CN114257137A - Control method and device of brushless direct current motor and motor system - Google Patents
Control method and device of brushless direct current motor and motor system Download PDFInfo
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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
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Abstract
The application discloses a control method and device of a brushless direct current motor and a motor system. The motor comprises a rotor and a multi-phase stator, and the control method comprises the following steps: respectively detecting first time of each phase stator from a first commutation time of each phase stator of the motor, wherein the first time is the zero-crossing time when the counter electromotive force of the corresponding phase stator reaches zero for the first time from the first commutation time; determining a second commutation moment of each phase stator of the motor according to the detected first time of each phase stator; and at the second commutation moment of each phase of stator, sequentially commutating the motor to drive the rotor to rotate. The control method can obtain the accurate reversing time of the motor, and greatly improves the running stability of the motor.
Description
Technical Field
The present invention relates to the field of motor technologies, and in particular, to a method and an apparatus for controlling a brushless dc motor, and a motor system.
Background
Brushless Direct Current motors (BLDCM) replace mechanical commutators with electronic commutators, and overcome the congenital defects of difficult maintenance, easy interference and the like of brushed dc motors, so the Brushless dc motors have the characteristics of good speed regulation performance and the like of the dc motors, and also have the advantages of simple structure, no commutation spark, reliable operation, easy maintenance and the like of the ac motors, and therefore the Brushless dc motors are increasingly applied to various occasions requiring Motor driving.
The electronic commutator of the brushless dc motor can be classified into a sensor type and a sensorless type, and the sensorless type electronic commutator has more advantages in terms of volume and cost. The current electronic commutator without sensor needs to perform commutation after the zero-crossing time of the back electromotive force is delayed by 30 degrees of electrical angle in order to perform commutation at a correct time by detecting the zero-crossing time of the back electromotive force, for example, after the zero-crossing time of the back electromotive force is detected, that is, the commutation needs to be performed after a certain time delay, and the time delay determines whether the commutation point is correct or not. For this reason, the prior art provides two methods to calculate the delay time: (1) the method is suitable for the motor with fixed rotating speed, and has larger error for the application needing to change the rotating speed of the motor; (2) the method is suitable for motors needing to change the rotating speed according to the rotating speed calculation delay time, but the rotating speed calculation generally needs several cycles, certain delay exists, and the condition that the rotating speed of the motor changes rapidly cannot be well handled. The two methods for calculating the delay time have the problems of inaccurate delay, poor adaptability to different motors and easy influence of rotating speed.
Therefore, in order to solve the above problems, it is desirable to provide a further improved control method for a motor, so as to provide an accurate commutation delay, thereby improving the stability of the motor operation, and to adapt to different motor speeds and different models of motors.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a control method, a control device, and a motor system for a brushless dc motor, which can obtain an accurate commutation timing of the motor.
According to a first aspect of the present invention, there is provided a control method of a brushless dc motor, the motor including a rotor and a multiphase stator, the control method comprising: detecting a first time from a first commutation time of the electric machine, the first time ending at a zero-crossing time at which a back electromotive force of an unexcited phase stator among the multi-phase stators reaches zero for a first time from the first commutation time; determining a second commutation moment of the motor according to the first time; and at a second commutation moment, commutating the motor to drive the rotor to rotate.
Optionally, detecting the first time from the first commutation time instant of the electric machine comprises: acquiring a first reversing time of the motor, and controlling a timer to start timing at the first reversing time; obtaining the zero-crossing time of the back electromotive force of the stator of the unexcited phase; and reading a count value of the timer at a zero-crossing time of the back electromotive force of the stator of the non-excited phase to obtain a first time.
Alternatively, the zero-crossing times of the back emf of the non-excited phase stators are obtained by a sample and hold circuit and an analog-to-digital converter.
Optionally, the zero-crossing time of the back emf of the un-excited phase stator is obtained by a comparator.
Optionally, a second time elapsed from the zero-crossing time of the back emf to the second commutation time is equal to the first time.
According to a second aspect of the present invention, there is provided a control apparatus of a brushless dc motor, the control apparatus being configured to perform the control method as described above, and the brushless dc motor including a rotor and a multiphase stator, the apparatus comprising: an inverter connected to a DC power supply and supplying a driving signal to the multiphase stator; a counter electromotive force detector for detecting a zero-cross timing of a counter electromotive force of an unexcited phase stator among the multi-phase stators; a controller configured to detect a first time from a first commutation time, the first time ending at a zero-crossing time at which a back electromotive force of an unexcited phase stator among the multi-phase stators reaches zero for a first time from the first commutation time; determining a second commutation moment of the motor according to the first time; and at a second commutation moment, commutating the motor.
Optionally, the back emf detector comprises a sample and hold circuit and an analog to digital converter.
Optionally, the back emf detector comprises a comparator.
Optionally, the control device further comprises a timer, wherein the timer starts timing at a first commutation time and ends timing at a first zero-crossing time after the back emf detector detects the back emf of the stator of the non-excited phase at the first commutation time.
