CN103986397A - Method for detecting fault of permanent magnet of brushless direct-current motor - Google Patents

Abstract

The invention discloses a method for detecting a fault of a permanent magnet of a brushless direct-current motor. The method comprises the following steps that a rotor is fixed, a locked-rotor test is carried out on the motor, and the following relational expression can be obtained: e=-KsIsin (gamma')=-Ksibeta; corresponding stator currents I and the coefficient Ks of a coil flux linkage can be obtained through the relational expression; in the operating process of the motor, counter electromotive force e on a motor coil is detected, and the density amplitude Bfsin (gamma) of a space magnetic field generated at the position, with the space electrical angle of gamma-90 degrees, of the permanent magnet is calculated according to the counter electromotive force e; the obtained density amplitude Bfsin (gamma) of the space magnetic field of the permanent magnet is compared with a preset reference amplitude, and whether demagnetization or loss of excitation occurs can be determined. The method for detecting the fault of the permanent magnet of the brushless direct-current motor has the advantages of being capable of obtaining the fault condition of the permanent magnet without dismounting the permanent magnet, fast and effective in detection and the like.

Description

Brshless DC motor permanent magnet fault detection method

Technical field

The present invention relates to a kind of brshless DC motor permanent magnet fault detection method.

Background technology

Brshless DC motor is made up of motor body and driver, is a kind of typical electromechanical integrated product.Brushless electric machine refers to the motor of brushless and commutator (or collector ring), claims again commutatorless machine.On the rotor of motor, be stained with the permanent magnet having magnetized, in order to detect the polarity of motor rotor, at the in-built position sensor of motor.

In the application of brshless DC motor, permanent magnet fault location is a difficult point normally.Due to the impact of the winding method of stator coil, can detect the faults such as the loss of excitation of motor permanent magnet by specific algorithm, but cannot accurately locate it, so just the maintenance of motor be caused to very large difficulty, because the dismounting of permanent magnet, installation, detection are all cumbersome.

Summary of the invention

The present invention is the weak point existing in above-mentioned prior art for avoiding, and provides a kind of brshless DC motor permanent magnet fault detection method, fast and effeciently to detect the fault state of permanent magnet.

The present invention be technical solution problem by the following technical solutions.

Brshless DC motor permanent magnet fault detection method, is characterized in, comprises the steps:

Step 1: fixed rotor, motor is carried out to stall experiment, can obtain following relational expression:

e＝-K _sIsin(γ′)＝-K _si _β (1)；

In formula (1), e: back electromotive force; I: stator current; K _s: the coefficient of coil flux linkage, γ ' is the electrical degree of stator current in static α β coordinate system.

Step 2: the COEFFICIENT K that can be obtained corresponding stator current I and coil flux linkage by the relational expression in step 1 (1) _s;

Step 3: in motor operation course, detect the back electromotive force e on motor coil, and be the space magnetic field density amplitude B that γ-90 place produces according to back electromotive force e calculating permanent magnet in space electrical degree _fsin (γ);

Step 4: by the space magnetic field density amplitude B of the permanent magnet obtaining in step 3 _fsin (γ) contrasts with predefined reference amplitude, can determine whether that demagnetization or loss of excitation occur.First,, in the time that permanent magnet loss of excitation does not occur, measure K by no load test _fbB _fthe value of sin (γ), by K _f=K _scan calculate BB _fsin (γ) also saves as reference value; Then by the B detecting in running _fsin (γ), if detected value is less than the reference value that original measurement is preserved, illustrates that demagnetization or loss of excitation have occurred permanent magnet.

In described step 3, space magnetic field density amplitude B _fthe computational process of sin (γ) is:

When motor operation, magnetic test coil is opened circuit, now in magnetic test coil, no current flows through, and it does not exert an influence to motor space magnetic field, and the coil-end voltage of detection equals its back electromotive force:

$e=-\frac{{\mathrm{d\ψ}}_s+{\mathrm{d\ψ}}_f}{\mathrm{dt}}={-K}_{s}I\frac{d\cos \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{dt}}{-K}_f{B}_f\frac{d\cos \left(\mathrm{\γ}\right)}{\mathrm{dt}}={-\mathrm{\ωK}}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right){-\mathrm{\ωK}}_f{B}_f\sin \left(\mathrm{\γ}\right)---\left(2\right);$

Now above formula (2) can be become:

$K_f{B}_f\sin \left(\mathrm{\γ}\right)=-\frac{e+\mathrm{\ω}{K}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{\ω}}=-\frac{e+\mathrm{\ω}{K}_s{i}_{\mathrm{\β}}}{\mathrm{\ω}}---\left(3\right);$

Can calculate and obtain space magnetic field density amplitude B according to above formula (3) _fsin (γ).

