electrical power system
DESCRIPTION
Electrical Power System. By Aziatun Burhan. Overview. Design goal requirements throughout mission operation: Energy source generates enough electrical power Energy storage stores electrical power Power distribution distributes electrical power Power regulation controls electrical power - PowerPoint PPT PresentationTRANSCRIPT
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Electrical Power System
ByAziatun Burhan
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Overview
Design goal requirements throughout mission operation:
• Energy source generates enough electrical power • Energy storage stores electrical power• Power distribution distributes electrical power • Power regulation controls electrical power
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Power BudgetSubsystem Power consumption (W)
Total Power (inc. 20% safety margin)
Continuous operation
23.7
ADCS 4
Orbit Control 3.74
OBC 2
Power 5
Communication 3.05
Camera (idle) 2
Non-continuous operation
66
Thermal control ** 10
Propulsion ** 30
Camera ** 15
Total 89.7
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Mission Power Profile
Power Profile
0
10
20
30
40
50
60
70
80
0 1000 2000 3000 4000 5000 6000
time (s)
po
wer
(W
)
daylight
eclipse
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Trade studies summary• This trade study examines the option of using only non-
rechargeable battery vs solar cells+rechargeable battery system as satellite’s power source. To meet NANOsat requirements, a power source that has low mass and small size is desirable for this mission.
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Solar cells vs Battery• Factors that effect trade study: - Total power consumption and power profile during the
mission - Mission life of satellite : 24 hours - Mass and area constraints that come from NANOsat
requirement * Solar cells can produce lots of power with little increase in total mass * If power consumption is large, the mass and size of non-rechargeable battery could be greater. - Choice of orbit and type of attitude control - Operating environment
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Solar cells vs Battery• We choose solar cells as the main power source with
rechargeable battery to store energy and to provide power during eclipse
- Solar cells+ battery has little increase in mass for larger
increase in power consumption - Fewer non rechargeable battery that is qualified for
space application
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Solar cell vs Battery
Solar cell+battery Non rechargeable battery
Mass Less More
Power/mass High Low
Mission length Weeks-months Few hours-one/two days
Attitude/Orbit control
Optional / Dependant
Independant
Effect of Failure No power during eclipse
No power throughout mission
Thermal control Less dependant Extremely dependant
Cost Do you have cost estimates?
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Solar cells•Ultra triple junction Gallium Arsenide solar cell
• 28.0 % BOL efficiency
•2.31 V, 16.3 mA/cm² ( ~0.96 W/ cell)
•2.3gCustomized size:
3.69 cm
6.85cm
Area per cell: ~ 25cm²
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Solar cells layout & assemblies
Sides (A)
• 5 identical solar panels• Power source: Direct sunlight, at 45 ° angle from normal direction of plane• 91 UTJ GaAs solar cells per side - 13 solar cells per string : 30 V - 7 strings : 2.85 A• 40.68 Watt minimum per side during daylight • Dimension : 48 cm x 48 cm• Area: 2275 cm²
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Assumption:
•2 sides are exposed in direct sunlight at one time.
•Solar flux is at constant value of 1353 W/m^2
•Worst case hot temperature was used to find thermal efficiency for a solar cell , therefore the calculated power output from the a solar panel is the minimum value.
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Rechargeable Batteries
• Saft MPS 176065 Lithium-ion cells
• 8 cells in series in a battery box
• Capacity: 5.8 Ah
• Mean voltage: 3.6 V
• Battery mass: 1.4 kg (including casing)
• Maximum DOD: 70% for <500 cycles
• Charging method: Constant Voltage-constant current + balancing
• Space qualified
• 2 battery boxes (for redundant operation with one unit failed)
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• Energy storage requirements:
Peak power load: ~90 W Discharge time: 36 min (maximum) Charging time: 0.9 to 1 hour Charge/Discharge cycle / day: 16 Required battery capacity: 2.6 Ah for 75% DOD
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Demonstrationpower gererated and power stored per orbit
0
50
100
150
200
250
300
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
time (hr)
po
we
rge
ne
rate
d (
W)
/ c
ap
ac
ity
(w
.h)
ideal power from solar panel
battery capacity in W.h
power discharge at 1.5C
*will recheck the values this weekend
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Power Management & Distribution
•SmallSat power management electronics
•28V unregulated; MPPT; Modular & Scalable from 30W to 300W
•Consist of 3 main elements:
- Battery Charge Regulator (BCR)
- Power Conditioning Module (PCM)
- Power Distribution Module (PDM)
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Power Distribution Design
Power Bus
(~28 V)
DC-DC step down converter
DC-DC Step downconverter
ADCS
FCS
COMM
OBC
Payload (Camera)
Thermalcontrol
Propulsion Power
5V supply line
12 V supply line
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Power Distribution
** non continuous operation
•Continuous power per one orbit period: 23.7 W
•Maximum power per one orbit period: 89.7 W
•Average power per one orbit period: 47 W
•Average power during daylight: 42.5 W
•Average power during eclipse: 53 W
ADCS 5%
Orbit Control (FCS)5%
OBC3%
Power management7%
Communication4%
Camera (idle)3%
Thermal control **13%
Propulsion **40%
Camera **20%