Satellite Electrical Power Systems

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Power systems and their design considerations for Satellites

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  • Satellite Electrical Power Systems

    1. 1. Satellite Electrical Power Systems, design considerations Pratheek Manjunath 7th Semester, TC RVCE Bangalore
    2. 2. Contents 1. Power Budget Design Considerations 2. Primary Source – Solar Energy 3. Secondary Source - Batteries 4. Power distribution and management
    3. 3. Factors which determine the Power Budget 1. 2. 3. 4. Eclipse duration Altitude Orbit duration Battery charge/discharge cycles 5. Mission lifetime 6. Operating duration of Loads 7. Losses in the system GEO LEO N
    4. 4. Comparison between design factors of LEO and GSO 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
    5. 5. PRIMARY SOURCES – ENERGY GENERATION 1. SOLAR PANELS 2. FUEL-CELLS 3. NUCLEAR REACTORS SECONDARY SOURCES – ENERGY STORAGE AND REUSE 4. BATTERIES
    6. 6. Power Budget Solar array size is determined by: 1. Average power need for 1 orbit 2. Sun/eclipse ratio 3. 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
    7. 7. 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.
    8. 8. 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 2629%.
    9. 9. Solar Cells
    10. 10. Solar Arrays
    11. 11. 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 tumbling Solar cells are glued on the structure of the satellite The power is limited by the surface of the satellite
    12. 12. Secondary power source - Batteries The 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.
    13. 13. Space batteries, Ni technologies • Nickel- on GEO satellites – Heritage Hydrogen (Ni-new – No longer used for H2designs ) • Nickel-Cadmium (Ni-Cd) – Heritage on LEO satellites – No longer used for new designs
    14. 14. Space batteries, Li technologies • Lithium-ion – Higher energy density than the Nickel-based batteries – Heritage on LEO and GEO satellites, widely used for new designs • Lithium Polymer – Even higher energy density than Li-ion – Not yet qualified for use on satellite power subsystems
    15. 15. Comparison of typical Battery types Characteristics 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
    16. 16. Renowned Battery Manufacturers • SAFT – – – – – Dedicated development for space use Cells placed in parallel/series configuration Large single cell: 1.1 kg Battery cell balancing performed Relatively low shelf-life capacity fading • ABSL – – – – – Battery cells from commercial origin (Sony 18650HC) Cells placed in series/parallel configuration Small single cell: 42 g No Battery cell balancing performed Relatively high shelf-life capacity fading
    17. 17. Others; 1% Payload; 5% T&C; 5% Control; 4% Receiver; 5% HPA; 80% Power Distribution
    18. 18. Regulators To keep bus voltage constant in both from the point of view of the seasonal variations at the output of solar panel as well as backup batteries, it is essential to use regulators.
    19. 19. 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
    20. 20. Power distribution and management units Small PCU BAPTA (Bearing and Power transfer assembly) - Solar Array sun pointing by stepper motor - Peak power generation Power Control Unit – Directs power to the loads – Battery charge/discharge regulation – Communication to On-board Computer Power distribution Unit – Circuit protection – On/Off switching Large PCU
    21. 21. Architecture OBC Drive Loads Electr. Satellite bus SA SA BAPTA BAPTA SA pointing and power transfer PCU BAT PDU Circuit protection and power distribution

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