WO2016155409A1

WO2016155409A1 - Control method, apparatus and system for pulse width modulation of direct current brushless electrical motor

Info

Publication number: WO2016155409A1
Application number: PCT/CN2016/071721
Authority: WO
Inventors: 张卫新; 林建辉
Original assignee: 英特格灵芯片(天津)有限公司
Priority date: 2015-04-02
Filing date: 2016-01-22
Publication date: 2016-10-06
Also published as: JP2017514429A; JP6301466B2; CN104767431B; CN104767431A

Abstract

A control method, apparatus and system for pulse width modulation of a direct current brushless electrical motor. The method comprises: acquiring a pulse width modulation (PWM) high-accuracy duty ratio value (101); determining an accuracy extension mode of a PWM signal according to the PWM high-accuracy duty ratio value, wherein the accuracy extension mode comprises an accuracy extension period and an accuracy extension output sequence (102); and within the accuracy extension period, modulating a low-accuracy PWM signal according to the accuracy extension output sequence and outputting a control signal (103). The control method can weaken a speed staircase effect under open-loop control, and reduce a steady state speed error of closed-loop control.

Description

Method, device and system for controlling pulse width modulation of DC brushless motor

Technical field

The invention relates to the field of DC brushless motor control, in particular to a control method, device and system for pulse width modulation of a DC brushless motor.

Background technique

DC brushless motors have the advantages of high efficiency, low noise, reliable operation, etc. In recent years, they have been widely used and developed rapidly. In the brushless DC motor control, speed open loop control or speed/torque closed loop control is usually used. Both of these control methods need to use a Pulse Width Modulation (PWM) unit to control the power module. Performance puts higher requirements, such as the duty cycle of the PWM unit (corresponding to the PWM modulation frequency), especially the accuracy of the PWM unit (the minimum time resolution of the PWM unit determines the accuracy of the PWM unit). In the high-performance solution, the high-speed Micro Controller Unit (MCU) and the Digital Signal Processor (DSP) can easily meet the performance requirements of the PWM unit, but this is often accompanied by high system cost. In the low-cost solution, the PWM unit is forced to adopt lower precision when operating at a higher PWM modulation frequency due to limitations such as an Application Specific Integrated Circuit (ASIC)/microcontroller operating frequency. Lower PWM accuracy results in a significant speed step effect under open loop control, while steady state speed error fluctuations are greater under closed loop control. Therefore, how to improve system performance on the basis of lower performance PWM units in a low-cost solution has become an urgent problem to be solved.

Summary of the invention

The object of the present invention is to provide a control method, device and system for pulse width modulation of a DC brushless motor, which improve system performance and weaken on the basis of maintaining the original low performance PWM unit of the system. The speed step effect under open loop control reduces the steady state speed error of closed loop control.

In a first aspect, the present invention provides a method for controlling pulse width modulation of a brushless DC motor, the method comprising:

Obtaining a PWM pulse width modulation high precision duty value;

Determining the precision expansion mode of the PWM signal according to the PWM high-precision duty value, the precision expansion mode including the precision extension period and the precision extended output sequence;

During the precision expansion period, the output sequence is expanded according to the precision, the low-precision PWM signal is modulated, and the control signal is output.

Preferably, obtaining the PWM high-precision duty ratio value specifically includes: acquiring the PWM high-precision duty ratio value according to the running state data of the DC brushless motor.

Preferably, the step of determining the precision expansion mode of the PWM signal according to the PWM high-precision duty value comprises: comparing the PWM high-precision duty value with the previous PWM high-precision duty value to obtain a difference;

The accuracy spread mode of the PWM signal is determined when the difference is less than a predetermined threshold.

Preferably, the precision expansion period and the precision extended output sequence are selected according to the electromechanical parameters of the motor system;

Moreover, the accuracy of each sequence item of the precision extended output sequence is less than or equal to the precision of the low precision PWM signal.

Preferably, the control signal is used to control the turn-on and turn-off time of one or more sets of power switch tubes of the plurality of sets of power switch tubes.

In a second aspect, the present invention provides a driving device for a brushless DC motor, the device comprising:

a control module for acquiring a PWM high precision duty cycle value;

The precision expansion module is configured to determine a precision expansion mode of the PWM signal according to the PWM high-precision duty value, and the precision expansion mode includes an accuracy extension period and an accuracy extension output sequence;

A modulation module is configured to modulate the low-precision PWM signal and output the control signal according to the precision extended output sequence during the precision expansion period.

