CN117498750A - Motor control method, electric tool and computer readable medium - Google Patents
Motor control method, electric tool and computer readable medium Download PDFInfo
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- CN117498750A CN117498750A CN202311263588.5A CN202311263588A CN117498750A CN 117498750 A CN117498750 A CN 117498750A CN 202311263588 A CN202311263588 A CN 202311263588A CN 117498750 A CN117498750 A CN 117498750A
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- 238000004804 winding Methods 0.000 claims abstract description 31
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/24—Vector control not involving the use of rotor position or rotor speed sensors
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/0003—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/0003—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
- H02P21/0021—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control using different modes of control depending on a parameter, e.g. the speed
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/04—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation specially adapted for very low speeds
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/08—Arrangements for controlling the speed or torque of a single motor
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/14—Electronic commutators
- H02P6/16—Circuit arrangements for detecting position
- H02P6/18—Circuit arrangements for detecting position without separate position detecting elements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
Abstract
The invention discloses a motor control method, an electric tool and a computer readable medium, wherein the motor control method comprises an acceleration vector stage and a detection vector stage which are alternately performed, acceleration vector pulses are applied to a stator winding of a motor in the acceleration vector stage, the duty ratio of the acceleration vector pulses is adjusted by adopting a first modulation mode, and the quantity of the acceleration vector pulses is dynamically adjusted; in the detection vector stage, sequentially applying a first detection vector pulse and a second detection vector pulse to a stator winding of the motor, and adjusting the duty ratio of the first detection vector pulse and the second detection vector pulse by adopting a second modulation mode; wherein the duty cycle of the acceleration vector pulse is less than the duty cycle of the first detection vector pulse and the second detection vector pulse. The invention can realize the ultralow rotation speed control of the motor.
Description
[ field of technology ]
The present invention relates to the field of motor control technologies, and in particular, to a motor control method, an electric tool, and a computer readable medium.
[ background Art ]
A screwdriver is a commonly used electric tool for tightening and loosening screws and bolts. In performing the tightening operation, the user generally desires that the initial rotational speed of the screwdriver be as low as possible to facilitate alignment of the work piece. When the initial rotating speed of the screwdriver is too high, on one hand, the screw or the bolt can slip and fall off due to excessive shaking when rotating; on the other hand, very small size screws may be too high in rotational speed to allow the user to gain control of the reaction, resulting in the screw bottoming out and even piercing the workpiece. For this reason, it is common practice to minimize the initial PWM duty cycle of the driver so that a relatively low rotational speed can be output.
However, a low duty cycle sensorless (simply "sensorless") control method for brushless motors causes the following problems: the duty cycle is low, the rotational speed output of the motor is very low, and when the rotational speed is too low, the counter potential of the motor is very small, which brings great challenges to the non-inductive control method based on counter potential zero crossing detection. If no accurate back electromotive force zero crossing point is detected, accurate phase change control cannot be performed on the motor, and the subsequent back electromotive force zero crossing detection is further deteriorated, and finally the motor is in a vicious circle. Therefore, the non-inductive control method based on the back electromotive force zero crossing detection cannot output a very low duty ratio, and the motor cannot stably operate at a very low rotation speed.
In view of the foregoing, it is desirable to provide an improved motor control method that overcomes the shortcomings of the prior art.
[ invention ]
Aiming at the defects of the prior art, the invention aims to provide a motor control method capable of realizing ultralow rotation speed.
The technical scheme adopted for solving the problems in the prior art is as follows: a motor control method comprises an acceleration vector stage and a detection vector stage which are alternately performed, wherein in the acceleration vector stage, acceleration vector pulses are applied to a stator winding of a motor, the duty ratio of the acceleration vector pulses is adjusted by adopting a first modulation mode, and the quantity of the acceleration vector pulses is dynamically adjusted; in the detection vector stage, sequentially applying a first detection vector pulse and a second detection vector pulse to a stator winding of the motor, and adjusting the duty ratio of the first detection vector pulse and the second detection vector pulse by adopting a second modulation mode; wherein the duty cycle of the acceleration vector pulse is less than the duty cycle of the first detection vector pulse and the second detection vector pulse.
