Transcript Power Systems Design

Power Systems Design - 1
Morehead State University
Morehead, KY
Prof. Bob Twiggs
[email protected]
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Power Systems Design - 1
Power System Design Considerations
System Requirements
Sources
Storage
Distribution
Control
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Power Systems Design - 1
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Power Systems Design - 1
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Power Systems Design - 1
Operating regimes of spacecraft power sources
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Power Systems Design - 1
Operating regimes of spacecraft power sources
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Power Systems Design - 1
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Power Systems Design - 1
New Technology
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Power Systems Design - 1
Solar cell response
Peak sun irradiance
Sun spectral irradiance
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Power Systems Design - 1
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Power Systems Design - 1
Dual Junction Cell
Efficiency
Added by second junction
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Power Systems Design - 1
Use of the Sun’s Spectrum
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Power Systems Design - 1
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Power Systems Design 1
Triple Junction Cell
Efficiency
Added by second junction
Added by third junction
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Power Systems Design - 1
Good Efficiency
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Reduce Efficiency
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Power Systems Design 1
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Power Systems Design –I
Ended 10/21/10
Max Cell Current when short circuit
Max Cell Voltage when open circuit
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Power Systems Design - 1
Peak Power
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Power Systems Design - 1
String of cells
Solar Cell Strings
Parallel strings
to cover panel
Add cell
voltages
to get
string
voltage
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Power Systems Design - 1
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Power Systems Design - 1
Shadowing
Kills all power
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Power Systems Design - 1
Some Solar Notes
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Power Systems Design - 1
Approx Cosine
Sun
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Power Systems Design - 1
Satellite Orbit
Parallel Sun Rays
Eclipse
Sun
Earth
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Power Systems Design - 1
Gravity Gradient Stabilized
Sun
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Power Systems Design - 1
Passive Magnetic Stabilized
N
S
N
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N
N
Sun
S
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Power Systems Design - 1
Inertially Stabilized
Sun
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Power Systems Design - 1
Questions?
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Power Systems Design - 2
Morehead State University
Morehead, KY
Prof. Bob Twiggs
[email protected]
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Power Systems Design - 2
Power System Design Considerations
System Requirements
Sources
Storage
Distribution
Control
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Power Systems Design - 2
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Power Systems Design - 2
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Power Systems Design - 2
Primary
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Secondary
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Power Systems Design - 2
Electrical Power Battery Storage
• Primary – non rechargeable batteries
• Secondary – rechargeable batteries
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Not Rechargeable
Energy Storage
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Power Systems Design - 2
Not Rechargeable
Not Rechargeable
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Power Systems Design - 2
Not Rechargeable
Not Good
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Power Systems Design - 2
Rechargeable
Old Technology
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Power Systems Design - 2
Rechargeable
Old Technology
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Power Systems Design - 2
Rechargeable
Old Technology
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Power Systems Design - 2
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Rechargeable
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Power Systems Design 2
Rechargeable
New Technology
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Power Systems Design - 2
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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Power Systems Design - 2
How much Battery
Charge Left?
Discharging causes
heating
Charging causes
heating
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Power Systems Design - 2
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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Power Systems Design - 2
Battery selection:
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Considerations for power calculations
Two batteries in series.
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Power Systems Design - 2
Considerations for power calculations
Two batteries in parallel.
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Power Systems Design - 2
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Rechargeable
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Questions?
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Power Systems Design - 3
Morehead State University
Morehead, KY
Prof. Bob Twiggs
[email protected]
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Power Systems Design - 3
Power System Design Considerations
System Requirements
Sources
Storage
Distribution
Control
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Power Systems Design - 3
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Power Systems Design - 3
Power Systems Design 3 or EPS
Charge Control
Solar Panels
- source
Subsystem
Voltage
DC/DC
Voltage
Bus Voltage
Subsystem
DC/DC
Batteries
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Power Systems Design - 3
Radios
• Fixed voltage busses (5v, -5v, 7v, 3.3v, 12v, etc.)
• Quieter – generates less noise on voltage bus
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Power Systems Design - 3
• 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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Power Systems Design - 3
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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Power Systems Design - 3
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Power Systems Design - 3
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Power Systems Design - 3
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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Power Systems Design - 4
Morehead State University
Morehead, KY
Prof. Bob Twiggs
[email protected]
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Power Systems Design - 4
Power Systems or EPS
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Power Systems Design - 4
Look at the parts of the EPS
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Power Systems Design - 4
Take Solar Panel
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1350
1350
5.
6.
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What do we need from the solar panel?
What are the attributes of a solar panel?
1.
2.
3.
4.
5.
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels.
Lets go back and look at the solar cell.
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Lets go back and look at the solar cell.
This dual junction cell
1.
2.
3.
Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm
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Solar cell has an I-V curve like this
This dual junction cell
1.
2.
3.
Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm
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Power Systems Design - 4
Looked at the solar cell.
This dual junction cell
1.
2.
3.
Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm
What are the attributes of a solar panel?
1.
2.
3.
4.
5.
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels.
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Power Systems Design - 4
Need to select a battery to design for
solar panel voltage
What are the attributes of a solar panel?
1.
2.
3.
4.
5.
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels.