Preferably, the control module is specifically configured to: obtain a PWM high-precision duty value according to the operating state data of the DC brushless motor.

Preferably, the precision expansion module is specifically configured to compare the PWM high-precision duty value with the previous PWM high-precision duty value to obtain a difference;

In a third aspect, the present invention provides a driving system for a brushless DC motor, the system comprising:

Such as the above DC brushless motor drive device and power control module;

The power control module includes a plurality of sets of power switch tubes for receiving control signals from the modulation module, and controlling the turn-on and turn-off times of the one or more sets of power switch tubes of the plurality of sets of power switch tubes according to the control signals.

Preferably, the DC brushless motor driving device is further configured to control turn-on and turn-off of one or more sets of power switch tubes of the plurality of sets of power switch tubes according to a position signal of a rotor of the DC brushless motor.

The control method for the pulse width modulation of the DC brushless motor provided by the invention obtains the difference by comparing the high precision duty value of the current PWM with the previous PWM high precision duty value, and determines the accuracy expansion when the difference is less than the predetermined threshold. mode. The low-precision PWM signal is modulated by the precision extended output sequence in the precision extended mode. Thereby, the speed step effect under the open loop control is weakened, the steady-state speed error fluctuation range of the closed-loop control is reduced, and the system performance is improved.

DRAWINGS

1 is a schematic flow chart of a method for controlling pulse width modulation of a DC brushless motor according to an embodiment of the present invention;

2 is a schematic structural diagram of a driving device of a DC brushless motor according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a driving system of a DC brushless motor according to an embodiment of the present invention.

detailed description

The technical solution of the present invention will be further described in detail below through the accompanying drawings and embodiments.

1 is a control method for pulse width modulation of a DC brushless motor according to an embodiment of the present invention Schematic diagram of the process. As shown in FIG. 1 , the embodiment of the present invention specifically includes the following steps:

In step 101, a PWM high precision duty ratio value is obtained.

Specifically, the PWM high-precision duty value is obtained according to the operating state data of the DC brushless motor. The operating state data includes the rotor angular speed or torque current of the DC brushless motor in the closed loop control system, or the data directly set by the externally in the open loop control system. According to these operating state data, through a certain control algorithm calculation, the PWM high-precision duty value can be obtained.

Preferably, in the embodiment, the PWM high-precision duty value is obtained by the rotor angular velocity of the brushless DC motor.

Step 102: Determine a precision expansion mode of the PWM signal according to the PWM high precision duty ratio value.

Specifically, the current PWM high-precision duty value is recorded, and the current PWM high-precision duty value is compared with the previous PWM high-precision duty value, and the difference is calculated and recorded. When the difference is less than a predetermined threshold (the threshold is predetermined according to the actual situation), the precision expansion mode of the PWM signal is determined according to the current PWM high-precision duty value, wherein the precision expansion mode includes the precision expansion period and Precision extends the output sequence. Moreover, the precision extended period and the precision extended output sequence can be optimized according to the electromechanical parameters of the motor system; the accuracy of each sequence item of the precision extended output sequence is less than or equal to the precision of the low precision PWM signal.

Step 103: In the precision expansion period, the output sequence is expanded according to the precision, the low-precision PWM signal is modulated, and the control signal is output.

Specifically, in the precision expansion period, each precision extended output sequence is sequentially executed for modulating the low-precision PWM signal, and the time for executing each precision extended output sequence is the duty cycle time of the low-precision PWM signal. After all of the precision extended output sequences have been executed, the execution is repeated until a new PWM high precision duty cycle value is obtained and then compared to the previous PWM high precision duty cycle. After modulating the low-precision PWM signal, outputting a control signal corresponding to the precision extended output sequence for controlling the turn-on and turn-off times of one or more sets of power switch tubes in the plurality of sets of power switch tubes, thereby making each power The switching tube has a duty ratio value corresponding to the duty ratio value of the precision extended output sequence in the PWM unit duty cycle.

It should be noted that when the difference is greater than a predetermined threshold, the precision extended output sequence is no longer determined according to the high precision duty value, and the precision extended output sequence is executed, thereby outputting a control signal to control the conduction of the power switch. On and off times (this usually occurs during high-speed PWM duty cycle values that vary rapidly). Instead, the current PWM high-precision duty cycle value is converted to the nearest PWM low-precision duty cycle value in the system, and according to the low-precision duty cycle value, a corresponding control signal is output for controlling multiple sets of power. Turning on and off time of one or more sets of power switch tubes in the switch tube, so that each power switch tube has a duty ratio value and a duty ratio value of the low-precision PWM signal in a PWM unit duty cycle correspond.

