| Author: | Zhang, Jiangfeng |
| Title: | Mechanism analysis of subsynchronous oscillations in type-IV wind power plants-integrated power systems |
| Advisors: | Bu, Siqi (EEE) |
| Degree: | Ph.D. |
| Year: | 2026 |
| Department: | Department of Electrical and Electronic Engineering |
| Pages: | xvii, 153 pages : color illustrations |
| Language: | English |
| Abstract: | Compared with SGs, wind power plants (WPPs) rely on power electronic devices for grid integration, exhibiting low inertia, weak disturbance resistance, and multi-timescale dynamic responses. Consequently, WPP-integrated power systems are prone to subsynchronous oscillations (SSOs). Moreover, type-IV wind turbine generators (WTGs) employing full-power converters exhibit more pronounced power electronic characteristics, making power systems with type-IV WPPs more susceptible to SSO. Therefore, understanding the mechanisms and characteristics of SSOs in such systems is crucial for ensuring secure and stable operation. To reveal the damping degradation mechanism of dominant oscillation modes in type-IV WPPs, the quasi-electromechanical oscillation loop (quasi-EOL) model is proposed. This model characterizes the natural oscillation dynamics of the control oscillation mode (COM) and clearly illustrates the dynamic influence path from the external system. Based on the quasi-EOL model, the damping transfer path modeling method is introduced to enable damping contribution analysis (DCA). By applying the proposed DCA method, SSO risks detection and instability mechanisms analysis are conducted on a type-IV WPP connected to an external network through series compensation. The developed damping transfer path models of the example system enable the DCA method to systematically uncover how the closed-loop damping transfer paths of the dominant WPP COM are formulated and derive explicit expressions of the damping contribution coefficients from the remaining power system to the corresponding quasi-EOL model. Therefore, the DCA method provides clear physical insights into how and why the system parameters contribute to negative damping in the concerned control oscillation loop of the type-IV WPP, thus leading to SSOs in a type-IV WPP in series-compensated networks. To rapidly assess the risk of the open-loop modal resonance (OLMR)-induced SSOs in a complex power system with multiple type-IV WPPs, and to identify the trouble-making WPP, the damping transfer path modeling method has been further advanced. The enhanced damping transfer path model enables the DCA method to effectively and accurately identify the grid-connected type-IV WPP responsible for the OLMR with the concerned oscillation mode, without requiring modal computation to obtain the eigen-solutions of the studied system. Furthermore, the proposed DCA method provides physical insights into the occurrence of OLMR, helping to understand the fundamental mechanisms of OLMR-induced SSOs. Finally, the DCA method is extended from the d-q domain to the sequence domain to investigate the root cause and characteristics of PLL-dominated sideband oscillations in type-IV WPPs-integrated power systems. Using the developed sequence-domain damping transfer path model considering the frequency coupling effects (FCEs), the DCA method derives analytical expressions for the closed-loop PLL control oscillation modes (PCOMs) in the stationary reference frame, identifying the frequency range where sideband phase current components emerge. The concept of the mode observable degree (MOD) is introduced to provide a physical explanation for the varying amplitudes of the frequency-coupled sideband phase current oscillation components during the PLL-induced SSOs. Furthermore, the MOD ratio index serves as a predictive metric for estimating the amplitude ratio between the frequency-coupled sideband phase current oscillation components. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/14665