CN104767344A - Method for eliminating vibration of PWM powered brushless direct current motor through frequency calculation - Google Patents
Method for eliminating vibration of PWM powered brushless direct current motor through frequency calculation Download PDFInfo
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Abstract
The invention provides a method for eliminating vibration of a PWM powered brushless direct current motor through frequency calculation. For the motor preliminarily designed in a electromagnetic scheme, spatial harmonic distribution of air gap flux density is firstly calculated, then the time harmonic wave change of the air gap flux density is calculated within a commutation period and is compared with the inherent vibration frequency of a motor iron core, and if the frequencies are similar, resonance is produced, the electromagnetic design scheme of the motor is needed to be optimized, and the frequencies are re-calculated till the vibrations produced by spatial harmonic flux density and harmonic wave flux density are not resonant with the iron core. The space and time changes of flux density causing motor vibration under the operating working condition of the motor are fully considered in the method, the accuracy of motor vibration calculation in a motor product development phase is improved, accordingly the success rate of motor design is improved, a development and trial-manufacturing period of the motor is shortened, and non-renewable resources including copper, iron, aluminum and the like are effectively saved.
Description
Technical field
The present invention relates to a kind of for the brushless DC motor under PWM (pulse width modulation) power supply, by calculating electric machine stator iron vibration frequency that air gap flux density harmonic wave causes thus suppressing the method for motor oscillating, belong to DC motor technical field.
Background technology
The vibration source of brushless DC motor vibration can be divided into electromagnetic force, air force and mechanical structure three kinds, and these three kinds of vibration sources difference in vibration frequency is comparatively large, and the noise produced by vibration is easy to distinguish.The vibration produced as air force and the mechanical structure of vibration source is mechanical oscillation, can be optimized by motor construction, as improved motor ventilation structure, changing the physical dimension etc. of electric machine structure part, and the vibration that the electromagnetic force in vibration source produces is electric and magnetic oscillation, need to be calculated by the electromagnetism of motor analyze and optimize, it is all the most complicated for calculating and suppressing.
In the patent of motor oscillating, CN103219940A " a kind of suppression method of electromotor vibration ", CN103762806A " a kind of suppressing method of shaded-pole single-phase ac asynchronous motor Vibration Torque " and CN104158464A " suppress the control device of electric motor of intrinsic vibration " etc. and all propose the suppressing method of motor oscillating, but still do not solve the PWM close space harmonics binding time harmonic wave of lower magnetic of powering and cause the computational methods of motor oscillating.
The supply power mode of brshless DC motor generally adopts PWM power supply, in Speed Process of DC Motor, equivalent different supply voltage value is carried out by the duty ratio changing the pulse of PWM, to power with General Electric Network or compared with motor that DC power supply is directly powered as seen, it is close that the air-gap field of brushless, permanently excited direct current motor not only comprises space harmonics magnetic, and the impact of time harmonic voltage and current will be subject to, this just causes the vibration of motor more obvious, so the electric and magnetic oscillation change of motor under time harmonic can not be reflected by traditional method, objectively reduce the accuracy of design.
Generally adopted the computational methods of equivalent magnetic circuit in the past, namely the magnetic potential of stators and rotators is first calculated, then air-gap permeance is calculated, according to magnetic potential and permeance calculation air-gap field, finally according to the Reeb that stators and rotators magnetic field harmonics magnetic field produces, Reeb number of times is merged, calculates radial load according to the close amplitude of its magnetic, calculate Reeb frequency.
Conventional method calculates the vibration frequency of the brushless DC motor that PWM powers, and there is following defect:
1. what adopt is the computational methods of equivalent magnetic circuit, and the parameters such as magnetic conductance are equivalence value, do not consider the impact of slot form on magnetic conductance;
2. the close value of magnetic is by magnetic potential and permeance calculation, and air gap flux density result of calculation is equivalence value, and the crest meter of the close each harmonic of magnetic is not calculated accurately really;
3. only consider rotor produce the space harmonics of air gap flux density, reckon without air gap flux density situation over time when PWM powers.
Above-mentioned defect makes the motor oscillating frequency computation part under PWM powers inaccurate.
Summary of the invention
The technical problem to be solved in the present invention be to provide a kind of PWM is powered under brushless DC motor, by accurately calculating electric machine stator iron vibration frequency that air gap flux density harmonic wave causes thus suppressing the method for motor oscillating.
