PhD defence by Kaiqi Ma


23.06.2022 kl. 13.00 - 16.00


Kaiqi Ma, AAU Energy, will defend the thesis "Advanced Protection Schemes of Modern Transmission Grids with Large-scale Power Electronics "


Advanced Protection Schemes of Modern Transmission Grids with Large-scale Power Electronics 


Kaiqi Ma


Professor Zhe Chen


Professor Claus Leth Bak


Associate Professor Zhenyu Yang


Associate Professor Zhenyu Yang, Aalborg University, Denmark (Chairman)
Professor Matti Ilmari Lehtonen, Aalto University
Professor Peter Palensky, TU Delft


In the modern power system, the transition of conventional fossil sources to renewable energies has achieved huge progress, which benefits from power electronic technologies, including the aspects of topology, control, stability, and reliability, etc. It contributes to reducing the stress on the global environment and achieving the goals of sustainable development. However, the undergoing transition also causes various adaptability problems for the conventional power system protections, which result from different fault responses of the non-synchronous (power electronic) generators compared to the synchronous ones in general.

The transmission system plays a key role to support reliable power supply to electrical consumers. Line current differential protection and distance protection are two popular choices in the deployments of network protection. The Ph.D. project lays particular emphasis on the assessment of these two network protections in a system connecting non-synchronous generators (especially the full converter coupled ones), and the development of novel protections.
Concerning the fault response of the full converter coupled generator and its influence on the network protections, the thesis has pointed out,
o  For the full converter coupled generator, both the angular features of fault current and the sequence component circuits are fully determined by the converter fault control strategies.
o  The sensitivity of line differential protection is susceptible to the converter current angle features under different fault controls, during phase-to-phase faults in particular.
o  The selectivity of distance protection in the outgoing line of the non-synchronous generator plant during resistive grid faults is highly affected by the converter’s positive sequence current control angle in the rotating reference frame.

In terms of the novel line differential protection, the model mapping relationships of the fault sampling to the pre-defined fault model is used to implement the new time-domain differential protection. The thesis works are conducted as,
o  The compensated current-based time-domain differential principle is first validated.
o  By then, the compensated current-based differential protection suitable for the synchronous generator-dominated system is refined by incorporating the restraining equation.
o  Furthermore, the application of the new differential protection in the transmission system connecting non-synchronous generators is revised considering the feature of the converter sequence models. 

For the malfunction problem of distance protection in the outgoing line of the non-synchronous generator plant during resistive grid faults, the thesis focus on the following three aspects, 
o  The apparent impedance tilt feature-based complementary criterion is first introduced to enhance the performance of conventional distance protection during the asymmetrical (and resistive) grid faults. At the same time, 
o  To solve the adaptability issue of the existing reach setting of polygonal distance relay, the adaptive zone-setting scheme based on the impedance tilt angle is proposed in this thesis, showing better adaptability. 
o  In the perspective of the control-based solution, a protection compatible fault control for the converter can achieve the collaboration between the regulation of a non-synchronous generator for fault voltage support and the improvement of reactance measuring accuracy in distance protection. 

In the thesis, the assessments on conventional protections, and the validations for the proposed network protections (or the fault control) are based on the targeted test models built in DIgSILENT/PowerFactory platform, while the new algorithms are implemented in Matlab. Besides, the protection compatible fault control scheme is also validated in the real-time simulation platform (Opal-RT).


THE DEFENCE will be IN ENGLISH - all are welcome.




AAU Energy


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