Bo Hesselbæk

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.

Harmonic modelling, propagation and mitigation for large wind power plants connected via long HVAC cables: Review and outlook of current research

This paper presents a state-of-the-art review on grid connection of large offshore wind power plants (OWPPs) using extra-long high voltage AC (HVAC) cables. The paper describes research by DONG Energy Wind Power in close collaboration with Aalborg University addressing related challenges through an industrial PhD project. The overall goal is to gain a better understanding of extra-long HVAC cable connected OWPPs, in order to ensure reliability and availability of OWPPs. This will reduce the cost of energy, as the risk of costly delays and modifications after the project has been commissioned can be reduced and operational availability and the reliability can be improved. Challenges hereto include lower resonance frequencies due to the long cables, frequency dependent modelling of long submarine cables, passive filtering, and PLL dynamics in the control loops (from a harmonic stability point of view).

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.

Small-signal model of a decoupled double synchronous reference frame current controller

The converter behavior in harmonic studies or harmonic stability analysis can be evaluated by its output impedance. In order to overcome the nonlinearities introduced by the PLL, linearized models around the operating point are typically used. However, in the case of an imbalance in the system the dq signals are not dc anymore, and therefore, linearization cannot be done. In this paper a Decoupled Double Synchronous Frame PLL is used to eliminate the oscillations in the dq frame signals. The small signal model of this PLL including an unbalanced current controller is presented in this paper.

The Application of Vector Fitting to Eigenvalue-Based Harmonic Stability Analysis

Participation factor analysis is an interesting feature of the eigenvalue-based stability analysis in a power system, which enables the developers to identify the problematic elements in a multivendor project like in an offshore wind power plant. However, this method needs a full state-space (SS) model of the elements that is not always possible to have in a competitive world due to confidentiality. In this paper, by using an identification method, the SS models for power converters are extracted from the provided data by the suppliers. Some uncertainties in the identification process are also discussed and solutions are proposed, and in the end the results are verified by time domain simulations for linear and nonlinear cases with different complexities, no matter which domain (phase or dq) is used.