Optionally, the controller includes a plurality of control branches, each control branch generates a plurality of corresponding control signals based on a sampling result of the one-phase stator, and each control branch includes: the timing module receives the second feedback signal and starts timing; the timing module is connected with the timing module, receives a first feedback signal, and is used for reading a timing value of the timing module to obtain a first timing value when the first feedback signal is received, and generating a timing value based on the first timing value; the comparison module is respectively connected with the timing module and the timing module, receives the timing value, reads the timing value of the timing module in real time and generates an indication signal when the read timing value is equal to the timing value; and the signal generating module is connected with the comparing module and used for adjusting the level states of a plurality of output control signals according to the indication signal so as to realize the commutation of the motor body, wherein the first time from the beginning of timing to the first timing value of the timing module is equal to the second time from the first timing value to the timing value of the timing module.
Optionally, in the plurality of control branches of the controller, the indication signal generated by the first control branch may be used as the second feedback signal of the second control branch.
Optionally, in each control branch of the controller, the timing module starts timing based on a first commutation time of the corresponding phase stator, and the timing module reads a timing value based on a zero-crossing time of the corresponding phase stator to generate a timing value, where the first commutation time is a commutation time previous to the zero-crossing time.
According to a third aspect of the present invention, there is provided a brushless dc motor system comprising: the current level of the motor; and a control device as described above.
According to the control method, the control device and the control system of the brushless direct current motor, provided by the invention, the second commutation time for commutating the motor is determined by detecting the first time from the first commutation time of the motor to the zero-crossing time, and the quantitative calculation of the commutation time of the motor can be realized, so that the accurate commutation time of the motor can be obtained, and the running stability of the motor is greatly improved. Furthermore, the time of each commutation is calculated according to the previous commutation time, so that the control method and the control device can be well suitable for motors with different motor rotating speeds and different models, and the practicability of the control method and the control device is improved.
Furthermore, the control device of the motor provided by the embodiment of the invention has a simple structure, and can realize the functions of the whole control device by adopting a simple electronic circuit and/or a single chip microcomputer, so that the control device has high operation speed and low power consumption, and can further improve the accuracy of the second reversing time of the motor.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
fig. 1 shows a block diagram of a brushless dc motor system;
FIG. 2 shows a circuit schematic of a brushless DC motor system;
FIG. 3 is a waveform diagram illustrating a plurality of control signals during operation of an inverter according to an embodiment of the present invention;
FIG. 4 illustrates a back EMF waveform for a motor according to an embodiment of the present invention;
fig. 5a shows a schematic structural diagram of a back electromotive force detector provided according to a first embodiment of the present invention;
5b shows a schematic structural view of a back electromotive force detector provided according to a second embodiment of the present invention;
FIG. 6 is a schematic diagram of a controller according to an embodiment of the present invention;
fig. 7 shows a flow chart of a control method of a motor according to an embodiment of the invention;
fig. 8 shows a flowchart of a first time detection method provided according to a first embodiment of the present invention;
fig. 9 shows a flowchart of a first time detection method provided based on the second embodiment of the present invention.
Detailed Description
The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. Moreover, certain well-known elements may not be shown in the figures.
In the following description, numerous specific details of the invention, such as structure, materials, dimensions, processing techniques and techniques of the devices are described in order to provide a more thorough understanding of the invention. However, as will be understood by those skilled in the art, the present invention may be practiced without these specific details.
In this application, the term "commutation" refers to changing the conduction state of the motor drive circuit every time the rotor rotates through a certain electrical angle during operation of the motor.
The term "zero-crossing time" refers to the time when the back emf of the stator reaches zero; the term "first commutation moment" refers to a moment before this "zero-crossing moment" at which the motor is commutated and at which the motor has not been commutated at other moments than the "first commutation moment" between the "first commutation moment" and the "zero-crossing moment"; the term "second commutation time instant" refers to a time instant after which the motor is commutated after the "zero-crossing time instant" and at other times than the "second commutation time instant" between the "zero-crossing time instant" and the "second commutation time instant", the motor has not been commutated.
It should be understood that, the connection/coupling of a and B in the embodiments of the present application means that a and B may be coupled in series or in parallel, or a and B may be coupled through other devices, which is not limited in the embodiments of the present application.
Fig. 1 shows a block diagram of a brushless dc motor system, and fig. 2 shows a circuit diagram of the brushless dc motor system.
Referring to fig. 1 and 2, a brushless dc motor system 10 includes: control device 100 and motor body 200.
The motor body 200 includes a multi-phase stator coil (hereinafter referred to as a multi-phase stator) 210 and a rotor 220. The motor body 200 is, for example, a three-phase motor, and has three-phase stators (including a first-phase stator U, a second-phase stator V, and a third-phase stator W).
The control device 100 is connected to the stator coil 210 of the motor body 200 for obtaining a feedback signal according to a back electromotive force generated at the stator end by the rotor 220 of the motor body 200 cutting the magnetic field lines, and generating a driving signal (including a first driving signal V) according to the feedback signalUA second drive signal VVAnd a third drive signal VW) To drive the rotor 220 of the motor body 200 to normally operate.
