Design and Implementation of On-board Electrical Power ... - OUFTI-1
Design and Implementation of On-board Electrical Power ... - OUFTI-1 Design and Implementation of On-board Electrical Power ... - OUFTI-1
supplied in 5V. The circuit will be located on the batteries card.component since it will not be used in space.This is not a critical3.8 Power conditioning unitMost subsystems have to be supplied with a regulated voltage. The power conditioning unitprovides the required voltages by converting power from the batteries bus. The list of requiredvoltages and corresponding maximum currents is given in chapter 2.Output 1 Output 2 Output 3Voltage [V] 3.3 5 7.2Max. Current[mA] 200 200 420Max. Power [mW] 660 1,000 3,024Table 3.6: Specifications for the power conditioning unit in term of output voltage,max.current, and max. power.Early in the project [3], it was decided to use three DC/DC converters to produce thedesired voltages. The batteries bus voltage will be converted to 5V and 7.2V by two ”boost”DC/DC converters, and to 3.3V by one ”buck/boost” converter.3.9 Protection circuitsThe protection of subsystems against over-current was in the initial objectives of the EPS. Acurrent-limiting circuit was chosen in [3]. This circuit prevents the current at its output toget over a chosen threshold. The circuit has a “FAULT” logical output that will be used toindicate to the OBC when a protection circuit detected an over-current. It also has a ON/OFFinput, that allows to turn on and off the power on the output of the current-limiting circuit.If such a circuit is located on the EPS, it can protect each power bus (3.3V, 5V, and7.2V), but not each subsystem individually (there is a limited number of power busses in thePC104 port). With the OUFTI-1 team, we took the decision to use a current-limiting circuiton each subsystem. The protection circuit will be located on the user’s cards. Doing so, alot of space is saved on the EPS card. There will be only one protection circuit on the EPScard: the protection circuit of the measurement circuits. Another advantage of this structureis that the OBC can turn the power on and off for each subsystem individually.3.10 Measurement system (Housekeeping parameters measurements)There are several measurement circuits on the EPS. Current sense IC’s, temperature probe,and voltage scalers (two resistors) are connected to analogic-to-digital converters. All the correspondingcircuits must be supplied with 3.3V. Like other subsystems, measurement circuitshave to be protected against over-current. The corresponding protection circuit is placed38
on the EPS. The protected 3.3V bus will be connected to a pin of the PC104 port.measurement circuits in the satellite will be supplied from this bus.All3.11 Antennas deployment circuitThe antennas deployment circuit is a switch controlling whether the current flows or not in athermo-cutter. It is used only one time, around 30 minutes after the insertion into orbit. Theamount of current was unknown when the architecture of the EPS was designed. It was thendecided to design a circuit able to deliver up to 10W of power in the resistor. Since then,the required power was determined. The thermo-cutter will have a resistance of around 10Ω,which corresponds to a maximum power of 1.76W if the batteries voltage is 4.2V.There is no DC/DC converter able to deliver 10W on the EPS. Therefore, the circuit willbe supplied directly from the batteries bus. Even if a converter was able to deliver enoughpower, there would be no real convenience to supply the antennas deployment circuit bymeans of this converter. A failure of the converter would cause the antennas not to deploy,and as a consequence the failure of the whole mission.3.12 About the experimental EPSThe Experimental Electrical Power Supply, or EPS2, is a digitally controlled flyback converter.Its power input is connected to the batteries bus and it provides a stabilized 3.3V output.The EPS2 is designed to be able to supply the 3.3V bus of the CubeSat.The EPS2 will be connected in parallel with the 3.3V converter of the EPS. A switch willallow the OBC to chose whether the output of EPS2 is connected to the 3.3V bus or to a testload. The exact means of connecting the output of the EPS2 with the output of the 3.3Vregulator of the main EPS remains to be determined. A Schottky rectifier can be inserted onthe output of the 3.3V converter (before the feed-back loop) if needed. The behaviour of thisparallel connection will need to be investigated in tests.We chose to let the EPS2 supply the 3.3V most of time. The 3.3V converter of the EPSwill be a back-up solution. Since the efficiency of the EPS2 is very low compared to the 3.3Vconverter, this must be taken into account in the power budget.39
- 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 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
on the EPS. The protected 3.3V bus will be connected to a pin <strong>of</strong> the PC104 port.measurement circuits in the satellite will be supplied from this bus.All3.11 Antennas deployment circuitThe antennas deployment circuit is a switch controlling whether the current flows or not in athermo-cutter. It is used only one time, around 30 minutes after the insertion into orbit. Theamount <strong>of</strong> current was unknown when the architecture <strong>of</strong> the EPS was designed. It was thendecided to design a circuit able to deliver up to 10W <strong>of</strong> power in the resistor. Since then,the required power was determined. The thermo-cutter will have a resistance <strong>of</strong> around 10Ω,which corresponds to a maximum power <strong>of</strong> 1.76W if the batteries voltage is 4.2V.There is no DC/DC converter able to deliver 10W on the EPS. Therefore, the circuit willbe supplied directly from the batteries bus. Even if a converter was able to deliver enoughpower, there would be no real convenience to supply the antennas deployment circuit bymeans <strong>of</strong> this converter. A failure <strong>of</strong> the converter would cause the antennas not to deploy,<strong>and</strong> as a consequence the failure <strong>of</strong> the whole mission.3.12 About the experimental EPSThe Experimental <strong>Electrical</strong> <strong>Power</strong> Supply, or EPS2, is a digitally controlled flyback converter.Its power input is connected to the batteries bus <strong>and</strong> it provides a stabilized 3.3V output.The EPS2 is designed to be able to supply the 3.3V bus <strong>of</strong> the CubeSat.The EPS2 will be connected in parallel with the 3.3V converter <strong>of</strong> the EPS. A switch willallow the OBC to chose whether the output <strong>of</strong> EPS2 is connected to the 3.3V bus or to a testload. The exact means <strong>of</strong> connecting the output <strong>of</strong> the EPS2 with the output <strong>of</strong> the 3.3Vregulator <strong>of</strong> the main EPS remains to be determined. A Schottky rectifier can be inserted onthe output <strong>of</strong> the 3.3V converter (before the feed-back loop) if needed. The behaviour <strong>of</strong> thisparallel connection will need to be investigated in tests.We chose to let the EPS2 supply the 3.3V most <strong>of</strong> time. The 3.3V converter <strong>of</strong> the EPSwill be a back-up solution. Since the efficiency <strong>of</strong> the EPS2 is very low compared to the 3.3Vconverter, this must be taken into account in the power budget.39
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