CN109347375B - Sensorless starting method and device of brushless motor - Google Patents
Sensorless starting method and device of brushless motor Download PDFInfo
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- CN109347375B CN109347375B CN201811354398.3A CN201811354398A CN109347375B CN 109347375 B CN109347375 B CN 109347375B CN 201811354398 A CN201811354398 A CN 201811354398A CN 109347375 B CN109347375 B CN 109347375B
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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
- H02P6/20—Arrangements for starting
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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
- H02P2207/00—Indexing scheme relating to controlling arrangements characterised by the type of motor
- H02P2207/05—Synchronous machines, e.g. with permanent magnets or DC excitation
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Abstract
The invention relates to a sensorless starting method of a brushless motor, which comprises the steps of providing PWM driving signals set arbitrarily for two windings of the motor, forcibly phase-changing the motor after obtaining the voltage, continuously collecting the voltage generated on the winding which is not provided with the driving signals, phase-changing the motor according to the characteristics of the obtained voltage, and comparing the obtained voltage with bus voltage after multiple phase changes to obtain the electrical angle parameter of the motor, so as to obtain the self-synchronous phase change time and the phase change duration of the motor, and enable the motor to enter a self-synchronous state. The invention also relates to a device for realizing the method. The implementation of the sensorless starting method and the sensorless starting device of the brushless motor has the following beneficial effects that: it has strong adaptability.
Description
Technical Field
The invention relates to the field of electromechanical control, in particular to a sensorless starting method and a sensorless starting device of a brushless motor.
Background
The sensorless starting problem of the brushless motor is a technical difficulty which cannot be avoided in the motor driving industry, and how to ensure that the motor is reliably started under the working condition that the load is suddenly changed in the starting process is always a key and technical difficulty in the field. It is known that brushless motors can be driven by simple commutation as with brush motors if the rotor position is known at a certain moment, but there are many applications where there is no way to incorporate sensors in the motor, such as in hot or other harsh environments, where sensorless mode is required to drive the motor. In the sensorless mode, it is important to clearly and accurately obtain the rotor position. When the motor runs normally, the rotor position can be easily obtained through the back electromotive force of the motor, but how to make the motor from rest to a certain speed (the rotor position can be accurately obtained at the speed), in the process, the motor is under heavy load and the load irregularly changes, so that how to reliably start the motor, and further, the motor is switched into a self-synchronizing state, which is particularly important. In the prior art, there are generally several methods for starting a sensorless brushless motor: three-section type starting, pulse current method starting, counter potential integration starting, frequency-boosting and voltage-boosting starting and the like. In the methods, the three-stage starting and the frequency-boosting and pressure-boosting starting can not ensure that the position of the rotor is accurately known in the open-loop starting stage, and can not ensure whether the rotor reaches the designated position in the acceleration stage; the back electromotive force integration method is that after pre-positioning is finished, a motor is driven in an open loop mode at a certain speed, back electromotive force of a suspension phase is collected through AD, values collected each time are accumulated, and after a certain threshold value is reached, phase change is forced, so that a self-synchronizing state is entered, and the method has the defects that in the starting acceleration process, if load is suddenly changed, the back electromotive force shakes, the integral result is influenced, the forced phase change point of a rotor is influenced, and starting is occasionally failed; the pulse current method starting has the advantages that the position of the static rotor is determined, but high-frequency current pulses are required to be injected to judge the position of the rotor in the forced acceleration process, certain starting noise and loss are caused, and meanwhile, the main control single chip microcomputer has higher requirements. In summary, the existing sensorless starting method of the brushless motor has the following disadvantages: the adaptability is not strong, and parameters need to be readjusted when different motors are started; even if the motors are the same, parameters need to be adjusted under different load conditions; in addition, during the starting process, if the load is suddenly changed, the starting process can also fail.
Disclosure of Invention
The present invention provides a sensorless starting method and apparatus for a brushless motor with high adaptability, aiming at the defect of poor adaptability in the prior art.
