Lorenzo Zeni

Power Oscillation Damping From VSC–HVDC Connected Offshore Wind Power Plants

The implementation of power oscillation damping service on offshore wind power plants connected to onshore grids by voltage-source-converter-based high voltage direct current transmission is discussed. Novel design guidelines for damping controllers on voltage-source converters and wind power plant controllers are derived, using phasor diagrams and a test network model and are then verified on a generic power system model. The effect of voltage regulators is analyzed, which is important for selecting the most robust damping strategy. Furthermore, other often disregarded practical implementation aspects regarding real wind power plants are discussed: 1) robustness against control/communication delays; 2) limitations due to mechanical resonances in wind turbine generators; 3) actual capability of wind power plants to provide damping without curtailing production; and 4) power-ramp rate limiters.

Modular multilevel converter modelling, control and analysis under grid frequency deviations

A tool for component sizing for MMCs has been developed and tested through simulations in PLECS. The steady-state behaviour under grid frequency deviations - interesting for offshore wind farm connections - has been analysed, providing insights in MMC characteristics and further testing the proposed tool.

Control of VSC-HVDC in offshore AC islands with wind power plants: Comparison of two alternatives

The subject of this paper is the control of offshore AC collection and export networks behind a voltage source converter based high voltage direct current transmission system. The inertia-less nature of such grids makes the control of voltages and power flows potentially more flexible, but at the same time more prone to instabilities. Focus in this paper is on a voltage source converter based high voltage direct current connected wind power plant. Two state-of-art controllers for the offshore high voltage direct current converter station are compared, both at no-load and when wind turbine converters are producing power and controlled with usual vector current control. Sensitivity analyses help identify critical factors influencing stability. The influence of lumping the wind power plant into one converter is assessed by comparison with the full model. The conclusions identify the preferred control technique.

Asymmetrical fault analysis at the offshore network of HVDC connected wind power plants

Short-circuit faults for HVDC connected Wind Power Plants (WPPs) have been studied mostly for dc link and onshore ac grid faults, while the offshore ac faults, especially asymmetrical faults, have been mostly omitted in the literature. Requirements related to the offshore asymmetrical faults have been kept as future development at national levels in the recent ENTSO-E HVDC network code. In this paper offshore ac faults are studied using the classical power system fault analysis methods. It is shown that suppression of negative sequence current flow is not applicable and negative sequence current has to flow during the asymmetrical offshore faults, which implies that the offshore WPP and the HVDC offshore converter are required to provide flow of negative sequence current. The steady-state fault analysis is verified with time-domain simulations.

A Practical Approach for Parameter Identification with Limited Information

A practical parameter estimation procedure for a real excitation system is reported in this paper. The core algorithm is based on genetic algorithm GA which estimates the parameters of a real AC brushless excitation system with limited information about the system. Practical considerations are integrated in the estimation procedure to reduce the complexity of the problem. The effectiveness of the proposed technique is demonstrated via real measurements. Besides, it is seen that GA can converge to a satisfactory solution even when starting from large initial variation ranges of the estimated parameters. The whole methodology is described and the estimation strategy is presented in this paper.