Simulation and verification of Thomson actuator systems€¦ · Simulation and verification of...

Simulation and verification of Thomson actuator systemsThomson actuator systems

Ara Bissal, Göran Engdahl, Ener Salinas, Magnus Öhström

COMSOL Conference Paris 2010

Presented at the COMSOL Conference 2010 Paris

http://www.comsol.com/conf_cd_2011_eu

Table of contents

Introduction

Thomson Coil designs

Theory Theory

Modelling

Model verification

Conclusions

Movies

Questions

Introduction

Increased need for high speed actuators

Diverse applications like: Smart grids, electrical switches,

robotics, drilling machinery, etc…

Thomson Coils (TCs) can exert massive forces within fractions of a millisecond

It is important to model and simulate (TCs) to design or

accurately predict the performance of TC based high speed

actuators

What is a TC?

Double sided Thomson coil

Single sided

Thomson Coil

Helix- shaped

Thomson coil

Single sided Thomson Coil with a concentrator

Theory

( )c cI sini tω= ( )c cI sini tω=

( , )) ( )( c r z sinB t B tω=

( )rr siB nB tω=

( )zzsiB nB tω=

z rF i Bφ=

=TotalF ma=

Modelling

2D axisymmetric model

The Aluminum is in silver color, the coil turns are in red, thesurrounding air in light blue

Static model (DC)

10kA constant current source connected across the

terminals of a TC

Constant magnetic field will be generated

No eddy currents are induced in the aluminum disk

Surface: Magnetic flux density [T]Contour: Magnetic vector potential [Wb/m]Arrow: Magnetic flux density

Surface: Total Current density [A/m2]

Stationary model (AC)

Applied current: 10 kA

Frequency: 1kHz

Skin effect Skin effect

Proximity effect

The magnetic flux density is

concentrated in the air gap

region between the coil and

the aluminum disk

Transient multiphysics model

The single sided TC is highly dependent on position of the aluminum disk

As the disk moves away, the inductance, resistance, and induced

currents change greatly influencing the exerted forcecurrents change greatly influencing the exerted force

A multiphysics model with a moving mesh is indispensible.

COMSOL modules used: “Azimuthal induction currents”, and

“moving mesh (ALE) with dynamic remeshing”.

Setup Characteristics TC

Capacitor bank 7 mF

Initial voltage 400 V

Al Cross section area

in (mm^2)

50 x 14

Coil cross section area 2 mm x 4mm

Air gap between coil and Al 1 mm

Number of coil turns 9

Inter-distance coil turns 0.1 mm

Stray resistance 10 mΩ

Stray inductance 1 µH


100

200

300

400

Ca

pa

cito

r vo

lta

ge

in

vo

lts (

V)

1

1.5

2

2.5x 10

4

Forc

e in n

ew

tons

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7-200

-100

0

100

Time in milliseconds(ms)

Ca

pa

cito

r vo

lta

ge

in

vo

lts (

V)

7000

8000

9000

10000

Cu

rre

nt in

am

ps(A

)

6

7

8

Dis

pla

cem

ent in

millim

ete

rs (m

m)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7-0.5

0

0.5

1


Forc

e in n

ew

tons

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

1000

2000

3000

4000

5000

6000

7000


Cu

rre

nt in

am

ps(A

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7-1

0

1

2

3

4

5


Dis

pla

cem

ent in

millim

ete

rs (m

m)


Time: 0.1msArrow: magnetic fieldSurface: Total current density

Time: 0.18msArrow: magnetic fieldSurface: Total current density

Surface: Total current density

Time: 0.3 msArrow: magnetic fieldSurface: Total current density

Transient multiphysics modelTime: 0.18msContour lines: A [Wb/m]Surface: Magnetic flux density [T]

Time: 0.1msContour lines: A [Wb/m]Surface: Magnetic flux density [T]

Time: 0.3msContour lines: A [Wb/m]Surface: Magnetic flux density [T]


Penetration depthwiith respect to time

along the blue line

TC simulation 1

© ABB Group November 23, 2010 | Slide 14

TC simulation 2


TC simulation 3


Model verification

Experimental verification is carried out to verify the results

simulated in COMSOL.

The results are compared with two experiments:

Experiment I was already carried out at ABB Experiment I was already carried out at ABB

Experiment II is the custom built prototype of the TC


Model verificationExp I

Setup Characteristics

Capacitor bank 33 mF

Initial voltage 400 V

Al Cross section area 50 mm x 20 mm

Coil conductor cross section area 2 mm x 4 mm

Air gap between coil and Al 1 mmAir gap between coil and Al 1 mm

Number of coil turns 10

Gap between coil turns 0.1 mm

Stray resistance 10 mΩ

Stray inductance 1 µH

Model verificationExp 2

Three series of tests were carried out:

Test 1: The 33 mF capacitor bank is discharged in the coilwith no aluminum ring on top at three voltage levels: 25,with no aluminum ring on top at three voltage levels: 25,

50, and 100V

Aim: Determine the stray impedance

Step 1: The oscilloscope is used to measure the

voltage and current pulse without any influence from

the aluminum ring.

Step 2:The resistance and inductance of the coil aredetermined by running a COMSOL simulation with nodetermined by running a COMSOL simulation with no

aluminum disk.

Step3: The stray impedance can be approximated by

solving for the following differential equations inMATLAB and comparing with the voltage and current

waveforms measured in the lab:


1( )

Stray

C

C TC

i

V R i i

dV

dt C

diR−

= −

= −+

1000

1500

2000

2500

Current in

am

ps(A

)

Scope

Estimated

Current pulse at 50 V

( )Stray

Str

C

a

TC

y

V R i iRdt L L

−= −+

400

600

800

1000

1200

Curr

ent in

am

ps(A

)

Scope

Estimated

-2 0 2 4 6 8 10-500

0

500


Current in

am

ps(A

)

3000

3500

4000

4500

Current in

am

ps(A

)

Scope

Estimated

-2 0 2 4 6 8 10-200

0

200

400


Curr

ent in

am

ps(A

)

-2 0 2 4 6 8 10-500

0

500

1000

1500

2000

2500


Current in

am

ps(A

)




Test 2: A Teflon cylinder is used to guide the aluminumring.

Test 3: The guide is removed to record the displacement of

the aluminum disk without friction.the aluminum disk without friction.

1.5

2

2.5

3

Dis

pla

ce

me

nt [m

m]

COMSOL

Lab test run 1

Lab test run 2

Lab test run 3

0 0.5 1 1.5

0

0.5

1

1.5

Time [ms]

Dis

pla

ce

me

nt [m

m]


The sources of error are:

The coil is modeled as concentric rings in COMSOLand not as a spiral

Air resistance is neglected Air resistance is neglected

The impedance of the coil is not 100% accurate

The stray impedance is not constant

The discharged voltage from the capacitor bank is not

100% exact

:

No need for a guide since the aluminum follows a No need for a guide since the aluminum follows a

straight trajectory.

The model predicts the exerted forces on the

aluminum disk with high accuracy.

Conclusions

Static and stationary models serve as a good start to study

the behavior and characteristics of a TC at different

frequencies

A single equivalent frequency in a stationary model is not

sufficientsufficient

This experimentally validated multiphysics finite element

transient model can be used to design a TC to meet the

needed requirements

Movies- TC 50 V No guide, No bottom damper


Movies- TC 150 V with guide and bottom damper



Royal Institute of Technology

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