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

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