A New, Single Diode, Sequential Switching Shunt Regulator

Abstract

This paper describes the design improvement of a Sequential Shunt Switching Regulator (S3R) based on a power cell composed of one switching FET and one Diode connecting the Solar Array (SA) section to the Main Bus. This topology allows to minimize the S3R cells dimensions, to optimize the efficiency figures and complies with the electrical Single Point Failure Free (SPFF) requirement on the Main Bus. The single switching FET can cause the loss of one Solar array section if it fails in short circuit, while its failure in open can be compensated by the presence of one additional (spare) shunt section positioned on Main Bus to drain the power eventually in excess. If the series redundancy of the Diode is removed, its failure in short circuit, causes overload on the Main Bus when the switching FET turns ON. To avoid the possible subsequent failure in short circuit of the switching FET due to over-heating, with permanent loss of Main Bus, the maximum current drawn by the FET in failure condition and the duration of this operation mode must be strictly controlled in order to avoid thermal overstress and consequently thermal failure propagation. The adopted solution foresees a circuitry that controls the current in the FET, both the peak in the first transient and the subsequent limited value, and forces the FET in permanent open status after a short period, compatible with the overheat of the FET junction. No spurious cause leads to the permanent loss of the S3R section due to permanent activation of the protection, causing the switching element (FET) to be continuously open. In fact a dedicated circuit, activated by sensing of the Error Signal, unlatches the section to restore the power control. The presented design has found its first application in the PCDU for the COSMO-SkyMed Second Generation (CSG) satellite power system. A dedicated Elegant Bread Board of the S3R, integrated with the board designed to control the Battery Current and Voltage has been tested in the design and development plan of CSG PCDU.