The further improvement scheme is as follows: the first modulation mode is an H_PWM-L_ON modulation mode, and the second modulation mode is an H_PWM-L_PWM modulation mode.
The further improvement scheme is as follows: in the acceleration vector phase, the duty cycle of the acceleration vector pulse is less than 5%; in the detection vector stage, the duty ratio of the first detection vector pulse and the second detection vector pulse is more than 10%.
The further improvement scheme is as follows: after dynamically adjusting the number of acceleration vector pulses, the rotational speed of the motor is maintained in a manner that dynamically adjusts the duty cycle of the acceleration vector pulses.
The further improvement scheme is as follows: the duty cycle of the acceleration vector pulse is dynamically adjusted in one of the following ways: opening the loop according to the rotating speed and the current; open loop function mode according to the rotating speed and the current; the speed-current closed loop PI mode.
The further improvement scheme is as follows: and in the detection vector stage, respectively acquiring a first current corresponding to the first detection vector pulse and a second current corresponding to the second detection vector pulse, and controlling the motor to change the phase when the relation between the first current and the second current meets a phase change condition.
In order to solve the problems in the prior art, the invention also provides an electric tool, which comprises a processing module, wherein the processing module alternately executes an acceleration vector stage and a detection vector stage; in the acceleration vector stage, acceleration vector pulses are applied to a stator winding of the motor, the duty ratio of the acceleration vector pulses is adjusted by adopting a first modulation mode, and the number of the acceleration vector pulses is dynamically adjusted; in the detection vector stage, sequentially applying a first detection vector pulse and a second detection vector pulse to a stator winding of the motor, and adjusting the duty ratio of the first detection vector pulse and the second detection vector pulse by adopting a second modulation mode; wherein the duty cycle of the acceleration vector pulse is less than the duty cycle of the first detection vector pulse and the second detection vector pulse.
The further improvement scheme is as follows: the electric tool further comprises a current sampling module, wherein the current sampling module is used for respectively acquiring a first current corresponding to the first detection vector pulse and a second current corresponding to the second detection vector pulse in the detection vector stage, and the processing module is used for controlling the motor to change phases when the relation between the first current and the second current meets a phase change condition.
In order to solve the problems in the prior art, the invention also provides an electric tool, which comprises a memory and a processor, wherein the memory stores a computer program which can be run on the processor, and the processor realizes the method when executing the computer program.
To solve the problems of the prior art, the present invention also provides a computer readable medium having non-volatile program code executable by a processor, the program code causing the processor to perform the method.
Compared with the prior art, the invention has the following beneficial effects: the invention provides a motor control method, which comprises an acceleration vector stage and a detection vector stage which are alternately performed, wherein the duty ratio of acceleration vector pulses in the acceleration vector stage and the duty ratio of first detection vector pulses and second detection vector pulses in the detection vector stage are adjusted by adopting two different modulation modes, so that the duty ratio of the acceleration vector pulses is smaller than the duty ratio of the first detection vector pulses and the duty ratio of the second detection vector pulses, and the quantity of the acceleration vector pulses is dynamically adjusted; by the scheme, the ultra-low speed control of the sensorless direct current brushless motor can be realized.
[ 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 flow chart of a method of an embodiment of the present invention;
FIG. 2 is a sequence diagram of the resultant magnetic potential vectors and control vectors for a brushless DC motor;
FIG. 3 is a schematic diagram of a control system for a brushless DC motor according to an embodiment of the invention;
FIG. 4 is a schematic diagram of an H_PWM-L_ON modulation scheme according to an embodiment of the invention;
FIG. 5 is a schematic diagram of an H_PWM-L_PWM modulation scheme according to an embodiment of the invention;
FIG. 6 is a schematic diagram of an embodiment of the present invention using rotational speed and current open loop bang-bang regulation;
fig. 7 is a control block diagram of a speed-current double closed loop mode of an embodiment of the invention.