In a specific example, the PWM high-precision duty cycle value can be obtained by calculating the rotor angular velocity of the brushless DC motor through a certain control algorithm. For example, the current duty value obtained is 257/512 (50.19%), the previous PWM duty value is 255/512 (49.80%), and the precision of the low-precision PWM duty value is 6-bit precision. The current PWM duty cycle value is recorded and the current PWM duty cycle value is compared to the previous PWM duty cycle value with a difference of 0.39% and the set threshold is 1%. Therefore, the difference is less than the set threshold, and the precision expansion mode of the PWM signal can be determined according to the current PWM duty value 257/512 (50.19%).

According to the electromechanical parameter optimization of the motor system, a suitable precision expansion period is selected. For example, in this embodiment, the duty cycle of the eight low-precision PWM signals is selected as an accuracy extension period, and the precision extended output sequence can also be based on the electromechanical parameters of the motor system. Optimize the selection of modulation mode generation. For example, the precision extended output sequence obtained by single-bit modulation is: {32/64, 32/64, 32/64, 32/64, 32/64, 32/64, 32/64, (32+1)/64} The precision extended output sequence obtained by the multi-bit modulation method is: {32/64, 32/64, 32/64, (32-1)/64, 32/64, 32/64, 32/64, (32+2) ) / 64}, and the precision of each sequence item of the precision extended output sequence is equal to or less than the precision of the low precision PWM signal. During the precision expansion period, each sequence of precision extended outputs is sequentially executed for modulating the low-precision PWM signal, and the time for executing each of the precision extended output sequences is the duty cycle time of the low-precision PWM signal. After executing all the precision extended output sequences, repeat the execution process until the new PWM high precision duty cycle is obtained, and then the previous PWM high precision The duty cycle is compared. After modulating the low-precision PWM signal, outputting a control signal corresponding to the precision extended output sequence for controlling the turn-on and turn-off times of one or more sets of power switch tubes in the plurality of sets of power switch tubes, thereby making each power The switching tube has a one-to-one correspondence with the duty ratio of the precision extended output sequence during the duty cycle of the PWM unit.

It should be noted that if the previous PWM high-precision duty value is 248/512 (48.44%), the current PWM duty value 257/512 (50.19%) is recorded, and the current PWM duty value is compared with the previous one. The PWM duty cycle values are compared with a difference of 1.75% and a set threshold of 1%. It can be seen that the difference is greater than the set threshold, so the precision extended output sequence is no longer determined according to the high precision duty value 257/512 (50.19%), and the precision extended output sequence is executed, thereby outputting the control signal to control Turn-on and turn-off time of the power switch. Instead, the current PWM high-precision duty cycle value of 257/512 (50.19%) is converted to the nearest PWM low-precision duty cycle value in the system. For example, the closest duty cycle value in the system is 32/64 (50%). And outputting a control signal corresponding thereto according to the low-precision duty value for controlling the turn-on and turn-off times of one or more sets of power switch tubes in the plurality of sets of power switch tubes, thereby causing each The power switch tube has a duty ratio value corresponding to the duty ratio value of the low-precision PWM signal in the PWM unit duty cycle.

The control method for the pulse width modulation of the DC brushless motor provided by the embodiment of the present invention obtains the difference by comparing the duty value of the current PWM with the previous PWM duty value, and determines the precision expansion mode when the difference is less than a predetermined threshold. The low-precision PWM signal is modulated by the precision extended output sequence in the precision extended mode. Thereby, the PWM precision control of the DC brushless motor is realized, the speed step effect under the open loop control is weakened, the steady-state speed error fluctuation range of the closed loop control is reduced, and the system performance is improved.

2 is a driving device of a DC brushless motor according to an embodiment of the present invention; the device is used to implement a control method for a pulse width modulation of a DC brushless motor provided by the above embodiments. The device comprises: a control module 201, an accuracy expansion module 202, and a modulation module 203.

The control module 201 is configured to acquire a PWM high precision duty value. The accuracy expansion module 202 is configured to determine a precision expansion mode of the PWM signal according to the PWM high precision duty value. Specifically: PWM The high-precision duty value is compared with the previous PWM high-precision duty value to obtain a difference. When the difference is less than a predetermined threshold, the precision expansion mode of the PWM signal is determined. The precision extension mode includes a precision extension period and an accuracy extension output sequence. The modulation module 203 is configured to, according to the precision extended output sequence, modulate the low-precision PWM signal and output the control signal during the precision extension period.