In order to solve the problems of the technologies described above, technical scheme of the present invention be to provide a kind of PWM power brshless DC motor by frequency computation part suppress vibration method, described motor is the motor that electromagnetic structure Preliminary design is good, it is characterized in that: the method is made up of following 8 steps:
Step 1: according to the calculating rotating speed of operating mode setting motor;
Step 2: the commutation angle calculating the minimum period of the close changes in distribution of motor magnetic;
Step 3: according to switching frequency and the duty ratio of PWM, the voltage minimum step of setup algorithm;
Step 4: the air gap flux density value calculating motor, carries out Fourier decomposition by air gap flux density, obtains amplitude and the phase place of harmonic wave, calculate the rotating speed of harmonic wave, obtain humorous wave frequency according to same first harmonic at the phase difference of different step-length according to the close amplitude size of magnetic;
Step 5: each harmonic value extracting each step-length, obtains the change curve of each harmonic amplitude; Be that axle is arranged with time by the numerical value of each harmonic amplitude, carry out Fourier decomposition, obtain the frequency of time dependent each the time harmonic of air gap flux density amplitude;
Step 6: the eigentone calculating stator core;
Step 7: the frequency relation of comparison step 4, step 5 and step 6:
1) when magnetic close space harmonics frequency, time harmonic frequency and natural frequency three numerical value unshakable in one's determination are in resonance region, motor produces resonance;
2) when magnetic close space harmonics frequency and inherent frequency numerical value unshakable in one's determination are in resonance region, motor also can produce resonance;
3) when magnetic close time harmonic frequency and inherent frequency numerical value unshakable in one's determination are in resonance region, motor also can produce resonance;
Step 8: if there is resonance in step 7, then redesign electromagnetism or mechanical structure, repeats step 1 to step 7, till not producing resonance.
Preferably, in described step 3, the voltage minimum step frequency of calculating must higher than switching frequency.
Preferably, in described step 5, calculate for simplifying, can suppose that the Changing Pattern of each harmonic is substantially identical, the amplitude situation of change of each harmonic is replaced by the close amplitude situation of change of the magnetic of the magnetic that relative rotor is static close value maximum point, be that axle is arranged by this numerical value of the close amplitude of magnetic put with time, carry out Fourier decomposition, obtain the frequency of time dependent each the time harmonic of air gap flux density amplitude.
Preferably, in described step 7, if frequency-splitting natural frequency unshakable in one's determination ± 2% scope in, then think in resonance region.
Preferably, in described step 7, the scheme redesigning electromagnetic structure comprises: optimize stator and rotor cores trench structure, back down groove at stator tooth, adjustment gas length, stator core welding reinforcement.
The present invention has taken into full account the room and time change causing the magnetic of motor oscillating close under motor operating condition, improve the accuracy calculating motor oscillating in motor product development, this will improve the success rate of design of electrical motor, objectively shorten the Development and Trial cycle of motor, effectively save the non-renewable resources such as copper, iron, aluminium.
Accompanying drawing explanation
Fig. 1 is the electric machine structure figure of Preliminary design in embodiment;
Fig. 2 be PWM power brshless DC motor by frequency computation part suppress vibration method flow diagram;
Fig. 3 is the close curve of initial time motor gas-gap magnetic and its Fourier decomposition curve;
Fig. 4 is the frequency curve of time dependent each the time harmonic of air gap flux density amplitude.
Embodiment
PWM provided by the invention brshless DC motor of powering suppresses the thinking of method of vibration to be by frequency computation part: for the motor that an electromagnetic scheme Preliminary design is good, first the space harmonics distribution of air gap flux density is calculated, then within a commutation cycle, calculate the time harmonic change of air gap flux density, and compared with the eigentone of electric machine iron core, as frequency is close, namely in resonance region, then resonance can be produced, the Electromagnetic Design scheme of motor need be optimized, recalculate each frequency, until space harmonics magnetic is close and vibration that the is close generation of time harmonic magnetic is not all resonated with iron core.
The factors such as the frequency range of resonance region and the equivalent stiffness of stator core, quality are relevant, in electric machine frequency calculates by experience definition resonance region are generally: the frequency-splitting of each object electric machine iron core eigentone ± 2% scope in.
