The colloquium of the Center for Intelligent Power and Energy Systems (CiPES) was held on November 18, 2022. This is a monthly event where we invite students and experts in the area of power and energy to give presentations about their research.

Today the presenter is Ms. Ruiyu Pan from PSPAL. She gave an online talk on her research: " A Distance Protection Method and An Improved Source Model During Transient State of Line Faults in MMC-HVDC Systems".

Ms. Ruiyu Pan joined PSPAL in July 2020. She is currently a Ph.D. student in PSPAL (starting from September 2020). She received her B.S. degree of Electrical Engineering and Automation from Huazhong University of Science and Technology, Wuhan, China, in Summer 2019. Her research interests include transmission line protection and fault location in MMC-HVDC grids.

The abstract of this talk is as follows:

With increasing demand for clean energy to reduce carbon emissions, large-scale renewable energy sources are connected to the practical power grids via high voltage direct current (HVDC) transmission lines. Modular multilevel converter (MMC) has the advantages of high operating reliability, superior harmonic performance, high modularity and scalability. Therefore, MMC-HVDC grid is a promising candidate to integrate large amount of clean energy in future power systems. However, the protection of MMC-HVDC lines requires very high operational speed (typically within 3ms), without losing dependability and security of the protection. A novel distance protection for MMC-HVDC transmission lines is proposed. The method only utilizes single-ended measurements, and no communication channels between line terminals are required. The method borrows the idea of legacy distance protection scheme in HVAC transmission lines, and adopts state estimation algorithm to calculate the resistance and inductance “seen” by the distance relay. Afterwards, the calculated resistance and inductance are depicted in an R-L plane to formulate the protection logic and determine the faulted poles. In the meanwhile, the model of MMC during transient state is essential in the protection and fault location of HVDC transmission lines. There are two major types of MMC models including the switching model and the average model. Considering transient state of transmission line faults in HVDC grids, the improved model of the source during transient state of transmission line faults is derived. It is a six-order circuit model which could be used to represent the discharging process, including modular multilevel converter (MMC), filter inside bus and current limiting inductor.