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Power Processing Unit (PPU) for the CubeSAT. Carlos Thayer David Xiao. Introduction. The PPU is designed to meet specifications to power the CubeSat propulsion system called the microcavity discharge (MCD) thrusters. http://cubesat.ece.illinois.edu/CubeSat_3D.html. Project Overview.
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Power Processing Unit (PPU) for the CubeSAT Carlos Thayer David Xiao
Introduction • The PPU is designed to meet specifications to power the CubeSat propulsion system called the microcavity discharge (MCD) thrusters. http://cubesat.ece.illinois.edu/CubeSat_3D.html
Project Overview • Design Specifications • Operating temperature: 0-50 deg. Celsius • Input Voltage: 12V • Output Voltage: 3kV p-p • Output Frequency: >1MHz • Output Power: 10 W • Efficiency: >90% • Weight: 30g ( 3g/watt) • Circuit Lifetime: >60h • Design Modules • Voltage Source Inverter (VSI) -Timers -Gate Drivers -Switches • Transformer
Diagrams & Schematics Block Diagram VSI circuit with Timer (LM555) to Transformer
Voltage Source Inverter (VSI) • Designed to convert 12 V DC input into a 12 V peak-to-peak AC output driven at 1 MHz • LM555 Timers • BJT Emitter Follower Pair • Complementary MOSFET Switches
LM555 • 2 LM555 Timers -Astable -Monostable • Variable resistors allow duty cycle and frequency control • Astable circuit triggers monostable circuit • Timers drive BJT emitter follower pair
BJT Pair • Originally a BJT push-pull pair • Changed to NPN and PNP emitter followers with variable resistor between emitter and ground • Resistor allows for control of MOSFET switches by controlling current flow
Transformer • Specifications • 1 MHz operation • 1:250 turns ratio • Ferrite Toroid Cores • 22 AWG windings • 36 AWG windings
Transformer • Coilcraft CT1-Current Transformer
Transformer • Primary: 36 AWG • Secondary: 36 AWG
Transformer • Primary: 22 AWG • Secondary: 36 AWG
PCB • Software: OrCad PCB Editor
Efficiency Tests • Average Efficiency: 34% • 0.48 W dissipated on gate driver
Successes • VSI circuit can output 12 V peak-to-peak signal at 1 MHz • Noise in signal has been significantly reduced • Output can be stepped up with one transformer
Challenges • Stability • Circuit startup • Efficiency • Transformer • Costs/Availability • Large turns ratio • Stacking Transformers
Acknowledgements • Ariel Moctezuma • Professor Krein • YingyingKuai • Mark Smart and Dan Mast, Parts Shop