Further, the control device 100 includes: an inverter 110, a back electromotive force detector 120, and a controller 130.
Those skilled in the art will appreciate that the inverter 110 may be wired in a variety of ways, such as: three-phase full-bridge, three-phase half-bridge, four-switch, etc. The number of switching tubes included in each connection type inverter 110 is different from one another.
For example: when the inverter 110 is a three-phase full-bridge inverter, six switching tubes are arranged in the inverter 110; when the inverter 110 is a three-phase half-bridge inverter, there are three switching tubes in the inverter 110; when the inverter 110 is a four-switch inverter, there are four switching tubes in the inverter 110.
The inverter 110 receives a plurality of control signals, and controls the on and off of the corresponding switching tubes according to the plurality of control signals.
Further, the following description will be given taking as an example that the inverter 110 is a three-phase full-bridge inverter, and specifically, the three-phase full-bridge inverter 110 includes: the switch comprises a first switch tube Q1, a second switch tube Q2, a third switch tube Q3, a fourth switch tube Q4, a fifth switch tube Q5 and a sixth switch tube Q6. The first switch tube Q1 and the fourth switch tube Q4 are connected in series to form a first branch; the second switching tube Q2 and the fifth switching tube Q5 are connected in series to form a second branch; the third switch tube Q3 and the sixth switch tube Q6 are connected in series to form a third branch. And the first branch circuit, the second branch circuit and the third branch circuit are connected in parallel with the direct current power supply VDCBetween the positive and negative electrodes. A diode is connected between the first path terminal and the second path terminal of each switch tube, for example, a first diode D1 is connected between the first path terminal and the second path terminal of the first switch tube Q1, a second diode D2 is connected between the first path terminal and the second path terminal of the second switch tube Q2, a third diode D3 is connected between the first path terminal and the second path terminal of the third switch tube Q3, a fourth diode D4 is connected between the first path terminal and the second path terminal of the fourth switch tube Q4, and a fifth diode Q4 is connected between the first path terminal and the second path terminal of the fifth switch tube Q5A fifth diode D5 is connected, and a sixth diode D6 is connected between the first path terminal and the second path terminal of the sixth switching tube Q6.
The first switching tube Q1, the second switching tube Q2 and the third switching tube Q3 form an upper arm of the three-phase full-bridge inverter, and the fourth switching tube Q4, the fifth switching tube T5 and the sixth switching tube Q6 form a lower arm of the three-phase full-bridge inverter 110. The inverter 110 outputs a first driving signal V at a connection node between the first switch transistor Q1 and the fourth switch transistor Q4UA second driving signal V is outputted at the connection node of the second switch tube Q2 and the fifth switch tube Q5VAnd a third driving signal V is output at the connection node of the third switch tube Q3 and the sixth switch tube Q6W。
Preferably, the switching tube may be a MOS tube.
The back electromotive force detector 120 is configured to detect a zero-crossing time of back electromotive forces of an unexcited phase stator in the multi-phase stator of the motor, and generate a first feedback signal S1 when a sampling result of the unexcited phase stator is detected to indicate that the phase stator reaches the zero-crossing time. It is understood that the back emf detector 120 includes a plurality of sampling branches, specifically, the number of sampling branches is equal to the number of stator ends of the motor body 200, for example, 3 sampling branches in the embodiment of the present invention. Each sampling branch is used for sampling the voltage of one of the stator terminals of the motor body 200. Taking the voltage sampling of the first-phase stator U end of the motor body 200 (i.e. taking the first-phase stator U as the non-excited-phase stator) as an example, it can be understood that the voltage sampling principle of the second-phase stator V and the third-phase stator W end is the same or similar to that, and is not repeated herein.
Specifically, in the first embodiment of the present invention, referring to fig. 5a, fig. 5a shows a schematic structural diagram of the back electromotive force detector provided according to the first embodiment of the present invention. As shown in fig. 5a, in the present embodiment, the back electromotive force detector 120 performs voltage sampling by using an analog-to-digital converter, and each sampling branch of the back electromotive force detector 120 includes: a first resistor R1, a second resistor R2, a sample-and-hold circuit 121, an analog-to-digital converter 122 and a judgment unit 123.
The first resistor R1 and the second resistor R2 constitute a voltage dividing unit. The sample-and-hold circuit 121 samples the voltage. The analog-to-digital converter 122 is connected to the sample-and-hold circuit 121, and the analog-to-digital converter 122 is configured to perform digital-to-analog conversion on the sampled voltage and output a digital signal corresponding to the sampled voltage. The determining unit 123 is connected to the analog-to-digital converting unit 123, and is configured to determine whether a back electromotive force at the end U of the first phase stator reaches a zero crossing point according to the sampling voltage corresponding to the digital signal, and output a first feedback signal S1 when the sampling voltage corresponding to the zero crossing point is determined. The first resistor R1 and the second resistor R2 are configured to convert the voltage at the first-phase stator U terminal into a voltage recognizable by the sample-and-hold circuit 121 and the analog-to-digital converter 122 through voltage division.