[ 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 solution described in the present invention can be applied to electric tools/devices, which may be garden-type tools, hand-held tools, or other automated devices requiring the use of motor control techniques; it is within the scope of the present invention that the above-described tools/devices can employ the essence of the technical solutions disclosed below. The invention is particularly suitable for tools/devices adapted for sensorless control of brushless dc motors.
In the electric tool, a screwdriver is taken as an example, most brushless screwdrivers supporting low rotation speed operation in the initial starting stage currently use Hall sensors, and the use of the Hall sensors increases the whole volume of products, thereby increasing the manufacturing cost and the assembly difficulty.
The invention aims to provide a motor control method suitable for a brushless direct current motor, so as to realize ultra-low-speed operation of the brushless direct current motor controlled by no sense.
Referring to fig. 1, the motor control method of the present invention includes an acceleration vector stage and a detection vector stage, which are alternately performed, and includes the steps of:
s1: in the acceleration vector stage, acceleration vector pulses are applied to a stator winding of the motor, the duty ratio of the acceleration vector pulses is adjusted by adopting a first modulation mode, and the number of the acceleration vector pulses is dynamically adjusted;
s2: in the vector detection stage, a first detection vector pulse and a second detection vector pulse are sequentially applied to a stator winding of the motor, and the duty ratio of the first detection vector pulse and the duty ratio of the second detection vector pulse are adjusted by adopting a second modulation mode;
wherein the duty cycle of the acceleration vector pulse is less than the duty cycle of the first detection vector pulse and the second detection vector pulse.
The motor control method adopts a dynamic pulse detection method, and the principle is as follows:
in general, a current-carrying coil is wound around a stator core of a brushless dc motor, and when a current is applied to the current-carrying coil, a certain magnetic flux is generated in the stator core, and if an external magnetic field is applied to a stator winding (i.e., the current-carrying coil) at this time, the saturation degree of the stator core is determined by the external magnetic field and the magnetic flux generated by the winding current. The winding inductance changes along with the saturation degree of the magnetic circuit, so that when the motor is stationary or rotates, if the magnetic flux direction generated by the permanent magnet (rotor) is consistent with the magnetic flux direction generated by the winding current, a magnetization effect is generated, the saturation degree of the magnetic circuit of the stator core is increased, and the winding inductance is reduced; on the contrary, the saturation degree of the magnetic circuit of the stator core is reduced, and the winding inductance is increased. The relative positions of the rotor and the stator are different and are directly reflected on the magnitude of the winding inductance.
As is well known, the motor voltage formula is:
U＝Ri+L*di/dt+e (1)
wherein U is DC bus voltage, R is stator winding internal resistance, i is armature current, L is stator winding inductance, and e is counter-potential of the motor.
When the motor is stationary, the counter potential e of the motor is zero and, since in practice the internal resistance R of the stator winding is small, the voltage drop over it is negligible with respect to the dc bus voltage U applied to the stator winding, the above formula (1) can be simplified as:
U＝L*di/dt≈L*Δi/Δt (2)
as can be seen from equation (2), when U is constant, L is inversely proportional to the change in Δi, i.e., the greater L, the smaller Δi, and vice versa; Δi is proportional to Δt, and the larger Δt, the larger Δi.
The pulse positioning method (also called short-time pulse method) is to utilize the principle of the saturation effect of a stator core, sequentially apply voltage to a stator winding of a motor according to a corresponding energizing sequence by selecting 6 short-time voltage detection pulses with proper widths, sample current values and compare the current values to determine an electric angle interval where a rotor is located.
Each electrical cycle of the motor corresponds to 360 ° electrical angles, wherein each 60 ° electrical angle is a conducting interval, abbreviated as a sector, and there are 6 sectors. For ease of description and simplicity of analysis, a magnetic potential vector diagram is drawn, as shown in fig. 2.
Referring to fig. 3, a schematic diagram of a control system of a brushless dc motor is shown, wherein switching transistors Q1 to Q6 form a three-phase inverter bridge circuit, an inductor RAH, RAL, RBH, RBL, RCH, RCL forms a counter potential detection circuit, a current sampling resistor Rs and a current amplifying circuit Amp form a current sampling module, an MCU is a main control chip, and BLDC is a brushless motor of the whole machine.
