Transcript Power Systems Design

Power Systems Design -II
Introduction to Space Systems and Spacecraft Design
Space Systems Design
Power Systems Design II
Power Systems or EPS
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Look at the parts of the EPS
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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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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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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
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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
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1.
2.
3.
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.
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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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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?
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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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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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