This subsection deals with the generation, storage and distribution of energy for the satellite. To ensure the functionality of the other subsystems, a reliable energy supply is essential. The energy is generated by solar cells on the lateral surfaces of the satellite. A “Power Control and Distribution Unit” (PCDU) is used, which on the one hand charges batteries with the power from the solar cells and on the other hand distributes the power stored there to the other subsystems.
Lithium-ion batteries are planned for storing the energy. Special emphasis must be placed on good component properties, such as service life, possibilities for temperature control and protection against overcharging and deep discharge. Only if these conditions are given, the energy balance of the satellite can function as planned.
There are commercially available batteries that have been tested especially for space travel and meet the requirements of our mission. However, since these are very expensive and even ordinary batteries can be of sufficient quality, it is an option to order a large number of these and select the most suitable ones through our own tests.
In order to be able to test the functionality of the developed PCDU and the accumulators in our framework on Earth, a dummy is also to be built, which imitates the properties of the solar cells used later in orbit as well as possible.
In addition to the selection and development of the components, the observation of voltages, currents and temperatures is a central task of the Energy Subsection. For this purpose, appropriate sensors are installed at various positions in the circuits to track the operation of the individual components, check their functionality and detect problems at an early stage. An example of this is the temperature of the batteries, which must be kept constant despite large temperature fluctuations in orbit in order not to damage the batteries. However, the acquisition of raw data also offers good opportunities to reconstruct possible malfunctions or to investigate new issues after the satellite has been launched.
Several solar cells attached to the sides of the satellite will be used to generate energy. Different cell architectures and geometries provide different advantages in terms of efficiency, performance and price. For this purpose, we will create an overview of the common models on the market, collect the parameters and contact the companies.
The “Power Control and Distribution Unit” (PCDU) on the one hand regulates the voltage generated by the solar cells to a voltage suitable for charging the batteries and on the other hand transforms the voltage generated by the batteries to the system voltage required by the other subsystems. We are developing the necessary circuitry in cooperation with LibreCube, a team at ESOC, which is developing an open-source Cubesat platform. The first tests of the PCDU are planned for early 2020.
The simulation serves to predict the behavior of the power system. In doing so, various influences on the system must be taken into account. The orientation of the satellite relative to the sun, the crossing of the Earth’s shadow, the energy production by the solar cells, as well as the efficiency of the electronic components of the PCDU are to be simulated in order to finally enable an accurate and flexible model of the energy balance on the satellite. In order to be able to react as flexibly as possible to future design iterations and changing components, as many parts of the simulation as possible should be parametric.
For best possible cooperation with other subsections like the thermal subsection, the modeling environment OpenModelica is used.