The technical scheme adopted by the invention for solving the technical problems is as follows: a sensorless start-up method of constructing a brushless motor, comprising:
the method comprises the steps of providing PWM driving signals set arbitrarily for two windings of a motor, obtaining generated voltage on the winding of the motor which is not provided with the driving signals, forcibly phase-changing the motor after obtaining the voltage, continuously collecting the voltage generated on the winding which is not provided with the driving signals, phase-changing the motor according to the characteristics of the obtained voltage, comparing the obtained voltage with bus voltage after multiple phase changes to obtain electrical angle parameters of the motor, and obtaining self-synchronous phase change time and phase change duration of the motor so that the motor enters a self-synchronous state.
Still further, the method further comprises the steps of:
A) respectively providing preset PWM (pulse-width modulation) driving signals with the same waveform for any two windings in the motor, sampling voltage on a connected third winding, carrying out forced commutation when the voltage is acquired, continuously carrying out voltage sampling on the third winding after the forced commutation, and carrying out commutation on the motor when a first set condition is met;
B) judging whether the commutation frequency after the forced commutation reaches a set value, if so, executing the next step on the basis of continuing voltage sampling and commutation, otherwise, continuing voltage sampling and commutation;
C) comparing the voltage values acquired on the third winding with half of the voltage values detected on the motor bus one by one, and selecting sampling points which are equal to each other as zero-crossing points;
D) and obtaining the time between two adjacent zero-crossing points on one winding or the time between two adjacent zero-crossing points on the two windings respectively, namely obtaining the duration time of the difference between the set electrical angles, using the duration time for calculating the self-synchronization commutation moment and the commutation duration time to obtain self-synchronization parameters, and enabling the motor to enter a self-synchronization state according to the obtained self-synchronization parameters.
Further, a voltage is collected on the third winding, and a counter potential generated on the third winding due to the input of the driving signal is collected; the first setting condition includes that the absolute value of the differential value of the back electromotive voltage for two adjacent collected back electromotive voltages is smaller than a set value.
Still further, the step a) further comprises the following steps:
when determining whether phase conversion is needed, judging whether the currently obtained differential value is positive, if so, judging that the counter potential is in the rising period, and combining the currently given phase and the phase conversion table to judge the next phase conversion; meanwhile, the differential value is compared with a set threshold value, and phase inversion is forced when the differential value reaches the set threshold value; otherwise, the counter potential is in the falling period, and the next commutation is judged by combining the current given phase and the commutation table; at the same time, the differential value is reversed and compared with the set threshold value, and the phase is forced to change when the differential value is reached.
Further, in the step a), the voltage sampling of the third winding is performed at a middle point of the PWM pulse of the driving waveform.
Furthermore, the duration time between the electrical angles is obtained by that the electrical angle between the adjacent zero-crossing points on the same winding is 180 degrees, and the electrical angle between the adjacent zero-crossing points between the adjacent windings is 60 degrees, so that the duration time of any electrical angle difference can be calculated, and further the self-synchronization parameter of the motor is obtained.
Still further, the step a) further comprises the following steps:
monitoring the current on the motor bus, and gradually increasing the duty ratio of driving waveforms on the coils respectively connected with the first-phase alternating current and the second-phase alternating current under the condition that the current of the motor bus is smaller than a set threshold; and reducing the duty cycle of the driving waveform in a case where the current is equal to or greater than the set threshold.
The invention also relates to a device for realizing the method, which comprises the following steps:
starting a control module: the method is used for providing PWM driving signals set arbitrarily for two windings of the motor, obtaining generated voltage on the winding of the motor which is not provided with the driving signals, forcibly changing the phase of the motor after obtaining the voltage, continuously collecting the voltage generated on the winding which is not provided with the driving signals, changing the phase of the motor according to the characteristics of the obtained voltage, and comparing the obtained voltage with bus voltage after multiple phase changes to obtain the electrical angle parameter of the motor, so that the self-synchronous phase change time and the phase change duration of the motor are obtained, and the motor enters a self-synchronous state.
