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Blog 4 - Stability issues in future power systems: revisiting conventional and emerging challenges

Tao, 26 July 2023

Power system stability can be described as the ability of a power system to maintain its balance during normal operations and restore equilibrium after disturbances [1]. In conventional power systems, dominated by synchronous generators (SGs), three main stability concerns can be identified [2]: rotor angle stability, frequency stability and voltage stability. Rotor angle stability ensures the synchronism of the interconnected SGs and the rest of the power system, frequency stability keeps the operating frequency within an acceptable limit, and voltage stability maintains steady voltages close to nominal value at all buses in the system.

The increasing penetration and integration of renewable energy sources (RESs) has led to a shift towards more sustainable and greener power systems with a large number of power electronic-based devices. While this transition brings environmental benefits, it also introduces new stability challenges. To address the challenges and account for the emerging instabilities, an IEEE working group revisited the classification of power system stability in 2020 and extended two new forms of stability issues: converter-driven stability and resonance stability [3].

A classification of power system stability: conventional and emerging issues

Converter-driven stability concerns the wide-range frequency oscillation within a power system due to the coupling interactions of electromechanical dynamics and electromagnetic transients between power electronic devices and grid networks, caused by the fast response control loops of power electronic converters (e.g., PLLs, inner current control loops). Based on the frequency of these phenomena, slow-interactions and fast-interactions are identified. In addition, unstable low-frequency oscillations occur in power electronic-based power systems due to various forms of interaction between the controllers of the converters and other system components. The outer (power and voltage) control loops and the PLL of converters lead to unstable low-frequency oscillations, and the system strength at the PCC has a significant influence on the stability of low-frequency oscillations.

Resonance stability accounts for oscillations caused by periodic and insufficient energy dissipation within the system. It includes sub-synchronous resonance (SSR), which encompasses torsional resonance between the series compensation grid and the turbine generator shaft, and electrical resonance between the series compensation and the electrical characteristics of the generator. It is worth noting that resonance stability and converter-driven stability issues are related, because resonance stability can also be driven by converter-based devices.  


In conclusion, addressing stability issues in future power systems requires considering both conventional and emerging challenges. The extension of the classifications of power system stability was necessary to accommodate the unique characteristics of power electronic devices, which differ from traditional synchronous generators.

[1] P. Kundur, Power System Stability and Control. McGraw- Hill, New York, 1994.
[2] P. Kundur et al., “Definition and classification of power system stability,” IEEE Trans. Power Syst., vol. 19, no. 3, pp. 1387–1401, May 2004.
[3] N. Hatziargyriou et al., “Definition and Classification of Power System Stability - Revisited & Extended,” IEEE Trans. Power Syst., vol. 36, no. 4, pp. 3271-3281, July 2021.



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