CN114362608B - Method for detecting counter electromotive force zero crossing point of brushless direct current motor - Google Patents
Method for detecting counter electromotive force zero crossing point of brushless direct current motor Download PDFInfo
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Abstract
The invention discloses a brushless direct current motor counter electromotive force zero crossing point detection method, which is characterized in that a timing unit is used for synchronizing PWM period interruption, an ADC module starts to collect A, B, C three-phase voltage in the brushless direct current motor, the frequency of the ADC module collecting the three-phase voltage is calculated in a PWM-ON stage, and according to the collection frequency, two conducting phase voltage and a third counter electromotive force collected by the ADC module, the magnitudes of the third counter electromotive force and half of the voltages of the two conducting phase lines are compared in a PWM rising edge or a PWM falling edge, so as to judge whether the third counter electromotive force crosses zero. The invention not only detects whether the third phase back electromotive force crosses the zero point in the PWM-ON stage, but also introduces a back electromotive force zero crossing pre-judging program in the PWM-OFF stage, thereby solving the problem that the third phase back electromotive force zero crossing point can not be detected in the PWM-OFF stage, greatly improving the phase-changing precision of the brushless DC motor and further improving the motor efficiency and the stability thereof.
Description
[ field of technology ]
The invention relates to the field of brushless motors, in particular to a method for detecting zero crossing points of back electromotive force of a brushless direct current motor.
[ background Art ]
In the technical field of sensorless drive control of a brushless direct current motor, an operation process of the brushless direct current motor may include a rotor pre-positioning stage, a low-speed operation stage, and a medium-high speed operation stage. In the prior art, the commutation operation is generally performed by detecting whether the back electromotive force of the suspended phase crosses zero: and sampling the phase voltage of the suspended phase of the brushless direct current motor once in each PWM control period by adopting an ADC module, and comparing the sampling result with a reference voltage to judge whether zero crossing occurs.
Because the counter electromotive force obviously exists in the PWM-ON phase, the ADC module only collects in the PWM-ON phase, once the real zero crossing point of the counter electromotive force occurs in PWM-OFF, the delay of zero crossing point time judgment can occur, especially in the high-speed (more than 10 ten thousand rotations) running process of the brushless direct current motor, the number of PWM cycles in one phase change interval is less, the counter electromotive force zero crossing detection delay can possibly cause the phase change delay of the brushless direct current motor, the reduction of the motor efficiency is extremely easy to cause even abnormal shutdown after the motor is out of step.
Therefore, it is necessary to design a method for detecting zero crossing point of back electromotive force of a brushless direct current motor to solve the above problems.
[ invention ]
Aiming at the defects of the prior art, the invention aims to provide a back electromotive force zero crossing point detection method of a brushless direct current motor, which is used for detecting the back electromotive force zero crossing point of a suspended phase.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a brushless DC motor back EMF zero crossing point detection method is used for detecting the suspended phase back EMF zero crossing point and comprises the following steps:
s1: the timing unit synchronizes the interruption of the PWM period, and simultaneously the ADC module starts to collect the voltage of the A, B, C three phases in the brushless direct current motor, wherein the brushless direct current motor operates in a 'two-phase conduction three-phase six-state' mode, each working state is only two-phase conduction, and the third phase is in a suspended state;
s2: entering a PWM-ON time period, the ADC module collects two conducting phase voltages and a floating phase counter electromotive force and stores the two conducting phase voltages and the floating phase counter electromotive force in a storage unit;
s3: in the PWM-ON time period, according to the fact that the counter electromotive force of the suspended phase is in a rising edge stage or a falling edge stage, comparing the last counter electromotive force of the suspended phase acquired by the ADC module with half of the voltages of the two conducting phase lines through an operation module, judging whether the counter electromotive force of the suspended phase is zero-crossing, entering a zero-crossing processing program if the counter electromotive force of the suspended phase is zero-crossing, and returning to S1 after finishing the zero-crossing; if the zero crossing is not achieved, entering a back electromotive force zero crossing pre-judging program in a PWM-OFF time period;
s4: entering a back electromotive force zero crossing prejudging program: taking the last two suspended counter electromotive force differences acquired by the ADC module in the PWM-ON time period as a reference, and calculating by the operation module: the times that the ADC module needs to collect three-phase voltages are when the time point of the last time of the collection of the floating phase counter electromotive force in the PWM-ON time period reaches the time point that the floating phase counter electromotive force is equal to half of the voltage of the two conducting phase lines;
s5: and comparing the times of the ADC module needing to collect the three-phase voltage with the times of the ADC module pre-collecting the three-phase voltage in the PWM-OFF time period by the operation module, judging whether the counter electromotive force of the suspended phase crosses zero in the PWM-OFF stage, and returning to S1 after the counter electromotive force of the suspended phase crosses zero.
