Safe Trajectory Gradient Flow Control of a Grid-Interfacing Inverter

TL;DR

This paper introduces a novel control framework for grid-interfacing inverters that directly incorporates hardware constraints into the control process, ensuring safe operation and optimal performance through a trajectory gradient flow method.

Contribution

The work presents a safe trajectory gradient flow control method that explicitly enforces constraints during inverter control, improving stability and performance over traditional ad hoc limiters.

Findings

Successfully maintains inverter states within safe bounds.

Achieves optimal inverter output values in simulations.

Operates effectively with limited optimization steps per cycle.

Abstract

Grid-interfacing inverters serve as the interface between renewable energy resources and the electric power grid, offering fast, programmable control capabilities. However, their operation is constrained by hardware limitations, such as bounds on the current magnitude. Existing control methods for these systems often neglect these constraints during controller design and instead rely on ad hoc limiters, which can introduce instability or degrade performance. In this work, we present a control framework that directly incorporates constraints into the control of a voltage-source inverter. We propose a safe trajectory gradient flow controller, which applies the safe gradient flow method to a rolling horizon trajectory optimization problem to ensure that the states remain within a safe set defined by the constraints while directing the trajectory towards an optimal equilibrium point of a nonlinear program. Simulation results demonstrate that our approach can drive the outputs of a simulated inverter system to optimal values and maintain state constraints, even when using a limited number of optimization steps per control cycle.