Edwin Wiggelinkhuizen

ABSTRACT Europe is rapidly expanding its offshore wind energy capacity. Hence, the construction of a multi-terminal dc (MTDC) infrastructure to accommodate the generated electrical energy brings several advantages, but also comes with many challenges. Operation and control of a MTDC network is one of these challenges. This paper explains the operation and control of MTDC networks. Moreover, a study is carried on how to optimally operate and control an offshore VSC-based MTDC network. It focus on the development plans for an offshore transnational grid in the North Sea. A genetic algorithm (GA) will be employed to obtain an optimal power flow inside the offshore network. The MTDC grid is composed of 19 nodes, interconnecting 9 OWFs to 5 European countries. The optimal power flow results obtained from the genetic algorithm are tested in a simulation model for three case studies.

An open source software environment for the design of wind turbine control algorithms has been created. The modularisation enables to modify and to add or remove functionality in a user friendly way. This software environment established the point of departue for the development of specific control algorithms within the project. It consistst of so called functions and scripts in the MATLAB programming language. These MATLAB modules support modelling, control synthesis and data and signal handling. They thus enable a user to implement a modular parametrisation procedure for the control algorithm and a Simulink compatible evaluation of the designed controller. The software has been made typical for the variable speed windturbines with pitch control. However, other wind turbine concepts can also be dealt with.

As part of the EU 6th FP project "UpWind" Work Package 9.3 the dynamic response of two different electrical designs of offshore wind farms has been evaluated for symmetrical onshore grid faults. The first design uses an HVDC connection to shore based on voltage source con-verters and the second design uses an HVAC connection. In both cases the wind farm consists of variable speed turbines, with a with permanent magnet generator and full-power voltage source converter, grouped into 5 feeders connected to a single bus. The simulation results of a 3-phase fault in the onshore grid have been compared for different minimum grid voltages, for different wind speeds and for different power ratings of the dc-link braking resistor. In all cases the HVAC and HVDC connected wind farms did ride-through the 3-phase onshore grid fault while supporting the grid voltage during and shortly after the fault. The applied method of active power reduction of the HVDC connected wind farm by a fas...

In The Netherlands offshore wind power is on the brink of implementation. Specific plans exist for two offshore wind farms of about 100 MW, located 12 and 25 km from the coast of the province of North Holland. The effects of the incorporation of 6000 MW offshore wind power in the Dutch high voltage grid are currently investigated. Until now only the steady state behaviour is considered, resulting in suggestions for grid reinforcement. This investigation will be comple- mented by a study on the dynamic interaction of wind power and grid. Tools for this investigation, viz. dynamic models of wind farms including all relevant electrical components, have recently been developed. This paper gives an overview of wind farm dynamic models and concentrates on their use in a case study. Special concern exists about wind farm behaviour during extreme wind speed changes and abnormal grid conditions (voltage and frequency dips); these may cause complete wind farms to shut down instantaneously. As...

A new method for monitoring of bird collisions has been developed using video and audio registrations that are triggered by sound and vibration measurements. Remote access to the recorded images and sounds makes it possible to count the number of collisions as well as to identify the species. After the successful proof of principle and evaluation on small land-based turbines the system is now being designed for offshore wind farms. Currently the triggering system and video and audio registration are being tested on large land-based wind turbines using bird dummies. Tests of three complete prototype systems are planned for 2005.

To investigate whether a cost-effective integral condition monitoring system can be realized in practice the European project CONMOW (Condition Monitoring for Offshore Wind Farms) was started in November 2002. A small wind farm of five turbines has been instrumented with several condition monitoring systems and also with the "traditional" measurement systems. Data analysis of these measurements aims to develop algorithms that can be integrated in SCADA systems. This should lower the cost of condition monitoring systems and produce more accurate information for O&M planning. In this paper the approach of the project, the instrumentation of the wind farm, and the results are outlined.

ABSTRACT This paper discusses the results of an extensive investigation to assess the added value of various techniques of health monitoring to optimize the maintenance procedures of offshore wind farms. This investigation was done within the framework of the EU funded Condition Monitoring for Offshore Wind Farms (CONMOW) project, which was carried out from 2002 to 2007. A small wind farm of five turbines has been instrumented with several condition monitoring systems and also with the "traditional" measurement systems for measuring mechanical loads and power performance. Data from vibration and traditional measurements, together with data collected by the turbine's system control and data acquisition (SCADA) systems, have been analyzed to assess (1) if failures can be determined from the different data sets; (2) if so, if they can be detected at an early stage and if their progress over time can be monitored; and (3) if criteria are available to assess the component's health. Several data analysis methods and measurement configurations have been developed, applied, and tested. This paper first describes the use of condition monitoring if condition based maintenance is going to be applied instead of only scheduled and corrective maintenance. Second, the paper describes the CONMOW project and its major results, viz., the assessment of the usefulness and capabilities of condition monitoring systems, including algorithms for identifying early failures. Finally, the economic consequences of applying condition monitoring systems have been quantified and assessed.

ABSTRACT Although HVDC transmission systems have been available since mid-1950s, almost all installations worldwide are point-to-point systems. In the past, the lower reliability and higher costs of power electronic converters, together with complex controls and need for fast telecommunication links, may have prevented the construction of multiterminal DC (MTDC) networks. The introduction of voltage-source converters for transmission purposes has renewed the interest in the development of supergrids for integration of remote renewable sources, such as offshore wind. The main focus of the present work is on the control and operation of MTDC networks for integration of offshore wind energy systems. After a brief introduction, this paper proposes a classification of MTDC networks. The most utilized control structures for VSC-HVDC are presented, since it is currently recognized as the best candidate for the development of supergrids, followed by a discussion of the merits and shortcomings of available DC voltage control methods. Subsequently, a novel control strategy-with distributed slack nodes-is proposed by means of a DC optimal power flow. The distributed voltage control (DVC) strategy is numerically illustrated by loss minimization in an MTDC network. Finally, dynamic simulations are performed to demonstrate the benefits of the DVC strategy.