Power Systems Design 1 Morehead State University Morehead

Power Systems Design - 1 Morehead State University Morehead, KY Prof. Bob Twiggs RJTwiggs@gmail. com

Power Systems Design - 1 Power System Design Considerations System Requirements Sources Storage Distribution Control SSE -122

Power Systems Design - 1 SSE -122

Power Systems Design - 1 SSE -122

Power Systems Design - 1 Operating regimes of spacecraft power sources SSE -122

Power Systems Design - 1 Operating regimes of spacecraft power sources SSE -122

Power Systems Design 1 SSE -122

Power Systems Design - 1 New Technology SSE -122

Power Systems Design 1 Solar cell response Peak sun irradiance Sun spectral irradiance SSE -122

Power Systems Design - 1 SSE -122

Power Systems Design - 1 Dual Junction Cell Added by second junction SSE -122 Efficiency

Power Systems Design - 1 Use of the Sun’s Spectrum SSE -122

Power Systems Design - 1 SSE -122

Power Systems Design 1 Triple Junction Cell Added by second junction Added by third junction SSE -122 Efficiency

Power Systems Design - 1 Good Efficiency Reduce Efficiency SSE -122

Power Systems Design 1 SSE -122

Power Systems Design –I 10/21/10 Max Cell Current when short circuit Max Cell Voltage when open circuit SSE -122 Ended

Power Systems Design 1 Peak Power SSE -122

Power Systems Design - 1 String of cells Add cell voltages to get string voltage SSE -122 Solar Cell Strings Parallel strings to cover panel

Power Systems Design 1 SSE -122

Power Systems Design - 1 Shadowing Kills all power SSE -122

Power Systems Design - 1 Some Solar Notes SSE -122

Power Systems Design - 1 Approx Cosine Sun SSE -122

Power Systems Design - 1 Satellite Orbit Parallel Sun Rays Eclipse Sun Earth SSE -122

Power Systems Design - 1 Gravity Gradient Stabilized Sun SSE -122

Power Systems Design 1 Passive Magnetic Stabilized N N S S N N S Sun S N N N S SSE -122 S N S

Power Systems Design 1 Inertially Stabilized Sun SSE -122

Power Systems Design - 1 Questions ? SSE -122

Power Systems Design - 2 Morehead State University Morehead, KY Prof. Bob Twiggs RJTwiggs@gmail. com

Power Systems Design - 2 Power System Design Considerations System Requirements Sources Storage Distribution Control SSE -122

Power Systems Design - 2 SSE -122

Power Systems Design - 2 SSE -122

Power Systems Design - 2 Primary SSE -122 Secondary

Power Systems Design - 2 Electrical Power Battery Storage • Primary – non rechargeable batteries • Secondary – rechargeable batteries SSE -122

Power Systems Design 2 Not Rechargeable Energy Storage SSE -122

Power Systems Design - 2 Not Rechargeable SSE -122

Power Systems Design - 2 Not Rechargeable Not Good SSE -122

Power Systems Design - 2 Rechargeable Old Technology SSE -122

Power Systems Design - 2 Rechargeable Old Technology SSE -122

Power Systems Design - 2 Rechargeable Old Technology SSE -122

Power Systems Design - 2 SSE -122 Rechargeable

Power Systems Design 2 Rechargeable New Technology SSE -122

Power Systems Design - 2 Close sw to crowbar • Use of Ni. Cd batteries required reconditioning crowbar battery second battery • Reconditioning not required for Li Ion batteries. Reconditioning battery system SSE -122

Power Systems Design - 2 How much Battery Charge Left? Discharging causes heating Charging causes heating SSE -122

Power Systems Design - 2 Batteries Most common form of electrical storage for spacecraft Battery terms: Ampere-hour capacity = Depth of discharge (DOD) = Watt-hour capacity = Charge rate = charge Average discharge voltage = SSE -122 total capacity of a battery (e. g. 40 A for 1 hr = 40 A-hr 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. rate at which battery can accept (measured in A) number of cells in series times cell discharge voltage (1. 25 v for most commonly used cells)

