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© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

PM Machine Demagnetization Analysis due to Fault Conditions

PM Machine Demagnetization Analysis due to Fault Conditions

Scott StantonRyan MagargleJulius Saitz

ANSYS, Inc.

Scott StantonRyan MagargleJulius Saitz

ANSYS, Inc.

© 2009 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Motivation

1. In many permanent magnet motors during the startup condition, the incident field can push the operating point the knee and thus never allowing the magnet to fully recover.

2. The knee point can lie in either in the 2nd or 3rd quadrant


Test Case

Linear High Permeable Material: μr = 20,000

Non-Linear MagnetN

I


Determine Demag Point #1 using I=I1and Original B-H Curve

rB

O


Determine Demag Point #1 using I=I1and Original B-H Curve

1

rB

O


Draw a Line from the Origin to Point #1

1

rB

O


Determine Point #2: Intercept off Original BH Curve in 3rd Quadrant

1

rB

O2


Determine New Remanent Point Br’

Parallel to Original B-H Curve Slope

1

rB

O2

rB′

Parallel


Solve again, using Br’ and Calculate Point #3

rB

O

rB′

3


Draw a Line from the Origin to Point #3

rB

O

rB′

3


Determine Point #4 which is the Intercept off Original BH Curve in 3rd

Quadrant

rB

O

rB′

34


Determine New Remanent Point Br’’

Parallel to Original B-H Curve Slope

rB

O

rB′

34

rB ′′


Solve again, using new Br and Calculate Point #5

-920

rB

O

5

rB ′′′


Determine Point #6 which is the Intercept off Original BH Curve in 3rd

Quadrant

-920

rB

O

5

rB ′′′

6


Continue to Iterate Until the Solved Point Lies on the Original B-H Curve within an Acceptable Tolerance

-920

rB

O

1rB


This process is done on an element-by-element basis

-920

rB

O

1rB

2rB

3rB

4rB

nB

nrH4rH3rH2rH1rH 5rH

5rB


Extend Nonlinear BH Curve Into the 3rd Quadrant

MQP-B+ from Magnequench

Demag point

Hc′ afterdemag

Working point

rB′

rB


Test Case

Linear High Permeable Material: μr = 20,000

Non-Linear MagnetN

I


Non-linear definition into the 3rd

Quadrant: Maxwell V13


Step 1: Analyze Design with I = 0 amps


Step 2: Compute Demagnetization PointsExcitation is Starting Current


By and Hy on Magnet


By is Below the Knee Point into the 3rd Quadrant

Expect to recoil in this range


Step 3: Create a Dynamically Linked Design


Use the Same Mesh as the Source Design: Don’t Refine the Mesh


Reset Coil Current to Zero


Magnetic Field and Flux Density in Magnet


Demag and Recoil Permeabilities

Demag Operating Points

Recoil Operating Points


B-H Curve for Alnico 9


Dynamic demagnetization

Time

Current


BH curve at a point inside magnet


Working with demagnetized magnet


Generator Fault Example

• 550 W PM generator• 4 Pole• 3 Phase, 50HZ AC• Ceramic 8D PM• Rated Speed,

Open-Circuit toShort-Circuit Fault


Magnet

• 2nd quadrant demagnetization (demag)• Spatially dependent demag due to fault

Initial Radial Magnetization


0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]

Ansoft LLC Maxwell3DDesign23D_EMF_save_demag ANSOFT

Curve InfoInducedVoltage(PhaseA)

Setup1 : TransientInducedVoltage(PhaseB)

Setup1 : TransientInducedVoltage(PhaseC)

Setup1 : Transient

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]





Setup1 : Transient

Short-Circuit Analysis

• Short circuit at 15.2ms: Phase A peak

Bus short for all phases

-3.00E+005 -2.00E+005 -1.00E+005 0.00E+000H [A/m]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

B [T

]

Ansoft LLC Maxwell3DDesign2BH_Data_Points_Initial_Demag ANSOFT

-3.00E+005 -2.00E+005 -1.00E+005 0.00E+000H [A/m]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

B [T

]

Ansoft LLC Maxwell3DDesign2BH_Data_Points_Initial_Demag ANSOFT

Material BH Curve

Operating Point



• Subsequent use of the magnet results in reduced performance

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]

Ansoft LLC Maxwell3DDesign33D_EMF_demaged ANSOFT




Setup1 : Transient

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]





Setup1 : Transient

Addt’l short for all phasesWeak Back EMF

-3.00E+005 -2.00E+005 -1.00E+005 0.00E+000H [A/m]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

B [T

]

Ansoft LLC Maxwell3DDesign3BH_Data_Points_Demag ANSOFT

-3.00E+005 -2.00E+005 -1.00E+005 0.00E+000H [A/m]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

B [T

]

Ansoft LLC Maxwell3DDesign3BH_Data_Points_Demag ANSOFT

Operating Points



• Leading edge is weakened significantly

0.00 5.00 10.00 15.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]


0.00 5.00 10.00 15.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]


0.00 5.00 10.00 15.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]


0.00 5.00 10.00 15.00Time [ms]

-80.00

-25.00

30.00

80.00

Volts

[V]


Original

Fault


Conclusion

• To account for non-linear permanent magnets in your designs, the ability to accurately calculate the demagnetization point can be critical.

• It has been shown that Maxwell® 3D accurately accounts for this effect.




rB


Determine Working Point #1 using I=I1 and Original B-H Curve


Working point

rB


Freeze mur in Each Element, Set I=0 to Determine No-Load Point


Working point

rB


Determine Magnet Load Line at I=0 amps


Load line without other sources

Working point

rB


Determine Magnet Load Line for the Working Point



Load line with other sources

Working point

rB


Determine Demag Point




Demag point

Working point

rB


Determine New Remanent Point Br

’and Coercive Point Hc’




Demag point

Hc′ afterdemag

Working point

rB′

rB






Demag point

Hc′ afterdemag

Working point

rB′

rB


Add Magnetization Capability

B

H0

• Based on the original non-remanent B-H curve

• Construct line b at the operating point p, which is parallel to the line a

• Br is the intersection of line b with B-axis

• Element by element

Br Line b

Line a

p

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