Taming the Electromagnetic Soleno i d: Building a System That Achieves a Soft Landing

Taming the Electromagnetic Solenoid: Building a System That Achieves a Soft Landing

Gary BergstromMagnesense

Gary Bergstrom, Magnesense

Simplified valve


Flux in an E-core


Electrical

• Rtotal=Rdrive+Rsolenoid• L is inductance of solenoid• Rsolenoid is a function of

temperature• Inductance is a strong function

of position+

-Drive

Solenoid

L

Rsolenoid

Rdrive


Inductance vs. Position

0

0.001

0.002

0.003

0.004

0.005

0.006

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

meters

Henr

ies

Inductance


Mass, spring damper – mechanical model

x

m mass, Kgc damping coeffk spring coeff, N MF force, Nx displacement, Mx velocity, M/Sx acceleration, M/S^2

m is all moving mass, including part of springs

k is the net restoring force from all springsF is the net electromagnetic force from both stators

c is damping from mechanical friction and gas flow

x is displacement, symbolized by a pointer moving along scale

m x + c x + k x = Fk c

m

F


Force vs. Position, various flux densities

0

200

400

600

800

1000

1200

0.00000 0.00100 0.00200 0.00300 0.00400 0.00500 0.00600 0.00700 0.00800

gap in meters

forc

e in

N

0.10.30.50.70.91.11.31.51.71.9

1.9

1.7

1.5


Force vs. Flux density, various gaps

0

200

400

600

800

1000

1200

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Flux density in T

Forc

e in

N 0.000000.001170.002180.00400

gap

0.00000

0.00117

0.00218

0.00400


Flux summary

• Flux resists changes• V=L*dI/dt only when:

– x doesn’t change– no eddy current– no saturation

• Flux is the integral of inductive voltage • Force goes as the square of flux and is a non-linear

function of position


Excel spreadsheet of simulation


Voltage drive

• I=V/Rtotal• if V=40V and Rtotal=.25

then I=160 Amps• This can occur at saturation• Power lost is I^2 * Rtotal so

we want to minimize R

42V

Solenoid


Position, voltage and current80% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00100 0.00200 0.00300 0.004000

5

10

15

20

25

30

35

40

45

position - x

voltage

I


Flux density and force

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

200

400

600

800

1000

1200

flux density

mag force


Voltage drive details

• Time is in seconds• Position 4.5 mm to 0 mm

(plot starts near “middle”)• Voltage 0 to 40 volts• Flux density in Teslas• Force is in Newtons

• Flux must = ~1.65 T to hold in this example

• “bounce” was set to 70% of the incoming velocity (or ½ the energy)

• Flux goes as integral of applied inductive voltage

• Force is function of position and square of flux



0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00100 0.00200 0.00300 0.004000

5

10

15

20

25

30

35

40

45

position - x

voltage

I



0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

200

400

600

800

1000

1200

flux density

mag force



0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000

0.00050

0.00100

0.00150

0.00200

0.00250

0.00300

0.00350

0.00400

0

5

10

15

20

25

30

35

40

45

position - x

voltage

I



0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

position - x

voltage

I


Position, voltage and current 30V supply80% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

position - x

voltage

I


Voltage drive summary

• Sensitive to changes in power supply • Very prone to saturating core, but need to run close to

saturation due to size considerations• No good correlation between applied voltage and resulting

force • Cannot always achieve soft landing and holding flux level

at same time with simple drive • Landing time very sensitive to changes in initial energy


Current drive

• Rs (current sense) should be small (more I^2 * R loss)

• R1/R2 gain circuit is to reduce noise

• Diode must include both Solenoid and Rs in loop

R2R1

Solenoid

42V

Rs.01


Position, voltage and current

80% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I



0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.003500

200

400

600

800

1000

1200

B

mag force



0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I



76% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I


Position, voltage and current 30V supply

80% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I


Current drive summary

• Not very sensitive to power supply changes• Saturation is not as big a problem (current is limited,

saturation still occurs)• Unstable – the current changes in the opposite direction

from what is needed for a soft landing• Back EMF forces the current around in counter-intuitive

ways


Flux drive

• Flux sensor needed• This design uses full

bridge drive• More parts, more

performance

Driver

OutIn Flux

Sensor

Flux

Solenoid

42V



80% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I



0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

100

200

300

400

500

600

700

800

900

1000

B

mag force



85% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I



75% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I


Position, voltage and current 30V supply80% energy

0.00000

0.00100

0.00200

0.00300

0.00400

0.00500

0.00600

0.00700

0.00000 0.00050 0.00100 0.00150 0.00200 0.00250 0.00300 0.00350 0.004000

5

10

15

20

25

30

35

40

45

X

voltage

I


Flux drive summary

• Less sensitive than voltage drive to changes in power supply• Stable like voltage drive but without the saturation problem• Flux, therefore force is known (if position is known)• Allows position to be calculated since:

x ~ current / flux• Position PID loop can now be closed giving us closed loop

position drive, with a well behaved open loop system


So how do we sense flux?

• Hall effect sensor• Sense coil• “Sensorless”


Hall effect sensor

Good points:• Simple• DC response• Low cost• Small

Bad points:• Temperature (reliability)• Some cost• Extra wires• Measurement position

Flux

5VHall


Sense coil

Good points:• Simple circuit• Rugged• Low cost• No temperature problems

Bad points:• More parts• Higher cost• Takes up core area• Extra wires

Flux

INT


“Sensorless”

Good points:• No wires• Reliable• No size (at valve)• Can be done in software

Bad points:• Small temperature sensitivity• Even more parts• Difficult to develop• Difficult to understand

Fluxexistingdrive

Rtotal

MULT

Rsense

INT

Taming the Electromagnetic Soleno i d: Building a System That Achieves a Soft Landing

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