arXiv:2611.05683v1 Announce Type: new Abstract: In complex grid scenarios, with many power electronics (PE) converters connected, having specifications for converters can ease the design process. A practical approach is to impose the specifications on the converter's small-signal impedance in the frequency domain. This is advantageous since impedance is a physical property that can be measured. This paper focuses on providing decentralized impedance specifications for each converter connected to an ac bus. With decentralized specifications, each converter has its own specifications, which are independent of other converters' impedance. This enables a competitive multi-vendor environment while guaranteeing system stability. Existing methods of imposing decentralized specifications, based on the small-gain, passivity and Gershgorin theorems, are formulated within a common frequency-domain framework. Building on this, two new solutions that reduce the conservativeness of the specifications are proposed. First, Gershgorin-based decentralized specifications are formulated in the modified sequence domain. Second, a framework for combining different specification types across frequency ranges is developed and mathematically proven. The methods are compared on examples covering sub-synchronous and harmonic-range interactions of grid-following converters, grid-forming converters, and a mixed grid-forming/grid-following system, using analytical models, black-box impedance measurements, and time-domain responses obtained from simulations and an experimental setup.