In the second embodiment of the present invention, referring to fig. 5b, fig. 5b shows a schematic structural diagram of a back electromotive force detector provided according to the second embodiment of the present invention. As shown in fig. 5b, in the present embodiment, the bemf detector 120 performs bemf zero-crossing check based on the comparator, and each sampling branch of the bemf detector 120 includes: a voltage dividing unit 124 and a comparator 125.
The input terminal of the voltage dividing unit 124 receives the voltage V of the first phase stator U terminal of the brushless dc motor 10UTo apply the voltage VUThe voltage is divided to a voltage that can be recognized by the comparator 125. The voltage dividing unit 124 may be implemented by, for example, a voltage dividing resistor.
The comparator 125 is connected to the voltage dividing unit 124, receives the divided sampling voltage and the reference voltage Vref, determines whether the back electromotive force of the first-phase stator U end reaches a zero crossing point based on the reference voltage Vref, and outputs a first feedback signal S1 when it is determined that the sampling voltage corresponding to the zero crossing point is reached. The reference voltage Vref received by the comparator 125 is, for example, a motor midpoint voltage (neutral point voltage), and may also be a voltage V applied by the voltage dividing unit 124UThe voltage is obtained after the secondary voltage division, or obtained after the voltage division of other potential points in the brushless dc motor 10, or output by a separate voltage generation circuit, as long as a suitable voltage value can be provided to accurately distinguish whether the back electromotive force at the U end of the first-phase stator reaches the zero crossing point.
Further, a filtering unit may be further disposed at the output end of the comparator 125 to filter the first feedback signal S1 output by the comparator 125 to provide a signal output with a stable waveform, so as to improve the detection and identification accuracy.
Alternatively, the back electromotive force detector 120 with the above structure may also realize detection of the first commutation timing of the brushless dc motor 10, for example: when the voltage V of the U end of the first-phase stator is detectedUIs reduced from the maximum value, it can be determined that this time is the first commutation moment of the motor. It is understood that the above process can be implemented by a combination of hardware and software.
Note that the first commutation timing of the motor detected by the back emf detector 120 differs from the zero-crossing timing by about 30 electrical degrees.
The controller 130 is connected to the inverter 100 and the back electromotive force detector 120 respectively, and is configured to receive the first feedback signal S1 and generate a plurality of control signals according to the first feedback signal S1 to control the on and off of the corresponding switching tubes in the inverter 110. That is, the controller 130 is arranged to detect a first time from a first commutation time instant, the first time ending at a zero-crossing time instant at which the back emf of an unexcited one of the multi-phase stators reaches zero for the first time from the first commutation time instant, and to determine a second commutation time instant of the electric machine on the basis of the first time instant, and to commutate the electric machine at the second commutation time instant.
In this embodiment, the controller 130 includes a plurality of control branches, and each control branch generates a plurality of control signals based on a sampling result of one phase stator of the multi-phase stators. Referring to fig. 6, fig. 6 shows a schematic structural diagram of a controller according to an embodiment of the present invention, in this embodiment, as shown in fig. 6, each control branch of the controller 130 includes: a timing module 131, a timing module 132, a comparison module 133 and a signal generation module 134.
The timing module 131 receives the second feedback signal S2 (the second feedback signal S2 is a signal generated at the first commutation time of the first phase stator U), and starts timing when receiving the second feedback signal S2. The timing module 132 is connected to the timing module 131, and configured to read the timing value t1 of the timing module 131 at this time when receiving the first feedback signal S1, and generate a timing value 2t1 which is twice the timing value t 1. The comparing module 133 is connected to the timing module 131 and the timing module 132, respectively, for reading the timing value t2 of the timing module 131 in real time, and generating the indication signal Sc when the timing value t2 is equal to the timing value 2t 1. The signal generating module 134 is connected to the comparing module 133 for receiving the indication signal Sc, so as to adjust the level states of the first to sixth control signals G1 to G6 according to the indication signal Sc, so as to commutate the motor body 200. Wherein the second feedback signal S2 may be provided by a second commutation time instant determined from the further phase stator terminal, as will be described in more detail later. It can be understood that the time when the timing value t2 is equal to the timing value 2t1 is the second commutation time of the first phase stator U of the motor body 200.
It should be noted that the timing module 131, the timing module 132, and the comparison module 133 may be integrated into a microprocessor, and one or more timers in the microprocessor or a combination of software programs may implement the same functions.
In other embodiments of the invention the control means 100 comprises a timer arranged to start timing at the first commutation time instant and to end timing at the first zero crossing time instant after the first commutation time instant when the back emf detector detects the back emf of the un-excited phase stator. That is, in this embodiment, the timer is used to re-time after the first zero-crossing after the first commutation time to determine the second time and the second commutation time, so that the reading delay that may exist when reading the timing value can be prevented from affecting the accuracy of the second time and the second commutation time.
