阅读说明：本技术 一种用于无刷直流电机的转子换相控制系统及方法 (Rotor phase change control system and method for brushless direct current motor ) 是由 李延吉 李家良 于 2019-08-27 设计创作，主要内容包括：用于无刷直流电机的转子换相控制系统及方法,包括逆变器、检测模块以及主控模块。逆变器包括三个上管和三个下管,逆变器根据接收的换相信号和脉冲信号调整上管和下管的工作状态,从而控制转子进行换相,以驱动无刷直流电机。检测模块在一个脉冲调制周期内检测到非导通相的反电势的过零点时,输出过零点信号给主控模块,由主控模块延迟预设电角度后输出换相信号；并且,主控模块根据当前非导通相的反电势升降情况相应输出第一斩波信号或第二斩波信号,以相应控制下管斩波或上管斩波,使得在任一完整脉冲调制周期内,均可检测反电势的过零点,从而高精度换相,可靠性高；并且,无需采用位置传感器检测转子位置,简化了电机结构和降低了整体成本。(The rotor phase-change control system and method for the brushless direct current motor comprise an inverter, a detection module and a main control module. The inverter comprises three upper tubes and three lower tubes, and the inverter adjusts the working states of the upper tubes and the lower tubes according to the received commutation signals and pulse signals, so that the rotor is controlled to carry out commutation to drive the brushless direct current motor. When the detection module detects the zero crossing point of the counter potential of the non-conductive phase in a pulse modulation period, a zero crossing point signal is output to the main control module, and a phase change signal is output after the main control module delays a preset electrical angle; in addition, the main control module correspondingly outputs a first chopping signal or a second chopping signal according to the back electromotive force lifting condition of the current non-conductive phase so as to correspondingly control lower tube chopping or upper tube chopping, so that the zero crossing point of the back electromotive force can be detected in any complete pulse modulation period, and therefore high-precision phase change is realized, and the reliability is high; and moreover, a position sensor is not required to be adopted to detect the position of the rotor, so that the structure of the motor is simplified, and the overall cost is reduced.)

1. The utility model provides a rotor commutation control system for brushless DC motor, brushless DC motor adopts two liang to switch on and the working method of six states of three-phase, its characterized in that, rotor commutation control system includes:

the inverter comprises three bridge arms which are connected in parallel, each bridge arm comprises an upper tube and a lower tube, and the inverter is used for correspondingly adjusting the working states of the three upper tubes and the three lower tubes according to a received phase change signal and a pulse signal so as to enable a rotor of the brushless direct current motor to carry out phase change to drive the brushless direct current motor;

the detection module is connected with the inverter and is used for detecting a zero crossing point of counter electromotive force of the non-conductive phase in one pulse modulation period and outputting a zero crossing point signal when the zero crossing point of the counter electromotive force of the non-conductive phase is detected; and

the main control module is connected with the inverter and the detection module and is used for delaying a preset electrical angle to output the commutation signal to the inverter after receiving the zero crossing point signal;

the main control module is further configured to output a first chopping signal to chop the lower tube that is connected and corresponding to the lower tube when it is determined that the back electromotive force of the non-conductive phase in the brushless dc motor is in a rising state, or output a second chopping signal to chop the upper tube that is connected and corresponding to the upper tube when it is determined that the back electromotive force of the non-conductive phase in the brushless dc motor is in a falling state.

2. The rotor commutation control system of claim 1, further comprising:

and the calculation module is connected with the detection module and the inverter and used for calculating the virtual center point voltage of the brushless direct current motor in real time and feeding back the virtual center point voltage to the detection module.

3. The rotor commutation control system of claim 2, wherein the detection module is implemented using a comparator;

the positive phase input end of the comparator is connected with the inverter and is used for receiving the terminal voltage of a non-conducting phase in the brushless direct current motor in real time;

and the inverting input end of the comparator is connected with the computing module and is used for receiving the virtual center point voltage in real time.

4. The rotor commutation control system of claim 1, further comprising:

and the power supply module is connected with the inverter and used for providing direct current signals for the inverter.

5. The rotor commutation control system of claim 1, wherein the preset electrical angle is 30 °.

6. The rotor commutation control system of claim 1, wherein three upper tubes and three lower tubes are implemented with power switching tubes; and the grids of the power switching tubes are connected with the main control module and used for receiving the pulse signals.

7. A rotor commutation control method for a brushless direct current motor adopts a working mode of two-to-two conduction and three-phase six-state; the rotor commutation control method is characterized by comprising the following steps:

the method comprises the steps that an inverter is adopted to correspondingly adjust working states of three upper tubes and three lower tubes according to received phase change signals and pulse signals, so that a rotor of the brushless direct current motor is controlled to carry out phase change to drive the brushless direct current motor, the inverter comprises three bridge arms which are connected in parallel, and each bridge arm comprises one upper tube and one lower tube;

detecting a zero crossing point of counter electromotive force of the non-conductive phase in a pulse modulation period by using a detection module, and outputting a zero crossing point signal when the zero crossing point of the counter electromotive force of the non-conductive phase is detected;

adopting a main control module to delay a preset electrical angle to output the commutation signal to the inverter after receiving the zero crossing point signal;

judging the lifting condition of the counter electromotive force of the non-conducting phase under the current state of the brushless direct current motor by adopting the main control module;

when the main control module is adopted to judge that the back electromotive force is in a rising state, a first chopping signal is output so as to chop the lower tube which is conducted correspondingly;

and when the main control module is adopted to judge that the back electromotive force is in a descending state, outputting a second chopping signal to chop the upper tube which is conducted correspondingly.

