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

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3.3.3 CapacityA important value to know is the required minimum capacity of the battery for our CubeSat.The battery must provide enough energy to allow the CubeSat to be operational during eacheclipse. The consumed power during an an eclipse can be computed with the power budgetworksheet (Appendix).Assumptions:• Cold case (max. eclipse duration, heater on 24% of time).• D-STAR or AX-25 transmission turned on 25% of time.• 3.3V provided by EPS2.The power consumed during eclipse is around 1.2Wh (= 324 mAh at 3.7V). A capacityof 324 mAh is the strict minimum for the batteries.The capacity of Li-Pol batteries slightly decreases at each charge and discharge cycle. Agood practice to limit this effect is to chose a low Depth of Discharge (DoD). A DoD of 30%means that a battery is discharged of 30% of its capacity before being charged again. Theeffect of DoD is shown in Fig. 3.15 and 3.16 [25]. Several batteries (C - Nominal capacity= 0.80 Ah, D - Nominal capacity = 1.45 Ah and F - Nominal capacity = 1.05 Ah) arecompared, first with a DoD of 30% , and then with a DoD of 80%, at atmospheric pressureand in vacuum. The loss of capacity with a DoD of 30% is about the same than with a DoDof 80% after three times as many cycles. During the test, the charge rate is “C” and thedischarge rate is “C/2” (3.2). “C” is the nominal capacity of the battery. For a battery witha nominal capacity of 0.80 Ah, a discharge rate of C/2 means that the discharge current isequal to 400 mA.Figure 3.15: Capacity vs. number of cycles (cycling to 30% DoD).Discharge rateCharge rateTemperatureCC/2 + tapering20 ◦ CTable 3.2: Test conditions30
Figure 3.16: Capacity vs. number of cycles (cycling to 80% DoD).The orbit of OUFTI-1 will have a duration of around 103 minutes. This corresponds to5,103 cycles in one year. A DoD of 30% or less is recommended for this kind of application.The ideal capacity for our battery is thus at least 324mAh0.3= 1, 070mAh.3.3.4 RedundancySince the battery is a critical and sensible component, it is wise to add redundancy. Therewill be two batteries in parallel, connected to the main power bus (the main power bus canbe called “the batteries bus”). Using two batteries for redundancy means that the CubeSatmust be operational with only one battery. A second benefit of having two batteries is thereduction of the DoD. The DoD will be reduced to 15% or less, which will increase the lifespanof the batteries.3.3.5 KOKAM batteriesThe choice of batteries is discussed in [3]. A very interesting model was the Varta Poliflex Li-Pol cells. They are no longer being produced, and the SwissCube team strongly recommendsnot using Varta batteries that are more than two years old. Contacts have been taken (byPhilippe Ledent) with several battery manufacturers, and KOKAM accepted to provide thebatteries for OUFTI-1.Two models of KOKAM batteries were purchased, the SLPB554374H and the SLPB723870H4,the characteristics of which are compared in Table 3.3.From an electrical point of view, the SLPB723870H4 (1,500 mAh) was more interestingthan the SLPB554374H (1,250 mAh) since it has a better capacity and a lower impedance.However, the second model (i.e. SLPB554374H) was chosen for mechanical reasons. Thethickness of the SLPB723870H4 was too important to place two batteries on the batteriescard.The SLPB554374H cell has a nominal capacity of 1,250mAh. The depth of discharge willbe 26% for one cell and thus 13% for two cells. The voltage range of the batteries, and thusof the batteries bus, will be 2.7V to 4.2V. The maximum consumed power has been estimated31
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 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
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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