Titel: Optimum DC-Link Solution in HVDC Wind Park Actively Interfaced to the Grid, Elforsk report 08:45
Författare: Mikael Wämundson & Fainan Hassan
Utgivare: Elforsk, Vindforsk
Årtal: 2009
Ämnesord: Infrastruktur
Sökord/Keywords: VSC, HVDC, front-end converter.
Rapport
Sammanfattning/Abstract: The active control capability of an HVDC wind-park installation has been the main focus in this study. Through controlling both the active and reactive power, the wind park has the potential to contribute to power system security measures and stabilization and in the same time improve the local power quality.
This capability has been studied here through analytical discussions and simulation. The impedance of the grid as seen by the wind-park installation and the current limit of the front-end converter of the HVDC link are highlighted as main factors to put limitations over the active operation of the wind-park. However, reducing the active power, for short time duration, relieves the active interface limitation and serves for better transients’ compensation. This has been shown through a case study, where a reduction of the number of trips, due to voltage dips, with a factor of 2 has been found for nearby equipment with voltage sensitivity of 0.8 p.u. Moreover, an improvement of the compensation of grid voltage-amplitude variation has been found when assuming a controllable active power. Using a three-phase voltage data-measurement at the terminals of an arc furnace and using the PST (short term flicker severity) as a comparison value, it has been found that applying only reactive power control has reduced the PST value by 13 % while controlling both the active and reactive power has reduced the PST value by 27%.
To realize the active power control, a DC chopper has been proposed as an optimum front-end controller, to respond fast against the transient phenomena at the grid, which could be followed by a storage control that is activated in case of a further need of its storage energy. A detailed design and simulation for the current chopper has been carried out, showing that in case of voltage amplitude variation the chopper has provided better regulation for both the grid and the DC-link voltages. A discussion of different energy storage controls has been also carried out. It has been shown that if less costly and available with higher ratings, the superconducting magnetic energy storage is a promising candidate in order to provide better interface capability, where it could easily stand for both the chopper and the storage performance requirements.