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

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

Gary Bergstrom

Magnesense

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

Hen

ries

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

0.1

0.3

0.5

0.7

0.9

1.1

1.3

1.5

1.7

1.9

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

Fo

rce

in N 0.00000

0.00117

0.00218

0.00400

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 current

80% 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 0.00400

0

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 0.00400

0

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



80% 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 0.00400

0

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 0.00400

0

200

400

600

800

1000

1200

flux density

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

0.00400

0

5

10

15

20

25

30

35

40

45

position - 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 0.00400

0

5

10

15

20

25

30

35

40

45

position - 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 0.00400

0

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



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 0.00400

0

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 0.00350

0

200

400

600

800

1000

1200

B

mag force



84% 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 0.00400

0

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 0.00400

0

5

10

15

20

25

30

35

40

45

X

voltage

I



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 0.00400

0

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 0.00400

0

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 0.00400

0

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 0.00400

0

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 0.00400

0

5

10

15

20

25

30

35

40

45

X

voltage

I



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 0.00400

0

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 Solenoid: Building a System That Achieves a Soft Landing Gary Bergstrom...

Documents

Transcript of Taming the Electromagnetic Solenoid: Building a System That Achieves a Soft Landing Gary Bergstrom...