8. The rotor commutation control method of claim 7, further comprising:

calculating the virtual center point voltage of the brushless direct current motor in real time by adopting a calculation module and feeding back the virtual center point voltage to the detection module, wherein the calculation formula is as follows:

wherein, the V_refFor the virtual center point voltage, the V_AIs the voltage of the U-phase terminal, V_BIs a voltage at the V-phase terminal, said V_CIs the voltage of the W phase terminal.

9. The rotor commutation control method of claim 8,

the method comprises the following steps of detecting a zero crossing point of counter electromotive force of a non-conductive phase in a pulse modulation period by using a detection module, and outputting a zero crossing point signal when the zero crossing point of the counter electromotive force of the non-conductive phase is detected, wherein the detection module specifically comprises the following steps:

receiving the terminal voltage of a non-conducting phase of the brushless direct current motor in real time by adopting a comparator through a positive phase input end;

receiving the virtual center point voltage in real time by adopting a comparator through an inverting input end;

and comparing the terminal voltage of the non-conducting phase with the virtual central point voltage in real time by adopting the comparator, and outputting a first level signal through an output end when the terminal voltage of the non-conducting phase is greater than the virtual central point voltage, or outputting a second level signal through the output end when the terminal voltage of the non-conducting phase is less than the virtual central point voltage.

10. The rotor commutation control method of claim 7,

the main control module is adopted to judge the lifting condition of the counter electromotive force of the non-conducting phase under the current state of the brushless direct current motor, and the method specifically comprises the following steps:

the main control module judges that the conducting phase sequence is VW phase conducting, and when the U phase is non-conducting, the counter potential of the U phase is judged to be in a descending state under the current state;

the main control module judges that the conducting phase sequence is VU phase conducting, and when the W phase is non-conducting, the counter potential of the W phase is judged to be in a rising state under the current state;

the main control module judges that the conduction phase sequence is WU phase conduction, and when the V phase is not conducted, the main control module judges that the counter potential of the V phase is in a descending state under the current state;

the main control module judges that the conduction phase sequence is WV phase conduction, and when the U phase is non-conduction, the counter potential of the U phase is in a rising state under the current state;

the main control module judges that the conducting phase sequence is UV phase conducting, and when the W phase is not conducting, the counter potential of the W phase is in a descending state under the current state;

and the main control module judges that the conducting phase sequence is UW phase conduction, and when the V phase is non-conducting, judges that the counter potential of the V phase is in a rising state under the current state.

Technical Field

The invention belongs to the technical field of brushless direct current motors, and particularly relates to a rotor phase commutation control system and method for a brushless direct current motor.

Background

Brushless dc motors are widely used in everyday electronic products. For a brushless direct current motor adopting a pairwise conduction three-phase six-state working mode, a rotor needs to be controlled to accurately change phases. Currently, conventional brushless dc motor control techniques typically employ a position sensor to detect position information of the rotor to determine when the brushless dc motor is to be phase-commutated. However, position alignment is required when mounting the position sensor; in the using process of the motor, once the position sensor shifts due to an external force factor, the precision of position detection of the position sensor is greatly reduced; also, the use of a position sensor increases the cost of the motor and makes its structure more complicated.

Therefore, the conventional brushless dc motor control technology has the problems of low reliability and complex motor structure due to the dependence on the position sensor to detect the position information of the rotor.

Disclosure of Invention

In view of this, embodiments of the present invention provide a system and a method for controlling phase commutation of a rotor of a brushless dc motor, so as to solve the problems of low reliability and complex motor structure caused by relying on a position sensor to detect position information of the rotor in the conventional brushless dc motor control technology, and achieve the beneficial effect that the rotor of the brushless dc motor can perform accurate phase commutation without relying on the position sensor.

A first aspect of an embodiment of the present invention provides a rotor commutation control system for a brushless dc motor, the brushless dc motor operating in a two-by-two conduction and three-phase six-state mode, the rotor commutation control system including:

the inverter comprises three bridge arms which are connected in parallel, each bridge arm comprises an upper tube and a lower tube, and the inverter is used for correspondingly adjusting the working states of the three upper tubes and the three lower tubes according to a received phase change signal and a pulse signal so as to enable a rotor of the brushless direct current motor to carry out phase change to drive the brushless direct current motor;

the detection module is connected with the inverter and is used for detecting a zero crossing point of counter electromotive force of the non-conductive phase in one pulse modulation period and outputting a zero crossing point signal when the zero crossing point of the counter electromotive force of the non-conductive phase is detected; and

the main control module is connected with the inverter and the detection module and is used for delaying a preset electrical angle to output the commutation signal to the inverter after receiving the zero crossing point signal;

the main control module is further configured to output a first chopping signal to chop the lower tube that is connected and corresponding to the lower tube when it is determined that the back electromotive force of the non-conductive phase in the brushless dc motor is in a rising state, or output a second chopping signal to chop the upper tube that is connected and corresponding to the upper tube when it is determined that the back electromotive force of the non-conductive phase in the brushless dc motor is in a falling state.