It can be understood by those skilled in the art that, when the inverter 110 is in operation, only two of the six switching tubes (Q1-Q6) are turned on at a time, and the two switching tubes turned on at a time are respectively located in different branches, and one switching tube is located in the upper arm of the three-phase full-bridge inverter 100 and one switching tube is located in the lower arm of the three-phase full-bridge inverter.
Therefore, by adopting the structure, the influence of different rotating speeds of the motor body in different reversing intervals on the accuracy of the calculation of the reversing time can be avoided, and the method can be better suitable for the condition of changing the rotating speed of the motor.
Referring to fig. 3, fig. 3 is a schematic diagram illustrating waveforms of a plurality of control signals when the inverter according to the embodiment of the present invention is in operation.
As shown in fig. 3, the brushless dc motor 10 is operated based on six-step commutation, that is, six times of commutation is required to drive the rotor 220 in the motor body 200 to rotate for one turn, and the rotor 220 in the motor body 200 is driven to rotate for an angle of 60 ° after each commutation.
Specifically, in the time period (r), the first control signal G1 and the fifth control signal G5 are at a high level, and then the first switching tube Q1 and the fifth switching tube Q5 are respectively controlled to be turned on, so that a magnetic field pointing to the first direction is generated between the first phase stator U and the second phase stator V of the motor body 200; then in the second time period, the first control signal G1 and the sixth control signal G6 are at a high level, and then the first switching tube Q1 and the sixth switching tube Q6 are respectively controlled to be conducted, so that a magnetic field pointing to the second direction is generated between the first phase stator U and the third phase stator W of the motor body 200; by analogy, in the time period (c), the second control signal G2 and the sixth control signal G6 are at a high level, and then the second switching tube Q2 and the sixth switching tube Q6 are respectively controlled to be conducted, so that a magnetic field pointing to the third direction is generated between the second-phase stator V and the third-phase stator W of the motor body 200; in the time period (iv), the second control signal G2 and the fourth control signal G4 are at a high level, and then the second switching tube Q2 and the fourth switching tube Q4 are respectively controlled to be conducted, so that a magnetic field pointing to a fourth direction is generated between the second-phase stator V and the first-phase stator U of the motor body 200; in the fifth time period, the third control signal G3 and the sixth control signal G6 are at a high level, and then the third switching tube Q3 and the sixth switching tube Q6 are respectively controlled to be turned on, so that a magnetic field pointing to a fifth direction is generated between the third-phase stator W and the first-phase stator U of the motor body 200; in the time period, the third control signal G3 and the fifth control signal G5 are at a high level, and then the third switching tube Q3 and the fifth switching tube Q5 are respectively controlled to be conducted, so that a magnetic field pointing to a sixth direction is generated between the third phase stator W and the second phase stator V of the motor body 200. The second direction is clockwise 60 degrees on the basis of the first direction, the third direction is clockwise 60 degrees on the basis of the second direction, and so on, the sixth direction is clockwise 60 degrees on the basis of the fifth direction, and the first direction is clockwise 60 degrees on the basis of the sixth direction, so that clockwise rotation of the rotor 220 is realized.
Further, referring to fig. 4, fig. 4 shows a back electromotive force waveform diagram of a motor according to an embodiment of the present invention.
In fig. 4, curves a/B/C respectively show the back electromotive force waveform diagrams of the respective stators of the motor. Taking a three-phase brushless dc motor as an example, during the operation of the motor, the energized stator coil of the motor body 200 has only two phases at each moment, and the stator coil of the other phase is in the air (not energized), and the air coil generates a counter electromotive force, which is derived from the rotation of the rotor magnet of the motor and causes the stator coil to cut magnetic lines of force and the mutual inductance when the coil of the other two phases is energized. After the rotor rotates by a certain electrical angle, the rotor needs to be reversed to change the conduction state of the driving circuit, so that the motor rotor is driven to rotate continuously.
One drive cycle of a brushless dc motor consists of six equal 60 intervals. Referring to fig. 2, 3 and 4, it can be seen that when two of the stators of the brushless dc motor 10 are energized and the third stator is not energized, the magnetic field strength of the rotor corresponding to the energized two-phase coils is not changed, the directions are opposite, and the magnetic field strength is always the maximum magnetic field strength of the magnetic steel, so that the back electromotive voltages of the two phases have the same amplitude and opposite directions. The magnetic field intensity of the third phase is increased from 0 to the opposite direction. For example, during the first period (r) in fig. 3, the first phase stator U and the second phase stator V are energized, and the third phase stator W is floating, and the corresponding electrical angle is within 0 ° to 60 ° in fig. 4, and at this time, the back electromotive force amplitude of the curve a (corresponding to the first phase stator U) and the back electromotive force amplitude of the curve B (corresponding to the second phase stator V) are the same and opposite in direction during this period, and the back electromotive force amplitude of the curve C (corresponding to the third phase stator W) is changed from the maximum value to 0 during this period, and continues to increase reversely to the maximum value. The amplitude change of the back electromotive force of the three-phase stator of the brushless dc motor 10 in each subsequent stage of 60 ° to 360 ° can be understood by referring to the same principle, and will not be described herein again.