Further, in the step S1, the timing unit reads the PWM-ON duration T1, the PWM-OFF duration T2, and the interruption period T of the ADC module for collecting the three-phase voltage of the brushless dc motor A, B, C;
in the step S2, the operation module invokes the T1 value in the timing unit, and calculates the number of times N of the ADC module to acquire the three-phase voltage in the T1 time period according to the formula "n=t1/T";
in the step S3, when n=1, the ADC module collects three-phase voltages only once, and when the counter electromotive force of the suspended phase is in the rising edge phase, if the counter electromotive force of the suspended phase is greater than or equal to half of the voltages of the two conducting phase lines, the ADC module enters a zero-crossing processing procedure, returns to S1 after finishing, and if the counter electromotive force of the suspended phase is less than half of the voltages of the two conducting phase lines, returns to S1 directly; in the falling edge stage of the suspended phase counter electromotive force, if the suspended phase counter electromotive force is less than or equal to half of the voltages of the two conducting phase lines, entering a zero-crossing processing program, returning to the step S1 after finishing, and if the suspended phase counter electromotive force is greater than half of the voltages of the two conducting phase lines, directly returning to the step S1;
when N is more than or equal to 2, in the rising edge stage of the suspended phase counter electromotive force, when the last suspended phase counter electromotive force acquired by the ADC module is more than or equal to half of the voltage of the two conducting phase lines, judging that the suspended phase counter electromotive force is zero crossing, entering a zero crossing processing program, and returning to S1 after finishing; when the last suspended phase counter electromotive force acquired by the ADC module is less than half of the voltage of the two conducting phase lines, entering S4; when the back electromotive force of the suspended phase is in a falling edge stage and the back electromotive force of the suspended phase acquired by the ADC module is less than or equal to half of the voltage of the two conducting phase lines, judging that the back electromotive force of the suspended phase is zero-crossing, entering a zero-crossing processing program, and returning to S1 after finishing; when the last suspended phase counter electromotive force acquired by the ADC module is greater than half of the voltage of the two conducting phase lines, entering S4;
in the step S4, the operation module invokes the value T2 in the timing unit, the number P of pre-collecting three-phase voltages by the ADC module in the period T2 is calculated by using the formula "p=t2/T", the absolute value Vt of the last two suspended counter electromotive forces collected by the ADC module in the PWM-ON period is used as a reference, the time point at which the last suspended counter electromotive force collected by the ADC module in the PWM-ON period reaches the time point at which the suspended counter electromotive force is equal to half of the two conducting phase voltages is calculated, and the number Q of three-phase voltages required to be collected by the ADC module is equal to the absolute value of the half of the difference between the last suspended counter electromotive force and the two conducting phase voltages collected by the ADC module in the PWM-ON period and divided by Vt;
in the step S5, when Q is more than P, returning to the step S1; when Q is less than or equal to P, the counter electromotive force of the suspended phase is judged to be zero-crossing in the PWM-OFF stage, and the ADC module is informed to acquire the counter electromotive force of the suspended phase in the PWM-OFF stage to generate zero crossing of the counter electromotive force in the Q-th interruption, the zero-crossing processing program is entered, and the S1 is returned after the zero-crossing processing program is finished.
Further, the method is based on a back electromotive force zero crossing detection circuit of the brushless direct current motor, the circuit comprises a direct current power supply, a three-phase inverter, the brushless direct current motor and a controller, wherein the direct current power supply is electrically connected with the three-phase inverter and used for driving the brushless direct current motor, and the controller is electrically connected with the three-phase inverter through a power driving module and used for controlling the brushless direct current motor to perform phase inversion.
Further, the controller comprises the ADC module, the storage unit electrically connected to the ADC module, the operation module electrically connected to the storage unit, a PWM control module electrically connected to the operation module, and the timing unit, where the ADC module is electrically connected to the three-phase inverter, and is configured to collect two conducting phase voltages and a suspended phase counter electromotive force of the brushless dc motor in one PWM period, and store the two conducting phase voltages and the suspended phase counter electromotive force in the storage unit;
the operation module is used for judging the zero crossing point of the suspended phase back electromotive force in the PWM period and transmitting a back electromotive force zero crossing signal to the PWM control module;
the PWM control module is electrically connected with the power driving module and is used for controlling the on-off of a switching tube of the three-phase inverter so as to drive the brushless direct current motor to operate;
the timing unit is electrically connected with the PWM control module and the ADC module, and is used for reading PWM wave duty ratio data in the PWM control module, recording PWM-ON duration time T1 and PWM-OFF duration time T2, and controlling an interruption period T when the ADC module collects three-phase voltage.
Further, the ADC module is electrically connected with the three-phase inverter through a voltage sampling circuit, the three-phase inverter comprises upper bridge switching tubes Q1-Q3 and lower bridge switching tubes Q4-Q6, drain electrodes of the upper bridge switching tubes Q1-Q3 are electrically connected with a positive electrode of a direct current power supply, source electrodes of the lower bridge switching tubes Q4-Q6 are electrically connected with a negative electrode of the direct current power supply, source electrodes of the upper bridge switching tube Q1 are electrically connected with an A phase, source electrodes of the upper bridge switching tube Q2 are electrically connected with a B phase, source electrodes of the upper bridge switching tube Q3 are electrically connected with a C phase, and grid electrodes of the upper bridge switching tubes Q1-Q3 and the lower bridge switching tubes Q4-Q6 are electrically connected with a power driving module;
the voltage sampling circuit comprises voltage dividing resistors R1-R6, the voltage dividing resistor R1 is connected with the voltage dividing resistor R2 in series, the upper end of the voltage dividing resistor R1 is electrically connected between the source electrode of the switching tube Q1 and the phase A, and the lower end of the voltage dividing resistor R2 is grounded;
the voltage dividing resistor R3 is connected with the voltage dividing resistor R4 in series, the upper end of the voltage dividing resistor R3 is electrically connected between the source electrode of the switch tube Q2 and the phase B, and the lower end of the voltage dividing resistor R4 is grounded;
the voltage dividing resistor R5 is connected with the voltage dividing resistor R6 in series, the upper end of the voltage dividing resistor R5 is electrically connected between the source electrode of the switch tube Q3 and the C phase, and the lower end of the voltage dividing resistor R6 is grounded;
the voltage dividing resistors R1 and R2, R3 and R4, and R5 and R6 are all electrically connected to the ADC module.