A second aspect of an embodiment of the present invention provides a rotor commutation control method for a brushless dc motor, where the brushless dc motor adopts a two-by-two conduction and three-phase six-state working mode, and the rotor commutation control method includes:

the method comprises the steps that an inverter is adopted to correspondingly adjust working states of three upper tubes and three lower tubes according to received phase change signals and pulse signals, so that a rotor of the brushless direct current motor is controlled to carry out phase change to drive the brushless direct current motor, the inverter comprises three bridge arms which are connected in parallel, and each bridge arm comprises one upper tube and one lower tube;

detecting a zero crossing point of counter electromotive force of the non-conductive phase in a pulse modulation period by using a detection module, and outputting a zero crossing point signal when the zero crossing point of the counter electromotive force of the non-conductive phase is detected;

adopting a main control module to delay a preset electrical angle to output the commutation signal to the inverter after receiving the zero crossing point signal;

judging the lifting condition of the counter electromotive force of the non-conducting phase under the current state of the brushless direct current motor by adopting the main control module;

when the main control module is adopted to judge that the back electromotive force is in a rising state, a first chopping signal is output so as to chop the lower tube which is conducted correspondingly;

and when the main control module is adopted to judge that the back electromotive force is in a descending state, outputting a second chopping signal to chop the upper tube which is conducted correspondingly.

According to the rotor phase change control system and method for the brushless direct current motor, when the detection module detects the zero crossing point of the counter electromotive force of the non-conducting phase in a pulse modulation period, the zero crossing point signal is output to the main control module, the main control module outputs the phase change signal to the inverter after delaying the preset electric angle, a position sensor is not needed to be adopted for detecting the position of the rotor, and the structure and the overall cost of the motor are simplified; and the main control module correspondingly outputs a first chopping signal or a second chopping signal according to the back electromotive force lifting condition of the current non-conductive phase so as to correspondingly control lower tube chopping or upper tube chopping, so that the detection module can detect the zero crossing point of the back electromotive force in any complete pulse modulation period, and therefore phase commutation is carried out, and the phase commutation precision and the reliability are high.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

Fig. 1 is a schematic block diagram of a rotor commutation control system for a brushless dc motor according to a first aspect of an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a rotor commutation control system according to another embodiment of the present invention;

FIG. 3 is a schematic circuit diagram of an inverter in the rotor commutation control system shown in FIG. 1 or FIG. 2;

FIG. 4 is a schematic circuit diagram of a detection module in the rotor commutation control system shown in FIG. 1 or FIG. 2;

FIG. 5 is a diagram of back emf waveforms of the three-phase windings of the brushless DC motor during a one-point cycle;

fig. 6 is a specific flowchart of a rotor commutation control method for a brushless dc motor according to a second aspect of the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Fig. 1 is a schematic structural diagram of a rotor commutation control system for a brushless dc motor according to a first aspect of an embodiment of the present invention, and for convenience of description, only parts related to the embodiment are shown, and detailed descriptions are as follows:

the rotor commutation control system provided in this embodiment includes an inverter 10, a detection module 20, and a main control module 30.

The brushless dc motor M adopts a two-to-two conduction and three-phase six-state working mode, and the following part of the contents will simply refer to the "brushless dc motor M" as the "motor".

The inverter 10 is connected with the detection module 20, the detection module 20 is connected with the main control module 30, and the main control module 30 is connected with the inverter 10.

The inverter 10 is configured to correspondingly adjust working states of the three upper tubes and the three lower tubes according to the received phase change signal and the pulse signal, so that a rotor of the brushless dc motor M performs phase change to drive the brushless dc motor M.

The detection module 20 is configured to detect a zero crossing point of the counter potential of the non-conductive phase in one pulse modulation period, and output a zero crossing point signal when the zero crossing point of the counter potential of the non-conductive phase is detected.

The main control module 30 is configured to delay a preset electrical angle to output a phase change signal to the inverter 10 after receiving the zero crossing point signal.

Specifically, the Pulse signal is a PWM (Pulse Width Modulation) signal. The pulse modulation period is a period of the PWM signal, and the pulse modulation period includes two states of PWM-ON and PWM-OFF, where the PWM signal is at a high level and is called a PWM-ON state, and the PWM signal is at a low level and is called a PWM-OFF state.

Optionally, the preset electrical angle is an electrical angle of 30 degrees, and when the main control module 30 receives a zero-crossing point signal output by the detection module 20, it indicates that the back emf reaches the zero-crossing point at this moment, and the time when the back emf reaches the zero-crossing point is delayed by 30 degrees by an electrical angle, which is a commutation point, so that the commutation point can be accurately detected by accurately detecting the zero-crossing point, and the rotor of the motor M is controlled to perform commutation at the commutation point, thereby avoiding generating commutation offset, and further influencing the normal operation of the motor M.

