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

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Chapter 3Design of EPS architecture3.1 IntroductionFrom the analysis of the EPS architecture of other CubeSats by Philippe Ledent, two decisionswere taken [3]:• The main power bus is not regulated.• There is no Maximum Power Point Tracking.In this chapter, the design of the Electrical Power System (EPS) of OUFTI-1 is builtstep-by-step. The solar cells and the batteries are analyzed first, because their characteristicsdetermine the design of the architecture. The batteries have to be protected against overdischargeand over-charge. It is the role of the battery protection circuits and the dissipationsystem. A battery heater circuit is also inserted in the design because the temperature of thebatteries must be kept over 0 ◦ C. There is an USB battery charger to charge the batteries asnecessary before launch. The power conditioning unit provides three stabilized voltages tosupply the subsystems of OUFTI-1. It is composed of three DC/DC converters. The EPSalso includes several circuits for housekeeping parameters measurements and a circuit for thedeployment of the antennas. The current architecture of the EPS is illustrated in figure 3.1.3.2 Solar CellsThe first element of an EPS is the power source. The more practical power source for satellitesis without contestation a set of solar cells.3.2.1 TheoryA solar cell is a semiconductor device that converts sunlight energy into electric energy bythe photovoltaic effect. A basic solar cell consists of a large-area silicon (Si) P-N junction.All solar cells are characterized by their current versus voltage curve (I-V curve). In the dark,20
Figure 3.1: Block diagram of EPS.the I-V curve of a solar cell is the same as that of a reverse-biased diode (Fig. 3.2). Whenphotons with enough energy (higher than the silicon band gap value) penetrate the solar celland hit the semiconductor material, the density of mobile electron-hole pairs is increased.The I-V curve is then moved upward (Fig. 3.3). More advanced solar cells can be made ofother semiconductors, like gallium arsenide (GaAs), and have several junctions.Figure 3.2: I-V curve of Si cell in the dark. Figure 3.3: I-V curve of Si cell in the light.A power versus voltage curve (P-V curve) can be derived from the I-V curve. The P-V curve has a maximum, called the Maximum Power Point (MPP). Manufacturers rarelyprovide the I-V curve of their solar cells, but some important values (Fig. 3.4):• The open-circuit voltage (1) on Figure 3.4• The short-circuit current (2) on Figure 3.421
Page 2 and 3: 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
Page 10 and 11: 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 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 84 and 85:
The schematics is shown on figure 5
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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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