With continued reference to fig. 3, the three-phase inverter bridge may adopt a two-phase conduction mode or a three-phase conduction mode, specifically, the vectors listed in the two-phase conduction mode are:
q1, Q4 are on→a+b- (denoted AB), i.e. when the switching transistors Q1 and Q4 are on, the current flow direction is: the positive end P+ of the direct current bus voltage, the switching tube Q1, the A-phase stator winding, the B-phase stator winding, the switching tube Q4, the negative end P-of the direct current bus voltage and the corresponding vector A+B-, are marked as AB phase conduction of the stator winding;
q1 and Q2 are conducted to A+C- (denoted as AC);
q3 and Q2 are conducted to B+C- (shown as BC);
q3 and Q6 are conducted to B+A- (denoted as BA);
q5 and Q6 are conducted to C+A- (marked as CA);
q5 and Q4 are on- & gtC+B- (denoted as CB).
The vector under the three-phase conduction mode is as follows:
q1, Q4, Q2 are on→A+B-C- (denoted as A+), i.e. when the switching transistors Q1, Q4 and Q2 are on, the current flow is: the positive end P+ of the direct current bus voltage, the switching tube Q1, the A-phase stator winding, the B-phase stator winding and the C-phase stator winding, the switching tube Q4 and the switching tube Q2, the negative end P-of the direct current bus voltage and the corresponding vector A+B-C-, are marked as A+phase conduction of the stator winding;
q3, Q6, Q2 are on- > B+A-C- (denoted as B+);
q4, Q6, Q4 on- > C+A-B- (noted C+);
q6, Q3, Q5 are on- & gt, A-B+C+ (denoted as A-);
q4, Q1, Q5 are on- > B-A+C+ (denoted as B-);
q2, Q1, Q3 are on- > C-A+B+ (denoted as C-).
When the motor is positioned, a group of vectors in a two-phase conduction mode or a three-phase conduction mode can be selected as positioning pulse vectors.
Referring to fig. 2 and 3, two-phase conduction is taken as an example: assuming the rotor is in the BA position, in order to rotate the rotor clockwise, an AC vector needs to be applied, i.e. switching on the switching transistors Q1 and Q2, which is defined as an acceleration vector. In order to obtain the rotor position, a rotor position detection vector is required to be inserted in the acceleration vector application process, wherein the vector is BA and BC, and when the rotor position is in a 30 DEG interval between BA and B+, the BA current vector is larger than the BC current vector (iAB > iBC); when the rotor position is within 30 DEG between B+ and BC, the BA current vector is smaller than the BC current vector (iAB < iBC), and the acceleration vector is commutated from AC to AB, namely, the switching tubes Q1 and Q4 are conducted, so that one commutation operation is completed, and then the detection vector is updated to BC and AC.
Taking three-phase conduction as an example: assuming that the rotor is in the b+ position, in order to rotate the rotor clockwise, an a+ vector needs to be applied, i.e. the switching transistors Q1, Q4, Q2 are turned on, which is defined as a three-phase acceleration vector. In order to obtain the position of the rotor, during the application of the three-phase acceleration vector, the rotor needs to be inserted to set three-phase detection vectors, wherein the vectors are B+ and C-, and when the rotor position is in a 30 DEG interval between B+ and BC, the B+ current vector is larger than the C-current vector (iB+ > iC-); when the rotor position is within 30 DEG between BC and C-, the B+ current vector is smaller than the C-current vector (iB+ < iC-), and the acceleration vector is commutated from A+ to B-, namely, the switching tubes Q1, Q4 and Q5 are conducted, so that one commutation operation is completed, and then the detection vector is updated to C-and A+.
Thus, there are four combinations of acceleration vectors and detection vectors: the two-phase acceleration vector+the two-phase detection vector, the two-phase acceleration vector+the three-phase detection vector, the three-phase acceleration vector+the two-phase detection vector, and the three-phase acceleration vector+the three-phase detection vector are shown in tables 1 to 4 below.
