Transcript Power Systems Design

Power Systems Design -I
Introduction to Space Systems and Spacecraft Design
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Power System Design Considerations
Power System Requirements
Power Sources
Power Storage
Power Distribution
Power Control
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Primary
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Secondary
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Electrical Power Battery Storage
Primary – non rechargeable batteries
Secondary – rechargeable batteries
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Operating regimes of spacecraft power sources
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Not Rechargeable
Energy Storage
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Power Systems Design -I Not Rechargeable
Not Rechargeable
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Not Rechargeable
Not Good
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Rechargeable
Old Technology
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Rechargeable
Old Technology
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Rechargeable
Old Technology
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Rechargeable
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Rechargeable
New Technology
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Batteries
Most common form of electrical storage for spacecraft
Battery terms:
Ampere-hour capacity =
total capacity of a battery (e.g. 40 A for
1 hr = 40 A-hr
Depth of discharge (DOD) =
percentage of battery capacity used in
discharge (75% DOD means 25%
capacity remaining. DOD usually
limited for long cycle life)
stored energy of battery, equal to A-hr
capacity times average discharge
voltage.
Watt-hour capacity =
Charge rate =
Average discharge voltage =
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rate at which battery can accept charge
(measured in A)
number of cells in series times cell
discharge voltage (1.25 v for most
commonly used cells)
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Considerations for power calculations
We have a battery that has a power capacity of:
1000mA (1000mAHrs)@ 1.2v
It can supply 1000mA for 1 hour or 500mA for 2
hours or 250mA for 4 hours @ a voltage of 1.2 v.
Power rating of 1000mA x 1.2 v = 1.2 watt hours
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Battery selection:
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Considerations for power calculations
Two batteries in series.
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Considerations for power calculations
Two batteries in parallel.
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Rechargeable
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Operating regimes of spacecraft power sources
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New Technology
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Solar cell response
Peak sun irradiance
Sun spectral irradiance
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Dual Junction Cell
Efficiency
Added by second junction
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Use of the Sun’s Spectrum
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Triple Junction Cell
Efficiency
Added by second junction
Added by third junction
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Good Efficiency
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Reduce Efficiency
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Max Cell Current when short circuit
Max Cell Voltage when open circuit
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Peak Power
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Solar Cell Strings
String of cells
Parallel strings
to cover panel
Add cell
voltages
to get
string
voltage
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Shadowing
Kills all power
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Close sw to
Close
sw to crowbar
• Use of NiCd
batteries
required reconditioning
crowbar battery
second battery
• Reconditioning not required for Li Ion batteries.
Reconditioning
battery system
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How much Battery
Charge Left?
Discharging causes
heating
Charging causes
heating
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Some Solar Notes
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Approx Cosine
Sun
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Satellite Orbit
Parallel Sun Rays
Eclipse
Sun
Earth
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Gravity Gradient Stabilized
Sun
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Passive Magnetic Stabilized
N
S
N
S
S
N
N
Sun
S
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Inertially Stabilized
Sun
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Power Systems Design I or EPS
Charge Control
Solar Panels
- source
Subsystem
Voltage
DC/DC
Voltage
Bus Voltage
Subsystem
DC/DC
Batteries
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Radios
• Fixed voltage busses (5v, -5v, 7v, 3.3v, 12v, etc.)
• Quieter – generates less noise on voltage bus
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• DC/DC Converter/Regulators
• Regulate 2 Li Ion batteries - ~7.2v  5v
Requires less circuitry, more
efficient to regulate down
• “Buck Up” 1 Li Ion battery - ~3.6v  5v
Requires more circuitry, less
efficient to “buck up” voltage.
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Could be caused by arcing
due to spacecraft charging
Failure in subsystem
that causes a short
Feedback on voltage bus
from some components
Multiple return paths for
current to battery – don’t use
grounded frame
Power cycling required to
reset components that have
latch up due to radiation
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What type of solar panel system
does it take to generate 47.5 watts
peak and 27.8 watts average?
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Questions?
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