Compared with the prior art, beneficial effect of the present invention is embodied in:

Brshless DC motor permanent magnet fault detection method of the present invention, by calculating the space magnetic field density amplitude B that can try to achieve permanent magnet _fsin (γ), by the space magnetic field density amplitude B of permanent magnet _fsin (γ) contrasts with predefined reference amplitude, can determine whether that demagnetization or loss of excitation occur, and can know the fault state of permanent magnet without dismounting permanent magnet, detects fast effectively.

Brshless DC motor permanent magnet fault detection method of the present invention, has the fault state that can know permanent magnet without dismounting permanent magnet, detects the advantages such as quick effective.

Below, by embodiment, the invention will be further described.

Embodiment

Brshless DC motor permanent magnet fault detection method of the present invention, comprises the steps:

Step 1: fixed rotor, motor is carried out to stall experiment, can obtain following relational expression:

e＝-K _sIsin(γ′)＝-K _si _β (1)；

In formula (1), e: back electromotive force; I: stator current; K _s: the coefficient of coil flux linkage, γ ' is the electrical degree of stator current in static α β coordinate system.

Step 2: the COEFFICIENT K that can be obtained corresponding stator current I and coil flux linkage by the relational expression in step 1 (1) _s;

Step 3: in motor operation course, detect the back electromotive force e on motor coil, and be the space magnetic field density amplitude B that γ-90 place produces according to back electromotive force e calculating permanent magnet in space electrical degree _fsin (γ);

Step 4: by the space magnetic field density amplitude B of the permanent magnet obtaining in step 3 _fsin (γ) contrasts with predefined reference amplitude, can determine whether that demagnetization or loss of excitation occur.(first,, in the time that permanent magnet loss of excitation does not occur, measure K by no load test _fbB _fsin ( _γ) value, by K _f=K _scan calculate BB _fsin (γ) also saves as reference value; Then by the B detecting in running _fsin (γ), if detected value is less than the reference value that original measurement is preserved, illustrates that demagnetization or loss of excitation have occurred permanent magnet.)

In described step 3, space magnetic field density amplitude B _fthe computational process of sin (γ) is:

When motor operation, magnetic test coil is opened circuit, now in magnetic test coil, no current flows through, and it does not exert an influence to motor space magnetic field, and the coil-end voltage of detection equals its back electromotive force:

$e=-\frac{{\mathrm{d\ψ}}_s+{\mathrm{d\ψ}}_f}{\mathrm{dt}}={-K}_{s}I\frac{d\cos \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{dt}}{-K}_f{B}_f\frac{d\cos \left(\mathrm{\γ}\right)}{\mathrm{dt}}={-\mathrm{\ωK}}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right){-\mathrm{\ωK}}_f{B}_f\sin \left(\mathrm{\γ}\right)---\left(2\right);$

Now above formula (2) can be become:

$K_f{B}_f\sin \left(\mathrm{\γ}\right)=-\frac{e+\mathrm{\ω}{K}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{\ω}}=-\frac{e+\mathrm{\ω}{K}_s{i}_{\mathrm{\β}}}{\mathrm{\ω}}---\left(3\right);$

Can calculate and obtain space magnetic field density amplitude B according to above formula (3) _fsin (γ).

Now, can carry out failure diagnosis, wherein B to permanent magnet by the waveform of back electromotive force and stator current β component _fsin (γ), for permanent magnet is the magnetic density at γ-90 place in space electrical degree, by detecting the variation of corresponding magnetic density amplitude, can determine whether permanent magnet demagnetization has occurred.

The present invention's proposition additionally arranges induction coil mode by motor is added detects, the impact bringing can avoid stator coil to be connected time, effectively detects the fault state of permanent magnet, and coil axis is consistent with A phase axis, coil is that whole pole span is long, and it is as follows that it detects principle:

1, the magnetomotive force of space air gap is that stator current and permanent magnet linear superposition produce;

The single-phase magnetomotive peak swing of the whole first-harmonic producing on air gap apart from winding of concentrating is:

$F_{\mathrm{\φ}1}=\frac{4}{\mathrm{\π}}\frac{\sqrt{2}}{2}{\mathrm{qN}}_k{I}_k=\frac{4}{\mathrm{\π}}\frac{\sqrt{2}}{2}\frac{{\mathrm{pqN}}_k}{p}\frac{I_k}{a}=0.9\frac{N_{1}I}{p}=\mathrm{kI}---\left(4\right);$

In the time that motor is three-phase symmetric winding, the axis+A that gets A phase winding is initial point, and, in the time flowing through any size of current, the spatial distribution of synthetic magnetomotive force in α β coordinate system is:

In above formula (4) and (5), N ₁: the number of turn is often in series; Q: the full-pitched coil number of every pair of utmost point; A: parallel branch number; I: phase current; I _k: coil current;

Now the synthetic magnetomotive force of air gap is

${\stackrel{\→}{f}}_{\mathrm{air}}={\stackrel{\→}{f}}_f+{\stackrel{\→}{f}}_I=(\frac{3}{2}k(i_{\mathrm{\α}}+{\mathrm{ji}}_{\mathrm{\β}})+F_f{e}^{\mathrm{j\γ}})e^{\mathrm{j\θ}}---\left(6\right);$

In above formula (6), γ: the space electrical degree angle of permanent magnet axis and A phase axis; θ: be the A axle axis space electrical degree that is initial point.

2, synthetic air-gap field is produced by stator current and permanent magnet linear superposition;

When motor operates in linear zone, while not arriving saturation region, magnetic field intensity and magnetic density are linear, and its resultant magnetic field meets linear superposition theorem, and its magnetic density is the linear superposition of magnetic density and the stator current generation magnetic density of permanent magnet generation:

${\stackrel{\→}{B}}_{\mathrm{air}}={\stackrel{\→}{B}}_f+{\stackrel{\→}{B}}_I=\frac{\mathrm{\μ}}{l_{\mathrm{air}}}{\stackrel{\→}{f}}_{\mathrm{air}}---\left(7\right);$

In above formula (7), μ: air-gap permeance; l _air: gas length.

3, the magnetic linkage in coil;

The magnetic linkage being produced by stator current in coil is:

$\begin{array}{c}{\mathrm{\ψ}}_s=\frac{1}{p}{\∫}_{-\frac{\mathrm{\π}}{2}}^{\frac{\mathrm{\π}}{2}}{N}_2\mathrm{lR}{B}_I\cos ({\mathrm{\γ}}^{\′}+\mathrm{\θ})\mathrm{d\θ}=\frac{N_2\mathrm{lR\μ}}{{\mathrm{pl}}_{\mathrm{air}}}{\∫}_{-\frac{\mathrm{\π}}{2}}^{\frac{\mathrm{\π}}{2}}{f}_I\cos ({\mathrm{\γ}}^{\′}+\mathrm{\θ})\mathrm{d\θ}\\ =\frac{N_2\mathrm{lR\μ}}{{\mathrm{pl}}_{\mathrm{air}}}3\mathrm{kI}\cos \left({\mathrm{\γ}}^{\′}\right)=K_{s}I\cos \left({\mathrm{\γ}}^{\′}\right)=K_s{i}_{\mathrm{\α}}\end{array}---\left(8\right);$

In above formula (8), γ ': the angle of stator magnet kinetic potential and A axle axis.

The magnetic linkage that permanent magnet produces is in coil:

$\begin{array}{c}{\mathrm{\ψ}}_f=\frac{1}{p}{\∫}_{-\frac{\mathrm{\π}}{2}}^{\frac{\mathrm{\π}}{2}}{N}_2\mathrm{lR}{B}_f\cos (\mathrm{\γ}+\mathrm{\θ})\mathrm{d\θ}=\frac{N_2\mathrm{lR}}{p}{\∫}_{-\frac{\mathrm{\π}}{2}}^{\frac{\mathrm{\π}}{2}}{B}_f\cos (\mathrm{\γ}+\mathrm{\θ})\mathrm{d\θ}\\ =\frac{{2N}_2\mathrm{lR}}{p}{B}_f\cos \left(\mathrm{\γ}\right)=K_f{B}_f\cos \left(\mathrm{\γ}\right)\end{array}---\left(9\right);$