The rotor commutation control system provided by the embodiment detects the zero crossing point of the counter electromotive force of the non-conducting phase in a pulse modulation period through the detection module 20, and when the zero crossing point is detected, the zero crossing point signal is output to the main control module 30, and the main control module 30 outputs the commutation signal after delaying the preset electrical angle, so that commutation is realized, a position sensor is not needed to be adopted to detect the position of the rotor, the situation that the installation position of the position sensor has deviation or is in the use process of the motor M, once the position sensor shifts due to an external force factor, the obtained position information is incorrect, and the problem of low system reliability is caused, and the power consumption of the system is greatly saved, the system is energy-saving and environment-friendly, the circuit is simple, and.

In this embodiment, the main control module 30 is further configured to output a first chopping signal to chop the lower tube conducting the corresponding lower tube when determining that the back electromotive force of the non-conducting phase in the brushless dc motor M is in the rising state, or output a second chopping signal to chop the upper tube conducting the corresponding upper tube when determining that the back electromotive force of the non-conducting phase in the brushless dc motor M is in the falling state.

When the counter potential of the non-conducting phase rises, the lower tube is controlled to chop so that the zero crossing point of the counter potential can be detected in a complete pulse modulation period; when the back electromotive force of the non-conducting phase is reduced, the upper tube chopping is controlled, so that the zero crossing point of the back electromotive force can be detected in a complete pulse modulation period.

Therefore, compared with the conventional technology that zero crossing point detection can only be performed during PWM-ON, in this embodiment, the lower tube or the upper tube is controlled to perform chopping correspondingly according to the back emf rise and fall condition of the non-conducting phase during any conducting phase sequence, so that the detection module 20 can detect the zero crossing point of the back emf within a complete pulse modulation period, thereby greatly improving the detection precision of the zero crossing point, greatly improving the commutation precision, and achieving high reliability of the system.

Fig. 2 is a schematic structural diagram of a rotor commutation control system according to another embodiment of the present invention, and for convenience of description, only the parts related to this embodiment are shown, and detailed descriptions are as follows:

in an alternative embodiment, the rotor commutation control system further comprises a power module 40 and a calculation module 50.

The power module 40 is connected to the inverter 10, and is configured to provide a dc signal VCC to the inverter 10.

The calculating module 50 is connected to the detecting module 20 and the inverter 10, and is configured to calculate the virtual center point voltage of the motor M in real time, and feed back the virtual center point voltage to the detecting module 20.

Specifically, the calculation formula of the virtual center point voltage is as follows:

wherein, the voltage of the U-phase terminal, V_BIs a voltage at the V-phase terminal, said V_CIs the voltage of the W phase terminal.

Specifically, the detection module 20 outputs a zero-crossing point signal to the main control module 30 by comparing the terminal voltage of the non-conducting phase with the virtual center point voltage when the terminal voltage of the non-conducting phase jumps from being greater than the virtual center point voltage to being less than the virtual center point voltage, or when the terminal voltage of the non-conducting phase jumps from being less than the virtual center point voltage to being greater than the virtual center point voltage.

Fig. 3 is a schematic circuit diagram of the inverter 10 in the rotor commutation control system shown in fig. 1 or fig. 2, and for convenience of description, only the parts related to the present embodiment are shown, and detailed descriptions are as follows:

in an optional embodiment, the three upper tubes Q1, Q3, and Q5 and the three lower tubes Q2, Q4, and Q6 are implemented by power switching tubes, and gates of the power switching tubes are connected to the main control module 30 and are configured to receive the pulse signals output by the main control module 30.

As shown in fig. 3, an upper tube Q1 and a lower tube Q2 form one bridge arm, an upper tube Q3 and a lower tube Q4 form the other bridge arm, and an upper tube Q5 and a lower tube Q6 form the third bridge arm; each bridge arm comprises an upper pipe and a lower pipe, drain electrodes of the three upper pipes are connected with a direct current signal VCC, source electrodes of the three upper pipes are respectively connected with drain electrodes of the corresponding three lower pipes, and source electrodes of the three lower pipes are grounded; the inverter 10 further includes freewheeling diodes connected in parallel with the upper and lower tubes, respectively, one to one, for providing a freewheeling path when the upper tube in parallel therewith is disconnected. Optionally, the freewheeling diode may be replaced by an embedded diode of six power switching transistors Q1-Q6.

The conducting phase sequence of the motor M and the conducting sequence of the power switching tubes Q1-Q6 are shown in the following table 1:

table 1 shows that six power switching tubes Q1-Q6 form a full bridge driving circuit together, and are used to control the energization state of the M windings of the motor, the power switching tubes are turned on two by two, two power switching tubes are turned on at each instant, the rotor of the motor M performs phase change once in each 1/6 electrical period, that is, in 60 electrical angle, each power switching tube is continuously turned on for 120 electrical angle, and corresponding to each phase winding, the phase current direction is not changed in the period between two phase changes.