TABLE 1 two-phase acceleration vector + two-phase detection vector
| Rotor position | Two-phase acceleration vector | Two-phase detection vector 1 | Two-phase detection vector 2 | Detecting current (within a section) | Detecting current (commutation point) |
| A-~B+(BA±30°) | AC | BA | BC | iBA>iBC | iBA<iBC |
| B+~C-(BC±30°) | AB | BC | AC | iBC>iAC | iBC<iAC |
| C-~A+(AC±30°) | CB | AC | AB | iAC>iAB | iAC<iAB |
| A+-~B-(AB±30°) | CA | AB | CB | iAB>iCB | iAB<iCB |
| B-~C+(CB±30°) | BA | CB | CA | iCB>iCA | iCB<iCA |
| C+~A-(CA±30°) | BC | CA | BA | iCA>iBA | iCA<iBA |
Table 2 two-phase acceleration vector + three-phase detection vector
| Rotor position | Two-phase acceleration vector | Three-phase detection vector 1 | Three-phase detection vector 2 | Detecting current (within a section) | Detecting current (commutation point) |
| BA~BC(B+±30°) | AC | B+ | C- | iB+>iC- | iB+<iC- |
| BC~AC(C-±30°) | AB | C- | A+ | iC->iA+ | iC-<iA+ |
| AC~AB(A+±30°) | CB | A+ | B- | iA+>iB- | iA+<iB- |
| AB~CB(B-±30°) | CA | B- | C+ | iB->iC+ | iB-<iC+ |
| CB~CA(C+±30°) | BA | C+ | A- | iC+>iA- | iC+<iA- |
| CA~BA(A-±30°) | BC | A- | B+ | iA->iB+ | iA-<iB+ |
TABLE 3 three-phase acceleration vector + two-phase detection vector
| Rotor position | Three-phase acceleration vector | Two-phase detection vector 1 | Two phasesDetection vector 2 | Detecting current (within a section) | Detecting current (commutation point) |
| A-~B+(BA±30°) | C- | BA | BC | iBA>iBC | iBA<iBC |
| B+~C-(BC±30°) | A+ | BC | AC | iBC>iAC | iBC<iAC |
| C-~A+(AC±30°) | B- | AC | AB | iAC>iAB | iAC<iAB |
| A+-~B-(AB±30°) | C+ | AB | CB | iAB>iCB | iAB<iCB |
| B-~C+(CB±30°) | A- | CB | CA | iCB>iCA | iCB<iCA |
| C+~A-(CA±30°) | B+ | CA | BA | iCA>iBA | iCA<iBA |
Table 4 three-phase acceleration vector + three-phase detection vector
| Rotor position | Two-phase acceleration vector | Three-phase detection vector 1 | Three-phase detection vector 2 | Detecting current (within a section) | Detecting current (commutation point) |
| BA~BC(B+±30°) | A+ | B+ | C- | iB+>iC- | iB+<iC- |
| BC~AC(C-±30°) | B- | C- | A+ | iC->iA+ | iC-<iA+ |
| AC~AB(A+±30°) | C+ | A+ | B- | iA+>iB- | iA+<iB- |
| AB~CB(B-±30°) | A- | B- | C+ | iB->iC+ | iB-<iC+ |
| CB~CA(C+±30°) | B+ | C+ | A- | iC+>iA- | iC+<iA- |
| CA~BA(A-±30°) | C- | A- | B+ | iA->iB+ | iA-<iB+ |
With continued reference to fig. 1, the acceleration vector phase includes the following steps:
s101: the duty ratio of the acceleration vector pulse is adjusted by adopting a first modulation mode;
the first modulation mode is an h_pwm-l_on modulation mode, as shown in fig. 4, and the duty ratio of the acceleration vector pulse is less than 5% by using the h_pwm-l_on modulation mode;
s102: dynamically adjusting the number of acceleration vector pulses;
the number of acceleration vector pulses is dynamically adjusted using the following equation:
4+4=N accpmin +N detpmin ≤N pulse =N accp +N detp =E tp *F pwm /(F tclk *6*2)≤N pulsemax =[F tclk *60/(p*S min) ]*F pwm /(F tclk *6*2)=5*F pwm /(p*S min )；
wherein N is pulse N being the total number of pulses accp To accelerate the vector pulse number, N detp To detect the number of vector pulses, E tp For timer value corresponding to electric period, F pwm For PWM frequency, F tclk For timer frequency, N accpmin To minimize the number of acceleration vectors, N detpmin To minimize the number of detected vectors, N pulsemax For the maximum pulse number, p is the pole pair number of the motor, S min The lowest rotational speed supported for the maximum number of pulses.