Synthetic magnetic linkage in coil produces point other magnetic linkage linear superposition by permanent magnet and stator coil:

$\mathrm{\ψ}=\frac{1}{p}{\∫}_{-\frac{\mathrm{\π}}{2}}^{\frac{\mathrm{\π}}{2}}{N}_2\mathrm{lR}{B}_{\mathrm{air}}\mathrm{d\θ}=\frac{N_2\mathrm{lR\μ}}{{\mathrm{pl}}_{\mathrm{air}}}{\∫}_{-\frac{\mathrm{\π}}{2}}^{\frac{\mathrm{\π}}{2}}{f}_{\mathrm{air}}\mathrm{d\θ}={\mathrm{\ψ}}_s+{\mathrm{\ψ}}_f---\left(10\right);$

4, back electromotive force detects permanent magnet method

When motor operation, magnetic test coil is opened circuit, now in magnetic test coil, no current flows through, and it does not exert an influence to motor space magnetic field, and the coil-end voltage of detection equals its back electromotive force:

$e=-\frac{{\mathrm{d\ψ}}_s+{\mathrm{d\ψ}}_f}{\mathrm{dt}}={-K}_{s}I\frac{d\cos \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{dt}}{-K}_f{B}_f\frac{d\cos \left(\mathrm{\γ}\right)}{\mathrm{dt}}={-\mathrm{\ωK}}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right){-\mathrm{\ωK}}_f{B}_f\sin \left(\mathrm{\γ}\right)---\left(2\right);$

Now above formula (2) can be become:

$K_f{B}_f\sin \left(\mathrm{\γ}\right)=-\frac{e+\mathrm{\ω}{K}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{\ω}}=-\frac{e+\mathrm{\ω}{K}_s{i}_{\mathrm{\β}}}{\mathrm{\ω}}---\left(3\right);$

Now, can carry out failure diagnosis, wherein B to permanent magnet by the waveform of back electromotive force and stator current β component _fsin (γ), for permanent magnet is the magnetic density at γ-90 place in space electrical degree, by detecting the variation of corresponding magnetic density amplitude, can determine whether permanent magnet demagnetization has occurred.

Brshless DC motor permanent magnet fault detection method of the present invention, by calculating the space magnetic field density amplitude B that can try to achieve permanent magnet _fsin (γ), by the space magnetic field density amplitude B of permanent magnet _fsin (γ) contrasts with predefined reference amplitude, can determine whether that demagnetization or loss of excitation occur, and can know the fault state of permanent magnet without dismounting permanent magnet, detects fast effectively.

In above formula (1), e: back electromotive force; I: stator current; K _s: the coefficient of coil flux linkage.

In above formula (2), e is back-emf, and ψ s is the magnetic linkage that stator current produces, ψ _ffor the magnetic linkage that permanent magnet produces, γ is the angle of permanent magnet and A axle axis, and γ ' is the angle of stator magnet kinetic potential and A axle axis, K _sfor the coefficient of stator coil magnetic linkage, K _ffor permanent magnet flux linkage coefficient, ω is electric angle speed.

In above formula (3), e is back-emf, and γ is the angle of permanent magnet and A axle axis, and γ ' is the angle of stator magnet kinetic potential and A axle axis, K _sfor the coefficient of stator coil magnetic linkage, K _ffor permanent magnet flux linkage coefficient, ω is electric angle speed.

In above formula (4) and (5), N ₁: the number of turn is often in series; Q: the full-pitched coil number of every pair of utmost point; A: parallel branch number; I: phase current; I _k: coil current; P is number of pole-pairs, and k is that input current produces the magnetomotive winding coefficient in space, N _kfor the series line number of turns of every circle.I _a1refer to the amplitude of A phase input current, I _b1refer to the amplitude of B phase input current, I _c1refer to the amplitude of C phase input current, the first-harmonic magnetomotive force vector of specifying sub-A phase current to produce in space, the first-harmonic magnetomotive force vector of specifying sub-B phase current to produce in space, the first-harmonic magnetomotive force vector of specifying sub-C phase current to produce in space, the magnetomotive force vector of specifying electron current to produce in space, i _αand i _βspecify the component of electron current in α β coordinate system, θ is the space electrical degree that A axle axis is initial point.

In above formula (6), γ: the space electrical degree angle of permanent magnet axis and A phase axis; θ: be the A axle axis space electrical degree that is initial point.F _frefer to the magnetomotive force amplitude that permanent magnet produces in the air gap of space.

