */

ADC_APBxClock_FUN(ADC_CLK,ENABLE);

A/D interrupt programming:

The main purpose of the A/D interrupt program is to sample the terminal voltage and phase current of the three-phase winding of the motor on the one hand, and to sample the DC side voltage on the other hand. The flow chart of the A/D interrupt program is shown in Figure 12. In the A/D interrupt, its main function is to digitally filter the sampled value, and use the filter to estimate the back electromotive force, and it is also used for the software protection of the system. Immediately close the PWM signal output through the program to achieve software protection.

TIMx,x[6,7] interrupt priority configuration:

Priority setting code to configure ADC working mode:

Motor start program design:

The start-up procedure constitutes an important part of the brushless DC motor control, and its success is also related to the realization of the subsequent position sensorless control technology. Since the initial position of the rotor of the motor cannot be obtained, this design adopts the secondary positioning method to obtain the initial position of the rotor, which can not only ensure the reliable start of the motor, but also ensure that the motor will not be generated when the traditional brushed DC motor starts. Over-current shock, when an emergency occurs, the software can respond in time. The flow chart of motor startup control is shown in Figure 13.

As shown in Fig. 13, the three-stage starting method using twice pre-positioning realizes the forced starting of the motor from the static state. This method can not only effectively realize the motor start, but also avoid the motor start time is too long. The adopted secondary positioning method also avoids the problem of the first positioning failure caused by the poles of the rotor magnetic pole and the stator magnetic potential being reversed. While ensuring that the commutation frequency and the PWM duty cycle are fixed values, the conduction of the inverter switching devices is changed according to the set conduction sequence to ensure that the motor can run at a uniform acceleration. However, the time for controlling the acceleration operation varies depending on the motor itself. After configuring the PWM duty cycle and PID parameter values, turn on the commutation control interrupt, prepare for self-running first, and adjust the number of motor conduction steps in the acceleration stage. When the three-phase terminal voltage is detected, you can Switch to the self-synchronized operating phase. The cycle start count in the start-up program is used to realize the soft start of the motor on the one hand; on the other hand, it can effectively protect the motor by preventing the start-up time from being too long and the applied voltage being too large. When the soft start of the motor is successful, the start-up procedure ends, and the motor is smoothly switched to the position sensorless control mode.

Motor commutation program design: When the back EMF zero-crossing signal is detected, it is input to the capture port of the single-chip microcomputer. When a level jump occurs, the interrupt is entered, the interrupt flag is cleared, the interrupt is closed, and the phase delay is 30 electrical degrees time. After that, it is the rotor commutation time. The flow chart of motor commutation is shown in Figure 14.

The motor commutation setting program code is as follows:

Closed-loop operation program design: In the closed-loop control system, the output of the system is introduced into the input end of the system through the detection device, and the output signal is compared with the input as a feedback signal to obtain the deviation signal of the two. By correcting the deviation, the regulator produces a control effect on the controlled object, and the deviation tends to decrease, making the output infinitely close to the input. The closed-loop system not only enhances the anti-interference ability of the system, but also improves the control accuracy of the system, so it is widely used in motor control systems.

After the motor is started, it enters into the self-synchronized running state, and the corresponding PID parameters can be configured according to different set speeds. Double closed-loop operation control includes two parts: speed loop and current loop. In actual operation, PI control is generally used, and the differential parameter is set to 0. The general steps of PID controller parameter design are: first design the proportional constant, then set the integral constant, and finally set the differential constant. After the speed feedback is compared with the speed setting, the current reference value is output through the speed PI, and then compared with the feedback current, and the PWM duty cycle is output through the current PI. The tuning of this design is to first set the integral link to zero, adjust the proportional parameter until the system is stable, and then adjust the integral parameter. Among them, adjusting the integral parameter is used to improve the static stability and dynamic response of the system. The flow chart of the closed-loop operation program is shown in Figure 15.

Speed calculation: In the double closed-loop design, the calculation of feedback speed is the first problem to be solved. We can use the timer to determine the time between two adjacent back-EMF zero-crossing points to calculate the rotor speed from the time when the rotor turns 60 electrical degrees corresponding to the interval between two adjacent back-EMF zero-crossing points.

(转/分钟)。From the derivation, the motor speed is calculated as:

(rev/min).

Among them, f _PWM represents the frequency of the PWM signal; p represents the number of pole pairs; COUNT represents the count value of the PWM timing counter within a 60-degree electrical angle. When the program detects two adjacent back-EMF zero-crossing points, it reads the count value of COUNT and clears it, and COUNT counts again. The flow chart of the speed calculation program is shown in Figure 1.

Motor PWM driver program design: Only the above startup program, interrupt service program, back-EMF estimation function and speed and position estimation program can run normally, can the driving signal of the brushless DC motor be truly issued, and the correct PWM driving signal acts on the main circuit The inverter bridge can lead to the final operation of the motor. Therefore, the sending of the motor PWM drive signal needs to be completed under the cooperation of the startup program, the interrupt subroutine, and other protection programs. In the motor driver program, according to the specific position of the detected motor rotor, and then by looking up the table, the corresponding driving sequence is found in the switching vector table, and the driving signal of the brushless DC motor is sent out. The flow chart of the motor PWM driver is shown in Figure 16.

