Design and Implementation of On-board Electrical Power ... - OUFTI-1

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The schematics is shown on figure 5.41.Figure 5.41: Schematics of the protection circuit.A breadboard prototype was made. The tests of this prototype learnt us that the outputvoltage is decreasing when the output current exceeds I thr (it was not specified in thedatasheet).5.6 Design of the antennas deployment circuit5.6.1 FunctionalityThe role of the antenna deployment circuit on the EPS is to connect or disconnect a resistorto the batteries bus. The system is itself controlled by the OBC. The resistor is a thermocutter the resistance of which is unknown. As it may require a large amount of power, theswitch on the EPS will be designed to be able to deliver up to 10W in this resistor. Thecontrol signal is picked up on two PIN of the PC104 connector. The command voltage will bedigital, with a low state at 0V and a high state at 3.3V. The antenna deployment is a criticalfunction, so redundancy is desired. It is the reason why two independent control signals areprovided.5.6.2 ImplementationThe converters may be unable to provide enough power. In addition, the system is suppliedon the output of one converter, a trouble in this converter would paralyze the deploymentsystem. This system will rather use the batteries bus. This means that the system is criticalon two counts: it must work, or the satellite will be silent, and it must not have a shortcircuit, or the batteries will quickly be emptied.Using two transistors in parallel will add redundancy to ensure that the system be activated,but doubles the risk to have a short circuit (if a heavy ion strikes one transistor).Using two transistors in series highly reduces the risk of short circuit, but increases the riskof a system malfunction.84
There are two envisaged solutions:1. The switch could be one single transistor with very high reliability, in other word, aflight model. This philosophy was adopted for the shunt regulator, as the problem wasvery similar. In this case the system is composed of one FET, one decoupling capacitor,one pull-down resistor and the thermo cutter. Both command lines are connected tothe gate of the transistor. The schematics of this circuit is shown of the left of figure5.42.2. The switch could be composed of four transistors in quad-mount (two parallel branchesof two transistors in series). In this way, there is redundancy against a risk of malfunction,and the risk of a short circuit is kept very low. The disadvantage is of coursethe required surface on the PCB. This solution will be useful if we can’t find a spacecertified FET. The system would be composed of four FETs and the thermo cutterplus two capacitors and two resistors for the decoupling. Each branch is controlled byone control signal. Controlling two FET in series with the same voltage will not causeproblems for this application (each transistor withstand the bus voltage and there isno critical requirements about the rise time). This is the circuit shown on the right offigure 5.42.Figure 5.42: Propositions for the antennas deployment system.5.6.3 LocationThe deployment system (switch and decoupling) will be located on the EPS PCB. Doing so,it is close to the power source. The required surface is not a concern since there are fewcomponents. The thermo cutter is located near the antennas.5.6.4 ComponentsNo flight model for a low V g s FET has been found (investigations have been done at ThalesAlenia Space to find such a component, without results).85
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AcknowledgementsI want to thank the
Page 4 and 5:
Contents1 Introduction 91.1 Cubesat
Page 6 and 7:
4.4.2 Mean case . . . . . . . . . .
Page 8 and 9:
B Power budget worksheet 106C Pictu
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design and the tests are delegated
Page 12 and 13:
Chapter 2Requirements of the EPS2.1
Page 14 and 15:
• The Single-Event Upset (SEU)Thi
Page 16 and 17:
the P-POD. RBF pins must fit within
Page 18 and 19:
Figure 2.6: Top view of the PC104 c
Page 20 and 21:
Chapter 3Design of EPS architecture
Page 22 and 23:
• Voltage (4) and current (5) at
Page 24 and 25:
Figure 3.6: The equivalent circuit
Page 26 and 27:
of our Lithium-Polymer batteries va
Page 28 and 29:
Figure 3.12: I-V curve of a solar p
Page 30 and 31:
3.3.3 CapacityA important value to
Page 32 and 33:
Parameter SLPB723870H4 SLPB554374HN
Page 34 and 35: of the batteries is kept between -2
Page 36 and 37: Over Charge Prohibition 4.275 ± 0.
Page 38 and 39: supplied in 5V. The circuit will be
Page 40 and 41: Chapter 4The Power Budget4.1 Introd
Page 42 and 43: Figure 4.1: P-V curve of a solar pa
Page 44 and 45: 4.3.2 Efficiency of convertersTo at
Page 46 and 47: Figure 4.3: Consumptions in % in me
Page 48 and 49: Chapter 5Electrical Design of EPS5.
Page 50 and 51: V outV in= D. (5.1)Since D ≤ 1, t
Page 52 and 53: The power losses in the inductor ar
Page 54 and 55: ∆i L,1 + ∆i L,2 = 0, (5.16)V in
Page 56 and 57: Using the value of ∆i L given by
Page 58 and 59: There is no data about the case to
Page 60 and 61: Capacitor selectionFour 10µF ceram
Page 62 and 63: • Output voltage: 5V.• Maximum
Page 64 and 65: Figure 5.12: Burst mode operation (
Page 66 and 67: Figure 5.14: Simplified schematics
Page 68 and 69: Figure 5.15: Worksheet for 3.3V con
Page 70 and 71: sequently, the k was chosen above 0
Page 72 and 73: where G 1 is the initial control-to
Page 74 and 75: Figure 5.21: Measured Bode diagram
Page 76 and 77: Figure 5.26: Equivalence between th
Page 78 and 79: C f =12πf f R 0f,L f = R 2 0f C f
Page 80 and 81: Figure 5.37: Schematics of the firs
Page 82 and 83: R KR >1.45V100mA − 1.3A35= 23.07
Page 86 and 87: A commercial model meets all requir
Page 88 and 89: Figure 5.45: Schematics of the heat
Page 90 and 91: PrefixX7X5Y5Z5SuffixTemperature ran
Page 92 and 93: 6.2.1 The second dissipation system
Page 94 and 95: • The antenna deployment system.
Page 96 and 97: 6.3.3 TestsThe engineering model of
Page 98 and 99: 7.3 ActivitiesAs OUFTI-1 is designe
Page 100 and 101: 8.1.2 DesignA model of Li-Po batter
Page 102 and 103: [15] Fabien Jordan, Phase B Electri
Page 104 and 105: TaK = 273 + TaC;%Photo-current ther
Page 106 and 107: Appendix BPower budget worksheetIn
Page 108 and 109: 108
Page 110 and 111: Appendix CPictures of the prototype
Page 112 and 113: Appendix DSchematics of the enginee
Page 114 and 115: 876543213V3 CONVERTER AND INPUT FIL
Page 116: 87654321ANTENNA DEPLOYMENT CIRCUITB
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