Further, as can be seen from fig. 4, the first commutation time of the first-phase stator U of the motor body 200 occurs at the second commutation time for commutating the second-phase stator V, the first commutation time of the second-phase stator V occurs at the second commutation time for commutating the third-phase stator W, and the first commutation time of the third-phase stator W occurs at the second commutation time for commutating the first-phase stator U. That is, the indication signal Sc generated based on the second commutation timing of the first-phase stator U may serve as the second feedback signal of the third-phase stator W, the indication signal generated based on the second commutation timing of the third-phase stator W may serve as the second feedback signal of the second-phase stator V, and the indication signal generated based on the second commutation timing of the second-phase stator V may serve as the second feedback signal of the first-phase stator U.
In the control method for motor commutation, the back electromotive force zero-crossing time is usually detected to determine the rotor position, and after the back electromotive force zero-crossing time is detected, commutation is performed after the rotor rotates by an electrical angle of 30 ° again (the commutation points are shown as the first commutation time and the second commutation time in fig. 4). Generally speaking, the angle that the rotor rotated is unable accurate acquisition, therefore after zero crossing moment delay certain time, commutate the motor, and the size of delay time directly influences the stability of motor operation, can reduce motor efficiency for example, increases motor noise, is unfavorable for the even running of motor. The patent provides a method for accurately calculating delay time, thereby improving the control effect of a motor.
The first time elapsed between the first commutation time of the motor and the zero-crossing time of the back electromotive force is equal to the second time elapsed between the zero-crossing time of the back electromotive force and the second commutation time of the motor, for example, in the curve C, when the electrical angle of the rotor is changed from 180 ° to 240 °, the curve C is a linear function, and represents that the back electromotive force of the stator corresponding to the curve C is uniformly changed in the period of time. Meanwhile, the second commutation moment of the motor is determined based on the first time from the first commutation moment to the zero-crossing moment of the back electromotive force, the delay time can be dynamically calculated, and the method has good adaptability to the application that the motor has a large rotating speed range and a high changing speed. Based on this principle, the commutation control method of the motor body 200 will be described in detail with reference to the following drawings and embodiments.
Referring to fig. 7, there is illustrated a flowchart of a control method of a motor according to an embodiment of the present invention.
As will be understood from fig. 2 to 6, in the present embodiment, the control method of the motor body 200 includes steps S10 to S30. Alternatively, the motor has reached the steady operation state before step S10.
In step S10, a first time is detected from a first commutation time of the motor.
Fig. 8 shows a flowchart of a first time detection method provided in accordance with the first embodiment of the present invention. As shown in fig. 8, in the first embodiment of the present invention, detecting the first time from the first commutation time of the motor further includes performing steps S101 to S103.
In step S101, a first commutation time of the motor is obtained, and the timer is controlled to start timing at the first commutation time.
In this embodiment, referring to fig. 4, it can be seen that the starting time of the brushless dc motor is the second zero-crossing time of the first phase stator terminal of the motor body and the first commutation time of the third phase stator terminal. Then, a second commutation time of the third stator terminal can be obtained based on the first commutation time of the third stator terminal, and the second commutation time of the third stator terminal can be used as the first commutation time of the second stator terminal. The periodic acquisition of the first commutation moments of the stator ends of the phases can then be carried out on the basis of the same principle.
In step S102, the zero-crossing timing of the back electromotive force of the non-excited phase stator is obtained based on the sample-and-hold circuit and the analog-to-digital converter.
In this embodiment, referring to fig. 5a, firstly, the voltage V at each stator terminal of each phase of the motor body is divided by the resistor voltage divider network (including the first resistor R1 and the second resistor R2)U/VV/VWThe voltage is divided to reduce the voltage to a range that can be recognized by the analog-to-digital converter 122, then the sample holding unit 121 holds the divided sample voltage, stability and accuracy of the sample voltage are guaranteed, the analog-to-digital converter 122 performs analog-to-digital conversion on the analog voltage output by the sample holding circuit 121 to generate a corresponding digital signal, finally, the judgment unit 123 judges whether the digital signal obtained by sampling corresponds to a zero voltage, and outputs the first feedback signal S1 when the voltage corresponding to the digital signal is judged to be zero. And the time when the voltage corresponding to the digital signal is zero is the zero-crossing time of the stator end corresponding to the sampling voltage.
In this embodiment, if the voltage at each phase stator end of the motor body is zero, each bit of the corresponding digital signal is 0, and it is only necessary to determine whether the value of each bit in the corresponding digital signal is 0 when determining whether the voltage is zero-crossing based on the sampling voltage, and there is no need to compare the values with corresponding reference signals.
It can be understood that, in the present embodiment, when detecting the zero-crossing time of each phase stator end of the motor body, the detection may be implemented by using pure hardware, software, or a combination of hardware.
In step S103, the count value of the timer is read at the zero-crossing time of the counter electromotive force of the non-excited phase stator, and the first time is acquired.