Further, the ADC module calculates actual phase voltages UAN, UBN, UCN of the a phase, the B phase, and the C phase by collecting phase voltages UaN, ubN, and UcN of the a phase, the B phase, and the C phase after being divided by the voltage dividing resistors R1 to R6, and stores the actual phase voltages UAN, UBN, UCN in the memory cell, where half of the two conducting phase voltages are: or UAN-UBN or UAN-UCN 2 or UBN-UCN 2.
Further, the interruption of the synchronous PWM period is that the PWM wave is started in a high level state each time, that is, the ADC module is started in a PWM-ON state to collect the two-conducting phase voltage and the floating phase counter electromotive force, and when the PWM wave is started each time, all the data in steps S1 to S5 are reset and cleared.
Further, the zero-crossing processing program performs phase-change operation for the A phase, the B phase and the C phase of the brushless direct current motor, namely after the operation module detects the zero crossing point of the back electromotive force of the suspended phase, the zero crossing point is delayed by 30 degrees according to the phase-change point, the timing unit sets corresponding delay time, and when the delay time reaches, the motor changes phase to enter the next working state.
Preferably, the controller adopts an MCU controller.
Preferably, the interrupt period t is an equal time interval.
Compared with the prior art, the invention has the following beneficial effects:
the invention changes the back electromotive force zero crossing detection mode of the conventional brushless direct current motor, not only detects whether the back electromotive force of the suspended phase crosses the zero point in the PWM-ON stage, but also introduces a back electromotive force zero crossing pre-judging program in the PWM-OFF stage to judge whether the back electromotive force of the suspended phase crosses the zero point in the PWM-OFF stage, thereby solving the problem that the back electromotive force zero crossing of the suspended phase cannot be detected in the PWM-OFF stage, greatly improving the phase-changing precision of the brushless direct current motor, further improving the stability of the motor efficiency and avoiding abnormal shutdown caused by the step-out of the motor.
[ description of the drawings ]
The following describes the embodiments of the present invention in further detail with reference to the accompanying drawings:
fig. 1 is a diagram of a circuit for detecting zero crossings of back emf of a suspended phase of a brushless dc motor according to the present invention;
fig. 2 is a flow chart of detecting zero crossing points of back electromotive force of a suspended phase of the brushless direct current motor;
FIG. 3 is a flowchart of a pre-judging procedure for the back electromotive force of the suspended phase of the brushless DC motor according to the present invention;
FIG. 4 is a waveform of the periodic phase voltage during PWM-ON phase with the zero crossing of the C-phase back EMF of the suspended phase of the brushless DC motor at the rising edge;
FIG. 5 is a waveform diagram of the periodic end voltage of the brushless DC motor of the present invention with the suspended phase C-phase back EMF zero-crossing at the falling edge and during PWM-ON phase;
FIG. 6 is a graph of the voltage waveform at the periodic end of the PWM-OFF phase with the zero-crossing of the counter-electromotive force of the C-phase in the suspended phase of the brushless DC motor at the rising edge;
FIG. 7 is a waveform of the periodic end voltage at the PWM-OFF stage with the zero-crossing of the C-phase back EMF of the suspended phase of the brushless DC motor of the present invention at the falling edge;
FIG. 8 is a partial enlarged view of the three-phase voltages of the brushless DC motor collected by the ADC module of FIG. 6 according to the present invention;
meaning of reference numerals in the drawings:
1. the controller 2, the timing unit 3, the operation module 4, the ADC module 5, the storage unit 6, the DC power supply 7, the three-phase inverter 8, the brushless DC motor 9, the power driving module 10, the PWM control module 11 and the voltage sampling circuit
[ detailed description ] of the invention
The invention will be described in further detail with reference to the drawings and embodiments.
The terminology used in the present invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The words such as "upper", "lower", etc., indicating an orientation or a positional relationship are merely based on the orientation or the positional relationship shown in the drawings, and are merely for convenience of description and to simplify the description, and do not indicate or imply that the electronic components to be referred to must have a specific orientation or be constructed and operated in a specific orientation, and thus are not to be construed as limiting the invention.
As shown in fig. 1 to 3, a method for detecting zero crossing point of back electromotive force of a brushless direct current motor is used for detecting zero crossing point of back electromotive force of a suspended phase, and comprises the following steps:
s1: the timing unit 22 synchronizes the interruption of the PWM period, and simultaneously the ADC module 4 starts to collect the voltage of the A, B, C three phases in the brushless direct current motor 8, wherein the brushless direct current motor operates in a 'two-phase conduction three-phase six-state' mode, each working state is only two-phase conduction, and the third phase is a suspended phase;
s2: entering a PWM-ON time period, the ADC module 4 collects two conducting phase voltages and a floating phase counter electromotive force and stores the voltages in the storage unit 5;
s3: in the PWM-ON time period, according to the fact that the counter electromotive force of the suspended phase is in a rising edge stage or a falling edge stage, comparing the last counter electromotive force of the suspended phase acquired by the ADC module 4 with half of the voltages of the two conducting phase lines through the operation module 3, judging whether the counter electromotive force of the suspended phase is zero-crossing, if the counter electromotive force of the suspended phase is zero-crossing, entering a zero-crossing processing program, and returning to S1 after finishing; if the zero crossing is not achieved, entering a back electromotive force zero crossing pre-judging program in a PWM-OFF time period;
s4: entering a back electromotive force zero crossing prejudging program: taking the last two suspended counter electromotive force differences acquired by the ADC module 4 in the PWM-ON time period as a reference, and calculating by the operation module 3: the times that the ADC module 4 needs to collect three-phase voltages are between the time point that the ADC module 4 collects the last floating phase counter electromotive force in the PWM-ON time period and the time point that the floating phase counter electromotive force is equal to half of the voltage of the two conducting phase lines;
s5: and comparing the times of the ADC module 4 needing to collect the three-phase voltage with the times of the ADC module 4 pre-collecting the three-phase voltage in the PWM-OFF time period through the operation module 3, judging whether the counter electromotive force of the suspended phase crosses zero in the PWM-OFF stage, and returning to S1 after the counter electromotive force is finished.
In the step S1, the timing unit 2 reads the PWM-ON duration T1, the PWM-OFF duration T2, and the interruption period T of the three-phase voltage of A, B, C inside the brushless dc motor 8 collected by the ADC module 4;
in the step S2, the operation module 3 invokes the T1 value in the timing unit 2, and calculates the number of times N of the ADC module 4 to collect the three-phase voltage in the T1 time period according to the formula "n=t1/T";
in the step S3, when n=1, the ADC module 4 collects three-phase voltages only once, and in the rising edge stage, if the counter electromotive force of the suspended phase is greater than or equal to half of the voltages of the two conducting phase lines, the zero-crossing processing procedure is entered, and after finishing, the process returns to S1, and if the counter electromotive force of the suspended phase is less than half of the voltages of the two conducting phase lines, the process returns to S1 directly; in the falling edge stage of the suspended phase counter electromotive force, if the suspended phase counter electromotive force is less than or equal to half of the voltages of the two conducting phase lines, entering a zero-crossing processing program, returning to the step S1 after finishing, and if the suspended phase counter electromotive force is greater than half of the voltages of the two conducting phase lines, directly returning to the step S1;
when N is more than or equal to 2, in the rising edge stage of the suspended phase counter electromotive force, when the last suspended phase counter electromotive force acquired by the ADC module 4 is more than or equal to half of the voltage of the two conducting phase lines, judging that the suspended phase counter electromotive force has zero crossing, entering a zero crossing processing program, and returning to S1 after finishing; when the last suspended phase counter electromotive force acquired by the ADC module 4 is less than half of the voltage of the two conducting phase lines, entering S4; when the back electromotive force of the suspended phase is in the falling edge stage and the back electromotive force of the suspended phase acquired by the ADC module 4 is less than or equal to half of the voltage of the two conducting phase lines, judging that the back electromotive force of the suspended phase is zero-crossing, entering a zero-crossing processing program, and returning to S1 after finishing; when the last suspended phase counter electromotive force acquired by the ADC module 4 is greater than half of the voltage of the two conducting phase lines, entering S4;
in the step S4, the calculation module 3 invokes the value of T2 in the timing unit 2, calculates the number P of pre-acquired three-phase voltages of the ADC module 4 in the period of T2 according to the formula "p=t2/T", calculates the time point when the last acquired last suspended phase counter electromotive force of the ADC module 4 in the PWM-ON period reaches the time point when the suspended phase counter electromotive force of the ADC module 4 is equal to half of the two conducting phase voltages with reference to the absolute value Vt of the difference value of the last suspended phase counter electromotive force acquired by the ADC module 4 in the PWM-ON period, and the number Q of three-phase voltages required to be acquired by the ADC module 4 is equal to the absolute value of the half difference value of the last suspended phase counter electromotive force and the two conducting phase voltages acquired by the ADC module 4 in the PWM-ON period and divides Vt;
in the step S5, when Q > P, returning to S1; when Q is less than or equal to P, the counter electromotive force of the suspended phase is judged to be zero-crossed in the PWM-OFF stage, and the ADC module 4 is informed to acquire the counter electromotive force of the suspended phase in the PWM-OFF stage to be zero-crossed in the counter electromotive force of the Q-th interruption, the zero-crossing processing program is entered, and the S1 is returned after the zero-crossing processing program is finished.
The detection method of the above S1-S5 is based on a back electromotive force zero crossing detection circuit of the brushless direct current motor 8, and the circuit comprises a direct current power supply 6, a three-phase inverter 7, the brushless direct current motor 8 and a controller 1, wherein the direct current power supply 6 is electrically connected with the three-phase inverter 7 and is used for driving the brushless direct current motor 8, and the controller 1 is electrically connected with the three-phase inverter 7 through a power driving module 9 and is used for controlling the brushless direct current motor 8 to perform phase change.
The controller 1 comprises the ADC module 4, the storage unit 5 electrically connected to the ADC module 4, the operation module 3 electrically connected to the storage unit 5, the PWM control module 10 electrically connected to the operation module 3, and the timing unit 2, where the ADC module 4 is electrically connected to the three-phase inverter 7, and is used for collecting two conducting phase voltages and a floating phase counter electromotive force of the brushless dc motor 8 in one PWM period, and storing the two conducting phase voltages and the floating phase counter electromotive force in the storage unit 5; the operation module 3 is configured to determine a zero crossing point of a suspended phase back electromotive force in the PWM period, and transmit a back electromotive force zero crossing signal to the PWM control module 10; the PWM control module 10 is electrically connected to the power driving module 9 and is used for controlling the on-off of a switching tube of the three-phase inverter 7 so as to drive the brushless direct current motor 8 to operate; the timing unit 2 is electrically connected to the PWM control module 10 and the ADC module 4, and is configured to read PWM wave duty cycle data in the PWM control module 10, record PWM-ON duration T1, PWM-OFF duration T2, and control the ADC module 4 to interrupt the period T when collecting the three-phase voltage.
