Power Sources

• Utility: 60 Hz - 120/240 V - 1,2,3 Phase• Fixed Voltage Batteries• Fuel Cells• Photo Voltaic • Thermionic Generators• AC generators (“Alternators”) – variable frequency• DC Generators

Electrical Consumption

• AC motors – sync/async• DC Motors• Residential Heating/Cooling• Lighting AC/DC High frequency• Induction Heating HF• Electronic Systems – Fixed Voltage DC• Transmission Losses• Conversion Losses

Replacement of Legacy Technologies

• Automotive (Electric Vehicle Propulsion)• Hydraulic controls (Fly by wire)• Tele - commuting, tele - presence• Beam Weapons• Unmanned Aircraft

Critical Converter Parameters

• Efficiency• Weight• Size/Volume• Power handling Capacity• Power Density• Cost

Photo-voltaic Cells

UsN Type DopantsP Type Dopants

P

N

PN Junction

Diode Doping Profile

P

N

Diffusion Result

Depletion Region

Hole Diffusion

Electron Diffusion

+ + + + + +

+ + + + + +

- - - - - -

- - - - - -

Equilibrium Charge

Displacement

Internal E-FieldResulting from

ChargeDisplacement Inhibits

Further Diffusion

- Photon Generated Hole/Electron Pair

E- Field Accelerates Electron and Hole

ISS

(Proportional to

photon flux)

Equivalent effect of photon generated internal current.

+

Resistive Load

-

VSS

+

ISS

(Proportional to

photon flux)

0.0260 1

SSV

vJI I e

0

0.026 ln 1JSS

IV v

I

IJ

L SS JI I I

Shockley’s Equation:

Photo-voltaic Cell

SS

L

V

R

VSS

IJ

P VI

PI

V

Hyperbolic Curve

P1

P2 > P1

0.578 1.4 0.83

0.5780.403

1.4

Opt

Opt

P v A W

vR

A

To get maximum power out of the photovoltaic cell, the converter must make the cells see 0.403 ohms when ISS = 1.5 amps!

Power Converter

Load:R = ?

Photovoltaic Array

To make matters worse, POpt and ROpt vary with temperature as well as ISS!

Maximum Power Condition: Curves are Tangent

0.0260

0.0260 0

1SS

SS

VOptv

L SS J SSSS

V

vSS SS Opt

PI I I I I e

V

V I I e I P

0.02602

20.0260

0.026

0.026

SS

SS

VOptvL

SS SS

V

vSSOpt

PIdIe

dV v V

V Ie P

v

20.026 0.0260

0 0

0 0

0.026

0.026 0.0260.026 ln 1 0.026 ln

0.026

SS SSV V

v vSSSS SS

SS SSSS

SS SS

V IV I I e I e

v

I Iv vV v v

I V V V I

… which converges to ~ 0.1% in 4 or 5 iterations, but will be ~ 0.6 V for almost any reasonable conditions . . . so to hell with the math!

In full sunlight, the solar energy flux is ~ 1Kw/m2, and 15% efficiency is normal, so

2150Opt CellwP A

m 250

0.6Opt

SS Cell

PI A

v

ISS in amperes, ACell in m2.

General Power ConverterDefinitions

• Efficiency:

• Power Density

loss wasted source outP P P P

out out

source out loss

P P

P P P

1loss outP P

3

Watts

mout

P

PD

Vol

How much power can be delivered by a “small” package and not have it overheat?

ExampleYour trusty mechanical engineer has designed a cooling scheme that will allow a package having a volume of 0.027 m3 to dissipate 150 watts and keep the interior components below 55C.

Determine the power output capability and power density if your electrical design exhibits efficiencies of 80% and 90%.

80%

90%

3 3

.8150W 600 Watts

1 .2

600 W W22,222

0.027m m

out wasted

outP

P P

PD

V

3 3

.9150W 1350 Watts

1 .1

1350 W W50,000

0.027m m

out wasted

outP

P P

PD

V