Advanced Safety Filter for Smooth Transient Operation of a Battery Energy Storage System

TL;DR

This paper introduces an advanced safety filter for Battery Energy Storage Systems that ensures safety during grid transients, achieves finite-time convergence, and maintains nominal control actions, demonstrated through simulations.

Contribution

The paper develops a novel safety filter using Control Barrier and Lyapunov functions via Sum-of-Squares optimization, enabling finite-time safety certification and quadratic input constraints.

Findings

Effective safety certification during grid transients

Finite-time convergence to nominal operation

Improved control performance compared to standard controllers

Abstract

In this paper, we implement an advanced safety filter to smoothly limit the current of an inverter-based Battery Energy Storage System. The task involves finding suitable Control Barrier Function and Control Lyapunov Function via Sum-of-Squares optimization to certify the system's safety during grid transients. In contrast to the conventional safety filter, the advanced safety filter not only provides a safety certificate but also achieves finite-time convergence to a nominal region. Within this region, the action of the nominal control, i.e. the Enhanced Direct Power Control, remains unaltered by the safety filter. The advanced safety filter is implemented using a Quadratically Constrained Quadratic Program, providing the capability to also encode quadratic input constraints. Finally, we showcase the effectiveness of the implementation through simulations involving a load step at the Point of Common Coupling, and we compare the outcomes with those obtained using a standard vector current controller.