introduction to space systems and spacecraft design space systems design
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Power Systems Design -II. Introduction to Space Systems and Spacecraft Design Space Systems Design. Power Systems Design II. Power Systems or EPS. 2. Introduction to Space Systems and Spacecraft Design Space Systems Design. Power Systems Design II. 3. - PowerPoint PPT PresentationTRANSCRIPT
Introduction to Space Systems and Spacecraft DesignSpace Systems Design
Power Systems Design -II
Introduction to Space Systems and Spacecraft DesignSpace Systems Design
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Power Systems Design II
Power Systems or EPS
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Power Systems Design II
Look at the parts of the EPS
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Take Solar Panel
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5.6.
1350
1350
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What do we need from the solar panel?
What are the attributes of a solar panel?
1. Total output power of solar panel.2. Voltage of solar panel.3. Maximum packing factor.4. Efficiency of the solar cells.5. Operating temperature of the panels.
Lets go back and look at the solar cell.
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This dual junction cell
1. Has an efficiency of ~ 22%2. Open circuit voltage ~ 2.2v3. Size – 76 x 37 mm
Lets go back and look at the solar cell.
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This dual junction cell
1. Has an efficiency of ~ 22%2. Open circuit voltage ~ 2.2v3. Size – 76 x 37 mm
Solar cell has an I-V curve like this
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What are the attributes of a solar panel?
1. Total output power of solar panel.2. Voltage of solar panel.3. Maximum packing factor.4. Efficiency of the solar cells.5. Operating temperature of the panels.
This dual junction cell
1. Has an efficiency of ~ 22%
2. Open circuit voltage ~ 2.2v
3. Size – 76 x 37 mm
Looked at the solar cell.
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What are the attributes of a solar panel?
1. Total output power of solar panel.2. Voltage of solar panel.3. Maximum packing factor.4. Efficiency of the solar cells.5. Operating temperature of the panels.
Need to select a battery to design forsolar panel voltage
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RechargeablePower Systems Design II
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Use a lithium ion batteryLi Ion batteries = 3.6 v nominal
Design Criteria for charging Li Ion battery:
1. Need 10-15% more voltage to charge than the nominal voltage.
2. 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 batteriesLi Ion batteries = 7.2 v nominal
Design Criteria for charging Li Ion battery:
1. Need 10-15% more voltage to charge than the nominal voltage.
2. 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 are the attributes of a solar panel?
1. Total output power of solar panel.2. Voltage of solar panel.3. Maximum packing factor.4. Efficiency of the solar cells.5. Operating temperature of the panels.
What is packing factor?
Got
Got
Total Panel Area
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Packing Factor
Packing Factor = Total Cell Area/ Total Panel Area
Total Cell Area
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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?
Fixed solar panel size
Cell type 3
Cell type 1 Cell type
2
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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
11v
Total Panel Area
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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Can’t do. All cells for a single string must be on same face.
Got a cube? Put other cells on another face?
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Where are we now in the solar panel design?
What are the attributes of a solar panel?
1. Total output power of solar panel.2. Voltage of solar panel.3. Maximum packing factor.4. Efficiency of the solar cells.5. Operating temperature of the panels.
Assume we could mount the 5 cells on a panel, what is total power for the cells selected?
Got
Got
Not got, but understand
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How much power from these cells?5 cells for
11v
11v
One cell area = 76 x 37 mm = 2812 mm^2Total 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
Converted power = direct power x cell efficiency = 34.4 w x 0.22 eff
= 7.5 watts7.5 wattsFor this dual junction cell
1. Has an efficiency of ~ 22%
2. Open circuit voltage ~ 2.2v
3. 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?
1. Total output power of solar panel.2. Voltage of solar panel.3. Maximum packing factor.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 power2. operating temperature 20 degrees.. Centigrade –
22% eff
Got
Got
Not got, but understand
Got
Don’t forget, temperature counts a lot.
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Start here Tuesday for Idaho
Power Systems Design II
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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
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 1
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 Design IIPower Systems or EPS
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Power Systems Design IIPower Systems or EPS
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Power Systems Design IIExpanded subsystem control
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Power Systems Design IIExpanded subsystem control
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What does a charge regulator do?
1. Controls voltage from PV to battery2. Controls rate of charge3. Prevents overcharging4. Can “boost” or “buck” PV voltage to match
battery needs.
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Power Systems Design IIExpanded 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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Eclipse
Parallel Sun Rays
Sun
Earth
Satellite Orbit
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Gravity Gradient StabilizedPower Systems Design II
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Passive Magnetic Stabilized
N
S
SNSN
S N
S NS
N
S
N
S
N
S
N
S
N
S
N
S
N
SN
SN
SN
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Inertially StabilizedPower Systems Design II
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• 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%
Some Solar Notes
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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?