So, I have been in ESTCube-1 Electrical Power System (EPS) subsystem for a while, and my stay in there has gave me some ideas and thoughts, how to make one. I also looked on the CubeSatShop Power system category. New systems should combine the simplicity of those designs and the efficiency of our impossible to assemble monster system.
Random commercial EPS usually have - series solar cells, boost maximum power point trackers (MPPT), series 7.4V 18650 based liion battery and finally - two big and slow (~200 kHz) buck converters for 5 V and 3.3 V rails.
Short overview of our system: parallel solar cells with 6 inputs, boost converter with MPPT, current limit, 2 parallel liion cells with separate protection, double 5 V and 3.3 V converters (~600 kHz) with protection on input and output. And to top it all off 2 PCBs worth of measurement devices that turn out couple of thesis and articles worth of data. Although cool from university point of view - not cool at all from buyers. Also because of the device densities the thing is unsolderable with reflow.
The power rating of 1U system is fixed with solar panel size. ESTCube-1 assumes average of 1W of power and maximum at about 3W. Battery size is normally 16 Wh, that corresponds to 16h / 10 orbits of charging. Our rails have up to 600 mA output, NanoPower P31u have 5A output rails. Also when operating on low Earth orbit the radiation and temperature are not very big problems. After fixing some basic requirements, the design itself can be optimized for size and weight.
- Mechanically compatible with PC104 standard
- Automotive temperature range
- Duplicated outputs
- Raw battery outputs current limit up to several amperes (for burning resistors etc.)
- Duplicated 3.3V and 5 V rails with current limit
- Dual parallel batteries with around 15 Wh of energy
- Battery temperature monitoring and heating
- I2C, UART or SPI communication for information (battery status, fault codes)
- As thin and light as possible