A Power Control and Distribution Unit for Small Satellite Platforms

This paper presents a “Medium Power” compact, light and low cost PCDU (Power Control and Distribution Unit) which has been designed as a modular and configurable equipment for Low Earth Orbit (LEO) missions with a maximum power capability of 1500 W. The PCDU supports a maximum of 4 independent power inputs (up to 75 V), and provides a 28 V unregulated power bus. Maximum Power Point Tracking (MPPT) is independently performed on each input; MPPT relies on buck regulators with direct drive capability, operating in ‘N+1’ cold redundancy. The latter feature, together with the full cold redundancy of the Control Unit inside the PCDU, makes the device fully compliant with the Single Point of Failure free requirement. Moreover, the passive balancing managed by the PCDU guarantees the correct distribution of the cells charge, and contributes in improving the battery reliability. The unregulated bus is protected and distributed through nominal plus redundant LCL/RLCL and fuse protected lines for heaters and HDRMs. A cross-strapped architecture allows to control both nominal and redundant protected outputs from the nominal or redundant section of the unit, at the same time maximizing the PCDU availability. The PCDU, which is fully monitored, controlled and configured through the N+R CAN bus, can be easily tailored for various missions since its functionalities are segregated in different and specific stackable electronic boards (no backplane is used), and FPGAs are programmable. Finally, to balance the equipment radiation hardness and reliability figure versus costs, the PCDU has been designed with a mixed approach: COTS based supported by Sitael heritage [1] [2] and scheduled radiation tests, and the usage of MIL/Space qualified components for critical functions.