When the conducting phase sequence of the motor M is that the VW phase is conducting and the U phase is not conducting, according to the back potential waveform diagram shown in fig. 5, the back potential of the U phase is in a falling state, the back potential of the U phase gradually falls from a position larger than zero to a position smaller than zero, the main control module 30 controls the upper tube to chop, so that the Q3 is controlled to chop, the Q6 is normally open, and the remaining four power switching tubes are all in a cut-off state except that the Q3 and the Q6 are conducting.

When the conducting phase sequence of the motor M is that the VU phase is conducted and the W phase is not conducted, according to the back potential waveform diagram shown in fig. 5, the back potential of the W phase is in a rising state, the back potential of the W phase gradually rises from a position smaller than zero to a position larger than zero, the main control module 30 controls the lower tube to perform chopping, so that the Q2 is controlled to perform chopping, the Q3 is normally open, and the remaining four power switching tubes are in a cut-off state except that the Q2 and the Q3 are conducted.

When the conducting phase sequence of the motor M is WU phase conducting and V phase non-conducting, according to the back potential waveform diagram shown in fig. 5, the back potential of the V phase is in a falling state, the back potential of the V phase gradually falls from a position larger than zero to a position smaller than zero, the main control module 30 controls the upper tube to chop, so that the Q5 chop is controlled, the Q2 is normally open, and the remaining four power switching tubes are in a cut-off state except that the Q5 and the Q2 are conducting.

When the conducting phase sequence of the motor M is WV phase conducting and U phase non-conducting, according to the back potential waveform diagram shown in fig. 5, the back potential of the U phase is in a rising state, and the back potential of the U phase gradually rises from a position smaller than zero to a position larger than zero, the main control module 30 controls the lower tube to chop, so that the Q4 chop is controlled, the Q5 is normally open, and the remaining four power switching tubes are all in a cut-off state except that the Q4 and the Q5 are conducting.

When the conducting phase sequence of the motor M is that the UV phase is conducted and the W phase is not conducted, according to the back potential waveform diagram shown in fig. 5, the back potential of the W phase is in a falling state, the back potential of the W phase gradually falls from a position larger than zero to a position smaller than zero, the main control module 30 controls the upper tube to chop, so that the Q1 is controlled to chop, the Q4 is normally open, and the remaining four power switching tubes are in a cut-off state except that the Q1 and the Q4 are conducted.

When the conducting phase sequence of the motor M is UW phase conducting and V phase non-conducting, according to the back potential waveform diagram shown in fig. 5, the back potential of the V phase is in a rising state, and the back potential of the V phase gradually rises from a position smaller than zero to a position larger than zero, the main control module 30 controls the lower tube to chop, so that the Q6 chop is controlled, the Q1 is normally open, and the remaining four power switching tubes are all in a cut-off state except that the Q6 and the Q1 are conducting.

The brushless dc motor M operates in a two-to-two conduction mode, where two-to-two conduction mode means that only two power switching tubes are conducted at any instant in the inverter 10, so as to control two phases of the three phases to operate, three phases refer to three states of a U-phase, a V-phase, and a W-phase of a winding of the motor M, and six states refer to six conduction phase sequences of the motor M shown in table 1.

The rotor commutation control system provided by this embodiment controls the lower tube chopping when the back electromotive force of the non-conductive phase rises through the main control module 30, and controls the upper tube chopping when the back electromotive force of the non-conductive phase falls, so that in a complete pulse modulation period, the detection module 20 can detect the zero crossing point of the back electromotive force, the detection precision of the zero crossing point is greatly improved, and therefore the commutation precision is greatly improved, and the system reliability is high.

Fig. 4 is a schematic circuit diagram of the detection module 20 in the rotor commutation control system shown in fig. 1 or fig. 2, and for convenience of description, only the parts related to the present embodiment are shown, and detailed descriptions are as follows:

in an alternative embodiment, the detection module 20 is implemented by a comparator,

the positive phase input end of the comparator is connected with the inverter 10 and is used for receiving the terminal voltage of a non-conducting phase in the brushless direct current motor M in real time; the inverting input of the comparator is connected to the calculating module 50 for receiving the virtual center point voltage in real time.

Specifically, the virtual center point voltage is a virtual center point voltage of the motor M, and a calculation formula thereof is as follows:

wherein, the V_AIs the voltage of the U-phase terminal, V_BIs a voltage at the V-phase terminal, said V_CIs the voltage of the W phase terminal.

The comparator compares the terminal voltage of the non-conducting phase with the virtual center point voltage, outputs a first level signal when the terminal voltage of the non-conducting phase is greater than the virtual center point voltage, and outputs a second level signal when the terminal voltage of the non-conducting phase is less than the virtual center point voltage. Optionally, the first level signal is a high level 1, the second level signal is a low level 0, and when a zero-crossing point of a counter potential of the non-conducting phase occurs, the level signal output by the comparator jumps from 1 to 0 or jumps from 0 to 1; the level signal output by the comparator jumps from 0 to 1 when the counter potential of the non-conductive phase is in a rising state and crosses zero, and jumps from 1 to 0 when the counter potential of the non-conductive phase is in a falling state and crosses zero.

