Electronic Power System

The Electronic Power System (EPS) is designed to generate, store and distribute power to the satellite.

 
The EPS regulator board along with a solar panel and a battery cell

Power Generation
The power is generated through solar panels coated onto the outer walls of the satellite. Due to the small size of the satellite the total surface area of the panels are limited. This requires the use of high efficiency solar panels in order to produce the necessary power levels. The Spectrolab’s Ultra Triple Junction (UTJ) is chosen for this project. The panels have an approximate efficiency of 28%; the average power production during daylight has been calculated to be in the range of 4W.

Power storage
The power from the solar panels is regulated using a Maximum Power Point Tracker (MPPT). The MPPT is a regulator using the Peak Power Transfer (PPT) methodology which is preferred before the Direct power Transfer (DET) because the excessive heat is dissipated in the solar panels instead of inside the satellite structure. The regulator monitors the I-V curve of the solar panels and converts the voltage from the solar panels down to an appropriate charging voltage for the batteries.
Two 4.4Ah LiFePO4 battery packs from A123 Systems Inc. are chosen for the mission. These batteries were selected due to their thermal and chemical stability compared to lithium ion batteries. The drawback of LiFePO4 batteries is that they have somewhat lower energy density than conventional lithium ion batteries.

           Battery packs mounted inside the satellite structure

Power Bus
The EPS supplies a constant 3V bus to the satellites subsystem. The bus is voltage regulated, with current limiting sensors to protect the batteries from abuse by the subsystems. It was chosen for this mission to only provide a 3V bus because the discharge voltage for the LiFePO4 batteries is ~3.25V.