For making the present invention become apparent, hereby with a preferred embodiment, and accompanying drawing is coordinated to be described in detail below.
For the inner-rotor brushless DC motor of stator 6 pole, rotor 8 pole, stator winding is concentratred winding, and rotor is straight trough, without support, electric machine structure as shown in Figure 1, in Fig. 1, A is stator yoke, and B is stator winding, and C is stator tooth, D is rotor core, E is rotor magnetic steel, and F is axle, and G is air gap.Motor is PWM supply power mode, and switching frequency is 10kHz, adopts the modulation system of H_PWM-L_PWM.
Composition graphs 2, PWM provided by the invention brshless DC motor of powering suppresses the calculation procedure of method of vibration as follows by frequency computation part:
Step one, carry out computational analysis according to the parameter of electric machine of above-mentioned Preliminary design, and according to operating mode, the rotating speed setting this brushless DC motor is 3000r/min, and now duty ratio is 0.5.
Step 2, be 6 poles due to motor stator, rotor is 8 poles, completes the commutation of the corresponding relation of a rotor teeth groove when motor rotates 15 degree, so calculate the dynamic process that rotor rotates 15 degree.The close change of motor gas-gap magnetic in this cycle can represent the close situation of change of whole magnetic of motor under this operating mode.
Step 3, switching frequency are the pulse period of 10kHz is 1 × 10
-4s, high level and low level duration are 5 × 10
-5s, commutation cycle during 3000 turns, motor is 5 × 10-
3 s, selected material calculation is 5 × 10
-6s.
Step 4, FEM electromagnetic computing software can be utilized to carry out computer aided calculation; Or electric machine rotor structural member and air gap are divided into some zonules, whole for motor domain is divided into vortex and non-vortex, needs calculating magnetic field and electric field in vortex, use vector magnetic potential respectively
and electric scalar potential
state, only need calculating magnetic field in non-vortex, use vector magnetic potential
state.According to maxwell equation group, utilize above-mentioned
the boundary value problem that method obtains Three dimensional transient vortex field is as follows:
At the eddy region V of end model
1in:
At the non-vortex V of end model
2in:
In formula: J
sfor source current density; μ is magnetic permeability; σ is conductivity; T is the time; Y is reluctivity.
For making the above differential equation have unique solution, following definite condition need be provided:
ferromagnetic material external boundary
In formula,
for vector magnetic potential;
for scalar magnetic potential; N is normal vector; Y is reluctivity;
with
by obtaining the two-dimensional vortex Flow Field Calculation of electric machine iron core section.
By calculating the close distribution of initial time motor gas-gap magnetic and its Fourier decomposition curve as shown in Figure 3.In figure, abscissa is the mechanical angle of motor circumference, and ordinate is magnetic flux density tesla, and H is the distribution curve of air gap flux density, and other curve being Sine distribution is the Fourier decomposition curve of airgap density distribution curve.The curve chart in other moment is similar, does not here list one by one.According to Maxwell's law, the instantaneous value p of unit are radial electromagnetic force in motor gas-gap
rfor:
In formula, b
rfor the radial magnetic of air gap is close; μ
0for air permeability; θ is circumferential angle; T is the time.
As can be seen from the above equation, close square being directly proportional of the amplitude of radial Reeb and radial magnetic, namely motor radial air gap magnetic is close larger, and radial Reeb is also larger.Each harmonic is arranged from big to small by amplitude, obtain amplitude and the phase place of each harmonic, the frequency of each harmonic can be obtained by the phase place change of the air gap flux density of each time step, due to the slot effect of motor and the impact of saturation, the frequency calculated is change, can average and carry out equivalence.By the large minispread of amplitude, the harmonic amplitude of each harmonic, phase place and frequency are as shown in table 1.