When the counter potential of the non-conducting phase crosses the zero point, the level signal output by the comparator jumps, after the main control module 30 receives the jump signal, the jump signal is the zero point signal, and the main control module 30 delays the electric angle by 30 degrees to control and output the phase change signal to control the rotor to change the phase.

Optionally, the calculation module 50 is implemented by using three resistors, and one end of each of the three resistors is respectively connected to the U-phase terminal voltage, the V-phase terminal voltage, and the W-phase terminal voltage; the other ends of the three resistors are connected in common, and the voltage of the common end of the three resistors is a virtual center voltage point:

the rotor commutation control system provided by this embodiment detects the zero crossing point of the counter electromotive force of the non-conducting phase in a pulse modulation period through the comparator, and when the zero crossing point is detected, a zero crossing point signal is output to the main control module 30, and a commutation signal is output after the main control module 30 delays a preset electrical angle, thereby realizing commutation, without adopting a position sensor to detect the position of the rotor, and avoiding the installation position of the position sensor from deviating or in the use process of the motor M, once the position sensor shifts due to an external force factor, thereby causing the problem of low system reliability, and greatly simplifying the motor structure and reducing the cost.

As shown in fig. 5, it is a diagram of the back electromotive force waveform of the three-phase winding of the brushless dc motor M in one electrical cycle; the motor M carries out phase change at every 60-degree electrical angle, the rotor of the motor M takes the 60-degree electrical angle of a power-on sequence as a sector, and each sector corresponds to a conduction phase sequence, so that the rotor has six conduction phase sequences, namely six states; each conducting phase sequence shows that two phase windings are electrified, and one phase winding is suspended, namely two phase windings are conducted.

The main control module 30 outputs a pulse signal to the gate of each power switching tube in the inverter 10, and modulates the inverter 10 to operate based on the pulse signal. The period of the pulse signal is referred to as a pulse modulation period, and a state in which the pulse signal is at a high level in one pulse modulation period is referred to as PWM-ON, and a state in which the pulse signal is at a low level is referred to as PWM-OFF.

The following explains the working principle of the rotor commutation control system provided by the embodiment of the present invention by taking table 2 as an example and combining table 1, fig. 4 and fig. 5:

TABLE 2

The conventional position sensorless rotor position detection technique detects the back electromotive force only once in one pulse modulation period, and detects it only at the time of PWM-ON. Under the condition that the rotating speed of the motor M is low, compared with the electric period of the motor M, the pulse modulation period is very small, and the influence of the pulse modulation period can be ignored; however, when the rotation speed of the motor M is high, the difference between the PWM period and the electrical period of the motor M is small, and when there is an error in the pulse modulation period, the phase change of the motor M will be greatly shifted, which further causes the rotor of the motor M to perform phase change at a non-phase change point.

In view of the problems of the conventional rotor position detection technology without a position sensor, embodiments of the present invention provide a rotor commutation control system and method for a brushless dc motor, which can perform zero crossing point detection on the back electromotive force of a non-conducting phase in the entire pulse modulation period, thereby indirectly detecting the rotor position, deriving a commutation point, greatly improving commutation accuracy, and avoiding commutation offset.

As shown in table 2, the sectors of 270 ° to 330 ° are taken as examples to explain the principle and derived beneficial effects of the main control module 30 controlling the lower tube chopping when the back-emf of the non-conducting phase rises:

in the sector of 270-330 degrees, the conducting phase sequence is that the UW phase is conducted, the V phase is not conducted, the opposite potential of the V is in a rising state, the main control module 30 controls the lower tube Q6 to chop, and controls the upper tube Q1 to be normally open.

Setting the V opposite potential as x, when theta is less than 300 degrees, x is less than 0; when theta is larger than 300 DEG, x is larger than 0.

During PWM-ON, current flows from the power supply module 40 to ground via the upper tube Q1, the U-phase winding, the W-phase winding, and the lower tube Q6; in this process, the neutral point voltage of the motor M is: v_NVCC/2; the terminal voltage of the V phase is:

during PWM-OFF, current flows from the power supply module 40 back to the power supply module 40 through Q1, the U-phase winding, the W-phase winding, the embedded diode of the upper tube Q5; in this process, the neutral point voltage of the motor M is: v_NVCC; the terminal voltage of the V phase is: v_B＝V_N+x＝VCC+x。

(1) During PWM-ON, the voltage at the U-phase end is: v_AThe terminal voltage of the W phase is VCC: v_C0, the voltage at the V-phase terminal isThe virtual center point voltage input to the inverting input terminal of the comparator is:

it can be seen that when x < 0, V_ref＞V_BThe comparator outputs a second level signal; when x > 0, V_ref＜V_BThe comparator outputs a first level signal. Therefore, the zero-crossing detection of the non-conducting phase is realized through the edge jump of the comparator.

(2) During PWM-OFF period, the voltage at U phase terminal is V_AVCC, W phase terminal voltage is V_CVCC, the voltage at the V phase terminal is V_B＝VCC+x。

When theta is less than 300 degrees, x is less than 0, and the voltage of the virtual center point isThus V_B＜V_refAnd the comparator outputs a second level signal.