The ADC module 4 is electrically connected with the three-phase inverter 7 through a voltage sampling circuit 11, the three-phase inverter 7 comprises upper bridge switching tubes Q1-Q3 and lower bridge switching tubes Q4-Q6, drain electrodes of the upper bridge switching tubes Q1-Q3 are electrically connected with the positive electrode of the direct current power supply 6, source electrodes of the lower bridge switching tubes Q4-Q6 are electrically connected with the negative electrode of the direct current power supply 6, source electrodes of the upper bridge switching tube Q1 are electrically connected with the A phase, source electrodes of the upper bridge switching tube Q2 are electrically connected with the B phase, source electrodes of the upper bridge switching tube Q3 are electrically connected with the C phase, and grid electrodes of the upper bridge switching tubes Q1-Q3 and the lower bridge switching tubes Q4-Q6 are electrically connected with the power driving module 9;
the voltage sampling circuit 11 comprises voltage dividing resistors R1-R6, the voltage dividing resistor R1 is connected in series with the voltage dividing resistor R2, the upper end of the voltage dividing resistor R1 is electrically connected between the source electrode of the switch tube Q1 and the phase A, and the lower end of the voltage dividing resistor R2 is grounded; the voltage dividing resistor R3 is connected with the voltage dividing resistor R4 in series, the upper end of the voltage dividing resistor R3 is electrically connected between the source electrode of the switch tube Q2 and the phase B, and the lower end of the voltage dividing resistor R4 is grounded; the voltage dividing resistor R5 is connected with the voltage dividing resistor R6 in series, the upper end of the voltage dividing resistor R5 is electrically connected between the source electrode of the switch tube Q3 and the C phase, and the lower end of the voltage dividing resistor R6 is grounded; the voltage dividing resistors R1 and R2, R3 and R4, and R5 and R6 are all electrically connected to the ADC module 4.
The ADC module 4 calculates the actual phase voltages UAN, UBN, UCN of the a, B and C phases by collecting the phase voltages UaN, ubN and UcN of the a, B and C phases divided by the voltage dividing resistors R1 to R6, and stores the actual phase voltages UAN, UBN, UCN in the storage unit 5, wherein uan= UaN (r1+r2)/r2, UBN = UbN (r1+r2)/r2, ucn= UcN (r1+r2)/r2, and half of the two-conducting phase line voltages are: or UAN-UBN or UAN-UCN 2 or UBN-UCN 2.
The synchronous PWM period interruption is that PWM waves are started in a high level state each time, namely, the ADC module 4 is started in a PWM-ON state to collect two-conduction phase voltage and suspended phase counter electromotive force, and when the PWM waves are started each time, all data in the steps S1 to S5 are reset and cleared.
The zero-crossing processing program performs phase-change operation for three phases of a phase A, a phase B and a phase C of the brushless direct current motor 8, namely, after the operation module 3 detects the zero crossing point of the counter electromotive force of the suspended phase, the zero crossing point is delayed by 30 degrees according to the phase-change point, the timing unit 2 sets corresponding delay time, when the delay time arrives, the motor changes phase to enter the next working state, and the controller 1 adopts the MCU controller 1.
The working principle of the invention (taking AB phase conduction and C phase as suspension phases, a brushless direct current motor 58V and PWM output frequency of 10KHZ as examples) is as follows:
the C-phase counter electromotive force zero crossing point is in PWM-ON phase
1. The counter-electromotive force of phase C is in the rising edge phase (as shown in FIG. 4, the point E is the zero crossing point)
(1) Setting a PWM-ON duration 50us, a PWM-OFF duration 50us and an interruption period 10us for the ADC module 4 to collect A, B, C three-phase voltage inside the motor;
(2) In the PWM-ON phase, the number of times n=t1/t=5 of the ADC module 4 collecting the three-phase voltage in a period of 50us is calculated;
(3) The ADC module 4 collects three-phase voltages in the PWM-ON phase, and the storage unit 5 stores the fourth and fifth C-phase counter electromotive forces collected by the ADC module 4 and the fifth a-phase voltage and the B-phase voltage, which are denoted as ua5= 56V, UB5 = V, UC =30v and uc5=32v, and half of the AB conducting phase voltage is (UA 5-UB 5)/2=27v;
(4) The counter electromotive force of the C phase is judged to be in the rising edge stage by UC4=1 19V, UC5 =21V, and the counter electromotive force of the C phase is judged to be zero-crossing due to UC5 > (UA 5-UB 5)/2, so that the zero-crossing processing procedure is directly carried out, and the S1 is returned after the completion.
2. The counter-electromotive force of phase C is in the falling edge stage (as shown in figure 5, the point F is zero crossing point)
(1) Setting a PWM-ON duration 50us, a PWM-OFF duration 50us and an interruption period 10us for the ADC module 4 to collect A, B, C three-phase voltage inside the motor;
(2) In the PWM-ON phase, the number of times n=t1/t=5 of pre-acquisition of the three-phase voltage by the ADC module 4 in a period of 50us is calculated;
(3) The ADC module 4 collects three-phase voltages in the PWM-ON phase, and the storage unit 5 stores the fourth and fifth C-phase counter electromotive forces collected by the ADC module 4 and the fifth a-phase voltage and the B-phase voltage, which are denoted as ua5= 56V, UB5 = V, UC =26v and uc5=24v, and half of the AB conducting phase voltage is (UA 5-UB 5)/2=27v;
(4) The counter electromotive force of the C phase is judged to be in the falling edge stage by UC4= V, UC5 =24V, and the counter electromotive force of the C phase is judged to be zero-crossing because UC5 < (UA 5-UB 5)/2, and the counter electromotive force of the C phase directly enters a zero-crossing processing program, and the S1 is returned after the completion.