Power Systems Design 2 Considerations for power calculations We have a battery that has a power capacity of: 1000 m. A (1000 m. AHrs)@ 1. 2 v It can supply 1000 m. A for 1 hour or 500 m. A for 2 hours or 250 m. A for 4 hours @ a voltage of 1. 2 v. Power rating of 1000 m. A x 1. 2 v = 1. 2 watt hours SSE -122

Power Systems Design - 2 Battery selection: SSE -122

Power Systems Design 2 Considerations for power calculations Two batteries in series. SSE -122

Power Systems Design - 2 Considerations for power calculations Two batteries in parallel. SSE -122

Power Systems Design - 2 SSE -122 Rechargeable

Power Systems Design - 2 Questions ? SSE -122

Power Systems Design - 3 Morehead State University Morehead, KY Prof. Bob Twiggs RJTwiggs@gmail. com SSE -122

Power Systems Design - 3 Power System Design Considerations System Requirements Sources Storage Distribution Control SSE -122

Power Systems Design - 3 SSE -122

Power Systems Design - 3 Power Systems Design 3 or EPS Charge Control Solar Panels - source Batterie s SSE -122 Subsyste Voltagem DC/DC Voltage Subsyste Bus Voltage DC/DC m

Power Systems Design 3 Radios • Fixed voltage busses (5 v, -5 v, 7 v, 3. 3 v, 12 v, etc. ) • Quieter – generates less noise on voltage bus SSE -122

Power Systems Design - 3 • DC/DC Converter/Regulators • Regulate 2 Li Ion batteries - ~7. 2 v 5 v Requires less circuitry, more efficient to regulate down • “Buck Up” 1 Li Ion battery - ~3. 6 v 5 v Requires more circuitry, less efficient to “buck up” voltage. SSE -122

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 SSE -122

Power Systems Design 3 SSE -122

Power Systems Design - 3 SSE -122

Power Systems Design 3

Power Systems Design - 3 What type of solar panel system does it take to generate 47. 5 watts peak and 27. 8 watts average?

Power Systems Design 3

Power Systems Design - 3 Questions ?

Power Systems Design - 4 Morehead State University Morehead, KY Prof. Bob Twiggs RJTwiggs@gmail. com SSE-122

Power Systems Design - 4 Power Systems or EPS SSE-122

Power Systems Design - 4 SSE-122

Power Systems Design - 4 Look at the parts of the EPS SSE-122

Power Systems Design - 4 Take Solar Panel SSE-122

Power Systems Design - 4 1350 5. 6. SSE-122

Power Systems Design - 4 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. SSE-122

Power Systems Design - 4 Lets go back and look at the solar cell. This dual junction cell 1. Has an efficiency of ~ 22% 2. Open circuit voltage ~ 2. 2 v 3. Size – 76 x 37 mm SSE-122

Power Systems Design - 4 Solar cell has an I-V curve like this This dual junction cell 1. Has an efficiency of ~ 22% 2. Open circuit voltage ~ 2. 2 v 3. Size – 76 x 37 mm SSE-122

Power Systems Design - 4 Looked at the solar cell. This dual junction cell 1. Has an efficiency of ~ 22% 2. Open circuit voltage ~ 2. 2 v 3. Size – 76 x 37 mm What are the attributes of a solar panel? 1. 2. 3. 4. 5. SSE-122 Total output power of solar panel. Voltage of solar panel. Maximum packing factor. Efficiency of the solar cells. Operating temperature of the panels.

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. SSE-122 Total output power of solar panel. Voltage of solar panel. Maximum packing factor. Efficiency of the solar cells. Operating temperature of the panels.

Power Systems Design - 4 SSE-122 Rechargeable

Power Systems Design - 4 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. 2 v 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. 2 v/string)/(2. 2 v/cell) = 1. 9 or 2 cell for a string voltage of 4. 4 v SSE-122

Power Systems Design - 4 SSE-122

Power Systems Design - 4 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. 3 v 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. 3 v/string)/(2. 2 v/cell) = 3. 77 or 4 cell for a string voltage of 8. 8 v Lets be conservative and use 5 11 v. SSE-122 cells for

Power Systems Design - 4 Now we have: Two Li Ion batteries = 7. 2 v nominal 5 cells for 11 v to charge with. SSE-122

Power Systems Design - 4 What is packing factor? What are the attributes of a solar panel? 1. 2. 3. 4. 5. SSE-122 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.