Still further, the start control module further comprises:
forced commutation unit: the PWM driving circuit is used for respectively providing preset PWM driving signals with the same waveform for any two windings in the motor, performing voltage sampling on a connected third winding, performing forced commutation when the voltage is acquired, continuing to perform voltage sampling on the third winding after the forced commutation, and performing commutation on the motor when a first set condition is met;
commutation frequency judging unit: the zero crossing point detection unit is used for judging whether the commutation times after the forced commutation reaches a set value, if so, the zero crossing point detection unit is called on the basis of continuing voltage sampling and commutation, otherwise, the voltage sampling and commutation are continued;
a zero-crossing point detection unit: the voltage values collected on the third winding are compared with half of the voltage values detected on the motor bus one by one, and sampling points which are equal to the voltage values are selected as zero-crossing points;
a self-synchronization parameter acquisition unit: and the time acquisition module is used for acquiring the time between two adjacent zero-crossing points on one winding or the time between two adjacent zero-crossing points on the two windings respectively, namely the duration time of the difference between the set electrical angles, calculating the self-synchronization commutation time and the commutation duration time to acquire self-synchronization parameters, and enabling the motor to enter a self-synchronization state according to the acquired self-synchronization parameters.
Furthermore, in the forced commutation unit, the voltage collected on the third winding is the counter potential generated on the third winding due to the input of the driving signal; the first setting condition includes that the absolute value of the differential value of the back electromotive voltage for two adjacent collected back electromotive voltages is smaller than a set value.
The implementation of the sensorless starting method and the sensorless starting device of the brushless motor has the following beneficial effects that: when the brushless motor is started, a set driving signal is provided for any two windings of the motor, the counter electromotive force of the motor is collected on the third winding, and when the counter electromotive force is detected on the third winding, the two windings are subjected to forced phase change; then, the back electromotive force generated by the third winding (the third winding is changed along with the phase change, namely, the winding which is not provided with the driving signal) is accumulated, so that the zero crossing point of the driving signal can be accurately obtained, the time between the set electric angle difference is obtained, and the self-synchronization parameter is further obtained, and the motor can enter a self-synchronization state; meanwhile, when the obtained counter electromotive force is processed, a mode of differential calculation of two adjacent counter electromotive force voltages is adopted, so that the influence of load change on the counter electromotive force calculation is eliminated, errors cannot be accumulated, and the counter electromotive force voltage is insensitive to the load change during starting. Therefore, the adaptability is strong.
Drawings
FIG. 1 is a method flow in an embodiment of a sensorless startup method and apparatus for a brushless motor of the present invention;
FIG. 2 is a schematic diagram of waveforms of counter potentials collected by windings when the driving waveform is a trapezoidal waveform in the embodiment;
FIG. 3 is a schematic diagram of waveforms of counter potentials collected by windings when the driving waveform is a sine wave in the embodiment;
FIG. 4 is a schematic diagram of a driving circuit in the embodiment;
FIG. 5 is a flow chart showing the method implemented in one case of the embodiment;
fig. 6 is a schematic structural view of the device in the embodiment.
Detailed Description
The embodiments of the present invention will be further described with reference to the accompanying drawings.
As shown in fig. 1, in the embodiment of the sensorless starting method and apparatus for a brushless motor according to the present invention, the sensorless starting method for a brushless motor is to provide arbitrarily set PWM driving signals to two windings of the motor (in this embodiment, the duty ratio and frequency of the PWM driving signals provided to the two windings are preset, and the driving signals provided to the two windings may even be the same driving signal), forcibly phase-change the motor after obtaining the voltage, continuously collect the voltages generated on the windings not provided with the driving signals because the driving signals are added to the other two windings, phase-change the motor according to the characteristics of the obtained voltages, and compare the obtained voltages with the bus voltage after multiple phase changes to obtain the electrical angle parameters of the motor, so as to obtain the self-synchronization phase change time and the phase change duration of the motor, causing the motor to enter a self-synchronizing state. It is worth mentioning that in the present embodiment, for the motor, according to the existing convention, the winding of one motor is also referred to as one phase of the motor, and therefore, the commutation means in the present embodiment that the winding to which the driving signal is applied is switched, that is, the winding to which the driving signal is applied is changed, but in any case, when the motor is not brought into the self-synchronization state, only two windings (or two phases) are applied with the driving signal; regardless of which two windings the drive signal is applied to, the winding to which the drive signal is not applied is the third winding. In this embodiment, the specific steps of the method are shown in fig. 1, and include:
step S11 provides the set driving signal to any two windings, and obtains the counter potential on the third winding: in the step, PWM driving signals with the same set waveform are respectively provided for any two windings in the brushless motor, voltage sampling is carried out on the third winding, and the voltage collected on the third winding is counter potential generated on the third winding due to the input of the driving signals; the voltage sampling of the third winding is performed at the middle point of the PWM pulse of the drive waveform. For the brushless motor, the connection mode of the three windings can be any one of connection methods in the prior art, such as star connection; the driving waveforms or driving signals provided for any two windings may be identical in waveform, that is, may be the same driving signal; the third winding does not need to provide a drive signal. In this embodiment, the voltage picked up by the third winding is actually the voltage measured at one end of the third winding (the end not connected to it).
