Safe Control of Grid-Interfacing Inverters with Current Magnitude Limits

TL;DR

This paper introduces a safety filter method for grid-interfacing inverters that enforces current limits using control barrier functions, ensuring stable and minimally invasive control during overcurrent conditions.

Contribution

It proposes a novel safety filter framework with control barrier functions to enforce current limits in inverters, maintaining stability and control performance.

Findings

Feasibility of safe linear controllers proven.

Minimal alteration of inverter behavior during current limiting.

Ensures stability and safety in inverter control under constraints.

Abstract

Grid-interfacing inverters allow renewable resources to be connected to the electric grid and offer fast and programmable control responses. However, inverters are subject to significant physical constraints. One such constraint is a current magnitude limit required to protect semiconductor devices. While many current limiting methods are available, they can often unpredictably alter the behavior of the inverter control during overcurrent events leading to instability or poor performance. In this paper, we present a safety filter approach to limit the current magnitude of inverters controlled as voltage sources. The safety filter problem is formulated with a control barrier function constraint that encodes the current magnitude limit. To ensure feasibility of the problem, we prove the existence of a safe linear controller for a specified reference. This approach allows for the desired voltage source behavior to be minimally altered while safely limiting the current output.