For example, a brushless screwdriver has a PWM frequency of 16000Hz, a motor pole pair number p of 5, a controlled minimum rotation speed of about 250RPM, and a maximum pulse number N with a minimum rotation speed supported by 250×3=750 RPM set by a maximum pulse number in consideration of a detection margin and a detection reliability pulsemax The number of detected vector pulses is (2+2) and thus the number of acceleration vectors is 21-4=17, calculated as 5×16000/(5×750) =21.
S103: updating the number of acceleration vector pulses;
s104: dynamically adjusting the duty cycle of the acceleration vector pulse;
when the duty ratio of the acceleration vector pulse is low, the motor rotation speed is low, so that the output torque is correspondingly low; when the load of the motor is large, the output torque is insufficient to cause stalling, and in order to solve the problem, the duty ratio of the acceleration vector pulse needs to be dynamically adjusted according to the load, and the method is various and mainly comprises the following steps:
(a) Open loop bang-bang adjustment mode according to rotating speed and current
Referring to fig. 6, when the motor load increases, the rotation speed decreases, the current increases, and the rotation speed S is acquired<S min The current I is greater than or equal to I max Duty cycle d N =d c +Δd；
Wherein S is min A lower rotation speed threshold for increasing the duty ratio during dynamic pulse detection, I max An upper current threshold, d, for increasing the duty cycle during dynamic pulse detection N D is a new duty cycle c For the current duty cycle Δd is the duty cycle increased by a step value.
(b) According to the open loop function mode of the rotating speed and the current
A two-dimensional table of duty ratio, rotating speed and current is established, and the following table is exemplified:
table 5 two-dimensional table of duty cycle and rotational speed, current
| Electric current is a kind of | 1(A) | 2(A) | 3(A) | 4(A) | 5(A) | 6(A) | 7(A) | 8(A) | 9(A) |
| Rotational speed 50RPM | 1.0% | 2.0% | 3.0% | 4.0% | 5.0% | 6.0% | 7.0% | 8.0% | 9.0% |
| Rotational speed 100RPM | 2.0% | 3.0% | 4.0% | 5.0% | 6.0% | 7.0% | 8.0% | 9.0% | 10% |
| Rotational speed 150RPM | 3.0% | 4.0% | 5.0% | 6.0% | 7.0% | 8.0% | 9.0% | 10% | 11% |
| Rotational speed 200RPM | 4.0% | 5.0% | 6.0% | 7.0% | 8.0% | 9.0% | 10% | 11% | 12% |
| Rotational speed 250RPM | 5.0% | 6.0% | 7.0% | 8.0% | 9.0% | 10% | 11% | 12% | 13% |
| Rotational speed 300RPM | 6.0% | 7.0% | 8.0% | 9.0% | 10% | 11% | 12% | 13% | 14% |
| Rotational speed 350RPM | 7.0% | 8.0% | 9.0% | 10% | 11% | 12% | 13% | 14% | 15% |
| Rotational speed 400RPM | 8.0% | 9.0% | 10% | 11% | 12% | 13% | 14% | 15% | 16% |
| Rotational speed 450RPM | 9.0% | 10% | 11% | 12% | 13% | 14% | 15% | 16% | 17% |
(c) With the rotation speed-current closed loop PI mode, please refer to FIG. 7
Assuming a given target rotational speed N ref =200 RPM, two can be obtained by current detectionThe parameter, one being the current value of the current, i.e. the current feedback I in the figure fdb The method comprises the steps of carrying out a first treatment on the surface of the One is that the current motor rotor position, i.e. the position detection in the figure, can be obtained by means of current detection. The position detection of the rotor can judge whether the current phase change is needed, if the current phase change is needed, the phase change operation (phase operation in the figure) is executed, the difference value between the current phase change time and the last phase change time can be used for obtaining the phase change sector time, and the current rotating speed of the motor can be obtained by calculating the phase change sector time, namely the speed feedback N in the figure fdb Will give a target rotational speed N ref And actual speed feedback N fdb And taking a difference value, and carrying out speed PI adjustment on the difference value of the rotating speed. After passing through the speed PI regulating module, the output is the target current I ref The target current I ref And the current feedback I fdb And (3) performing difference value, performing current PI adjustment on the current difference value, and outputting the current difference value to be the corresponding duty ratio after the current difference value passes through a current adjustment module. Through the double closed loop PI control of the inner loop current loop and the outer loop speed loop, the motor rotating speed can follow the target rotating speed no matter how the load changes, so that the motor can operate at an extremely low rotating speed, can output very high torque, and ensures the load capacity of the motor for outputting enough torque.
With continued reference to fig. 1, the vector detection stage includes the following steps:
s201: the duty ratio of the first detection vector pulse and the second detection vector pulse is adjusted by adopting a second modulation mode;
the second modulation mode is an h_pwm-l_pwm modulation mode, as shown in fig. 5, and the duty ratio of the first detection vector pulse and the second detection vector pulse is greater than 10% by using the h_pwm-l_pwm modulation mode;
s202: setting a first detection vector pulse;
s203: sampling a first current corresponding to the first detection vector pulse;
s204: setting a second detection vector pulse;
s205, performing operation; sampling a second current corresponding to the second detection vector pulse;
s206: based on the motor rotor positioning principle, the magnitudes of the collected first current and the collected second current are compared, and when the commutation condition is met, the motor is controlled to commutate.
In order to have a very low motor output speed, the duty cycle needs to be very low, for example in screwdriver applications the duty cycle may be less than 5%. When the dynamic pulse detection method is used, the duty ratio of the acceleration vector pulse is generally consistent with that of the detection vector pulse, but when the duty ratio is too small, the current corresponding to the detection vector pulse is too small, so that detection cannot be performed or misjudgment can be performed, and the extremely low rotating speed cannot be output when the duty ratio is increased.
Therefore, the acceleration vector pulse and the detection vector pulse of the invention respectively adopt different PWM modulation modes and different duty ratios.
The H_PWM-L_PWM modulation mode outputs lower torque under the same duty ratio, so that the acceleration vector pulse adopts the H_PWM-L_ON modulation mode, the very low duty ratio is used for outputting extremely low rotating speed, the detection vector pulse adopts the H_PWM-L_PWM modulation mode, the higher duty ratio can be used for obtaining higher detection current, and the position is easy to judge. In this way, accurate commutation of the motor at very low rotational speeds can be achieved.
By adopting a dynamic pulse detection method, the rotor position can be identified and judged only in a vector detection stage, if more acceleration vector pulses exist, fewer vector detection pulses exist, the output torque is stable, but when the rotating speed is gradually increased, the rotor position is detected and the step out is caused because fewer vector detection pulses do not reach the speed; when the acceleration vector pulses are fewer, the detection vector pulses are more, so that the total torque obtained by the motor is smaller, and the detection vector pulses are more, so that the problem of obvious abnormal sound is also caused; when the quantity of the acceleration vector pulse and the quantity of the detection vector pulse are relatively large, the supported rotating speed is very low, and the control step out is caused by slightly raising the rotating speed; when the quantity of the acceleration vector pulse and the quantity of the detection vector pulse are small, the occupation of the detection vector pulse is high in the very low rotating speed in the starting stage, the total torque obtained by the motor is influenced, the abnormal sound is obvious, and meanwhile, misjudgment is easy to occur. Therefore, the method for dynamically adjusting the quantity of the acceleration vectors is adopted, and the running stability of the motor in a low-speed state is improved.
Finally, it should be noted that: the foregoing examples are merely illustrative of specific embodiments of the present invention, and are not intended to limit the scope of the present invention, but although the present invention has been described in detail with reference to the foregoing examples, it will be understood by those skilled in the art that any modification or variation of the technical solutions described in the foregoing examples or equivalent substitution of some of the technical features thereof may be easily performed within the scope of the present invention disclosed by the present invention; such modifications, changes and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention. The scope of the invention should, therefore, be determined with reference to the appended claims.
Claims (10)
1. A motor control method comprising alternating acceleration vector phases and detection vector phases, characterized in that:
in the acceleration vector stage, acceleration vector pulses are applied to a stator winding of the motor, the duty ratio of the acceleration vector pulses is adjusted by adopting a first modulation mode, and the number of the acceleration vector pulses is dynamically adjusted;
in the detection vector stage, sequentially applying a first detection vector pulse and a second detection vector pulse to a stator winding of the motor, and adjusting the duty ratio of the first detection vector pulse and the second detection vector pulse by adopting a second modulation mode;
wherein the duty cycle of the acceleration vector pulse is less than the duty cycle of the first detection vector pulse and the second detection vector pulse.
2. The motor control method according to claim 1, characterized in that: the first modulation mode is an H_PWM-L_ON modulation mode, and the second modulation mode is an H_PWM-L_PWM modulation mode.
3. The motor control method according to claim 1, characterized in that: in the acceleration vector phase, the duty cycle of the acceleration vector pulse is less than 5%;
in the detection vector stage, the duty ratio of the first detection vector pulse and the second detection vector pulse is more than 10%.
4. The motor control method according to claim 1, characterized in that: after dynamically adjusting the number of acceleration vector pulses, the rotational speed of the motor is maintained in a manner that dynamically adjusts the duty cycle of the acceleration vector pulses.
5. The motor control method according to claim 4, characterized in that: the duty cycle of the acceleration vector pulse is dynamically adjusted in one of the following ways:
opening the loop according to the rotating speed and the current;
open loop function mode according to the rotating speed and the current;
the speed-current closed loop PI mode.
6. The motor control method according to claim 1, characterized in that: and in the detection vector stage, respectively acquiring a first current corresponding to the first detection vector pulse and a second current corresponding to the second detection vector pulse, and controlling the motor to change the phase when the relation between the first current and the second current meets a phase change condition.
7. An electric tool, characterized in that: the electric tool comprises a processing module, wherein the processing module alternately executes an acceleration vector stage and a detection vector stage;
in the acceleration vector stage, acceleration vector pulses are applied to a stator winding of the motor, the duty ratio of the acceleration vector pulses is adjusted by adopting a first modulation mode, and the number of the acceleration vector pulses is dynamically adjusted;
in the detection vector stage, sequentially applying a first detection vector pulse and a second detection vector pulse to a stator winding of the motor, and adjusting the duty ratio of the first detection vector pulse and the second detection vector pulse by adopting a second modulation mode;
wherein the duty cycle of the acceleration vector pulse is less than the duty cycle of the first detection vector pulse and the second detection vector pulse.
8. The power tool of claim 7, wherein: the electric tool further comprises a current sampling module, wherein the current sampling module is used for respectively acquiring a first current corresponding to the first detection vector pulse and a second current corresponding to the second detection vector pulse in the detection vector stage, and the processing module is used for controlling the motor to change phases when the relation between the first current and the second current meets a phase change condition.
9. A power tool comprising a memory and a processor, the memory having stored thereon a computer program executable on the processor, characterized by: the method of any of the preceding claims 1-6 being implemented when said computer program is executed by said processor.
10. A computer readable medium having non-volatile program code executable by a processor, characterized by: the program code causes the processor to perform the method of any of claims 1-6.
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