morehead state university morehead, ky prof. bob twiggs rjtwiggs@gmail
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Morehead State UniversityMorehead, KY
Prof. Bob TwiggsRJTwiggs@gmail.com
Power Systems Design - 1
1
2
Power System Design Considerations
Power Systems Design - 1
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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Operating regimes of spacecraft power sources
Power Systems Design - 1
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Operating regimes of spacecraft power sources
Power Systems Design - 1
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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
Sun spectral irradiance
Solar cell response
Peak sun irradiance
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Power Systems Design - 1
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Power Systems Design - 1
Dual Junction Cell
Added by second junction
Efficiency
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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
Added by second junction
Added by third junction
Efficiency
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Power Systems Design - 1
Reduce Efficiency
Good Efficiency
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Power Systems Design - 1
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Power Systems Design –I Ended 10/21/10
Max Cell Voltage when open circuit
Max Cell Current when short circuit
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Power Systems Design - 1
Peak Power
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Power Systems Design - 1
Add cell voltages to get string voltage
String of cells
Parallel strings to cover panel
Solar Cell Strings
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Power Systems Design - 1
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Power Systems Design - 1
ShadowingKills all power
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Power Systems Design - 1
Some Solar Notes
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Power Systems Design - 1
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Sun
Approx Cosine
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Power Systems Design - 1
Eclipse
Parallel Sun Rays
Sun
Earth
Satellite Orbit
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Power Systems Design - 1
25
Gravity Gradient Stabilized
Sun
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Power Systems Design - 1
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
Sun
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Inertially StabilizedPower Systems Design - 1
Sun
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Power Systems Design - 1
Questions?
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Morehead State UniversityMorehead, KY
Prof. Bob TwiggsRJTwiggs@gmail.com
Power Systems Design - 2
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30
Power System Design Considerations
Power Systems Design - 2
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 Secondary
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Power Systems Design - 2
• Primary – non rechargeable batteries
• Secondary – rechargeable batteries
Electrical Power Battery Storage
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Power Systems Design - 2
Energy Storage
Not Rechargeable
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Power Systems Design - 2 Not Rechargeable
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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 Rechargeable
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Power Systems Design - 2 Rechargeable
New Technology
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Power Systems Design - 2
• Use of NiCd batteries required reconditioning
• Reconditioning not required for Li Ion batteries.
Reconditioning battery system
Close sw to crowbar battery
Close sw to crowbar second battery
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Power Systems Design - 2
How much Battery Charge Left?
Charging causes heating
Discharging 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-hrDepth of discharge (DOD) = percentage of battery capacity used in
discharge (75% DOD means 25% capacity remaining. DOD usually limited for long cycle life)Watt-hour capacity = stored energy of battery, equal to
A-hr capacity times average discharge voltage.Charge rate = rate at which battery can accept
charge (measured in A)Average discharge voltage = number of cells in series times
cell discharge voltage (1.25 v for
most commonly used cells)SSE -122
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Power Systems Design - 2
Considerations for power calculations
We have a battery that has a power capacity of:
1000mA (1000mAHrs)@ 1.2vIt 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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Power Systems Design - 2
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 Rechargeable
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Power Systems Design - 2
Questions?
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Morehead State UniversityMorehead, KY
Prof. Bob TwiggsRJTwiggs@gmail.com
Power Systems Design - 3
52SSE -122
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Power System Design Considerations
Power Systems Design - 3
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
Solar Panels - source
Charge Control
Batteries
Voltage
Bus
Voltage
DC/DC
Voltage
DC/DC
Subsystem
Subsystem
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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
• “Buck Up” 1 Li Ion battery - ~3.6v 5v
Requires less circuitry, more efficient to regulate down
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
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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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Power Systems Design - 3
Questions?
Morehead State UniversityMorehead, KY
Prof. Bob TwiggsRJTwiggs@gmail.com
Power Systems Design - 4
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Power Systems Design - 4
Power Systems or EPS
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Power Systems Design - 4
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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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5.6.
1350
1350
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Power Systems Design - 4
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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Power Systems Design - 4
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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Power Systems Design - 4
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 - 4
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Power Systems Design - 4
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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Power Systems Design - 4
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
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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?
Power Systems Design - 4
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Power Systems Design - 4
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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Power Systems Design - 4
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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Power Systems Design - 4
What if the cells were bigger?
Oh Oh!
Now you have only 4.4v in the string.
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Power Systems Design - 4
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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Power Systems Design - 4
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 mmSSE-122
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Power Systems Design - 4
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 - 4
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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 - 4Power Systems or EPS
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Power Systems Design - 4Power Systems or EPS
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Power Systems Design - 4Expanded subsystem control
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Power Systems Design - 4Expanded subsystem control
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Power Systems Design - 4
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 - 4Expanded 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
Power Systems Design - 4
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Gravity Gradient StabilizedPower Systems Design - 4
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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
Power Systems Design - 4
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Inertially StabilizedPower Systems Design - 4
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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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Power Systems Design - 4
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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