Step S12 takes the counter potential, forcibly inverts, and continues to detect the counter potential on the third winding: in this step, when the counter potential is detected on the third winding, i.e. the motor is controlled to perform forced phase change, for example, assuming that the driving signal is currently applied to the BC two phases, if the driving signal is currently from C to B, and the counter potential differential of the a phase of the third phase is detected to be positive, the voltage of the a phase is continuously detected at the midpoint of the PWM and differentiated, when the differential is reduced to a set threshold, the phase change is forced, so that the AB two phases of the driving signal are applied, the voltage of the C phase is detected, the differential is performed, and at this time, the C counter potential should be in a falling channel, the differential is negative, the differential value is inverted and compared with the threshold, and when the set threshold is reached, the phase change is forced, and the cycle is repeated.
Step S13 satisfies the first setting condition, commutation: in this step, the voltage value collected at the third winding is processed, that is, the trend of the collected voltage value is determined. In this embodiment, the differential value is obtained by differentiating the counter potential voltage values of two adjacent collected counter potential voltage values, and the variation trend is obtained accordingly. And performing forced phase change on the motor when a first set condition is met; in the present embodiment, the first setting condition includes that the differential value for two adjacent collected counter potentials is smaller than a set value. When the phase change is determined to be needed, judging whether the currently obtained differential value is positive or not, if so, judging that the next phase change is carried out by combining the currently given phase and the phase change table when the counter potential is in the rising period; meanwhile, the differential value is compared with a set threshold value, and phase inversion is forced when the differential value reaches the set threshold value; otherwise, the counter potential is in the falling period, and the next commutation is judged by combining the current given phase and the commutation table; at the same time, the differential value is reversed (e.g., made positive) and compared with a set threshold, and when it is reached, the phase is forced to be changed. It is to be noted that, in the present embodiment, the commutation in the present step is, as in the specific operation in step S12 described above, to cause the two phases to which the drive signals are applied to be changed.
Step S14, if the number of commutation reaches the set number, if so, the next step is executed on the basis of keeping the commutation driving signal being continuously supplied to the winding; otherwise, return to step S12. It should be noted that, in this embodiment, actually, a driving signal is provided to the winding to rotate the motor, and the counter potential on the third winding is collected at the same time, and the step of commutation is not stopped all the time, but when the number of commutation reaches a set number, the following steps are performed on the basis of continuing to rotate the motor and commutation; if the phase change does not reach the set times, the steps are continuously executed until the forced phase change is achieved, and the following steps are continuously executed.
Step S15 determines the zero-crossing point of the back emf: in this embodiment, the voltage values collected on the third winding are compared with half of the voltage values detected on the motor bus one by one, that is, half of the voltage values on the bus are compared with the voltage values detected on the third winding, and the sampling points equal to the half of the voltage values are selected as zero-crossing points; it should be noted that, in this embodiment, the voltage detection on the bus is actually always present, but the voltage detected on the bus is not used until this step is not performed. In other words, in the present embodiment, the detection of the voltage on the bus has already been started by the execution of step S11.
Step S16 obtains a self-synchronization parameter according to the obtained back emf zero-crossing point, and enters a self-synchronization state: in this step, the time between two adjacent zero-crossing points on one winding or the time between two adjacent zero-crossing points on the two windings respectively is obtained, that is, the duration time of the difference between the set electrical angles is obtained and used for calculating the self-synchronization commutation time and the commutation duration time to obtain the self-synchronization parameter, and the motor enters the self-synchronization state according to the obtained self-synchronization parameter.