Preferably, the control module 201 acquires a PWM high-precision duty value according to the operating state data of the DC brushless motor, wherein the operating state data specifically includes: a rotor angular velocity or a torque current of the DC brushless motor in the closed-loop control system, or is on Externally set data is used directly in the ring control system.

The DC brushless motor driving device provided by the embodiment of the present invention acquires a PWM high-precision duty value through a control module, and obtains an accuracy expansion mode according to the duty value; the modulation module uses the precision in the precision expansion mode to expand the output sequence to a low The precision PWM signal is modulated. Thereby, the speed step effect under the open loop control is weakened, and the steady-state speed error fluctuation range of the closed loop control is reduced.

FIG. 3 is a driving system of a brushless DC motor according to an embodiment of the present invention. The system includes a power control module 204 in addition to the driving device described above.

The power control module 204 includes a plurality of sets of power switch tubes for receiving control signals from the modulation mode 203, and controlling turn-on and turn-off of one or more sets of power switch tubes of the plurality of sets of power switch tubes according to the control signals time.

In addition, the driving device is further configured to control the turning on and off of one or more sets of the power switching tubes of the plurality of sets of power switching tubes according to the position signals of the rotors of the DC brushless motor.

In a specific example, the control module 201 calculates the PWM high-precision duty cycle value according to the rotor angular velocity of the brushless DC motor through a certain control algorithm. For example, the current duty ratio obtained by the control module 201 is 257/512 (50.19%), the previous PWM duty value is 255/512 (49.80%), and the precision of the low-precision PWM duty value is 6-bit precision. The accuracy expansion module 202 records the current PWM duty cycle value and compares the current PWM duty cycle value to the previous PWM duty cycle value with a difference of 0.39% and a set threshold of 1%. Therefore, the difference is less than a predetermined threshold and can be based on the current PWM duty value of 257/512 (50.19%). Determine the precision expansion mode of the PWM signal.

The precision expansion module 202 selects a suitable precision expansion period according to the electromechanical parameter optimization of the motor system. For example, in this embodiment, the duty cycle of the eight low-precision PWM signals is selected as an accuracy extension period, and the precision extended output sequence can also be based on the motor. The electromechanical parameters of the system are optimized and the modulation mode is generated. For example, the precision extended output sequence obtained by single-bit modulation is: {32/64, 32/64, 32/64, 32/64, 32/64, 32/64, 32/64, (32+1)/64} The precision extended output sequence obtained by multi-bit modulation is: {32/64, 32/64, 32/64, (32-1)/64, 32/64, 32/64, 32/64, (32+2) ) /64}. Moreover, the accuracy of each sequence item of the precision extended output sequence is equal to or less than the precision of the low precision PWM signal. During the precision extension period, the modulation module 203 sequentially performs a sequence of each precision extended output for modulating the low precision PWM signal, and the time for executing each of the precision extended output sequences is the duty cycle time of the low precision PWM signal. After the modulation module 203 executes all the precision extended output sequences, the execution process is repeated until a new PWM high precision duty value is obtained, and then compared with the previous PWM high precision duty value. After modulating the low-precision PWM signal, the modulation module 203 is further configured to output a control signal corresponding to the precision extended output sequence.

The power control module 204 receives the control signal sent by the modulation module 203, and controls the turn-on and turn-off times of one or more sets of power switch tubes in the plurality of sets of power switch tubes according to the control signal, thereby causing each power switch During the PWM unit duty cycle, the duty cycle value corresponds to the duty cycle value of the precision extended output sequence. In addition, the driving device is further configured to control the turning on and off of one or more sets of the power switching tubes of the plurality of sets of power switching tubes according to the position signals of the rotors of the DC brushless motor.

