Our aim is to provide the voltage and current required to power the satellite's payload sensor, the ADCS sensors, the on-board data processing chip, and the communication (RF) system that will allow us to transmit data to our ground station.
An EPS System usually consists of a combination of solar panels, Microcontrollers, sensors, and power converters. Our system will contain:
A preliminary list of system components and their datasheets can be found on the System Components List page. All our current projects are in Phoenix Projects.
NOTE: MPPT and Solar charge controllers usually come as one chip, but we might be separating the two given stock shortages.
We will be using 4 lithium ion batteries in series: datasheet
Updated batteries datasheet here, purchasing link here.
The MCU being used for EPS is the STM32G431RBT6. https://www.st.com/en/microcontrollers-microprocessors/stm32g431rb.html
The solar panels are located on the external faces of the satellite and are each made up of 8 solar cells. The solar panels are our source of power generation by using the photovoltaic effect of converting the solar energy from the Sun to electrical power. We are planning to use GaAs solar cells from AzureSpace. The solar panel will be connected to the MPPT module to supply the satellite with power.
Figure 1: GaAs solar cell from AzureSpace.
tRIPLE jUNCTION gAn cell (best EOL values -3G30C)
https://satsearch.co/products/azur-space-tj-solar-cell-3g30c-advanced
The purpose of MPPT is to ensure we are delivering the maximum amount of power from the solar panels to the downstream loads (the batteries and onboard systems). It is connected to the solar panels and to the main voltage bus. The reason an MPPT module is needed is because the photovoltaic cells vary in voltage depending on the amount of solar radiation it is exposed to and the temperature (this is known as the cell's I-V curve). The MPPT module is able to adjust its own impedance to track the maximum power point of the I-V curve and maintain the best energy conversion efficiency from the solar cells. The MPPT IC we are using uses the Constant Voltage (CV) algorithm.
This chip also performs charge controlling - it charges the battery when the solar panels are producing energy, and allows the battery to discharge (power the system) when the solar panels are no longer generating power (i.e., when the satellite is in eclipse or not facing the sun).
The battery management system is directly connected to the cells of our battery pack from the main voltage bus. The purpose of the management system is to ensure safe charge and discharge of our batteries and to extend their lifetime through cell balancing. The IC we are using allows for both autonomous and host-controlled passive cell balancing, as well as a long list of protection measures for each of our cells including and not limited to cell under-voltage/over-voltage protection, overcurrent charge/discharge protection, and under-temperature/over-temperature charge/discharge protection. It also provides a State of Charge readouts, calculated using the Coulomb Counting (CC) method.
The buck converter steps down the voltage from the main voltage bus of the satellite to the required voltage for the EPS MCU and the satellite's subsystems. Due to EPS' distributed architecture (more in Power System Architecture page), each buck converter will be implemented on the subsystem's PCB. A 5V and 3.3V converter have been designed but will be the responsibility of each subsystem to implement. Therefore, EPS will be connecting to each subsystem delivering the same power line that will interface with the system's unique buck converter.