Graungaard, Mads Kjedal



PROJECT TITLE: Modeling of Multi-Converters under Grid Fault Conditions    


PhD period: 2017.09.01 – 2021.08.31.
Section: Power Electronic Systems
Research Programmes: Efficient and Reliable Power Electronics 
Supervisor: Frede Blaabjerg
Co-Supervisors: Xiongfei Wang and Pooya Davari
Contact Information

Collaborator: To be announced later.
Funding: Villum Fonden.

ABSTRACT

The increasing demand to connect renewable energy sources such as wind and photo- voltaic to the grid, puts high demand on the grid architecture including power electronic converters and their reliability. This implies that the capacity of distributed generators is increasing rapidly and a significant sharing of these compared to centralized generators are to be seen in the next few decades.

Today the main production of electrical energy comes from large coal fired power plants, which due to their large inertia gives the conventional grid high stability and robust performance. Therefore when distributed generators do not constitute a big part of the full grid capacity, the power system stability is not at risk, but for future higher constitution of distributed generators in the grid capacity, system stability cannot be guaranteed if not properly controlled and understood.

A future power system dominated by power electronic converters interfaced with wind- farms, micro-grids and big photovoltaic power generation, gives a high degree of freedom regarding grid controllability. This also includes better utilization of harvested energy due to high efficient converter topologies and control. However a power system dominated by a decentralized production from renewable energy sources, connected through multiple paralleled converters introduces several problems. One disadvantage is that the high system stability due to large inertia of large rotating machines at the power plants is lost since converters do not contain inertia. Another problem is the high frequency switching noise generated by converters. This increases the harmonic content of the grid current, which results in poor power quality and system stability degradation. Paralleling multiple converters can introduce undesired couplings between different parts of the system including filters and can trigger fatal resonances between converters and other subsystems connected to the grid. Therefore in order to successfully transition from conventional electrical machines to multiple paralleled voltage source converters for renewable energy generation, how multi-converters influence system stability has to be understood and modelled.

Papers

Publications in journals and conference papers may be found at VBN.