When θ > 300 °, x >0, at this time V_BIs clamped to VCC and thereforeThe output state of the comparator is unstable, but because the counter potential x of the non-conducting phase has already passed through the zero point at the moment, if the comparator outputs a first level signal, level jump is determined to occur, and a zero-crossing point signal is output; if the comparator outputs a second level signal at this time, a zero crossing point may be detected in the PWM-ON phase of the next pulse modulation period.

To sum up, in the section of (1) and (2), the main control module 30 outputs the first chopping signal to control the lower tube to chop in the sector where the back electromotive force of the non-conducting phase rises, so that in a complete pulse modulation period, the comparator can judge the zero crossing point of the back electromotive force of the non-conducting phase according to whether the output level signal has edge jump or not in the PWM-ON period and the PWM-OFF period.

As shown in table 2, the 330 ° to 30 ° sectors are taken as an example to explain the principle and the derived beneficial effects of the main control module 30 for controlling the upper tube chopping when the back electromotive force of the non-conducting phase is reduced:

in a sector of 330 degrees to 30 degrees, the conducting phase sequence is VW phase conducting, U phase is non-conducting, and the reverse potential of U is in a descending state, and the main control module 30 controls the lower tube Q3 to chop and controls the upper tube Q6 to be normally open.

Setting the reverse potential of U as x, when theta is less than 360 degrees, x is more than 0; when theta is more than 360 degrees, x is less than 0.

During PWM-ON, current flows from the power supply module 40 to ground via the upper tube Q3, the V-phase winding, the W-phase winding, and the lower tube Q6; in this process, the neutral point voltage of the motor M is: v_NVCC/2; the terminal voltage of the U phase is:

during PWM-OFF period, current V phase winding, W phase winding, lower tubeThe embedded diodes of Q6 and lower tube Q4 flow back to the V-phase winding; in this process, the neutral point voltage of the motor M is: v_N0; the back-emf of the U-phase is x, and the terminal voltage of the U-phase is: v_A＝V_N+x＝x。

(3) During PWM-ON, the voltage at the V-phase terminal is: v_BThe terminal voltage of the W phase is VCC: v_CThe voltage at the U-phase end is 0The virtual center point voltage input to the inverting input terminal of the comparator is:

it can be seen that when x > 0, V_ref＜V_BThe comparator outputs a first level signal; when x is less than 0, V_ref＞V_BAnd the comparator outputs a second level signal. Therefore, the zero-crossing detection of the non-conducting phase is realized through the edge jump of the comparator.

(4) During PWM-OFF period, the voltage at U phase terminal is V_A0, W phase terminal voltage is V_C0, V phase terminal voltage V_B＝x。

When theta is less than 360 degrees, x is more than 0, and the voltage of the virtual center point isThus V_B＜V_refThe comparator outputs a first level signal.

When theta is greater than 360 DEG, x is less than 0, and V is_AIs clamped to 0, and thusThe output state of the comparator is unstable, but because the counter potential x of the non-conducting phase has already passed through the zero point at the moment, if the comparator outputs a second level signal, level jump is determined to occur, and a zero-crossing point signal is output; if the comparator outputs the first level signal at this time, a zero crossing point may be detected at the PWM-ON stage of the next pulse modulation period.

To sum up, in the section where the back electromotive force of the non-conducting phase decreases, the main control module 30 outputs the second chopping signal to control the lower tube to chop, so that in a complete pulse modulation period, the comparator can judge the zero crossing point of the back electromotive force of the non-conducting phase according to whether the output level signal has edge jump or not in the PWM-ON period and the PWM-OFF period.

To sum up, as described in the points (1), (2), (3) and (4), in this embodiment, when the back electromotive force of the non-conducting phase rises, the chopper of the lower tube is controlled, so that the zero-crossing point of the back electromotive force can be detected in a complete pulse modulation period; when the back electromotive force of the non-conducting phase is reduced, the upper tube chopping is controlled, so that the zero crossing point of the back electromotive force can be detected in a complete pulse modulation period. Therefore, compared with the conventional technology that zero crossing point detection can only be performed during PWM-ON, in this embodiment, the lower tube or the upper tube is controlled to perform chopping correspondingly according to the back emf rise and fall condition of the non-conducting phase during any conducting phase sequence, so that the detection module 20 can detect the zero crossing point of the back emf within a complete pulse modulation period, thereby greatly improving the detection precision of the zero crossing point, greatly improving the commutation precision, and achieving high reliability of the system.

Fig. 6 is a specific flowchart of a rotor commutation control method for a brushless dc motor according to a second aspect of the embodiment of the present invention, and for convenience of description, only the parts related to the embodiment are shown, and the details are as follows:

a rotor commutation control method for a brushless direct current motor is characterized in that the brushless direct current motor M adopts a working mode of two-to-two conduction and three-phase six-state; the rotor commutation control method comprises the following steps:

s01: the inverter 10 is adopted to correspondingly adjust the working states of the three upper tubes and the three lower tubes according to the received commutation signal and the pulse signal, so as to control the rotor of the brushless direct current motor M to carry out commutation to drive the brushless direct current motor M, wherein the inverter 10 comprises three bridge arms which are mutually connected in parallel, and each bridge arm comprises one upper tube and one lower tube;

s02: the detection module 20 is adopted to detect the zero crossing point of the counter electromotive force of the non-conductive phase in a pulse modulation period, and when the zero crossing point of the counter electromotive force of the non-conductive phase is detected, a zero crossing point signal is output;

s03: after receiving the zero crossing point signal, the main control module 30 delays a preset electrical angle to output a commutation signal to the inverter 10;

s04: the main control module 30 is adopted to judge the lifting condition of the back electromotive force of the non-conducting phase under the current state of the brushless direct current motor M;

s05: when the main control module 30 is adopted to judge that the back electromotive force is in a rising state, a first chopping signal is output so as to chop the lower tube which is conducted correspondingly;

s06: when the main control module 30 is used to determine that the back emf is in a decreasing state, a second chopping signal is output to chop the upper tube corresponding to the conduction.

Specifically, the pulse modulation period is a period of the PWM signal, and the pulse modulation period includes two states, PWM-ON and PWM-OFF, where the PWM signal is at a high level and is called as a PWM-ON state, and the PWM signal is at a low level and is called as a PWM-OFF state.

In an optional embodiment, the above rotor commutation control method further includes the following steps:

s07: the calculating module 50 is adopted to calculate the virtual center point voltage of the brushless dc motor M in real time and feed back the virtual center point voltage to the detecting module 20, and the calculation formula is as follows:

wherein, V_refIs a virtual center point voltage, V_AIs the voltage of the U-phase terminal, V_BIs the voltage of the V phase terminal, V_CIs the voltage of the W phase terminal.

Specifically, step S07 is executed before step S02.

In an alternative embodiment, step S02 specifically includes:

receiving the terminal voltage of a non-conducting phase of the brushless direct current motor M in real time by adopting a comparator through a positive phase input end;

a comparator is adopted to receive the virtual center point voltage in real time through an inverting input end;

and adopting a comparator to compare the terminal voltage of the non-conducting phase with the virtual central point voltage in real time, and outputting a first level signal through the output end when the terminal voltage of the non-conducting phase is greater than the virtual central point voltage, or outputting a second level signal through the output end when the terminal voltage of the non-conducting phase is less than the virtual central point voltage.

When the comparator detects the zero crossing point of the counter potential of the non-conducting phase in a pulse modulation period, a zero crossing point signal is output to the main control module 30, the main control module 30 outputs a phase change signal to the inverter 10 after delaying a preset electrical angle, a position sensor is not needed to be adopted for detecting the position of a rotor, the motor design is simplified, and the cost is reduced.

In an alternative embodiment, step S04 specifically includes:

the main control module 30 determines that the conducting phase sequence is VW phase conducting, and when U phase is non-conducting, determines that the back electromotive force of U phase is in a descending state in the current state;

the main control module 30 determines that the conducting phase sequence is VU phase conducting, and when the W phase is non-conducting, determines that the back electromotive force of the W phase is in a rising state in the current state;

the main control module 30 determines that the conduction phase sequence is WU phase conduction, and when the V phase is non-conduction, determines that the back electromotive force of the V phase is in a descending state in the current state;

the main control module 30 determines that the conduction phase sequence is WV phase conduction, and when U phase is non-conduction, determines that the back electromotive force of U phase is in a rising state in the current state;

the main control module 30 determines that the conducting phase sequence is UV phase conducting, and when the W phase is non-conducting, determines that the back electromotive force of the W phase is in a descending state in the current state;

the main control module 30 determines that the conducting phase sequence is UW phase conducting, and when the V phase is non-conducting, determines that the back electromotive force of the V phase is in a rising state in the current state.

Of course, the lifting condition of the non-conducting phase can be set according to actual requirements in six states of the motor M corresponding to the six conducting phase sequences, and the above shows one corresponding relationship between the lifting conditions of the conducting phase sequence and the non-conducting phase, and other corresponding relationships can be used in actual operation.

In summary, embodiments of the present invention provide a rotor commutation control system and method for a brushless dc motor, where a detection module detects a zero crossing point of a back electromotive force of a non-conducting phase in a pulse modulation period, and when the zero crossing point is detected, a zero crossing point signal is output to a main control module, and the main control module outputs a commutation signal after delaying a preset electrical angle, so as to implement commutation.

Compared with the traditional technology which can only detect the zero crossing point during PWM-ON, the invention correspondingly controls the lower tube or the upper tube to chop by the main control module according to the back electromotive force lifting condition of the non-conducting phase during any conducting phase sequence, so that the detection module can detect the zero crossing point of the back electromotive force in a complete pulse modulation period, the detection precision of the zero crossing point is greatly improved, the commutation precision is greatly improved, and the reliability of the system is high.

Various embodiments are described herein for various systems, circuits, and methods. Numerous specific details are set forth in order to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. However, it will be understood by those skilled in the art that the embodiments may be practiced without such specific details. In other instances, well-known operations, components and elements have been described in detail so as not to obscure the embodiments in the description. It will be appreciated by those of ordinary skill in the art that the embodiments herein and shown are non-limiting examples, and thus, it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the embodiments.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.