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Rechargeable
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Use a lithium ion battery
Li Ion batteries = 3.6 v nominal
Design Criteria for charging Li Ion battery:
1.
2.
Need 10-15% more voltage to charge than the
nominal voltage.
Here we would need solar panel voltage of ~ 4.0 –
4.2v to charge this battery.
Design Criteria solar panel:
1. Number of cells = Max voltage/cell voltage.
2. Take minimum number of whole cells.
# cells = (4.2v/string)/(2.2v/cell)
= 1.9 or 2 cell for a string voltage of 4.4v
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Use two lithium ion batteries
Li Ion batteries = 7.2 v nominal
Design Criteria for charging Li Ion battery:
1.
2.
Need 10-15% more voltage to charge than the
nominal voltage.
Here we would need solar panel voltage of ~ 8.0 –
8.3v to charge this battery.
Design Criteria solar panel:
1. Number of cells = Max voltage/cell voltage.
2. Take minimum number of whole cells.
# cells = (8.3v/string)/(2.2v/cell)
= 3.77 or 4 cell for a string voltage of 8.8v
Lets be conservative and use 5
cells for 11v.
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Now we have:
Two Li Ion batteries = 7.2 v nominal
5 cells for 11v to charge with.
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What is packing factor?
What are the attributes of a solar panel?
1.
2.
3.
4.
5.
Total output power of solar panel.
Got
Voltage of solar panel.
Maximum packing factor.
Got
Efficiency of the solar cells.
Operating temperature of the panels.
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Packing Factor
Total Cell Area
Total Panel Area
Packing Factor = Total Cell Area/ Total Panel Area
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Packing Factor
Cell
type 1
Cell type 2
Fixed solar panel size
Cell type 3
What do you do if given a fixed size panel on which to put
solar cells and you have these different size solar cells?
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Packing Factor
What do you do if given a fixed size panel on which to put
solar cells and you have these different size solar cells?
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Now we have:
5 cells for 11v where the string has all
of the cells hooked in series
Total Panel Area
11v
How do you mount these 5
cells on this panel?
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How do you mount these 5
cells on this panel?
NO!
OK!
Visually we can see a very
poor packing factor.
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What if the cells were bigger?
Oh Oh!
Now you have only 4.4v in the string.
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Got a cube? Put other cells on another face?
Can’t do. All cells for a single string
must be on same face.
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Where are we now in the solar panel design?
What are the attributes of a solar panel?
1.
2.
3.
4.
5.
Total output power of solar panel.
Got
Voltage of solar panel.
Not got, but
Maximum packing factor.
understand
Got
Efficiency of the solar cells.
Operating temperature of the panels.
Assume we could mount the 5 cells on
a panel, what is total power for the cells
selected?
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How much power from these cells?
5 cells for 11v
One cell area = 76 x 37 mm = 2812 mm^2
Total cell area = 8*2812 = 22496 mm^2 = 2.25 x10-2 m^2
We have 1350 watts/m^2 from the sun in space
Direct power = (1350 w/m^2) x (2.25 x10-2 m^2)
= 34.4 watts
11v Converted power = direct power x cell efficiency
= 34.4 w x 0.22 eff
= 7.5
watts
For this dual junction cell
1.
2.
3.
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Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm
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Where are we now in the solar panel design?
What are the attributes of a solar panel?
Got
1. Total output power of solar panel.
Got
2. Voltage of solar panel.
Not got, but
3. Maximum packing factor.
understand
Got
4. Efficiency of the solar cells.
5. Operating temperature of the panels.
Now we can assume to start:
1. panel is at 90 degrees with sun – max power
2. operating temperature 20 degrees.. Centigrade – 22% eff
Don’t forget, temperature
counts a lot.
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Start here Tuesday for Idaho
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Now that we have beat our way through the solar
panel design ----- lets go look at the some more
parts of the EPS.
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Power Systems or EPS
What is this?
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Power Systems or EPS
Back bias diode
Panel 1
When panel 1 is shaded, the
back bias diode keeps the
current from flowing
backwards through panel 1,
when panel 2 is generating a
voltage across it.
Panel 2
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Power Systems or EPS
What is this?
R
V
Measure current by measuring
voltage across a low resistance
precision resistor
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Power Systems or EPS
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Expanded subsystem control
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Expanded subsystem control
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What does a charge regulator do?
1.
2.
3.
4.
Controls voltage from PV to battery
Controls rate of charge
Prevents overcharging
Can “boost” or “buck” PV voltage to match
battery needs.
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Expanded subsystem control
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Consider:
When high current occurs in a subsystem, it
could be from latch-up. What to do? Cycle
power. Where do you do this – hardware
controlled in the EPS.
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Consider the satellite’s attitude control
for solar power generation.
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Satellite Orbit
Parallel Sun Rays
Eclipse
Sun
Earth
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Power Systems Design - 4 Gravity Gradient Stabilized
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Passive Magnetic Stabilized
N
S
N
S
S
N
N
S
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Inertially Stabilized
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Some Solar Notes
• Power from sun in orbit ~ 1350 watts/meter2
• Power from cells on ground ~ 35% less than in space
• Can get some power form albedo – earth shine ~ 35%
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Need to consider the power requirements
of all of the subsystems and when they are
used to build a power budget.
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Questions?
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