(II) C-phase counter-electromotive force zero crossing point in PWM-OFF stage
1. The counter electromotive force of phase C is in the rising edge stage (the zero crossing point is shown in fig. 6 and 8,K)
(1) Setting a PWM-ON duration time of 40us, a PWM-OFF duration time of 60us and an interruption period of 10us for an ADC module to collect A, B, C three-phase voltage inside the motor;
(2) In the PWM-ON phase, the number of times n=t1/t=4 of pre-acquisition of the three-phase voltage by the ADC module 4 in a period of 40us is calculated;
(3) The ADC module 4 collects three-phase voltages in the PWM-ON phase, and the storage unit 5 stores the back electromotive force of the C phase and the B phase voltages of the a phase and the B phase collected by the ADC module 4 for the third and fourth times, which are denoted as ua4= 56V, UB4 = V, UC =19v and uc4=21v, and half of the AB conducting phase voltage is (UA 4-UB 4)/2=27v;
(4) When the counter electromotive force of the C phase is judged to be in the rising edge stage by UC3=19V, UC 4=21V and is also judged to be < (UA 4-UB 4)/2, a counter electromotive force zero crossing pre-judging program of a PWM-OFF time period T2 is entered;
(5) Entering a back electromotive force zero crossing prejudging program: calculating the times P=T2/t=6 of pre-acquisition voltage of the ADC module 4 in the T2 time period;
(6) Calculating the number of times q= ((UA 4-UB 4)/2-UC 4)/vt=3 times of pre-acquisition of the three-phase voltage by the ADC module 4 when the time point where the ADC module 4 acquires UC4 reaches half (UA 4-UB 4)/2=27v of the AB conducting phase voltage based ON the last two C-phase counter electromotive force difference values vt=uc4-uc3=2v acquired by the ADC module 4 in the PWM-ON period T1;
(7) Because Q is smaller than P, it is judged that the counter electromotive force of the C phase crosses zero in the PWM-OFF stage, and the ADC module 4 acquires the counter electromotive force of the C phase in the PWM-OFF stage, the counter electromotive force breaks for the 3 rd time to cross zero, the zero-crossing processing program is entered at the 3 rd time of interruption, and S1 is returned after the zero-crossing processing program is completed;
if no back electromotive force zero crossing pre-judging program is introduced in the PWM-OFF stage, the judgment of the back electromotive force zero crossing point is delayed by one PWM-OFF time, namely, the back electromotive force zero crossing point can be detected at the starting point H of the PWM wave when the synchronization is interrupted in the next PWM period.
2. The counter electromotive force of phase C is in the falling edge stage (the point of 7,G is zero crossing point)
(1) Setting a PWM-ON duration time of 40us, a PWM-OFF duration time of 60us and an interruption period of 10us for an ADC module to collect A, B, C three-phase voltage inside the motor;
(2) In the PWM-ON phase, the number of times n=t1/t=4 of pre-acquisition of the three-phase voltage by the ADC module 4 in a period of 40us is calculated;
(3) The ADC module 4 collects three-phase voltages in the PWM-ON phase, and the storage unit 5 stores the back electromotive force of the C phase and the B phase voltages of the a phase and the B phase collected by the ADC module 4 for the third and fourth times, which are denoted as ua4= 56V, UB4 = V, UC =35V and uc4=33v, and half of the AB conducting phase voltage is (UA 4-UB 4)/2=27v;
(4) Judging that the counter electromotive force of the C phase is in a falling edge stage by UC3=35V, UC4 =33V, and entering a counter electromotive force zero crossing pre-judging program of a PWM-OFF time period T2 when UC4 > (UA 4-UB 4)/2;
(5) Entering a back electromotive force zero crossing prejudging program: calculating the times P=T2/t=6 of the pre-acquisition of the three-phase voltage of the ADC module 4 in the T2 time period;
(6) Calculating the number of times q= (UC 4- (UA 4-UB 4)/2)/vt=3 times of pre-acquisition of three-phase voltages by the ADC module 4 when the distance of the time point at which the ADC module 4 acquires UC4 reaches half (UA 4-UB 4)/2=27v of the AB conducting phase voltage, based ON the last two C-phase counter electromotive force difference values vt=uc3-uc4=2v acquired by the ADC module 4 in the PWM-ON time period T1;
(7) Because Q is smaller than P, it is judged that the counter electromotive force of the C phase crosses zero in the PWM-OFF stage, and the ADC module 4 acquires the counter electromotive force of the C phase in the PWM-OFF stage, the counter electromotive force breaks for the 3 rd time to cross zero, the zero-crossing processing program is entered at the 3 rd time of interruption, and S1 is returned after the zero-crossing processing program is completed;
if no back electromotive force zero crossing pre-judging program is introduced in the PWM-OFF stage, the judgment of the back electromotive force zero crossing point is delayed by one PWM-OFF time, namely, the back electromotive force zero crossing point can be detected at the starting point L of the PWM wave when the synchronization is interrupted in the next PWM period.
In addition, the detection methods of BA phase conduction, C phase suspension or AC phase conduction, B phase suspension or CA phase conduction, B phase suspension or BC phase conduction, A phase suspension or CB phase conduction and A phase suspension are all detected according to the steps of S1 to S5.
