Corrective control: stability analysis of Unified Controller combining frequency control and congestion management

TL;DR

This paper investigates the stability of a unified control approach that integrates frequency regulation and congestion management, identifying issues with higher-order turbine models and proposing a decoupling modification to ensure system stability.

Contribution

The authors extend previous stability analysis of the Unified Controller by addressing higher-order turbine models and introducing a decoupling method to guarantee eigenvalue negativity.

Findings

Higher-order turbine models cause eigenvalues with positive real parts.

Decoupling physical and control systems stabilizes the eigenvalues.

Modified controller is effective on a realistic 39-bus power system model.

Abstract

This paper analyses stability of the Unified Controller (UC) that combines frequency control and congestion management and therefore makes it possible to move from preventive to corrective power system control. Earlier work by the authors of UC proved asymptotic stability of the methodology but the proof was based on a simplified first-order model of the turbine and turbine governor. We show that a higher order model of the turbine governor leads to eigenvalues with small but positive real parts. Consequently, we develop a modification of the methodology that decouples the physical and control systems and therefore results in all the eigenvalues having negative real parts. We illustrate the effectiveness of the modification on a realistic model of 39-bus model of New England power system implemented in Power System Toolbox (PST).