Paolo Mattavelli | Search arXiv

arXiv2026

Decentralized Impedance Specifications for Grid-Connected Converters: a Sequence-Domain Gershgorin Method, and a Frequency-Wise Framework for Combining Different Criteria

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.

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arXiv2026

Internal-Model-Control-Based Virtual Admittance Emulation for Enhanced Grid-Forming Performance

The large-scale integration of renewable energy into electrical power systems places a growing reliance on grid-forming converters (GFMs) to overcome critical stability and control hurdles. By emulating a slowly varying voltage source behind a tunable resistive?inductive impedance, GFMs enable precise setpoint tracking and vital grid support. In this regard, virtual admittance (VA)-based inner-loop control provides exceptional flexibility in shaping the converter's small-signal immittance at connection terminals, allowing for advanced GFM functionalities. This article addresses a novel internal-model-control-based VA approach, which inherently accounts for the effects of the inner current-control loop and the voltage feedforward. Unlike the state-of-the-art VA control, the proposed VA control ensures that, at frequencies outside the influence of outer loops, the converter's terminal admittance closely matches the target admittance, which is shown to be relevant for stability. It is revealed how, with the state-of-the art VA control, a small-signal instability in the harmonic range may arise if a low-pass filter with a high cut-off frequency is used for the voltage feedforward. However, the proposed VA control ensures stable operation regardless of this cut-off frequency. The methodology is experimentally validated using a laboratory prototype that features three-phase voltage-source converters.

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