In summary, the invention changes the back electromotive force zero crossing detection mode of the conventional brushless direct current motor, not only detects whether the back electromotive force of the suspended phase crosses zero in the PWM-ON stage, but also introduces a back electromotive force zero crossing pre-judging program in the PWM-OFF stage: the absolute value Vt of the difference value of the last two suspended phase counter electromotive forces acquired by the ADC module 4 in the PWM-ON time period is taken as a reference, the time point that the last suspended phase counter electromotive force acquired by the ADC module 4 in the PWM-ON time period reaches the time point that the suspended phase counter electromotive force is equal to half of the voltage of the two conducting phase lines is calculated, the times that the three-phase voltage is required to be acquired by the ADC module 4 are compared with the times that the three-phase voltage is pre-acquired by the ADC module 4 in the PWM-OFF stage, whether the suspended phase counter electromotive force crosses zero in the PWM-OFF stage is judged, the problem that the zero crossing point of the suspended phase counter electromotive force cannot be detected in the PWM-OFF stage is well solved, the commutation precision of the brushless direct current motor is greatly improved, the stability of the motor efficiency is further improved, and abnormal shutdown caused by motor step loss is not easy to occur.
The present invention is not limited to the above-described embodiments, and those skilled in the art will readily appreciate that many other alternatives are possible for the back emf zero crossing detection method of a brushless dc motor of the present invention without departing from the spirit and scope of the present invention, and the scope of the present invention is defined by the appended claims.
Claims (9)
1. A brushless DC motor back EMF zero crossing detection method is characterized in that: the method for detecting the zero crossing point of the back electromotive force of the suspended phase comprises the following steps:
s1: the timing unit is used for synchronizing the interruption of the PWM period, namely the timing unit reads the PWM-ON duration time T1 and the PWM-OFF duration time T2, and simultaneously the ADC module starts to collect the three-phase voltage of the brushless direct current motor A, B, C and the interruption period T of the three-phase voltage; the brushless direct current motor operates in a 'two-phase conduction three-phase six-state' mode, each working state is conducted by two phases only, and the third phase is a suspended phase;
s2: entering a PWM-ON time period, the ADC module collects two conducting phase voltages and a floating phase counter electromotive force and stores the two conducting phase voltages and the floating phase counter electromotive force in a storage unit; the operation module calls a T1 value and a T2 value in the timing unit, and the number N of times that the ADC module needs to collect the three-phase voltage in a T1 time period is calculated according to a formula of 'N=T1/T'; the timing unit calculates the frequency P of pre-collecting the three-phase voltage of the ADC module in the T2 time period according to the formula of P=T2/T;
s3: in the PWM-ON time period, according to the fact that the counter electromotive force of the suspended phase is in a rising edge stage or a falling edge stage, comparing the last counter electromotive force of the suspended phase acquired by the ADC module with half of the voltages of the two conducting phase lines through the operation module, judging whether the counter electromotive force of the suspended phase is zero-crossing or not, if the counter electromotive force of the suspended phase is zero-crossing, entering a zero-crossing processing program, and returning to S1 after finishing; if the zero crossing is not achieved, entering a back electromotive force zero crossing pre-judging program of the PWM-OFF time period; when n=1, the ADC module collects three-phase voltages only once, and in the rising edge phase of the suspended phase counter electromotive force, if the suspended phase counter electromotive force is greater than or equal to half of the two conducting phase voltages, the ADC module enters a zero-crossing processing procedure, returns to S1 after finishing, and if the suspended phase counter electromotive force is less than half of the two conducting phase voltages, returns to S1 directly; in the falling edge stage of the suspended phase counter electromotive force, if the suspended phase counter electromotive force is less than or equal to half of the voltages of the two conducting phase lines, entering a zero-crossing processing program, returning to the step S1 after finishing, and if the suspended phase counter electromotive force is greater than half of the voltages of the two conducting phase lines, directly returning to the step S1;
when N is more than or equal to 2, in the rising edge stage of the suspended phase counter electromotive force, when the last suspended phase counter electromotive force acquired by the ADC module is more than or equal to half of the voltage of the two conducting phase lines, judging that the suspended phase counter electromotive force is zero crossing, entering a zero crossing processing program, and returning to S1 after finishing; when the last suspended phase counter electromotive force acquired by the ADC module is less than half of the voltage of the two conducting phase lines, entering S4; when the back electromotive force of the suspended phase is in a falling edge stage and the back electromotive force of the suspended phase acquired by the ADC module is less than or equal to half of the voltage of the two conducting phase lines, judging that the back electromotive force of the suspended phase is zero-crossing, entering a zero-crossing processing program, and returning to S1 after finishing; when the last suspended phase counter electromotive force acquired by the ADC module is greater than half of the voltage of the two conducting phase lines, entering S4;
s4: entering a back electromotive force zero crossing prejudging program: calculating, by the operation module, a time point when the last suspended phase counter electromotive force acquired by the ADC module in the PWM-ON period reaches a time point when the suspended phase counter electromotive force is equal to half of the voltage of the two conducting phase lines by taking the last two suspended phase counter electromotive forces acquired by the ADC module in the PWM-ON period as a reference, wherein Q is equal to an absolute value of a half difference value between the last suspended phase counter electromotive force acquired by the ADC module in the PWM-ON period and the voltage of the two conducting phase lines, and dividing by Vt;
s5: comparing the times Q of the three-phase voltage to be acquired by the ADC module with the times P of the three-phase voltage pre-acquisition by the ADC module in the PWM-OFF time period by the operation module, and judging whether the counter electromotive force of the suspended phase is zero crossing in the PWM-OFF stage; returning to S1 when Q > P; when Q is less than or equal to P, the counter electromotive force of the suspended phase is judged to be zero-crossing in the PWM-OFF stage, and the ADC module is informed to acquire the counter electromotive force of the suspended phase in the PWM-OFF stage to generate zero crossing of the counter electromotive force in the Q-th interruption, the zero-crossing processing program is entered, and the S1 is returned after the zero-crossing processing program is finished.