Power Systems Design 4 Packing Factor Total Cell Area Total Panel Area Packing Factor = Total Cell Area/ Total Panel Area SSE-122

Power Systems Design - 4 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? SSE-122

Power Systems Design - 4 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? SSE-122

Power Systems Design - 4 Now we have: 5 cells for 11 v where the string has all of the cells hooked in series Total Panel Area 11 v How do you mount these 5 cells on this panel? SSE-122

Power Systems Design - 4 How do you mount these 5 cells on this panel? NO! Visually we can see a very poor packing factor. SSE-122 OK!

Power Systems Design - 4 What if the cells were bigger? Oh Oh! Now you have only 4. 4 v in the string. SSE-122

Power Systems Design - 4 Got a cube? Put other cells on another face? Can’t do. All cells for a single string must be on same face. SSE-122

Power Systems Design - 4 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? SSE-122

Power Systems Design - 4 How much power from these cells? 5 cells for 11 v One cell area = 76 x 37 mm = 2812 mm^2 Total cell area = 8*2812 = 22496 mm^2 = 2. 25 x 10 -2 m^2 We have 1350 watts/m^2 from the sun in space Direct power = (1350 w/m^2) x (2. 25 x 10 -2 m^2) = 34. 4 watts 11 v Converted power = direct power x cell efficiency = 34. 4 w x 0. 22 eff = 7. 5 watts For this dual junction cell 1. Has an efficiency of ~ 22% 2. Open circuit voltage ~ 2. 2 v 3. Size – 76 x 37 mm SSE-122

Power Systems Design - 4 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. SSE-122

Power Systems Design - 4 SSE-122 Start here Tuesday for Idaho

Power Systems Design - 4 Now that we have beat our way through the solar panel design ----- lets go look at the some more parts of the EPS. SSE-122

Power Systems Design - 4 Power Systems or EPS What is this? SSE-122

Power Systems Design - 4 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. SSE-122 Panel 2

Power Systems Design - 4 Power Systems or EPS What is this R ? V Measure current by measuring voltage across a low resistance precision resistor SSE-122

Power Systems Design - 4 SSE-122 Power Systems or EPS

Power Systems Design - 4 SSE-122 Power Systems or EPS

Power Systems Design - 4 SSE-122

Power Systems Design - 4 SSE-122

Power Systems Design - 4 SSE-122 Expanded subsystem control

Power Systems Design - 4 SSE-122 Expanded subsystem control

Power Systems Design - 4 What does a charge regulator do? 1. 2. 3. 4. SSE-122 Controls voltage from PV to battery Controls rate of charge Prevents overcharging Can “boost” or “buck” PV voltage to match battery needs.

Power Systems Design - 4 SSE-122 Expanded subsystem control

Power Systems Design - 4 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. SSE-122

Power Systems Design - 4 Consider the satellite’s attitude control for solar power generation. SSE-122

Power Systems Design - 4 Satellite Orbit Parallel Sun Rays Eclipse Sun Earth SSE-122

Power Systems Design - 4 Gravity Gradient Stabilized SSE-122

Passive Magnetic Stabilized Power Systems Design - 4 N N S S N N S S S N N N S SSE-122 S N S

Power Systems Design - 4 SSE-122 Inertially Stabilized

Power Systems Design - 4 SSE-122

Power Systems Design - 4 SSE-122

Power Systems Design - 4 Some Solar Notes • Power from sun in orbit ~ 1350 watts/meter 2 • Power from cells on ground ~ 35% less than in space • Can get some power form albedo – earth shine ~ 35% SSE-122

Power Systems Design - 4 SSE-122

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. SSE-122

Power Systems Design - 4 Questions? SSE-122