Power Analyses

Power Budget

Solar Array Sizing

Power Simulations

A series of dynamic power simulations were done using Simulink to further verify the design parameters for the power subsystem. This simulation will further be integrated with the AODCS simulations to provide more detailed results for the performance of the satellite, discover worst case scenarios, and plan ahead for low power cases. 

Under normal operation conditions, the power simulator shows that the battery will charge to 100% and during eclipses, the state of charge drops to around 93%, and goes back to 100% right after getting back to the sun. 

This was true for sun angles up to 45°, after which the spacecraft will enter a power negative state that depletes the batteries. 

In power negative cases, the fall of battery's state of charge results into autonomous switching of the power mode to low-power, survival, and critical hold mode. In the lower power modes, the spacecraft will consume less power, which in result, will help with storing more energy in the batteries. 

One of these worst cases were simulated with the approximate sun angle of 75°. Results below show how the switching of the power mode to critical hold helped preserving more energy and increasing the battery's state of charge. 

Generated Solar Power Vs. Temperature

The power simulations presented above assume a solar panel temperature of 28°C, which is consistent with the thermal simulation results. It is worth noting that the power generated by these solar panels are negatively affected when their temperature rises. 

Figures below shows the P-V and I-V curves of one string of the solar panels at different temperatures. Please note that, because our power system uses DET, the operation voltage of the solar panels will stay consistent as it is dictated by the main bus voltage (from battery pack). This means that at high temperatures, the generated solar power will reduce significantly as the battery voltage approaches full state of charge which corresponds to a bus voltage of 7.3V.