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Multi-Port Storage Elements Energy storage elements can have multiple ports Power into/out of element via multiple ports Examples:
o Actuators: motors1, relays, generators o Sensors: probes o Distributed elastic devices: beams o Piezoelectricity & Magnetostriction
Energy stored in field, accessible to multiple “ports”
1 Multiport energy storage devices are more accurate models for motors and generators than simple GY models.
Example: Capacitative Actuator or Sensor
x+
-
V
+ + + + + +
+ + + + + ++
+
++
++
-
- - - - - -
-
-
-
-
R
Parallel plates: area A, separation x, charge q Capacitance: C = C(x) = εA/x Voltage drop (effort) across plates: Vc = q/C Oppositely charged plates attract => forces F Potential energy stored in electric field:
o E = ∫ Vc dq = q2/[2C(x)] = E(q, x) o Changing x changes E: work ∫ F dx done,
electric field acts like “spring” o Nature wants to minimize potential energy
Two efforts from energy: o Vc = ∂E/∂q = q/C o F =∂E/∂x = (-q2/2C2)(∂C/∂x)
= (-q2/2C2)(−εA/x2) F = q2/(2εA)
2-port capacitor has:
o electrical port: effort Vc = Vc (q, x), displacement q, flow dq/dt
o mechanical port: effort F = F(q, x), displacement x, flow dx/dt
CVc
q.
x.F
System with 2-port capacitor:
CVc
q.
x.F
1Se:VV(t)
R:R
1
I:Mplate
p.
p/Mplate
Extract state equations:
!
˙ q =1
RV (t)"V
c(q, x)[ ] =
V (t)" qx /#A
R
!
˙ x =p
Mplate
!
˙ p = F(q, x) =q
2
2A"
Multi-port Capacitance
C
e1
ke
em
...
...
fm
f1
kf
m-Port Capacitance Cm o Flows on C via kinematics:
fk = qk.
o Displacements: qk
o Power: P = ∑k = 1
m Pk = ∑
k = 1
m ek fk
o o Potential energy in capacitance’s field:
E = ∫ P dt
Total potential energy stored:
E = ⌡⌠
∑k = 1
m Pk dt =
⌡⌠
∑k = 1
m ek fk dt
= ⌡⌠
∑k = 1
m ek qk
. dt = ⌡⌠
∑k = 1
m ek dqk
E = E(q1, q2, ..., qm) depends on all displacements qk
Energy & Power: dEdt = P = ∑
k = 1
m ek fk
Derivative of E = E(q1, q2, ..., qm) via chain rule:
dEdt = ∑
k = 1
m ∂E∂qk
dqkdt = ∑
k = 1
m ∂E∂qk
fk Compare blue terms’ coefficients of fk:
ek = ek(q1, q2, ..., qm) = ∂E∂qk
Effort on kth bond = partial of energy with respect to displacement on kth bond.
Example: 3-Port C Electrical port (V, q) Translational port (F, x) Rotational port (T, θ) E = E(x, θ, q) = 2xq2 + 4qx3θ + 3θ2
Torque: T = ∂E/∂θ = 4qx3 + 6θ Voltage: V = ∂E/∂q = 4xq + 4x3θ Force: F = ∂E/∂x = 2q2 + 12qx2θ
Example: Electromechanical Relay
Magnetic energy produced by coil Magnetic field energy stored in iron core & air gap Relay minimizes magnetic potential energy by
adjusting displacements (flux φ and gap size x).
GY:N
Cleak
Cleft
1 0Se:VV(t)
1
R
Cbottom
Cair:1/!M
".F
x. 1 C: k
I: Marm
R: FµRleft Ctop
1
Rtop
Rbottom
Cbar
Rbar
electrical magnetic mechanical
2-Port C
C : 1/!air
M
".
F
x.
Magnetic & Mechanical Ports Potential energy
Eair = Eair(φ , x) =
φ2←(x)2 Efforts
o F = ∂Eair∂x =
φ22
∂←(x)∂x =
φ22 µair A
o M = ∂Eair∂φ = φ ℜ(x) = φ
xµair A
Example: Electric Motors
•rotor: squirrel cage with solid bars & steel laminations •stator: 3 – phase AC coils
0
0
0
0
0
1
1
1
1
1
:mm
:Rr1
:r1
R
R
R
R
R
MGY
MGY
MGY
MGY
MGY
1
TF
1 I
R
:r2
:r3
:r4
:r5
:Rr2
:Rr3
:Rr4
:Rr5
:c
:J
:mr1MTF
:mr2MTF
:mr3MTF
:mr4MTF
:mr5MTF
:mr6MTF
:mr7MTF
:mr8MTF
:mr9MTF
:mr10MTF
:nr10
:nr9
:nr8
:nr7
:nr6
:nr5
:nr4
:nr3
:nr2
:nr1
:1/m1
TF
:1/m2TF
:1/m3TF
:1/m4TF
:1/m5
TF
GY
GY
GY
GY
GY
GY
GY
GY
GY
GY
1
1
0
0
C
C
0
0
1
1
:R sc
:R sb
:R sa
R
1
1
1
R
R
:ns2
:ns3
:ns1
GY
GY
GY
:Rsc
:Rsb
:Rsa
. .va
. .vb
. .vc
MSe
MSe
MSe
R
1
1
1
R
R
MechanicalMagnetic Mathematical ElectricalMathematicalElectrical Magnetic
MechanicalMagnetic Mathematical ElectricalMathematicalElectrical Magnetic
Energy stored in magnetic field of air gap between stator and rotor
Multiport C’s couple magnetic energy stored by stator and rotor
Example: Electrostatic Micro-motor
MEMS (Micro Electro Mechanical Systems)
device Operation
o Voltage applied to electrodes o Very sharp tips (curvature ~ 2 µm) o Intense electric field ionizes air molecules o Electrodes repel like charged ions o Ions drift to rotor, deposit charge on rotor o Electrode repels rotor
Generates torque Generates bearing action: pushes rotor
center to stator center
1
Rotor Surface
Tilt angle
ElectrodeRotor
Stator electrodes
(a) Motor configuration (b) Stator electrode’s tilt angle
Rotor Surface
Tilt angle
ElectrodeRotor
Stator electrodes
Rotor
Stator electrodes
Rotor
Stator electrodes
(a) Motor configuration (b) Stator electrode’s tilt angle
Figure 1 Rotor and stator configuration and stator electrode's tilt angle
0 250 5000.1
0.25
0.4
Printing Gap (um)
MD
E (u
m)
Proximity Printing
Contact Printing
< Simulation Condition > T = 300 um r = 4 wavelength = 1 nm
Figure 2 Maximum diffraction error (MDE) versus normal proximity printing gaps (gp)
Figure 1 Stator and electrodes of a corona motor
Figure 2 PMMA rotor and shaft/rotor assembly
Figure 3 Assembled motor and size of a stator
Bond Graph Model
0Se:VV(t)
C:Cfield
V.q
T
x.
.!
1
I: Mrotor
I: Jrotor
R:Rgas bearing
R:Relectrode
1
electrical
rotational
R:Rcathode
R:Ranode
R:Relectrode
F1
translational
Example: Magnetostriction
• Ferromagnetic materials iron, nickel, cobalt, rare earths magnetostrictive strains s ≈ 10-5
• Transformer hum: Fe core vibrates (extends/contracts) under AC • Rare earth alloy, terfenol D: strains ≈
10-3 to 10-2
Constitutive Equations: Linear Magnetostriction
H = H(s,B) = d s + Bµs
T = T(s,B) = YB s + d B T: normal stress in rod s: normal strain in rod B: magnetic flux density H: magnetic field intensity Parameters
o Young’s modulus YB measured with B = 0 o permeability µs measured with s = 0 o magnetically induced stress (d B) o strain-induced magnetic field (d s)
Multiport capacitance:
o displacements (s, B) o efforts (T,H)
Magnetostrictive Actuator
25.4mm
Aluminum Attachment
BodyTop Cover
Belleville Washers
Coil 2
Plunger Rod
Terfenol Rod
Coil 1
Permanent Magnet
Steel SpacerBottom Cover
Aluminum Spool
Nylon Bearing
Bond Graph
1V
I:Lair
R:Relec
Se
!•
!/Lair
GY:N 1 CM(",x)
1
•pn
1
p1/m1
I:m1•p1
0 OUTfOUT
1
I:M
•P P/M
R:Bb
xp•
eOUT.
.
...
..
.
R:b1
C:1/#ret
R:Rmag
Fn(",x)#ret " TF:nn
TF:n1
1 TF:nr
C:1/kp
kpxp
I:mn
R:bnpn/mn
F1(",x)
•xn
•x1
Fr(", x)
•xr
"•
electrical magnetic mechanical translational
"•
Multi-port Inertances
I
e1= p1
.
...
fm = pm
.
em
f1
ek = pk
.
fk
Stores kinetic energy
E = E(p1, p2, ..., pm)
Multiple ports with momenta pk
Flows: fk = ∂E/∂pk = fk(p1, p2, ..., pm)
IC Device
Stores kinetic & potential energies in same “field” E = E(p1, p2, ..., pm, q1, q2, ..., qn)
Ports with momenta pk & displacements ql Flows on I bonds:
fk = ∂E/∂pk = fk(p1, p2, ..., pm, q1, q2, ..., qn) Efforts on C bonds:
el = ∂E/∂ql = el(p1, p2, ..., pm, q1, q2, ..., qn)
IC