Hierarchical Frequency Control of Hybrid Power Plants Using Frequency Response Observer

TL;DR

This paper introduces a hierarchical frequency control method for hybrid power plants, utilizing a novel frequency response observer to improve robustness and coordination across different control levels for grid services.

Contribution

A new hierarchical frequency control framework with a frequency response observer is proposed for hybrid power plants, enabling effective coordination of fast and slow frequency response services.

Findings

The approach effectively estimates frequency response across control levels.

The scheme demonstrates robustness against system uncertainties.

Simulation results validate improved control performance.

Abstract

Frequency control (FC) enables utility-scale grid-connected hybrid power plants (HPPs) to operate in compliance with grid code requirements while to capture value streams from provision of frequency control services (FCSs). In this paper, a novel hierarchical FC approach is proposed to allow HPPs to provide three types of FCSs, namely fast frequency response (FFR), frequency containment response (FCR) and frequency restoration response (FRR). To accommodate state-of-the-art fast FC, controllers for fast FCSs, such as FFR and FCR, are implemented at asset controllers, while controllers for slow FCSs like FRR are implemented at plant controllers or the HPP controller (HPPC). Control counteraction issue, which arises across control hierarchy, is then discussed. To solve this issue, an innovative frequency response observer (FROB) is proposed. Inspired by the concept of disturbance observer (DOB), FROB at plant controllers and the HPPC accurately estimates frequency response initiated at asset controllers, and the obtained estimation is used for control compensation at plant controllers and the HPPC to avoid control counteraction. This scheme achieves robust performance even when there are system uncertainties existing in HPPs, such as parameter uncertainty, unknown control malfunction, and time-varying communication delays. The proposed approach is implemented in a power system dynamic model in MATLAB/Simulink to highlight its effectiveness and robustness.