Public defence in Power Electronics and Electric Drives, M.Sc.(Tech.) Ville Pirsto

M.Sc.(Tech.) Ville Pirsto will defend the thesis "Digital Control in Grid Converters: Methods and Comparative Analyses" on 16 September 2022 at 12 (EET) in Aalto University School of Electrical Engineering, Department of Electrical Engineering and Automation, in lecture hall AS1, Maarintie 8, Espoo.

Opponent: Prof. Heng Wu, Aalborg University, Denmark
Custos: Prof. Marko Hinkkanen, Aalto University School of Electrical Engineering, Department of Electrical Engineering and Automation

Thesis available for public display at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/
Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53

Public defence announcement:

During the last decade, the share of renewable energy generation used in energy production has increased in strides to combat the environmental detriment caused by the use of fossilized fuels. Consequently, voltage-source converters that act as interfaces between the renewable energy source and the electric grid have been deployed in unprecedented numbers. Such voltage-source converters are also referred to as grid converters.

As a result of this paradigm change in energy production, new challenges related to the stability of the electric grid and individual grid converters have been observed. One of the most prominent challenges is related to ensuring converter stability in varying grid conditions. A particularly challenging operating condition for the grid converters is that of weak grid, that is, when the grid impedance as observed from the converter output terminals is high. This high grid impedance may cause detrimental interactions between the converter and the grid, which results in interconnection instability.

This doctoral thesis studies a wide range of methods applicable to digital control of grid converters to improve their operability under various grid conditions, providing new results as well as shedding light on the relations between existing methods. The topics can be divided into three categories: converter modeling, identification, and control design. A continuous-time converter output admittance modeling method that considers the digital nature of the converter system is presented. Moreover, real-time identification methods for the physical parameters of the converter filter as well as unbalanced grid impedance are developed. Finally, comparative analyses of various state-feedback current controllers are carried out to examine their properties as well as reveal connections between them. The results of this thesis find applications in renewable energy generation, such as wind turbine and solar photovoltaic systems, as well as in the active front ends of motor drives.

Contact information of doctoral candidate: