Coordinated control and network integration of wave power farms

Significant progress has been made in the development of wave energy c onverters (WECs) during recent years, with prototypes and farms of WECs being installed in d ifferent parts of the world. With increasing sizes of individual WECs and farms, it becomes nec essary to consider the impacts of connecting these to the electricity network and to investigate means b y which these impacts may be mitigated. The time-varying and the unpredictable nature of th e power generated from wave power farms supplemented by the weak networks to w hich most of these farms will be connected to, makes the question of integrating a large quantity of wave power to the network more challenging. The work reported here focuses on the fluctuations in the rms-voltage intro duced by the connection of wave power farms. Two means to reduce these rms-voltage fluctuation s re proposed. In the first method, the physical placement of the WECs within a farm is selecte d prior to the development of the farm to reduce the fluctuations in the net real power ge n at d. It is shown that spacing the WECs or the line of WECs within a farm at a distance greater th n half the peak wavelength and orienting the farm at 90 ◦ to the dominant wave direction produces a much smoother power output. The appropriateness of the following conclusions has been tested and proven for a wave power farm developed off the Outer Hebrides, usin g real wave field and network data. The second method uses intelligent reactive power control algorithms, whic h have already been tested with wind and hydro power systems, to reduce voltage fluctuations. The application of these intelligent control methods to a 6 MW wave power farm connected to a re alistic UK distribution network verified that these approaches improve the voltage profile of the distribution network and help the connection of larger farms to the network, without any n eed for network management or upgrades. Using these control methods ensured the conn ection of the wave power farm to the network for longer than when the conventional control methods are used, which is economically beneficial for the wave power farm developer. The use of such intelligent voltage reactive power (volt/VAr) control meth ods with the wave power farm significantly affects the operation of other onshore voltage c ontrol devices found prior to the connection of the farm. Thus, it is essential that the control of th e arm and the onshore control devices are coordinated. A voltage estimation method, which uses a one-stepahead demand predictor, is used to sense the voltage downstream of the su bstation at the bus where the farm is connected. The estimator uses only measurements made at th e substation and historical demand data. The estimation method is applied to identify the operatin g mode of a wave power farm connected to a generic 11 kV distribution network in th e UK from the upstream substation. The developed method introduced an additional level of control and can be used at rural substations to optimise the operation of the network, without any new addition of measuring devices or communication means. Declaration of originality I hereby declare that the research recorded in this thesis and the thesis its lf wa composed and originated entirely by myself in the Institute for Energy Systems at The Uni versity of Edinburgh. Anup Jayaprakash Nambiar