The amplitude of table 1 motor each space harmonics, phase place and frequency
| Harmonic number | Harmonic amplitude/T | Phase angle/deg | Frequency/Hz |
| 4 | 0.7013 | 269.9857 | 207 |
| 10 | 0.1760 | 90.0498 | 12929 |
| 2 | 0.1746 | 89.9962 | 121 |
| 28 | 0.1135 | 269.8754 | - |
| 12 | 0.0934 | 89.9630 | 5632 |
| 8 | 0.0640 | 89.9574 | 1744 |
| 36 | 0.0525 | 89.7463 | - |
| 14 | 0.0492 | -89.8154 | 9889 |
| 52 | 0.0486 | 269.8624 | - |
| 34 | 0.0469 | 90.2877 | 10389 |
Step 5, be that axle is arranged to the numerical value of the close amplitude of magnetic of the close maximum point of rotor geo-stationary magnetic with time, carry out Fourier decomposition, obtain the frequency of time dependent each the time harmonic of air gap flux density amplitude as shown in Figure 4.In Fig. 4, abscissa is the step number calculated, and amount to 168, ordinate is magnetic flux density tesla, and I is the curve of air gap flux density along Annual distribution, and other curve being Sine distribution is the Fourier decomposition curve of the close curve of time magnetic.Amplitude and the phase place of gained each harmonic are as shown in table 2.
The amplitude of table 2 motor each time harmonic and frequency
| Harmonic number | Harmonic amplitude/T | Frequency/Hz |
| 1 | 0.0290 | 1200 |
| 2 | 0.0228 | 2400 |
| 3 | 0.0184 | 3600 |
| 4 | 0.0149 | 4800 |
| 5 | 0.0148 | 6000 |
| 8 | 0.0184 | 9600 |
The eigentone of step 6, calculating stator core, result is as shown in table 3.
The exponent number of table 3 motor intrinsic vibration and frequency
| Exponent number | Frequency/Hz |
| 2 | 2415 |
| 3-1 | 6102 |
| 3-2 | 6839 |
| 4 | 11503 |
| 5 | 16235 |
| 6 | 13698 |
The vibration frequency of step 7, contrast table 1, table 2 and table 3 can be found out:
1, the close space harmonics of magnetic, time harmonic and natural frequency unshakable in one's determination be not in resonance region, do not produce obviously resonance;
2, the close space harmonics of magnetic and natural frequency unshakable in one's determination be not in resonance region, do not produce obviously resonance;
3, the close time harmonic of magnetic and natural frequency 2400Hz unshakable in one's determination and 6000Hz are in resonance region, can produce resonance.
Step 8, optimization design of electrical motor scheme, consider that the electromagnetic performance of design of electrical motor scheme meets the requirements, and the space harmonics of motor and time harmonic do not resonate, so adopt the scheme only changing stator core eigentone, namely weld the ring stiffener of 2 circumferencial directions at stator core cylindrical.Now the space harmonics of motor and time harmonic result of calculation remain unchanged, and only need to re-start calculating to the intrinsic vibration frequency of electric machine stator iron, result is as shown in table 4:
The exponent number of table 4 motor intrinsic vibration and frequency
| Exponent number | Frequency/Hz |
| 2 | 2474 |
| 3-1 | 6248 |
| 3-2 | 6984 |
| 4 | 11737 |
| 5 | 16489 |
| 6 | 13707 |
The vibration frequency of contrast table 1, table 2 and table 4 can find out the close space harmonics of magnetic, time harmonic and stator core natural frequency not in resonance region, do not resonate, motor can not produce obvious vibration.
Claims (5)
1. PWM power brshless DC motor by frequency computation part suppress vibration a method, described motor is the motor that electromagnetic structure Preliminary design is good, it is characterized in that: the method is made up of following 8 steps:
Step 1: according to the calculating rotating speed of operating mode setting motor;
Step 2: the commutation angle calculating the minimum period of the close changes in distribution of motor magnetic;
Step 3: according to switching frequency and the duty ratio of PWM, the voltage minimum step of setup algorithm;
Step 4: the air gap flux density value calculating motor, carries out Fourier decomposition by air gap flux density, obtains amplitude and the phase place of harmonic wave, calculate the rotating speed of harmonic wave, obtain humorous wave frequency according to same first harmonic at the phase difference of different step-length according to the close amplitude size of magnetic;
Step 5: each harmonic value extracting each step-length, obtains the change curve of each harmonic amplitude; Be that axle is arranged with time by the numerical value of each harmonic amplitude, carry out Fourier decomposition, obtain the frequency of time dependent each the time harmonic of air gap flux density amplitude;
Step 6: the eigentone calculating stator core;
Step 7: the frequency relation of comparison step 4, step 5 and step 6:
1) when magnetic close space harmonics frequency, time harmonic frequency and natural frequency three numerical value unshakable in one's determination are in resonance region, motor produces resonance;
2) when magnetic close space harmonics frequency and inherent frequency numerical value unshakable in one's determination are in resonance region, motor also can produce resonance;
3) when magnetic close time harmonic frequency and inherent frequency numerical value unshakable in one's determination are in resonance region, motor also can produce resonance;
Step 8: if there is resonance in step 7, then redesign electromagnetism or mechanical structure, repeats step 1 to step 7, till not producing resonance.
2. a kind of PWM as claimed in claim 1 power brshless DC motor by frequency computation part suppress vibration method, it is characterized in that: in described step 3, the voltage minimum step frequency of calculating is higher than switching frequency.
3. a kind of PWM as claimed in claim 1 power brshless DC motor by frequency computation part suppress vibration method, it is characterized in that: in described step 5, calculate for simplifying, can suppose that the Changing Pattern of each harmonic is substantially identical, the amplitude situation of change of each harmonic is replaced by the close amplitude situation of change of the magnetic of the magnetic that relative rotor is static close value maximum point, be that axle is arranged by this numerical value of the close amplitude of magnetic put with time, carry out Fourier decomposition, obtain the frequency of time dependent each the time harmonic of air gap flux density amplitude.
4. a kind of PWM as claimed in claim 1 power brshless DC motor by frequency computation part suppress vibration method, it is characterized in that: in described step 7, if frequency-splitting natural frequency unshakable in one's determination ± 2% scope in, then think in resonance region.
5. a kind of PWM as claimed in claim 1 power brshless DC motor by frequency computation part suppress vibration method, it is characterized in that: in described step 7, the scheme redesigning electromagnetic structure comprises: optimize stator and rotor cores trench structure, groove is backed down at stator tooth, adjustment gas length, stator core welding reinforcement.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110210086A (en) * | 2019-05-20 | 2019-09-06 | 上海电机系统节能工程技术研究中心有限公司 | A kind of motor electromagnetic design method based on probability analysis |
| CN114019907A (en) * | 2021-10-25 | 2022-02-08 | 安徽理工大学 | Implementation method for eliminating self-excited vibration of linear feeding servo system |
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| US4435751A (en) * | 1980-07-03 | 1984-03-06 | Hitachi, Ltd. | Vibration/noise reduction device for electrical apparatus |
| JPH09289787A (en) * | 1996-04-23 | 1997-11-04 | Toyo Electric Mfg Co Ltd | Pwm controller for making effective value of harmonic current minimum |
| CN103633917A (en) * | 2013-12-11 | 2014-03-12 | 陈卫兵 | Method and device for reducing vibration noise of motor |
| CN104270047A (en) * | 2014-09-30 | 2015-01-07 | 山东艾磁驱动科技有限公司 | Method and system for achieving voltage reduction control in low-speed running process of motor |
-
2015
- 2015-04-14 CN CN201510174204.1A patent/CN104767344B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4435751A (en) * | 1980-07-03 | 1984-03-06 | Hitachi, Ltd. | Vibration/noise reduction device for electrical apparatus |
| JPH09289787A (en) * | 1996-04-23 | 1997-11-04 | Toyo Electric Mfg Co Ltd | Pwm controller for making effective value of harmonic current minimum |
| CN103633917A (en) * | 2013-12-11 | 2014-03-12 | 陈卫兵 | Method and device for reducing vibration noise of motor |
| CN104270047A (en) * | 2014-09-30 | 2015-01-07 | 山东艾磁驱动科技有限公司 | Method and system for achieving voltage reduction control in low-speed running process of motor |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110210086A (en) * | 2019-05-20 | 2019-09-06 | 上海电机系统节能工程技术研究中心有限公司 | A kind of motor electromagnetic design method based on probability analysis |
| CN110210086B (en) * | 2019-05-20 | 2023-02-03 | 上海电机系统节能工程技术研究中心有限公司 | Motor electromagnetic design method based on probability analysis |
| CN114019907A (en) * | 2021-10-25 | 2022-02-08 | 安徽理工大学 | Implementation method for eliminating self-excited vibration of linear feeding servo system |
| CN114019907B (en) * | 2021-10-25 | 2023-07-18 | 安徽理工大学 | Realization method for eliminating self-excited vibration of linear feed servo system |
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