In this embodiment, referring to fig. 6, the second feedback signal S2 is generated after the first commutation time of each phase stator end of the motor body is obtained, and the first feedback signal S1 is generated after the zero-crossing time of each phase stator end of the motor body is detected. The second feedback signal S2 can control the timing module 131 to start timing from 0, and the first feedback signal S1 can control the timing module 132 to read the timing value t1 of the timing module 131 when receiving the second feedback signal S2, where the timing value t1 of the timing module 131 read by the timing module 132 is the first time.
Further, fig. 9 shows a flowchart of a first time detection method provided based on the second embodiment of the present invention. As shown in fig. 9, in the second embodiment of the present invention, detecting the first time from the first commutation time of the motor further includes performing steps S111 to S113.
In step S111, a first commutation time of the motor is obtained, and the timer is controlled to start timing at the first commutation time. In this embodiment, step S111 can be understood by referring to step S101, which is not described herein again.
In step S112, the zero-cross timing of the back electromotive force of the stator of the non-excited phase is obtained based on the comparator.
Referring to fig. 5b, in the present embodiment, the voltage V of each phase stator terminal of the motor body is first divided by the voltage dividing unit 124U/VV/VWThe voltage division is performed to reduce the voltage to a range that can be recognized by the comparator 125, and then the divided sampling voltage is compared by the comparator 125 based on the reference voltage Vref, and a corresponding digital signal is output according to the comparison result. Wherein, the comparator 125 outputs a digital signal corresponding to the first voltage value (one of "1" and "0") when the sampling voltage is greater than the reference voltage Vref, the comparator 125 outputs a digital signal corresponding to the second voltage value (the other of "1" and "0") when the sampling voltage is less than the reference voltage Vref, and a rising edge or a falling edge generated when the sampling voltage changes from the first voltage value to the second voltage value of the digital signal output by the comparator 125 can be used as a trigger signal for triggering the timing module 132 in fig. 6 to read the timing value t1 of the timing module 131, i.e. the first feedback signal S1, so that the zero-crossing time of the sampling voltage corresponding to the corresponding stator terminal can be identified by reasonably setting the voltage value of the reference voltage Vref.
In step S113, the count value of the timer is read at the zero-crossing time of the counter electromotive force of the stator of the non-excited phase, and the first time is acquired. In this embodiment, step S113 can be understood by referring to step S103, which is not described herein again.
Note that the first commutation time and the zero-cross time of each phase stator terminal of the motor body detected by the back electromotive force detector 120 are adjacent to each other.
Optionally, the motor is a multi-phase motor,
in step S20, a second commutation time of the motor is determined based on the first time.
Referring to fig. 6, after the timing module 132 acquires the first time (i.e., the timing value t1) of a certain phase stator end of the motor body based on the first feedback signal S1, the timing module 132 further generates a timing value 2t1 which is twice as large as the timing value t1 based on the timing value t1 and outputs the timing value 2t1 to the comparison module 133, and the comparison module 133 starts to read the timing value t2 of the timing module 131 in real time after receiving 133, where a time when the timing value t2 is equal to the timing value 2t1 is the second commutation time of the certain phase stator end of the motor body. The method for determining the second reversing time of each phase stator end of the motor body can dynamically calculate the delay time, has good adaptability to the application that the motor rotating speed range is large, the rotating speed changes and the changing speed is high, is simple in implementation method, does not increase processor burden, has good adaptability to a sensorless algorithm using a comparator or a sensorless algorithm using ADC acquisition, and is wide in application range.
It will be appreciated that the second time elapsed from the zero-crossing time of the back emf to the second commutation time is equal to the first time.
In step S30, the motor is commutated at a second commutation timing.
Referring to fig. 2 and 6, at the second commutation time, that is, the time when the timing value t2 read by the comparing module 133 is equal to the timing value 2t1, the comparing module 133 generates the indication signal Sc and outputs the indication signal Sc to the signal generating module 134, and the signal generating module 134 adjusts the level states of the first control signal G1 to the sixth control signal G6 after receiving the indication signal Sc, and further adjusts the first control signal G1 to the sixth control signal G66 controlling inverter 100 to correspondingly change first driving signal V output by inverter 110UA second drive signal VVAnd a third drive signal VWThe commutation of the motor body 200 is realized.
In the above embodiments, only the steps occurring in one commutation process are described, and in the embodiments of the present invention, it should be understood that, when the motor is a multi-phase motor, it is necessary to detect the zero point time of the multi-phase stator and the change of the back electromotive force to complete the continuous multi-commutation of the motor, so as to drive the motor to operate continuously. For example, taking a three-phase motor as an example, referring to fig. 4, it can be seen that the indication signal generated based on the second commutation timing of the first-phase stator U may serve as the second feedback signal of the third-phase stator W, the indication signal generated based on the second commutation timing of the third-phase stator W may serve as the second feedback signal of the second-phase stator V, and the indication signal generated based on the second commutation timing of the second-phase stator V may serve as the second feedback signal of the first-phase stator U. And by analogy, the zero-crossing time of the first-phase stator U, the second-phase stator V and the third-phase stator W of the motor body is detected in sequence, and the motor is commutated at the second commutation time of each phase stator, so that the motor is driven to operate continuously. Therefore, the reversing efficiency and the reversing quality of the motor can be greatly improved.