In the embodiment, in order to ensure the safety of hardware, when starting, the current on the motor bus is also monitored, and under the condition that the current is smaller than a set threshold, the duty ratio of driving waveforms on the coils respectively connected with the first-phase alternating current and the second-phase alternating current is gradually increased; and in the case where the current is equal to or greater than the set threshold, the duty ratio of the drive waveform is decreased, or is gradually increased after being temporarily decreased. The benefit of this arrangement is to ensure that no large currents will break down the switching device.
In one case of the present embodiment, a trapezoidal wave driving signal is taken as an example to describe a complete process of starting the driving circuit. Fig. 2 is a schematic diagram of counter potentials collected at the respective windings when the drive waveform is a trapezoidal wave. FIG. 3 is a schematic diagram of the back emf collected on each winding when the drive waveform is sinusoidal; fig. 4 is a driving circuit diagram in the above case, and fig. 5 shows a start-up flow chart in this case in more detail.
In the above situation in this embodiment, as can be seen from fig. 4, the main control chip alternately collects terminal voltages (H1, H2, and H3), i.e., the back electromotive force of the motor, through three routes of ADs (AD1, AD2, and AD3), and at the same time, the AD4 collects the voltage of the sampling resistor R4 to obtain the bus current and the AD5 collects the bus voltage, i.e., the supply voltage. Wherein R1, R2, R3 and R4 are resistance voltage dividing networks and low-pass filter networks, and are used for dividing voltage to obtain a voltage range suitable for AD acquisition and filtering some high-frequency noise; r5 is a sampling resistor, the current flowing through the motor also passes through a secondary sampling resistor, the current information is obtained by collecting the differential voltage at the two ends of the sampling resistor, and OP is an operational amplifier and a low-pass filter network, so that the voltage signal which is suitable for AD collection and represents the current information is obtained. S1, S2, S3, S4, S5 and S6 are switching tubes, which can be mosfets or igbt, and the main control chip controls the on and off of the six switching tubes through a driving circuit to realize the zone driving of the motor. L1, L2, and L3 are three windings (three phases) of the motor M, but the drive motor is not limited to this Y connection, and may be a Δ connection.
In the present embodiment, the sensorless brushless motor is in a self-synchronizing state, that is, the motor rotor position is obtained through the back electromotive force information, and the commutation driving is performed through the position information. However, the back electromotive force of the motor is in a direct proportion to the speed of the motor, and when the motor is static or the speed is low, the back electromotive force is small and is not enough to detect or observe so as to obtain the position information of the rotor. The difficulty of sensorless brushless motor driving is that how to obtain back electromotive force under the condition of static or low speed becomes the key of smooth switching into self-synchronization state.
In the embodiment, terminal voltage, namely phase voltage, of the motor is acquired by using AD to obtain rotor position information, and waveforms in fig. 2 represent three-phase counter potentials of the motor with counter potentials of trapezoidal waves, which are respectively taken from positions H1, H2 and H3 in fig. 4. When the motor starts from a standstill, any two phases of the motor are electrified, the duty ratio is gradually increased from small to large, and the counter electromotive force of the current and the suspended phase starts to be detected; assuming the motor initial given phase is the CB phase (i.e., CB two windings) as shown in fig. 4, i.e., PWM chopping at S3 and normally high at S5, current will flow from H3 to H2, with L1 being the suspended phase. The AD collects voltage signals at the point H1 at each PWM midpoint, and differential operation is carried out on the signals obtained twice. It can be seen that from the initial moment of phase commutation of CB, the back electromotive force at a1 point is collected to A3 point, the differential representation of the back electromotive force is a rising slope, until A3 point, the measured differential is always a positive value, but when a4 point is collected, the differential value is zero, and the differential threshold value of phase commutation is set, so that phase commutation is forced at a4 point; similarly, during the process of the back-off potential drop, from A5 to A8, the phase is forced to change at the point A8, and the rest is similar.
In addition, the AD4 collects current at each PWM midpoint simultaneously, when the current is too large in the phase change process and reaches a set threshold value, the duty ratio is properly reduced and then increased, but the current cannot exceed the set current threshold value, and hardware damage is prevented.
In the embodiment, after the commutation with fixed steps, the counter potential of the motor is fully established, the AD5 acquires the bus voltage and obtains VDC/2, the counter potential is compared with the counter potential to obtain self-synchronizing counter potential zero-crossing points A2 and A5, the two zero-crossing points of the same phase are in an electrical angle of 180 degrees, and therefore the electrical angle time of 30 degrees, 60 degrees, 120 degrees and the like can be obtained, and the self-synchronizing commutation time and commutation duration are calculated.
