satellite electrical power systems
TRANSCRIPT
Satellite Electrical Power Systems, design considerations
Pratheek Manjunath7th Semester, TC
RVCEBangalore
Contents
1. Power Budget Design Considerations
2. Primary Source – Solar Energy
3. Secondary Source - Batteries
4. Power distribution and management
1. Eclipse duration2. Altitude3. Orbit duration4. Battery charge/discharge
cycles5. Mission lifetime6. Operating duration of Loads7. Losses in the system
GEOLEO
N
Factors which determine the Power Budget
Factor LEO GSO
Altitude Upto 2,000 km > 35,000 km
Orbit Duration 88 – 127 min 24 hours
Eclipse Duration 20 – 35 min 0 – 72 minutes
Mission Lifetime 7 years 15 years
Average Battery cycles 300 1,350
Discharge depth 20% 80%
Application Remote sensing Telecommunication, Weather forecast
Comparison between design factors of LEO and GSO
PRIMARY SOURCES – ENERGY GENERATION
1.SOLAR PANELS2.FUEL-CELLS3.NUCLEAR REACTORS
SECONDARY SOURCES – ENERGY STORAGE AND REUSE
4.BATTERIES
Power Budget
Solar array size is determined by:
1. Average power need for 1 orbit2. Sun/eclipse ratio3. Losses in the system
Battery sizing is determined by:
1. Eclipse power need
2. Eclipse duration
3. Capacity fading (due to mission lifetime and charge/disch. cycles
4. Losses in the system
Primary Power Source - Solar Arrays
• A solar cell is composed of a semiconductor material and converts photons to electrons.
• The solar cells work on the principle of photovoltaic effect.
Solar Arrays
• The solar flux is reflected, absorbed by the solar cell or crosses it• Every absorbed photon whose energy is greater than
semiconductor gap is going to release an electron and to create a positive « hole » (lack of electron). This electron is part of the crystalline network
• Photons with excess energy dissipate it as heat in the cell, leading to reduced efficiency
• An electrical field is introduced in the cell in order to separate this pair of opposite charges
• The efficiency of Silicon semiconductor is 17-19%, whereas GaAs is 26-29%.
Solar Cells
Solar Arrays
Solar Array types
• Rotating wings– Satellite can be earth-pointing
Provides 1 degree of freedom
• Fixed wings– Satellite must be sun-pointing as the
panels are attached rigidly to the body
• Body-mounted
Satellite can be tumblingSolar cells are glued on the structure of the satelliteThe power is limited by the surface of the satellite
Secondary power source - BatteriesThe number and type of batteries depends on:
• Expected life of satellite.• Type of Orbit – LEO/MEO/GEO• Backup power required.• Charging cycles.• Extent of discharge or load.• Temperatures of operation.
Space batteries, Ni technologies• Nickel-Hydrogen (Ni-H2)
––
Heritage on GEO satellitesNo longer used for new designs
• Nickel-Cadmium (Ni-Cd)––
Heritage on LEO satellitesNo longer used for new designs
Space batteries, Li technologies• Lithium-ion
– Higher energy density than theNickel-based batteriesHeritage on LEO and GEO satellites, widely used for new designs
–
• Lithium Polymer– Even higher energy density than
Li-ionNot yet qualified for use on satellite power subsystems
–
Comparison of typical Battery typesCharacteristics Ni-Cd Ni-H2 Ag-Zn
Energy Density 25 70 120
Life Cycle High Highest Low
Optimum Operating Temp
-10 to 25 10 to 15 Better
Voltage Constant Discharge
Not as good as NiCd
Poor
Charge Discharge Cycles
1000 900 200
Suitability Up to 7 years Up to 10 years Short life satellites
Renowned Battery Manufacturers
• SAFT–––––
Dedicated development for space useCells placed in parallel/series configurationLarge single cell: 1.1 kgBattery cell balancing performedRelatively low shelf-life capacity fading
• ABSL–––––
Battery cells from commercial origin (Sony 18650HC)Cells placed in series/parallel configurationSmall single cell: 42 g
No Battery cellRelatively high
balancing performedshelf-life capacity fading
Payload5%
T&C5%
Control4%
Receiver5%
HPA80%
Others1%
Power Distribution
Regulators
To keep bus voltage constant in both fromthe point of view of the seasonal
variationsat the output of solar panel as well asbackup batteries, it is essential to useregulators.
The types of voltage regulators 1. Series regulator.2. Shunt regulator.3. Switch mode regulator.
For constant loads - shunt regulators can be used
large fluctuations of input supply - switch mode varying loads - series regulators
Power distribution and management units
BAPTA (Bearing and Power transfer assembly)
- Solar Array sun pointing by stepper motor- Peak power generation
Power Control Unit–––
Directs power to the loadsBattery charge/discharge regulationCommunication to On-board Computer
Power distribution Unit––
Circuit protectionOn/Off switching
Small PCU
Large PCU
SA BAPTA
DriveElectr
Architecture
Loads.
Satellite bus
SA pointing and Circuit protectionand power distributionpower transfer
BAT
OBC
SA BAPTA PCU PDU