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

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Chapter 4The Power Budget4.1 IntroductionThe goal of the power budget is to verify that the consumed power on board does not exceedthe produced power. The power budget is defined on a time interval. In our case, the choseninterval is one orbit. The power input over one orbit is computed for several scenarios (coldcase, mean case, and hot case). Then, the consumed power is estimated for several operationmodes of the CubeSat and the time sharing of these modes is discussed.4.2 Estimation of input powerThe maximum instantaneous electrical power that can be captured by solar cells is given by:whereP = ηA eff C s• η is the efficiency of the solar cells. It is expected to be 30% at BOL (Begin Of Life)and to drop to 23% at EOL (End Of Life).• A eff is the effective area of the solar cells. The effective area is the area of the projectionof the solar panels onto a plane perpendular to the direction of the solar rays. Themaximum value is 104.55cm 2 , and the mean value has been estimated to be 76.6cm 2 bysimulations [6].• C s is the solar constant, with a minimum value of 1, 321W/m 2 , a mean value of1, 358W/m 2 , and a maximum value of 1, 413W/m 2 [6].This formula would be useful if the extracted power from the solar cells was alwaysthe maximum power. With an MPPT system, the input power would be given by P =η conv ηA eff C s where η conv is the efficiency of the MPPT converter.40
As no MPPT system is used in our architecture, the input power must be estimated in adifferent way.The P-V curves of each solar panel were computed in Chapter 3 from the correspondingMatlab model. The power produced by a solar cell is mainly dependent on three parameters:• The insolation.• The applied voltage at its terminals.• The temperature.When these parameters are known, the input power from one solar panel can be deducedfrom the Matlab model.In real operating conditions, the power is most of time provided not by a single solarpanel, but by three of them. The mean effective area of solar panels A effMean is calculatedin [6]. Knowing the batteries voltage, can the mean input power be estimated by taking theinput power of one solar panel and multiply it by the effective areas ratio A effMeanA panelwhereA panel is the area of one panel?P mean (V batt ) ∼ = A effMeanA panelP panel (V batt (4.1)Figure 4.1 shows that the power produced by one panel is essencially proportional to thereceived light power for all voltages up to the MPP voltage (corresponds to the maximum ofthe P-V curve of the solar panel) at G nom . The figure also shows that the MPP voltage ishigher in the case of a less exposed panel. Equation 4.1 is thus true for all voltage up to theMPP voltage at G nom .Figure 4.2 shows that the MPP voltage is above 4.2V when the temperature is between-35 ◦ C and 15 ◦ C. Equation 4.1 is thus true for all voltage in the batteries voltage range (2.6Vto 4.2V) if the temperature is under 15 ◦ C.The produced power for a given effective area can thus be expressed as the power producedby one panel multiplied by the areas ratios when the temperature is under 15 ◦ C.4.3 Estimation of consumed powerThe consumed power in the CubeSat depends on the operating state of the electrical subsystems.For each subsystem, the operation modes and the corresponding consumptions onthe different power busses are listed in a worksheet (given in Appendix B). During the firststeps of the project, the consumptions were estimated from datasheets and simulations, butthese consumptions should be determined by direct measurements on prototypes as soon assuch prototypes become available. It will be important to keep an eye on any change inconsumptions resulting from changes in design and construction.A fraction of the power delivered on each power bus is lost in the power conditioning unit.The real amount of consumed power can then be computed using41
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 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 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
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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