CubeSat project: experience gained and design methodology adopted for a low-cost Electrical Power System

Figures & data

Figure 1. Categories of launched nanosatellites.

Figure 2. Design process for EPS of CubeSat.

Figure 3. 1U CubeSat structure [27].

Table 1. Mission parameters.

Mission	Payload	Imaging Camera
	Mission Duration	One-year
Orbit	LEO/SSO	10:30 (LTDN)
	Altitude (Km)	500
	Semi-major axis (Km)	6878.14
	Eccentricity (e)	0
	Revolution Period T (mn)	94.72
	Eclipse Period (mn)	35.17
	Number of Orbits per day	15
Ground station	Beihang University	39.9824° N, 116.3488° E
	Satellite Visibility Period (mn)	9,04

Table 2. Power consumption of subsystems.

Subsystems	Minimum Power	Maximum Power
EPS	300 mW	400 mW
OBDH	130 mW	200 mW
TT & C	200 mW	2000 mW
ADCS	175 mW	1000 mW
Payload (Testing camera)	450 mW	450 mW

Table 3. Power of different mission modes.

Modes	Minimum power	Maximum power	Duration
Common mode	605 mW	705 mW	79,46 min
Mission mode	1125 mW	2050 mW	5 min
Communication mode	875 mW	3600 mW	5 min

Figure 4. Mission power consumption profile, baseline scenario (worst-case).

Figure 5. Proposed EPS configuration for CubeSat with open solar panels structure.

Figure 6. Flowchart of the implemented control strategy.

Figure 7. AzurSpace PV cell characteristics influenced by temperature: Curves of current and power versus voltage.

Figure 8. Proposed connection of solar cells for PV panel.

Figure 9. PV panel characteristics based on AzurSpace solar cells influenced by temperature: Curves of current and power versus voltage.

Figure 10. Generated power as a function of incident light angles: (a) Ideal case;(b) Worst case.

Figure 11. Solar panel PCB.

Table 4. Review of the Space commercially available Li-ion cell chemistries and their characteristics [44].

Battery technology	Chemical abbreviation	Characteristics
Lithium manganese oxide	LiMn2O4	Low cost, high discharge rate capability, good safety, low specific energy.
Lithium manganese nickel	LiNiMnCoO2	Low cost, high specific energy, good discharge rate capability, low resistance, good safety.
Lithium nickel cobalt aluminium oxide	LiNiCoAlO2	The highest specific energy and cycle life, lower discharge rate capability, good safety.
Lithium cobalt oxide	LiCoO2	Expensive, low specific energy, lower discharge rate capability, poor safety.
Lithium iron phosphate	LiFePO4	Highest discharge rate capability, low specific energy, excellent safety.

Figure 12. Discharge characteristics of rechargeable LiFePO₄ APR18650M1A battery.

Figure 13. Electrical schematic of the Power Storage Unit.

Figure 14. Power Storage Unit’s PCB.

Figure 15. Electrical circuit of DC-DC boost converter connected with solar panels.

Table 5. Boost converter parameter expressions for high and low duty cycles.

Low duty cycle	High duty cycle
$D_{min}=1-{\displaystyle \frac{V_{pv,max}}{V_{out,min}}}$	$D_{max}=1-{\displaystyle \frac{V_{pv,min}}{V_{out,max}}}$
$R_{min}={\displaystyle \frac{V_{out,min}^2}{P_{out}}}$	$R_{max}={\displaystyle \frac{V_{out,max}^2}{P_{out}}}$
IL=${\displaystyle \frac{V_{out,min}}{R_{min}}}{\displaystyle \frac{1}{1-D_{min}}}$	IL=${\displaystyle \frac{V_{out,max}}{R_{max}}}{\displaystyle \frac{1}{1-D_{max}}}$
$\mathrm{\Delta }{I}_{L,min}={\displaystyle \frac{I_{L,min}\mathrm{\Delta }{I}_L(\mathrm{\%})}{100}}$	$\mathrm{\Delta }{I}_{L,max}={\displaystyle \frac{I_{L,min}\mathrm{\Delta }{I}_L(\mathrm{\%})}{100}}$
$L_{min}={\displaystyle \frac{1}{2}}\left({\displaystyle \frac{V_{pv,max}}{\mathrm{\Delta }{I}_{L,min}}}(D_{min}{T}_s)\right)$	$L_{max}={\displaystyle \frac{1}{2}}\left({\displaystyle \frac{V_{pv,min}}{\mathrm{\Delta }{I}_{L,max}}}(D_{max}{T}_s)\right)$
$\mathrm{\Delta }{V}_{\text{out,min}}={\displaystyle \frac{V_{\text{out,min}}\mathrm{\Delta }{V}_{\text{out}}(\mathrm{\%})}{100}}$	$\mathrm{\Delta }{V}_{\text{out,max}}={\displaystyle \frac{V_{\text{out,max}}\mathrm{\Delta }{V}_{out}(\mathrm{\%})}{100}}$
$C_{1,min}={\displaystyle \frac{V_{out,min}}{8L_{min}\mathrm{\Delta }{V}_{out,min}{F}^2}}{D}_{min}$	$C_{1,max}={\displaystyle \frac{V_{out,max}}{8L_{max}\mathrm{\Delta }{V}_{out,max}{F}^2}}{D}_{max}$
$C_{2,min}={\displaystyle \frac{V_{out,min}}{2\mathrm{\Delta }{V}_{out,min}{R}_{min}}}{D}_{min}{T}_s$	$C_{2,max}={\displaystyle \frac{V_{out,max}}{2\mathrm{\Delta }{V}_{out,max}{R}_{max}}}{D}_{max}{T}_s$

Table 6. Parameters of boost converter obtained from the high and low duty cycle.

