Electrical Power System is responsible for power conversion from solar panels, energy storage in battery and power distribution to other subsystems. It is designed and it will be built by the EPS team of the PW-Sat2 project.

To generate electrical power from sunlight, we will use 12 pieces of space qualified triple-junction solar cells. And then the electrical power shall be harvested by corresponding circuits (MPPT regulated DCDC converters). To store energy a lithium-ion battery will be used.

The system should be as reliable as possible and simultaneously low cost is required. To meet these requirements the COTS components and redundancy of critical sub-circuits will be used.

EPS design

A simplified block diagram shows the main idea of the electrical power system:

MPPT regulators

There are three MPPT regulators which are responsible for converting electrical power which is harvested by solar panels. A single MPPT regulator consists of controlled DCDC converter, current and voltage measurement circuits.

Battery controller

This is a power stage for the battery controller feature. Both Controller A and B are responsible for controlling the power stage. Appropriate algorithms maintain the batteries in the suitable conditions.

Kill-switches

The kill-switch circuit ensures that the whole system is not active during launch. This circuit consists of two external electro-mechanical switches which are responsible to cut-off subsystems from both battery pack and solar panels.

Remove Before Launch

The RBL circuit ensures that the whole system is not active during transportation and storage. This circuit consists of internal cut-off circuits and external electromechanical switch. The electromechanical switch locks the internal cut-off circuits.

DCDC converters for 3V3 and 5V

DCDC converters are responsible for converting VBAT raw voltage to 3.3V and 5V. These voltages are supplied for subsystems to the PC-104 stack connector.
To protect both Main Power Bus (MPB) and DCDC converters, corresponding input LCL are applied.

Internal supply

This part provides supply voltages to internal EPS’ circuits.

Controllers

There are two independent controllers in the EPS. To increase reliability of the system, they are completely separated from point of view of electrical connections.

Distribution

Distribution contains current measurements, voltage measurements and RLCLs/LCLs for subsystems. RLCL are permanently turned-on, but LCLs are controlled with controller A. Controller B only controls redundant thermal knife for Sail.