Insertion of Power Electronic Elements into Modern Power Transmission Grids
Key words: power converters, HVDC, renevable energy sources, interaction and coordination, inter-area oscillations, small-signal stability, transmission delays, robust/predictive control
Power electronics is more and more used on the power transmission grids. Indeed, all wind and photovoltaic generation is connected to the grid by converters. Also, the reinforcement of the grid is frequently done with High-Voltage Direct Current (HVDC) lines which consist of 2 power converters into a back-to-back connection and a DC cable. This tendency will be extended in future in order to ensure the transition towards decarbonized energy systems as formulated, for example, in Europe.
This new technology based on power electronics is active in the sense that it provides several degrees of freedom for the power and voltage control. Thus, it has an impact on the dynamics of the neighbour AC power system. In particular, the small-signal and the transient stability depend on the way in which the regulators of the converters are synthesized. This raises several questions:
- how to improve the transient stability of the neighbour zone?
- how to quantify and diminish the interactions between two close HVDC ?
- how to damp inter-area modes (i.e., low frequency electromechanical oscillations of the power grid) via power-modulation control of the HVDC?
Research subject, general work plan:
Several levels of investigation are envisaged:
- quantify the grid interactions between two HVDCs. Explain the nature and the mechanism of these interaction and propose adequate quantitative measures
- study and formalize the lack of observability/controllability. State which measures/controls should be used and in which grid situation.
propose a new control framework in order to take full advantage for robustness and performances. Transient and small-signal stability are envisaged. Specific control methods will be used to answer the specifications, particularly:
- non-interacting control to diminish the interaction between several HVDC
- predictive control in case of transmission delays if distant measures (i.e., electrical variables measured on the transmission grid and not at the HVDC terminals) are used.
- nonlinear approaches to directly take into account the nonlinear behaviour of the system
This work is proposed in a general framework of collaboration with RTE – the French Transmission System Operator – and it is thus connected to real needs of the interconnected power systems. Realistic tests and validations of the theoretic developments mentioned above are possible on grid models and scenarios provided by RTE. The Control of Power Grids chair ( http://chairerte.ec-nantes.fr/ ) which exists between Ecole Centrale Nantes and RTE R&D guarantees the direction and the financial founding of this work. Several PhD subjects may be established for this general theme. The PhD work will be supervised in collaboration with specialists from Nantes and other research centres in France and abroad, according to the specificities of each subject.
The work will be carried out in Nantes-France.