Configure the mode of the PWM signal output by TIMx, such as period, polarity, duty cycle, etc. The program code is as follows:

To sum up, compared with the prior art, the present invention obtains the motor speed by dividing the count value of the number of zero-crossing points of the back EMF by the number of poles within a certain period of time. The output of speed PI is fed back to the input terminal of current PI, and then the detected phase current output value is converted by the A/D module of STM32, and then compared with the output value, and then the current loop control is formed through the current PI in the form of deviation. . The current PI module outputs a signal that can control the PWM duty cycle, and then enters the drive circuit to control the on-off of the power tube to adjust the rotor voltage, which can flexibly adjust the ideal no-load speed point of the motor. When the motor is under load, the relationship between voltage and current, current and output torque can also be adjusted by adjusting the speed, so as to achieve the purpose of controlling the output torque of the motor and complete double closed-loop control.

The control implementation process of the brushless DC motor control system, the introduction of the experimental platform, and the design of the functional unit circuits respectively, taking into account the rated operating voltage and output current indicators. The invention draws on the open-loop operation mode of the stepping motor to start the motor, then accelerates, and then smoothly switches to the closed-loop operation of zero-crossing detection. The other part is the most important part of the whole algorithm, that is, after the zero-crossing detection is started, the single-chip microcomputer must correctly detect the zero-crossing point, which is the basis of the commutation, and the real-time position of the rotor can be obtained, and then after the delay calculation, the next commutation can be obtained. Phase point, drive commutation, improve the accuracy of commutation.

Finally, it should be noted that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it is still The technical solutions described in the foregoing embodiments can be modified, or some technical features thereof can be equivalently replaced, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included. within the protection scope of the present invention.

Claims (5)

1. A method for precise commutation control of a position-sensing brushless DC motor, characterized in that: comprise the steps: S1. The timing value of the timer module is used to calculate the rotor speed of the motor to complete the timing function; S2. The A/D module samples the motor terminal voltage and phase current, and then converts them into corresponding line values for rotor position calculation; S3. The PWM module obtains the commutation logic signal according to the detected rotor position signal, sends out the corresponding driving signal, and controls the motor commutation to realize the control function of the commutation driving signal; S4. The start function makes up for the disadvantage that no position sensor can detect the zero-crossing point of the back electromotive force when it is stationary or at low speed, and realizes the soft start of the motor. 2 . The method for precise commutation control of a position-sensing brushless DC motor according to claim 1 , wherein the precise commutation control system for the position-sensing brushless DC motor comprises a brushless DC motor. 3 . body, rotor position detection unit, controller, inverter and DC power supply; The DC power supply is electrically connected to the brushless DC motor body through the inverter, the brushless DC motor body is connected to the controller through the rotor position detection unit, and the controller is electrically connected to the inverter; The rotor position signal of the brushless DC motor body is transmitted to the controller through the rotor position detection unit, and the controller outputs trigger pulses to drive the inverter, so that the windings of the brushless DC motor body are energized regularly, and the magnetic field of the rotor of the brushless DC motor body is And the magnetic field generated by the current passes through the synthetic electromagnetic torque, thereby driving the normal operation of the brushless DC motor body. 3. The method for precise commutation control of a position-sensing brushless DC motor according to claim 1, characterized in that: in the step S1, calculating the rotor speed of the motor comprises the following steps: The time for the rotor to rotate through 60 electrical degrees corresponds to the interval between two adjacent back-EMF zero-crossing points, and the timer module is used to determine the time between two adjacent back-EMF zero-crossing points to calculate the rotor speed; The motor speed is calculated as:

(revolution/minute), where f _PWM represents the frequency of the PWM signal; p represents the number of pole pairs; COUNT represents the count value of the PWM timer counter within a 60-degree electrical angle; When two adjacent back-EMF zero-crossing points are detected, the count value of COUNT is read and cleared, and COUNT is counted again. 4 . The method for precise commutation control of a position-sensing brushless DC motor according to claim 2 , wherein in the step S3 , the commutation logic signal is obtained by logical processing of the back-EMF zero-crossing signal. 5 . , which specifically includes: after the speed is compared with the given speed through negative feedback, the speed PI adjustment is performed; The output is used as the given value of the current loop, and after comparing with the output phase current, the output is adjusted by PI through the current loop. After the amplitude limiting and rectification processing, the duty cycle of the PWM can be adjusted. The logic switch signal is processed and processed, and the gate signal input of the inverter bridge module is obtained to act on the inverter, which indirectly controls the average voltage that the motor can obtain. 5 . The precise commutation control method for a position-sensing brushless DC motor according to claim 1 , wherein: in the step S5 , the motor soft-start specifically comprises: first, after positioning by the rotor pre-positioning method, 5 . Then block all the drive signals, so that the motor is in a state of power off; Then use the same method to pre-position the rotor to realize the accurate positioning of the motor. The pre-positioning position is based on the positioning of the first pre-positioning, and the conduction step is forwarded or backward. A commutation occurs; Position the motor rotor to a specific position, and then commutate the motor according to the commutation sequence of the brushless DC motor. This is the second stage of the three-stage starting method, that is, the external synchronous acceleration method; When the rotor positioning is completed, according to the rotation direction of the motor, the long pulse is used to accelerate the motor, and the short pulse is used to detect the rotor position signal; When the commutation signal is applied to the stator winding of the motor, on the one hand, the commutation signal should apply the drive signal to the inverter tube according to the six-step energization commutation sequence, and the duty cycle of the PWM signal should be gradually increased, continuously increasing by six. The commutation frequency of the power-on sequence is adjusted step by step, so that the stator winding voltage can be increased to the expected frequency, so that the motor can reach a certain speed, and the back EMF signal in it can be increased enough to be detected.

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