Parameters	Low duty cycle	High duty cycle
D	0,34	0.54
R(Ω)	10.52	12.5
IL (A)	0.963	1.225
Δ IL (A)	0.096	0.125
L (µH)	155.64	142.5
Δ Vdc2 (V)	0.132	0.144
Δ Vdc1 (V)	0.086	0.066
C2 (µF)	16.56	21.63
C1 (µF)	5.6	9.5

Table 7. DMC verification of boost converter obtained for high and low duty cycle.

DCM in high duty cycle	DCM in low duty cycle
$\frac{V_{pv}}{R}\frac{1}{{(1-D_{max})}^2}>\frac{V_{pv}}{R}{D}_{max}{T}_s\iff$	$\frac{V_{pv}}{R}\frac{1}{{(1-D_{max})}^2}>\frac{V_{pv}}{R}{D}_{max}{T}_s\iff$
$\frac{2L}{R{T}_s}>D_{min}(1-D_{min}{)}^2$	$\frac{2L}{R{T}_s}>D_{min}(1-D_{min}{)}^2$
1.14> 0.114	1.48> 0.148

Figure 16. Simulation of the boost converter with high duty cycle and low duty cycle: (Dashed line) Output currents; (Solid line with dots) Output voltages.

Figure 17. Electrical schematic of the Power Regulator Unit-based boost converters.

Figure 18. Power Regulation Unit’s PCB.

Figure 19. Flowchart of power regulation algorithm based on MPPT and BCR implemented in MCU.

Figure 20. Simulation of MCU circuit programmed with MPPT and BCR functions.

Figure 21. Simulation of MCU failure case: Boost converter driven by PWM signal from analogue MPPT selected by the arbitrating system.

Table 8. Truth table of arbitrating system for cold redundancy.

Outputs	Address	MPPT
X0, Y0 and Z0 to X, Y and Z	(ADRS_C1=A=0), (ADRS_C2=B=0) And (ADRS_C3=C=0)	Analogue
X1,Y1 and Z1 to X,Y and Z	(ADRS_C1=A=1), (ADRS_C2=B=1) And (ADRS_C3=C=1)	Digital

Figure 22. EPS design ETB: (a): (1): Computer; (2): Voltmeter; (3): Battery and Power Storage Unit; (4): MCU; (5): Power Regulation Unit; (6): Programmer and Debugging system; (7): Oscilloscope; (8) Power supply; (b): (9) Lighting system; (10): Assembled solar panel.

Figure 23. Line-up test block diagram of all EPS parts.

Figure 24. EL testing: (a) one solar cell, (b) one solar panel.

Figure 25. Solar panel characterization obtained from illumination test.

Figure 26. Experimental tests of the batteries: (a) charging characteristic; (b) discharging characteristic.

Figure 27. Charged battery level: (a) Battery voltage, (b) Voltage of electrical circuits.

Figure 28. (a) Input voltage 3.6V, (b) Input voltage 4.35V.

Figure 29. (a) High duty cycle PWM signal, (b) Low duty cycle PWM signal.

Figure 30. (a) Output voltage obtained by low duty cycle PWM signal, (b) Output voltage obtained by high duty cycle PWM signal.

Figure 31. Output PWM obtained by MCU: (a) Low duty cycle PWM signal, (b) High duty cycle PWM signal.

Table 9. Costs of EPS units.

EPS units	Cost
Solar panel	980 $
PSU	190 $
PRU	270 $
MCU	160 $

Figure 32. Distribution cost: (a) Solar panel, (b) PSU, (c) PRU and (d) MCU.

Table A1. Electrical characteristics of solar cells [37].

Open circuit voltage (mV)	2690
Short circuit current (mA)	519.6
Maximum power voltage (mV)	2409
Maximum power current (mA)	502.9
Efficiency (%)	29.6

Table A2. Electrical characteristics of battery cells [46].

Nominal capacity and voltage	1.1Ah, 3.3V
Recommended standard charge method	1.5A to 3.6V CCCV, 45 min
Recommended fast charge current	4A to 3.6V CCCV, 15 min
Maximum continuous discharge (A)	30
Operating temperature range (°C)	−30°C to +60°C
Core cell weight (g)	39

Figure A1. PIC16F877A pin connections.

Table A3. Acronyms list.

Acronyms	Signification
ADC	Analogue to Digital Converter
BCR	Battery Charge Regulator
CERs	Cost Estimating Relationships
CNES	Centre national d'études spatiales
DCM	Discontinuous Conduction Mode
D	Duty cycle
DC-DC	Direct Current to Direct Current
DET	Direct Energy Transfer
CNC	Computerised Numerical Control
COTS	Commercial-Off-The-Shelf
CT	Cost Total
ESA	European Space Agency
EL	Electroluminescence
ECSS	European Cooperation for Space Standardization
EMC	ElectroMagnetic Compatibility
EPS	Electrical Power System
HIL	Hardware In the Loop
GEO	Geostationary Earth Orbit
IC	Integrated Circuit
LEO	Low Earth Orbit
MCU	MicroController Unit
MOSFET	Metal Oxide Semiconductor Field Effect Transistor
MPPT	Maximum Power Point Tracking
PCB	Printed Circuit Board
P&O	Perturb and Observe
PPOD	Poly PicoSatellite Orbital Deployer
PPT	Peak Power Transfer
PRU	Power Regulation Unit
PSU	Power Storage Unit
PV	PhotoVoltaic
PWM	Pulse Width Modulation

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