This is the EPS design team of MOVE speaking, we wanted to introduce you the system we designed:
EPS stands for electrical power supply so we are responsible for everything related to power on the satellite. This starts with the solar cells which will generate the power on MOVE-III and includes our battery system and the power distribution. We designed the so-called Backplane which is like the backbone of the satellite. Every other system can be plugged into the Backplane to get the power it needs and to be part of the satellite’s internal communication. This means the Backplane provides everything from power, stability, communication, and regulation, a subsystem could possibly need.
The boards that are plugged into the Backplane and can be replaced or switched are called standard subsystem boards or short SSB. Those are standardized boards that provide standard pins every subsystem can use if they need to or if the sensors they are using need a special protocol to communicate. The SSBs are designed to fit perfectly onto the Backplane. The thought behind this is to create a system that is as modular and extendable as possible. We could therefore fly our satellite with only three boards or also with boards at all eight slots of the Backplane - doesn’t affect the system as a whole.
Apart from the Backplane and the SSBs, a big part of EPS are the battery boards that carry the satellite’s batteries. They can be charged over the Backplane and of course power the whole system after the connection to an external source is removed. On ground, we manually charge them, in space they will be connected to the solar cells through the battery charge regulators (BCR) which regulate the current and voltage we will charge the batteries with. As we are flying with Li-Ion batteries, the charging process, involving the battery boards and the BCR, is not as easy as just shoot power into the batteries. We use extra software and a lot of control theory to do it but we are still not finished with the design process in this field.
The last part of the EPS system is the under voltage protection (UVP). In case the internal EPS microcontroller does not work properly, we lose this controller due to harsh space conditions or it just cannot handle a situation, we must have the possibility to shut down the whole satellite to prevent further damage. This might be the case if the batteries are running low on power, but the satellite is flying through an eclipse (meaning it flies in the shadow of the earth). The EPS controller is not capable to react to this scenario and MOVE-III will be shut down until it is back in the sun and can charge again. The UVP removes every power connection between the satellite and the charging system (battery boards, BCR, and solar cells). Only after the batteries are recharged to a certain percentage, the connection will be restored again.
This was a short overview of our system, we hope you enjoyed it and maybe we got you interested in power electronics!