Comparison of Impedance-based Tools for Sub/Super Synchronous Oscillation Analysis

(RES) integration. The ‘Clean Power 2030’ report indicates that to fulfil the decarbonisation targets, half of Great Britain’s generation must be provided by offshore wind [1]. In 2024, wind power became the UK’s leading source of electricity generation, accounting for 30% of the total energy output. This marks a significant milestone as wind power surpassed all other sources for the first time. [2]. The total installed capacity of offshore wind in the UK is 15GW

(end of 2024).

This shift towards a higher proportion of Inverter Based Resources (IBRs) in the energy mix increases the importance of addressing stability challenges, like forced oscillations appearing above and below the fundamental frequency. During the detailed design phase, the current requirement for developers is to perform interaction analysis to ensure that the new connection does not adversely affect any nearby generation sites. However, a central requirement of such analysis is the frequency dependent impedance of the network from the point of connection.

This impedance should be able to represent the dynamics of the network including nearby IBRs in the frequency range of 1Hz to 100Hz.

Currently, the impedance provided by the UK System Operator for all projects is the Thevenin equivalent impedance of the network which is valid only at 50Hz. This limitation is due to two factors – (a) lack of an industry standard impedance scanning tool that provides the 2x2 matrix and (b) validated EMT model of the GB system with integrated User Models.

The focus of this paper is to discuss the former by comparing different impedance scanning tools available in the market and demystifying the complexities associated with different frames of reference. The paper first presents the mathematical background behind sequence, 𝛼𝛽 and

𝑑𝑞 domains and the transformation matrices necessary to convert from one domain to another.

Later, through a case study in an EMT software, the measured impedance from different tools is compared to show how the different domains can be used interchangeably.