In addition, in the present embodiment, the above method can be applied not only to the motor whose counter potential is a trapezoidal wave, but also to the motor whose counter potential is a sine wave. The counter potential waveform on one phase of the motor is shown in figure 3 when the counter potential is sinusoidal and can be seen to be approximately the same as a trapezoidal wave.
The invention also relates to a device for realizing the method, which comprises a starting control module 1, wherein the starting control module 1 is used for providing PWM driving signals which are set randomly for two windings of the motor, acquiring generated voltage on the winding of the motor which is not provided with the driving signals, comparing the acquired voltage with bus voltage to acquire the electrical angle parameter of the motor after the motor is subjected to phase commutation for multiple times according to the characteristics of the acquired voltage, and acquiring the self-synchronous phase commutation time and commutation duration of the motor to enable the motor to enter a self-synchronous state.
As shown in fig. 6, the start control module 1 further includes a forced commutation unit 11, a commutation frequency judging unit 12, a zero crossing point detecting unit 13, and a self-synchronization parameter obtaining unit 14; the forced commutation unit 11 is configured to provide preset PWM driving signals with the same waveform to any two windings in the motor, sample voltage on a connected third winding, perform forced commutation when the voltage is acquired, continue to sample voltage on the third winding after the forced commutation, and commutate the motor when a first set condition is met; (ii) a The commutation frequency judging unit 12 is configured to judge whether the commutation frequency after the forced commutation reaches a set value, if so, invoke the zero crossing point detecting unit 13 on the basis of continuing voltage sampling and commutation, otherwise, continue voltage sampling and commutation; the zero crossing point detection unit 13 is configured to compare the voltage value collected by the third winding with a half of the voltage value detected by the motor bus one by one, and select a sampling point where the two are equal as a zero crossing point; the self-synchronization parameter obtaining unit 14 is configured to obtain a time between two adjacent zero-crossing points on one winding or a time between two adjacent zero-crossing points on the two windings, that is, a time during which a difference between the set electrical angles lasts, and use the time for calculating a self-synchronization commutation time and a commutation duration to obtain a self-synchronization parameter, and enable the motor to enter a self-synchronization state according to the obtained self-synchronization parameter. In the commutation cell 11, a voltage is collected on the third winding, which is connected to the commutation cell, as a counter potential generated thereon as a result of the input of the drive signal; the first setting condition includes that the absolute value of the differential value of the counter electromotive forces for two adjacent collected counter electromotive forces is smaller than a set value.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A sensorless starting method of a brushless motor, comprising:
the method comprises the steps of providing PWM driving signals set arbitrarily for two windings of a motor, obtaining generated voltage on the winding of the motor which is not provided with the driving signals, forcibly phase-changing the motor after obtaining the voltage, continuously collecting the voltage generated on the winding which is not provided with the driving signals, phase-changing the motor according to the characteristics of the collected voltage, and comparing the collected voltage with bus voltage after multiple phase changes to obtain electrical angle parameters of the motor, so that the self-synchronizing phase change time and the phase change duration of the motor are obtained, and the motor enters a self-synchronizing state.
2. The sensorless startup method of a brushless motor of claim 1, characterized in that the method further comprises the steps of:
A) respectively providing preset PWM (pulse-width modulation) driving signals with the same waveform for any two windings in the motor, sampling voltage on a connected third winding, carrying out forced commutation when the voltage is acquired, continuously carrying out voltage sampling on the third winding after the forced commutation, and carrying out commutation on the motor when a first set condition is met;
B) judging whether the commutation frequency after the forced commutation reaches a set value, if so, executing the next step on the basis of continuing voltage sampling and commutation, otherwise, continuing voltage sampling and commutation;
C) comparing the voltage values acquired on the third winding with half of the voltage values detected on the motor bus one by one, and selecting sampling points equal to the voltage values as zero-crossing points;
D) and obtaining the time between two adjacent zero-crossing points on one winding or the time between two adjacent zero-crossing points on the two windings respectively, namely obtaining the duration time of the difference of the set electrical angles, using the duration time for calculating the self-synchronization commutation time and the commutation duration time to obtain self-synchronization parameters, and enabling the motor to enter a self-synchronization state according to the obtained self-synchronization parameters.