It should be noted that if the previous PWM high-precision duty value is 248/512 (48.44%), the accuracy expansion module 202 records the current PWM duty value 257/512 (50.19%) and the current PWM duty. The ratio is compared to the previous PWM duty cycle value with a difference of 1.75% and a predetermined threshold of 1%. Therefore, the difference is greater than the predetermined threshold, so the accuracy expansion module 203 no longer determines the precision extended output sequence according to the high precision duty value 257/512 (50.19%). The modulation module 203 also does not need to perform a precision extended output sequence, thereby outputting a control signal to control the on and off times of the power switch. Rather, the current PWM high-precision duty cycle value 257/512 (50.19%) is converted to the nearest PWM low-precision duty cycle value in the system by using a conversion device inside the modulation module 203, such as the closest duty cycle in the system. The ratio is 32/64 (50%), and the modulation module 203 outputs a control signal corresponding thereto according to the low-precision duty value, and the power control module 204 controls one or more groups of the plurality of power switch tubes. The turn-on and turn-off time of the power switch tube is such that each power switch tube has a duty ratio value corresponding to the duty ratio value of the low-precision PWM signal in the PWM unit duty cycle.

The driving system of the brushless DC motor provided by the invention obtains the PWM high-precision duty value by using the control module in the driving device; and obtains the precision expansion mode according to the duty value; the modulation module uses the precision extended output in the precision expansion mode The sequence modulates the low-precision PWM signal, and outputs a control signal for controlling the power switch tube, and the power control module controls the turn-on and turn-off time of the power switch tube. Thereby, the speed step effect under the open loop control is weakened, the steady-state speed error fluctuation range of the closed loop control is reduced, and the system performance is improved.

A person skilled in the art should further appreciate that the elements and algorithm steps of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both, in order to clearly illustrate hardware and software. Interchangeability, the composition and steps of the various examples have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the solution. A person skilled in the art can use different methods for implementing the described functions for each particular application, but such implementation should not be considered to be beyond the scope of the present invention.

The steps of a method or algorithm described in connection with the embodiments disclosed herein can be implemented in hardware, a software module executed by a processor, or a combination of both. The software module can be placed in random access memory (RAM), memory, read only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or technical field. Any other form of storage medium known.

The specific embodiments of the present invention have been described in detail with reference to the preferred embodiments of the present invention. All modifications, equivalent substitutions, improvements, etc., made within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims

A method for controlling pulse width modulation of a DC brushless motor, characterized in that the method comprises:

Obtaining a PWM pulse width modulation high precision duty value;

Determining, according to the PWM high-precision duty value, a precision extended mode of the PWM signal, where the precision extended mode includes a precision extended period and an accuracy extended output sequence;

During the precision expansion period, the output sequence is expanded according to the precision, the low-precision PWM signal is modulated, and the control signal is output.
The method according to claim 1, wherein the obtaining the PWM high-precision duty value comprises: acquiring the PWM high-precision duty value according to the operating state data of the DC brushless motor.
The method according to claim 1, wherein the determining the precision expansion mode of the PWM signal according to the PWM high-precision duty value comprises: the PWM high-precision duty value and the previous PWM high The precision duty cycle values are compared to obtain a difference value;

The precision expansion mode of the PWM signal is determined when the difference is less than a predetermined threshold.
The method according to claim 1, wherein the precision extension period and the precision extension output sequence are optimized according to electromechanical parameters of the motor system;

Moreover, each sequence item precision of the precision extended output sequence is less than or equal to the precision of the low precision PWM signal.
The method of claim 1 wherein said control signal is used to control the turn-on and turn-off times of one or more sets of power switch tubes of the plurality of sets of power switch tubes.
A driving device for a brushless DC motor, characterized in that the device comprises:

a control module for acquiring a PWM high precision duty cycle value;

And an accuracy expansion module, configured to determine, according to the PWM high-precision duty value, an accuracy expansion mode of the PWM signal, where the precision expansion mode includes an accuracy extension period and an accuracy extension output sequence;

a modulation module, configured to expand the output sequence according to the precision during the precision extension period, The low precision PWM signal is modulated and the control signal is output.
The device according to claim 6, wherein the control module is specifically configured to: acquire a PWM high precision duty value according to operating state data of the brushless DC motor.
The device according to claim 6, wherein the precision expansion module is specifically configured to compare a PWM high precision duty value with a previous PWM high precision duty value to obtain a difference;

The precision expansion mode of the PWM signal is determined when the difference is less than a predetermined threshold.
A driving system for a brushless DC motor, comprising: the driving device and the power control module according to claim 6;

The power control module includes a plurality of sets of power switch tubes for receiving control signals from the modulation module, and controlling conduction and conduction of one or more sets of power switch tubes of the plurality of sets of power switch tubes according to the control signals The time of shutdown.
The system according to claim 9, wherein the driving device is further configured to control one or more sets of the power switch tubes of the plurality of sets of power switch tubes according to a position signal of a rotor of the brushless DC motor Turn on and off.