Design techniques and methodologies for effective electromagnetic cleanliness in spacecraft power system

Electromagnetic compatibility (EMC) in electronics design is an indispensable aspect in the Design criteria/considerations of either terrestrial/ commercial systems/ equipments or Hi-Rel. systems like the spacecraft. EMC has a particular relevance to power systems design, as in most cases it is often the generator/source of Electrical/electromagnetic noise in any equipment or system. The predominant contributors to the electrical/electromagnetic noise, various effects of Electromagnetic noise in a Hi-rel. system like Spacecraft, the associated design guidelines/practices followed particularly in the spacecraft Power system design to minimize these effects of electromagnetic interference are briefly outlined. The Design techniques extends from basic choice of the materials, the associated fabrication/process methodologies, together with certain brute force methods of using additional components (Passive and active) to snub the amplitudes/excursions of the Electromagnetic noise and thereby aid in containment of the EMC levels. These methodologies are briefly explained. Power distribution is one of the major components of spacecraft power system. The type of wire/harness, the methodology of routing and the materials used contributes appreciably in the efforts aimed at the containment of electromagnetic noise. Generally radiation/arctarck resistant wires are used for high power lines, with live and return wires separately bundled and enclosed in additional layers of insulation before twisting to minimize the effects of electromagnetic noise for switching voltage/currents. As a basic precaution and guideline the power and signal lines in the wire harness are separated and enough care is taken to distribute' sensitive signal lines' through shielded wires. Generally in spacecraft power system a distributed Bus concept is preferred to centralized one, whereby individual users receive their power from the main bus via independent DC-DC converters. The DC-DC power converters and the Bus control is based on Switched mode concept from size and thermal management viewpoint, which is invariably accompanied by Electromagnetic noise. For the containment of this EM noise each power converters will have EMI filters both on the input and output sides. The switching elements, namely the Power transistors/MOSFETs of power conditioning/ control circuits and DC-DC converters are the main source of noise/EM interference on a spacecraft power Bus. Also the leakage inductance of the magnetic components, namely the inductors and transformers is the prime cause of the switching spikes which increases the levels of Electromagnetic noise. The use of snubbers across the switching elements, and the use of techniques like the Bifilar winding for transformers help in minimizing the switching noise amplitudes and aid in electromagnetic cleanliness.