Impact of multi-terminal HVDC grids on the transient behavior in transmission systems - Modelling and analysis
Due to the wide acknowledgement of renewable power sources (RES), such as wind power and solar power, the HVDC network has been accepted as an promising solution for connecting them into the AC system. Furthermore, in order to enhance the flexibility of whole power system, imbedding the RES into one system attracts interests from both industry and academia, i.e. establishing multi-terminal HVDC (MTDC) network. Unlike the conventional point-to-point (p2p) system, the responses of MTDC system after faults differ under different control modes, network topologies, and protection methods. Especially, the travelling wave of fault-incident surge can propagate the whole system in several milliseconds, which brings challenges to the system operation. The research aims at analyzing the transient behaviors based on typical system configuration and modelling method, and establishing a reliable MTDC system protection methodology.
For the sake of convincing research, two key factors must be taken into consideration: HVDC converter modelling and travelling wave modelling. They accounts for the accurate transient simulation of MTDC network. Thus, the EMT type software, PSCAD, is adopted, in which the efficient model (Type-4 model) of modular multi-level converter (MMC) and Frequency Dependent (Phase) model of transmission line are applied. Different types of DC fault situations are considered, and the simulation results are analyzed. And system operation and protection will be produced based on them.
This research will present a topology of MMC converter, which can restrain the DC fault current. Its power lossless control method will be demonstrated as well. Then, a travelling wave based protection scheme will be established. This non-unit protection method will be compared with another typical unit protection methods. In addition, the DC circuit breaker (DCCB) will be designed and implemented. Also, the simulation will be validated in real-time digital simulator (RTDS) system.
Lian Liu was born in Wuhan (China) in 1987. He received his Bachelor and Master degrees of Electrical Engineering from Wuhan University in 2010 and 2013 respectively. During his Master studies, he was focused on the establishment of harmonic model of three-phase transformer. He is now pursuing his PhD degree in Delft University of Technology on the topic of transient study of multi-terminal HVDC (MTDC) system. His research interests include: HVDC transient analysis, MTDC system fault detection and protection, and, real-time simulation of large scale power system.