Asymmetry of Frequency Distribution in Power Systems: Sources, Estimation, Impact and Control

TL;DR

This paper investigates the asymmetry in frequency distribution in inverter-based power systems, analyzing its causes, impacts, and proposing a nonlinear compensation control to mitigate it, supported by real-world data and simulations.

Contribution

It introduces a nonlinear compensation control method and a statistical metric to quantify and reduce frequency distribution asymmetry in power systems.

Findings

Asymmetry reduces frequency control quality and system stability.

Nonlinear compensation effectively reduces frequency asymmetry.

Automatic generation control and active power control influence asymmetry levels.

Abstract

This paper analyses an emerging real-world phenomena in inverter-based renewable-dominated power systems, namely, asymmetry of frequency distribution. The paper first provides a rationale on why asymmetry reduces the "quality" of the frequency control and system operation. Then it provides qualitative theoretical insights that explain asymmetry in terms of the nonlinearity of real-world power systems and associated models. In particular network losses and pitch angle-based frequency control of wind power plants are discussed. Then the paper proposes a nonlinear compensation control to reduce the asymmetry as well as a statistical metric based on the frequency probability distribution to quantify the level of asymmetry in a power system. Real-world data obtained from the Irish and Australian transmission systems serve to support the theoretical appraisal, whereas simulations based on an IEEE benchmark system show the effectiveness of the proposed nonlinear compensation. The case study also shows that, while automatic generation control reduces asymmetry, frequency control limits and droop-based frequency support provided by wind generation using a tight deadband of 15 mHz, namely active power control, leads to a significant increase in the asymmetry of the frequency probability distribution.