Constraint-Aware Grid-Forming Control for Current Limiting

TL;DR

This paper introduces a constraint-aware grid-forming control that explicitly incorporates current and modulation limits, enabling fast current limiting and stable transient response in power converters.

Contribution

It develops a novel control method that respects operational constraints while maintaining stability, validated through simulations and hardware experiments.

Findings

Achieves fast current limiting during faults.

Preserves transient stability with infinite critical clearing time.

Validated through comprehensive simulations and hardware tests.

Abstract

This work develops a constraint-aware grid-forming (GFM) control that explicitly accounts for current limits and modulation limits within the GFM oscillator dynamics generating the GFM voltage reference (i.e., phase angle and magnitude). Broadly speaking, the voltage reference generated by the constraint-aware GFM control minimizes the deviation from conventional unconstrained GFM droop control, while respecting current and modulation limits. The resulting GFM control achieves fast current limiting while preserving transient stability, e.g., exhibiting infinite critical clearing time. To develop the control, we first characterize and analyze the set of converter voltages that do not result in constraint violations. Next, an efficient algorithm for projecting voltages onto the feasible set is developed. Subsequently, these results are used to restrict the dynamics of GFM droop control to the set of feasible voltages. Finally, detailed simulation studies and hardware experiments are used to illustrate and validate the response to short-circuit faults and phase jumps.