2. The brushless dc motor back emf zero crossing detection method according to claim 1, wherein: the method is based on a back electromotive force zero-crossing detection circuit of a brushless direct current motor, and the circuit comprises a direct current power supply, a three-phase inverter, the brushless direct current motor and a controller, wherein the direct current power supply is electrically connected with the three-phase inverter and used for driving the brushless direct current motor, and the controller is electrically connected with the three-phase inverter through a power driving module and used for controlling the brushless direct current motor to perform phase change.
3. The brushless dc motor back emf zero crossing detection method according to claim 2, wherein: the controller comprises the ADC module, the storage unit electrically connected with the ADC module, the operation module electrically connected with the storage unit, a PWM control module electrically connected with the operation module and the timing unit, wherein the ADC module is electrically connected with the three-phase inverter and is used for collecting two-conduction phase voltage and suspended phase counter electromotive force of the brushless direct current motor in one PWM period and storing the two-conduction phase voltage and suspended phase counter electromotive force in the storage unit;
the operation module is used for judging the zero crossing point of the suspended phase back electromotive force in the PWM period and transmitting a back electromotive force zero crossing signal to the PWM control module;
the PWM control module is electrically connected with the power driving module and is used for controlling the on-off of a switching tube of the three-phase inverter so as to drive the brushless direct current motor to operate;
the timing unit is electrically connected with the PWM control module and the ADC module, and is used for reading PWM wave duty ratio data in the PWM control module, recording PWM-ON duration time T1 and PWM-OFF duration time T2, and controlling an interruption period T when the ADC module collects three-phase voltage.
4. A brushless dc motor back emf zero crossing detection method according to claim 3, wherein: the ADC module is electrically connected with the three-phase inverter through a voltage sampling circuit, the three-phase inverter comprises upper bridge switching tubes Q1-Q3 and lower bridge switching tubes Q4-Q6, drain electrodes of the upper bridge switching tubes Q1-Q3 are electrically connected with a positive electrode of a direct current power supply, source electrodes of the lower bridge switching tubes Q4-Q6 are electrically connected with a negative electrode of the direct current power supply, source electrodes of the upper bridge switching tube Q1 are electrically connected with an A phase, source electrodes of the upper bridge switching tube Q2 are electrically connected with a B phase, source electrodes of the upper bridge switching tube Q3 are electrically connected with a C phase, and grid electrodes of the upper bridge switching tubes Q1-Q3 and the lower bridge switching tubes Q4-Q6 are electrically connected with the power driving module;
the voltage sampling circuit comprises voltage dividing resistors R1-R6, the voltage dividing resistor R1 is connected with the voltage dividing resistor R2 in series, the upper end of the voltage dividing resistor R1 is electrically connected between the source electrode of the switching tube Q1 and the phase A, and the lower end of the voltage dividing resistor R2 is grounded;
the voltage dividing resistor R3 is connected with the voltage dividing resistor R4 in series, the upper end of the voltage dividing resistor R3 is electrically connected between the source electrode of the switch tube Q2 and the phase B, and the lower end of the voltage dividing resistor R4 is grounded;
the voltage dividing resistor R5 is connected with the voltage dividing resistor R6 in series, the upper end of the voltage dividing resistor R5 is electrically connected between the source electrode of the switch tube Q3 and the C phase, and the lower end of the voltage dividing resistor R6 is grounded;
the voltage dividing resistors R1 and R2, R3 and R4, and R5 and R6 are all electrically connected to the ADC module.
5. The brushless dc motor back emf zero crossing detection method according to claim 4, wherein: the ADC module calculates actual phase voltages UAN, UBN, UCN of the a phase, the B phase and the C phase by collecting phase voltages UaN, ubN and UcN of the a phase, the B phase and the C phase after being divided by the voltage dividing resistors R1 to R6, and stores the actual phase voltages UAN, UBN, UCN in the memory cell, wherein half of the two conducting phase voltages are: or UAN-UBN or UAN-UCN 2 or UBN-UCN 2.
6. The brushless dc motor back emf zero crossing detection method according to claim 1, wherein: the synchronous PWM period interruption is that PWM waves are started in a high level state each time, namely, the ADC module is started in a PWM-ON state to collect two-conduction phase voltage and suspended phase counter electromotive force, and when the PWM waves are started each time, all data in the steps S1 to S5 are reset and cleared.
7. The brushless dc motor back emf zero crossing detection method according to claim 1, wherein: the zero-crossing processing program is used for carrying out phase-change operation on three phases of A phase, B phase and C phase of the brushless direct current motor, namely, after the operation module detects the zero crossing point of counter electromotive force of the suspended phase, the zero crossing point is lagged by 30 DEG of electric angle according to the phase-change point, the timing unit sets corresponding delay time, and when the delay time arrives, the motor changes phase to enter the next working state.
8. The brushless dc motor back emf zero crossing detection method according to claim 2, wherein: the controller adopts an MCU controller.
9. The brushless dc motor back emf zero crossing detection method according to claim 1, wherein: the interrupt period t is an equal time interval.
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| CN115664275A (en) * | 2022-10-13 | 2023-01-31 | 江苏东成工具科技有限公司 | Compensation system and method for back electromotive force zero crossing point voltage of brushless direct current motor |
| CN116885982B (en) * | 2023-07-19 | 2024-04-19 | 西安瑞日电子发展有限公司 | Brushless direct current motor control device and method without position sensor |
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