Transient Slack Capability

TL;DR

This paper defines Transient Slack Capability (TSC), a set of device-level conditions ensuring stability during power disturbances, formalized using port-Hamiltonian framework and validated through simulations on power system models.

Contribution

It introduces the TSC concept, formalizes it with port-Hamiltonian methods, and demonstrates its applicability to both GFL and GFM converters in power systems.

Findings

TSC conditions are achievable in GFL and GFM converters.

Sensitivity analysis identifies storage and reserve requirements.

Inertia-less solutions can meet TSC conditions.

Abstract

This paper introduces the concept of Transient Slack Capability (TSC), a set of three necessary device-level conditions to ensure stability under sustained power perturbations. TSC states that a device must (1) possess sufficient stored energy; (2) a controlled input power; and (3) maintain internal energy balance and synchronization. The paper shows that the relation among the time-scales of storage, control, and power perturbation is at the core of the TSC concept. Using the port-Hamiltonian (PH) framework, these conditions are formalized and validated via simulations on an adapted model of the WSCC 9-bus system. Case studies demonstrate that TSC is achievable in both Grid-Following (GFL) and Grid-Forming (GFM) converter control schemes, provided the conditions above are satisfied. Sensitivity analysis serves to identify storage and power reserve requirements to meet Conditions 1 and 2; the impact of converter current limiters on Condition 3; and inertia-less solutions able to achieve TSC.