In summary, in this control method, in order to complete the consecutive multiple commutations of the motor, it is actually necessary to detect the back electromotive force of each phase stator separately, and after each commutation of the motor, steps S10 to S30 are performed once.
Optionally, the motor is a multi-phase motor, and when the controller 130 commutates the motor, the second commutation time of the first-phase stator U and the first commutation time of the third-phase stator W occur simultaneously, that is, the second commutation time of the first-phase stator U may be used as the first commutation time of the third-phase stator W, so that the second commutation time of the third-phase stator W may be determined more quickly, and the motor may be commutated multiple times continuously. The timing module 131 is further connected to the comparing module 133 and receives an indication signal Sc, which can be used to reset the timing module 131 to prepare for the next commutation of the motor.
It should be appreciated that the timing module 131, the timing module 132, and the comparison module 133 described above may be integrated into a microprocessor, with the same or similar functions being implemented by a timer module of one or more of the microprocessors or in conjunction with a software program.
It should be understood that, in the foregoing embodiments and the accompanying drawings, the technical solution of the present invention is described by taking a three-phase motor as an example, and it should be understood that the present application does not limit the type of the motor.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.
Claims (13)
1. A control method of a brushless dc motor, the motor including a rotor and a multiphase stator, the control method comprising:
detecting a first time from a first commutation time of the electric machine, the first time ending at a zero-crossing time at which a back electromotive force of an unexcited phase stator among the multi-phase stators reaches zero for a first time from the first commutation time;
determining a second commutation moment of the motor according to the first time; and
and at a second commutation moment, commutating the motor to drive the rotor to rotate.
2. The control method of claim 1, wherein detecting the first time from the first commutation time of the motor comprises:
acquiring a first reversing time of the motor, and controlling a timer to start timing at the first reversing time;
obtaining the zero-crossing time of the back electromotive force of the stator of the unexcited phase; and
and reading the counting value of the timer at the zero-crossing time of the back electromotive force of the stator of the non-excited phase to obtain a first time.
3. Control method according to claim 2, characterized in that the zero-crossing times of the back emf of the non-excited phase stators are obtained by means of a sample-and-hold circuit and an analog-to-digital converter.
4. Control method according to claim 2, characterized in that the zero-crossing instant of the back emf of the non-excited phase stator is obtained by a comparator.
5. The control method according to claim 1, characterized in that a second time elapsed from a zero-crossing time of the back electromotive force to the second commutation time is equal to the first time.
6. A control apparatus of a brushless dc motor including a rotor and a multiphase stator, the apparatus comprising:
an inverter connected to a DC power supply and supplying a driving signal to the multiphase stator;
a counter electromotive force detector for detecting a zero-cross timing of a counter electromotive force of an unexcited phase stator among the multi-phase stators;
a controller configured to detect a first time from a first commutation time, the first time ending at a zero-crossing time at which a back electromotive force of an unexcited phase stator among the multi-phase stators reaches zero for a first time from the first commutation time; determining a second commutation moment of the motor according to the first time; and at a second commutation moment, commutating the motor.
7. The control device of claim 6, wherein the back emf detector comprises a sample and hold circuit and an analog-to-digital converter.
8. The control device of claim 6, wherein the back electromotive force detector comprises a comparator.
9. The control apparatus of claim 6, further comprising a timer that starts timing at a first commutation time and ends timing at a first zero-crossing time after the back EMF detector detects back EMF of an un-energized phase stator at the first commutation time.
10. The control device of claim 6, wherein the controller comprises a plurality of control branches, each control branch generating a corresponding plurality of control signals based on the sampling result of the one-phase stator, respectively, each control branch comprising:
the timing module receives the second feedback signal and starts timing;
the timing module is connected with the timing module, receives a first feedback signal, and is used for reading a timing value of the timing module to obtain a first timing value when the first feedback signal is received, and generating a timing value based on the first timing value;
the comparison module is respectively connected with the timing module and the timing module, receives the timing value, reads the timing value of the timing module in real time and generates an indication signal when the read timing value is equal to the timing value;
a signal generating module connected with the comparing module and used for adjusting the level states of the output control signals according to the indication signals so as to realize the commutation of the motor body,
wherein a first time that the timing module reaches the first timing value from a start of timing is equal to a second time that the timing module reaches the timing value from the first timing value.
11. The control device of claim 10, wherein the indication signal generated by a first control branch of the plurality of control branches of the controller is used as the second feedback signal for a second control branch.
12. The control apparatus of claim 10, wherein in each control branch of the controller, the timing module starts timing based on a first commutation time of a corresponding phase stator, the timing module reads a timing value based on a zero-crossing time of the corresponding phase stator to generate a timing value,
wherein the first commutation moment is a commutation moment preceding the zero-crossing moment.
13. A brushless dc motor system, comprising:
a motor body; and
the control device according to any one of claims 6 to 12.
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