Input invariance as a method to reduce EMI filter interactions in Telecom DPS systems

Distributed power supply (DPS) systems are extensively used to supply different electronic equipment and systems such as e.g. telecom switching systems where switched-mode converters are supplying other switched-mode converters. Stringent electromagnetic compatibility (EMC) requirements necessitate the use of input filters as an individual filter for a converter, and as a common filter for a group of converters in order to suppress the electromagnetic interference (EMI) to acceptable level. The ratio of input and output impedances of the associated subsystems known as minor-loop gain is typically used to define the stability and performance indices for the DPS systems. Even if certain design rules may be established for the ratio, the associated impedances may be difficult quantitatively to be defined. This may force the system designers to use conservative design in order to avoid instability and degrading of dynamic performance. This paper proposes methods by means of which the interactions between the subsystems may be significantly reduced making the converters invariant to input phenomena in small-signal sense. This means that the input filter stability would be the only concern, and may be ensured based on the input power of the associated converters.