3. The sensorless starting method of the brushless motor of claim 2, wherein the voltage collected on the connected third winding is a counter potential generated thereon due to the input of the driving signal; the first setting condition comprises that the absolute value of the differential value of two adjacent collected back electromotive voltage is smaller than a set value.
4. The sensorless starting method of the brushless motor according to claim 3, wherein the step a) further comprises the steps of:
when determining whether phase conversion is needed, judging whether the currently obtained differential value is positive, if so, judging that the counter potential is in the rising period, and combining the currently given phase and the phase conversion table to judge the next phase conversion; meanwhile, the differential value is compared with a set threshold value, and phase inversion is forced when the differential value reaches the set threshold value; otherwise, the counter potential is in the falling period, and the next commutation is judged by combining the current given phase and the commutation table; at the same time, the differential value is reversed and compared with the set threshold value, and the phase is forced to change when the differential value is reached.
5. The sensorless startup method of the brushless motor of claim 4, wherein in the step A), the voltage sampling of the third winding is performed at a PWM pulse midpoint of the driving waveform.
6. The sensorless starting method of the brushless motor according to claim 5, wherein the duration of any difference in electrical angle is obtained by obtaining the duration between adjacent zero-crossing points through that the electrical angle between adjacent zero-crossing points on the same winding is 180 degrees and the electrical angle between adjacent zero-crossing points between adjacent windings is 60 degrees, thereby obtaining the self-synchronizing parameter of the motor.
7. The sensorless starting method of the brushless motor according to any one of claims 2 to 6, wherein the step A) further comprises the steps of:
monitoring the current on the motor bus, and gradually increasing the duty ratio of driving waveforms on coils respectively connected with the first-phase alternating current and the second-phase alternating current under the condition that the current of the motor bus is smaller than a set threshold; and reducing the duty cycle of the driving waveform in a case where the current is equal to or greater than the set threshold.
8. An apparatus for implementing the sensorless starting method of the brushless motor of claim 1, comprising:
starting a control module: the method is used for providing PWM driving signals set arbitrarily for two windings of the motor, obtaining generated voltage on the winding of the motor which is not provided with the driving signals, forcibly changing the phase of the motor after obtaining the voltage, continuously collecting the voltage generated on the winding which is not provided with the driving signals, changing the phase of the motor according to the characteristics of the collected voltage, and comparing the collected voltage with bus voltage after multiple phase changes to obtain the electrical angle parameter of the motor, so that the self-synchronizing phase change time and the phase change duration of the motor are obtained, and the motor enters a self-synchronizing state.
9. The apparatus of claim 8, wherein the start control module further comprises:
forced commutation unit: the PWM driving circuit is used for respectively providing preset PWM driving signals with the same waveform for any two windings in the motor, performing voltage sampling on a connected third winding, performing forced commutation when the voltage is acquired, continuing to perform voltage sampling on the third winding after the forced commutation, and performing commutation on the motor when a first set condition is met;
commutation frequency judging unit: the zero crossing point detection unit is used for judging whether the commutation times after the forced commutation reaches a set value, if so, the zero crossing point detection unit is called on the basis of continuing voltage sampling and commutation, otherwise, the voltage sampling and commutation are continued;
a zero-crossing point detection unit: the voltage values collected on the third winding are compared with half of the voltage values detected on the motor bus one by one, and sampling points equal to the voltage values are selected as zero-crossing points;
a self-synchronization parameter acquisition unit: the method is used for obtaining the time between two adjacent zero-crossing points on one winding or the time between two adjacent zero-crossing points on two windings respectively, namely the duration time of the difference of the set electrical angle, and the duration time is used for calculating the self-synchronization commutation time and the commutation duration time to obtain self-synchronization parameters, and the motor enters a self-synchronization state according to the obtained self-synchronization parameters.
10. The apparatus of claim 9, wherein in the forced commutation unit, a voltage is collected on a third winding connected thereto as a counter potential generated thereon due to the input of the driving signal; the first setting condition includes that the differential absolute value of the sampled adjacent back electromotive voltage is smaller than a set value.
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