Morehead State University Morehead, KY Prof. Bob Twiggs Power Systems Design - 1 1

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

3 Power Systems Design - 1 SSE -122

4 Power Systems Design - 1 SSE -122

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

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

7 Power Systems Design - 1 SSE -122

8 Power Systems Design - 1 New Technology SSE -122

9 Power Systems Design - 1 Sun spectral irradianceSolar cell responsePeak sun irradiance SSE -122

10 Power Systems Design - 1 SSE -122

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

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

13 Power Systems Design - 1 SSE -122

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

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

16 Power Systems Design - 1 SSE -122

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

18 Power Systems Design - 1 Peak Power SSE -122

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

20 Power Systems Design - 1 SSE -122

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

22 Power Systems Design - 1 Some Solar Notes SSE -122

23 Power Systems Design Sun Approx Cosine SSE -122

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

Power Systems Design Gravity Gradient Stabilized Sun SSE -122

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

27 Inertially Stabilized Power Systems Design - 1 Sun SSE -122

28 Power Systems Design - 1 Questions? SSE -122

Morehead State University Morehead, KY Prof. Bob Twiggs Power Systems Design

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

31 Power Systems Design - 2 SSE -122

32 Power Systems Design - 2 SSE -122

33 Power Systems Design - 2 PrimarySecondary SSE -122

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

35 Power Systems Design - 2 Energy Storage Not Rechargeable SSE -122

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

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

38 Power Systems Design - 2 Rechargeable Old Technology SSE -122

39 Power Systems Design - 2 Rechargeable Old Technology SSE -122

40 Power Systems Design - 2 Rechargeable Old Technology SSE -122

41 Power Systems Design - 2Rechargeable SSE -122

42 Power Systems Design - 2 Rechargeable New Technology SSE -122

43 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 SSE -122

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

45 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) 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

46 Power Systems Design - 2 Considerations for power calculations We have a battery that has a power capacity of: 1000mA 1.2v It can supply 1000mA for 1 hour or 500mA for 2 hours or 250mA for 4 a voltage of 1.2 v. Power rating of 1000mA x 1.2 v = 1.2 watt hours SSE -122

47 Power Systems Design - 2 Battery selection: SSE -122

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

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

50 Power Systems Design - 2 Rechargeable SSE -122

51 Power Systems Design - 2 Questions? SSE -122

Morehead State University Morehead, KY Prof. Bob Twiggs Power Systems Design SSE -122

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

54 Power Systems Design - 3 SSE -122

55 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 SSE -122

56 Power Systems Design - 3 Radios Fixed voltage busses (5v, -5v, 7v, 3.3v, 12v, etc.) Quieter – generates less noise on voltage bus SSE -122

57 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. SSE -122

58 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

59 Power Systems Design - 3 SSE -122

60 Power Systems Design - 3 SSE -122

61 Power Systems Design - 3

62 Power Systems Design - 3 What type of solar panel system does it take to generate 47.5 watts peak and 27.8 watts average?

63 Power Systems Design - 3

64 Power Systems Design - 3 Questions?

Morehead State University Morehead, KY Prof. Bob Twiggs Power Systems Design SSE-122

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

67 Power Systems Design - 4 SSE-122

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

69 Power Systems Design - 4 Take Solar Panel SSE-122

70 Power Systems Design SSE-122

71 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. SSE-122

72 Power Systems Design - 4 This dual junction cell 1.Has an efficiency of ~ 22% 2.Open circuit voltage ~ 2.2v 3.Size – 76 x 37 mm Lets go back and look at the solar cell. SSE-122

73 Power Systems Design - 4 This dual junction cell 1.Has an efficiency of ~ 22% 2.Open circuit voltage ~ 2.2v 3.Size – 76 x 37 mm Solar cell has an I-V curve like this SSE-122

74 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. SSE-122

75 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. Need to select a battery to design for solar panel voltage SSE-122

76 RechargeablePower Systems Design - 4 SSE-122

77 Power Systems Design - 4 Use a lithium ion battery Li 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 SSE-122

78 Power Systems Design - 4 SSE-122

79 Power Systems Design - 4 Use two lithium ion batteries Li 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. SSE-122

80 Power Systems Design - 4 Now we have: Two Li Ion batteries = 7.2 v nominal 5 cells for 11v to charge with. SSE-122

81 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. What is packing factor? Got SSE-122

Total Panel Area 82 Power Systems Design - 4 Packing Factor Packing Factor = Total Cell Area/ Total Panel Area Total Cell Area SSE-122

83 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 Power Systems Design - 4 SSE-122

84 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 SSE-122

85 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? SSE-122

86 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. SSE-122

87 Power Systems Design - 4 What if the cells were bigger? Oh Oh! Now you have only 4.4v in the string. SSE-122

88 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? SSE-122

89 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 Not got, but understand SSE-122

90 Power Systems Design - 4 How much power from these cells? 5 cells for 11v 11v One cell area = 76 x 37 mm = 2812 mm^2 Total cell area = 8*2812 = 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 watts = 7.5 watts For this dual junction cell 1.Has an efficiency of ~ 22% 2.Open circuit voltage ~ 2.2v 3.Size – 76 x 37 mm SSE-122

91 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 power 2.operating temperature 20 degrees.. Centigrade – 22% eff Got Not got, but understand Got Don’t forget, temperature counts a lot. SSE-122

92 Start here Tuesday for IdahoPower Systems Design - 4 SSE-122

93 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

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

95 Power Systems Design - 4 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 SSE-122

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

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

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

99 Power Systems Design - 4 SSE-122

100 Power Systems Design - 4 SSE-122

101 Power Systems Design - 4 Expanded subsystem control SSE-122

102 Power Systems Design - 4 Expanded subsystem control SSE-122

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

104 Power Systems Design - 4 Expanded subsystem control SSE-122

105 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

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

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

108 Gravity Gradient Stabilized Power Systems Design - 4 SSE-122

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

110 Inertially Stabilized Power Systems Design - 4 SSE-122

111 Power Systems Design - 4 SSE-122

112 Power Systems Design - 4 SSE-122

113 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% Some Solar Notes Power Systems Design - 4 SSE-122

114 Power Systems Design - 4 SSE-122

115 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

116 Power Systems Design - 4 Questions? SSE-122