Voltage Source Converter Stations Research Articles

A novel concept of offshore wind-power collection and transmission system based on cascaded converter topology

SUMMARY This paper presents a new concept for the grid integration of large-scale offshore wind farms. In the offshore wind farm, the wind turbines are integrated into the offshore DC collector grid by a cascaded converter. The high-voltage level for the high-voltage direct current (HVDC) transmission purpose is built by series connections of low voltage modules, without the use of an offshore step-up substation. The output power of each module is controlled by the switching of the related half-bridge, and a modified straightforward voltage balancing strategy is proposed to balance the storage capacitor voltages in the turbines. Supplementary balancing strategies are also presented to assist in balancing the capacitor voltages, when the differences in the wind velocities flowing to the turbines become larger. Because of the stable capacitor voltages, self-commutated voltage source converter (VSC) is adopted as the onshore inverter station connecting the HVDC link and the onshore AC grid. The VSC station not only regulates the DC-bus voltage of the HVDC link, but also provides reactive power compensation to the onshore grid. The time-domain simulation results show that the proposed offshore wind-power collection and transmission system provides a new option for integrating large-scale offshore wind farms. Copyright © 2012 John Wiley & Sons, Ltd.

Offshore Wind Farm Grid Integration by VSC Technology With LCC-Based HVDC Transmission

High-voltage dc (HVDC) transmission based on the line-commutated converter (LCC) is the most established and widespread technology around the world. However, HVDC based on the voltage source converter (VSC) has emerged as the best option to integrate renewable energy sources, e.g., offshore wind farms. This work investigates the feasibility of using a conventional LCC-HVDC transmission in combination with a VSC to integrate offshore wind farms. Such integration results in a hybrid HVDC connection, i.e., the connection of a VSC with an LCC through a dc cable. The operational features of a model of three-terminal hybrid HVDC, two LCC stations and one VSC station, is investigated using PSCAD/EMTDC. The simulations include an aggregate model to emulate the wind farm. The corresponding control strategies are proposed for each terminal and verified under various conditions including wind speed variations and ac faults.

HVDC, the Next Generation of Transmission: Highlights with Focus on Extruded Cable Systems

AbstractOur world carries an increasing burden of increasing CO2 emissions. Rather than rationing the use of electric power, we should all together organize ourselves toward a positive solution that benefits growth and a sustainable society. The high voltage direct current (HVDC) technology is a cornerstone that makes it possible to transport sustainable energy to the regions of consumptions that are often far away from the location of generation. Today's commercially available highest HVDC transmission voltage is 800 kV. This system makes use of classic converter stations. The newer HVDC Light technology, Voltage source converters (VSCs) and extruded cable systems, that are commercially available, are characterized today by a highest voltage of 320 kV and 1000–1200 MW of transmission power. This paper describes the need for higher HVDC transmission powers, the general technology of the VSC stations, and an in‐depth description of HVDC technology with a focus on extruded cable systems. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Operation and Control of HVDC-Connected Offshore Wind Farm

This paper presents operation and control strategies of an offshore wind farm interconnected to a high-voltage dc (HVDC) system. The offshore wind farm composed of variable speed wind turbines driving permanent magnet synchronous generators is considered in this study, based on dc-bus concept. The HVDC transmission system based on a three-level neutral point clamped voltage source converter (VSC) is used for the interconnection between the offshore wind farm and onshore grid. Detailed modeling and control strategies are developed for the individual component of the overall system. A simple fuzzy logic controller is adopted in the offshore VSC station, which is one of the salient features of this study. Real wind speed data is used in the simulation study to obtain realistic response. Both dynamic and transient analyses of the proposed system are carried out using the laboratory standard power system software package, PSCAD/EMTDC.

Autonomous AC Grid Based on Multi-infeed Voltage Source Converter Stations

It is desirable that remote isolated communities can become self-sufficient in electric power through harnessing energy from renewable energy sources. Taking advantage of the high controllability of voltage source converters, a scheme to realize a stand-alone AC grid for such an isolated community is examined. It uses voltage source converter stations as frequency changers. The multi-infeed voltage source converter design succeeds in the dual roles of maintaining the grid AC voltage while balancing real power generation and loads using local information only. The stability of the power system under the proposed control scheme, as affected by the control coefficients and operating conditions, is investigated. An analysis of eigenvalue sensitivity to control parameters is also included. Proof of the concept is carried by digital simulation studies.