In above formula (7), μ: air-gap permeance; l _air: gas length; for magnetic density vector synthetic in the air gap of space; for the magnetic density vector of permanent magnet generation in the air gap of space; for the magnetic density vector of stator current generation in the air gap of space.

In above formula (8) and (9), γ ': the angle of stator magnet kinetic potential and A axle axis, I is stator current amplitude, K _sfor the coefficient of stator coil magnetic linkage, p is number of pole-pairs, N ₂for magnetic test coil is connected around the number of turn, R is radius of circle in stator, and l is stator inner circle axial length, BB _ifor stator current is in the close size of first-harmonic magnetic of space generation; BB _ffor permanent magnet is in the close size of first-harmonic magnetic of space generation; θ is that magnetic test coil central axis is the space electrical degree that initial point launches.K _s: the coefficient of stator current coil flux linkage, K _f: the coefficient of permanent magnet flux linkage.

In above formula (10), ψ is the magnetic linkage size that stator current and permanent magnet acting in conjunction produce in magnetic test coil, ψ _sfor the magnetic linkage that stator current produces in magnetic test coil, ψ _fthe magnetic linkage producing in magnetic test coil for permanent magnet.

Claims (2)

1. brshless DC motor permanent magnet fault detection method, is characterized in that, comprises the steps:

Step 1: fixed rotor, motor is carried out to stall experiment, can obtain following relational expression:

e＝-K _sIsin(γ′)＝-K _si _β (1)；

In formula (1), e: back electromotive force; I: stator current; K _s: the coefficient of coil flux linkage, γ ' is the electrical degree of stator current in static α β coordinate system.

Step 2: the COEFFICIENT K that can be obtained corresponding stator current I and coil flux linkage by the relational expression in step 1 (1) _s;

Step 3: in motor operation course, detect the back electromotive force e on motor coil, and be the space magnetic field density amplitude B that γ-90 place produces according to back electromotive force e calculating permanent magnet in space electrical degree _fsin (γ);

Step 4: by the space magnetic field density amplitude B of the permanent magnet obtaining in step 3 _fsin (γ) contrasts with predefined reference amplitude, can determine whether that demagnetization or loss of excitation occur.

2. brshless DC motor permanent magnet fault detection method according to claim 1, is characterized in that, in described step 3, and space magnetic field density amplitude B _fthe computational process of sin (γ) is:

When motor operation, magnetic test coil is opened circuit, now in magnetic test coil, no current flows through, and it does not exert an influence to motor space magnetic field, and the coil-end voltage of detection equals its back electromotive force:

$e=-\frac{{\mathrm{d\ψ}}_s+{\mathrm{d\ψ}}_f}{\mathrm{dt}}={-K}_{s}I\frac{d\cos \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{dt}}{-K}_f{B}_f\frac{d\cos \left(\mathrm{\γ}\right)}{\mathrm{dt}}={-\mathrm{\ωK}}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right){-\mathrm{\ωK}}_f{B}_f\sin \left(\mathrm{\γ}\right)---\left(2\right);$

In above formula (2), e is back-emf, and ψ s is the magnetic linkage that stator current produces, ψ _ffor the magnetic linkage that permanent magnet produces, γ is the angle of permanent magnet and A axle axis, and γ ' is the angle of stator magnet kinetic potential and A axle axis, K _sfor the coefficient of stator coil magnetic linkage, K _ffor permanent magnet flux linkage coefficient, ω is electric angle speed.

Now above formula (2) can be become:

$K_f{B}_f\sin \left(\mathrm{\γ}\right)=-\frac{e+\mathrm{\ω}{K}_{s}I\sin \left({\mathrm{\γ}}^{\′}\right)}{\mathrm{\ω}}=-\frac{e+\mathrm{\ω}{K}_s{i}_{\mathrm{\β}}}{\mathrm{\ω}}---\left(3\right);$

Can calculate and obtain space magnetic field density amplitude B according to above formula (3) _fsin (γ);

In above formula (3), e is back-emf, and γ is the angle of permanent magnet and A axle axis, and γ ' is the angle of stator magnet kinetic potential and A axle axis, K _sfor the coefficient of stator coil magnetic linkage, K _ffor permanent magnet flux linkage coefficient, ω is electric angle speed.