Cost and losses associated with offshore wind farm collection networks which centralise the turbine power electronic converters

Costs and losses have been calculated for several different network topologies, which centralise the turbine power electronic converters, in order to improve access for maintenance. These are divided into star topologies, where each turbine is connected individually to its own converter on a platform housing many converters, and cluster topologies, where multiple turbines are connected through a single large converter. Both AC and DC topologies were considered, along with standard string topologies for comparison. Star and cluster topologies were both found to have higher costs and losses than the string topology. In the case of the star topology, this is due to the longer cable length and higher component count. In the case of the cluster topology, this is due to the reduced energy capture from controlling turbine speeds in clusters rather than individually. DC topologies were generally found to have a lower cost and loss than AC, but the fact that the converters are not commercially available makes this advantage less certain

Dynamic modelling of wind turbine and power system for fault ride-through analysis

This paper presents a Simulink model of a wind power system for the holistic analysis of wind turbine and power grid during grid faults, aiming to investigate wind turbine Fault Ride-Through performance. The model comprises a highly detailed dynamic model of a 2MW wind turbine and a generic electrical network model. The simulation result shows the behaviour of both wind turbine and power grid when grid faults occurs. The impact that a grid fault has on wind turbine components and grid transients is illustrated and discussed

Design of a hybrid PV/wind/diesel generator energy system for 120 residential apartments in Gusau

Gusau, a city in zamfara state, Nigeria is faced with the challenge of inadequate power supply as electricity supply from the national grid is unstable and inadequate, besides majority of those in the remote areas are isolated from the grid. The location has a potential for renewable resources, to overcome this challenge of inadequate power supply, a hybrid electric power system which employs the use of battery storage, solar and wind energy system with a diesel generator as reserve to provide adequate power to 120 residential apartments in a settlement isolated from the grid is being designed. The solar and wind energy resources in the location were assessed; the data from the two renewable energy resources available in the location was collected for the year 2015 from the Nigerian meteorological Agency, NIMET alongside the geographical coordinates and other useful parameters as input to the HOMER software simulator for analysis. The load profile of the location was carried out, the sizing of the energy mix from PV, wind, battery and generator was made using the software. The result of the simulation shows a yearly electricity production of 168,545KWh/yr, the yearly AC primary load is 67160KWh/yr. And the excess electricity is 88581Kwh/yr, this accounts for 52.6% of the total electricity generated hence, the hybrid energy system has the potential to provide the micro-grid with adequate power with high penetration of renewable energy

Provision of frequency support by offshore wind farms connected via HVDC links

The high penetration levels of wind power will obligate wind farms to contribute to the mitigation of frequency drops. Comprehensive case studies are presented to investigate the different methods of frequency support provision by wind power. The implemented test system is composed of an offshore wind farm connected to an external grid through a point-to-point HVDC link. Three different frequency support methods are compared; droop de-loading, battery storage banks and a mix between the two methods. Moreover, two different methods of sensing the frequency drop, at the point of common coupling, by the wind farm are examined. The impact of the HVDC is highlighted, especially its role to transmit the power surge provided by the wind farm. A modified de-loading controller is developed and integrated to all the wind turbines, according to the executed case studies. Results show that the proposed frequency support solutions have almost similar impact on the natural frequency response at the point of common coupling. The HVDC link does not worsen the frequency response, and the fluctuations in voltage levels at onshore and offshore buses are very minor. DIGsILENT PowerFactory is integrated as a simulation environment

Ecosystem Viable Yields

The World Summit on Sustainable Development (Johannesburg, 2002) encouraged the application of the ecosystem approach by 2010. However, at the same Summit, the signatory States undertook to restore and exploit their stocks at maximum sustainable yield (MSY), a concept and practice without ecosystemic dimension, since MSY is computed species by species, on the basis of a monospecific model. Acknowledging this gap, we propose a definition of "ecosystem viable yields" (EVY) as yields compatible i) with guaranteed biological safety levels for all time and ii) with an ecosystem dynamics. To the difference of MSY, this notion is not based on equilibrium, but on viability theory, which offers advantages for robustness. For a generic class of multispecies models with harvesting, we provide explicit expressions for the EVY. We apply our approach to the anchovy--hake couple in the Peruvian upwelling ecosystem

Applying series braking resistors to improve the stability of low inertia synchronous generators

Widely held concerns over the environmental impact of emissions from large fossil fuelled generating plants are serving to promote the connection of renewable or sustainable generation onto distribution networks. Many such generators are synchronous machines with low values of inertia, and thus possess short critical clearance times to avoid the onset of transient instability. With fault clearance times of up to 1s occurring in distribution networks, there is the potential for a growing problem as distributed generation makes up a larger proportion of installed capacity. This paper proposes the use of series braking resistors that are switched into circuit at the generator terminals as a means of improving transient stability, and thus avoid, or at least defer major upgrades to distribution system protectio

DC voltage control for fault management in HVDC system

This paper focuses on the transmission system options for connection of offshore wind farms and investigates the advantages and disadvantages of proposed concepts in order to draw a conclusion regarding their suitability for connection in the electricity system. Then, the most appropriate solution is implemented in Matlab/Simulink to show its benefits. For this purpose, 5 wind farms are connected to an offshore station and their power output is transferred onshore via a point – to – point DC link. Additionally a novel proposal of DC voltage control is included in the model to simulate the behaviour of the system when faults occur in the electricity grid

Comparison between flying capacitor and modular multilevel inverter

The paper describes the operational principle of flying capacitor and modular multilevel inverters. The detailed discussions of dc link capacitors voltage balancing methods for both inverters are given in order to enable fair comparison. The causes of dc link capacitors voltage imbalance in flying capacitor multilevel inverter with more than three levels are highlighted. Computer simulation is used to compare the performance of both inverters under several operating conditions

Comparison between two VSC-HVDC transmission systems technologies : modular and neutral point clamped multilevel converter

The paper presents a detail comparison between two voltage source converter high voltage dc transmission systems, the first is based on neutral point-clamped (also known as HVDC-Light) and the second is based on innovative modular multilevel converter (known as HVDC-Plus). The comparison focuses on the reliability issues of both technologies such as fault ride-through capability and control flexibility. To address these issues, neutral point-clamped and three-level modular converters are considered in both stations of the dc transmission system, and several operating conditions are considered, including, symmetrical and asymmetrical faults. Computer simulation in Matlab-Simulink environment has been used to confirm the validity of the results

Distribution voltage control utilising the reactive power capabilities of wind generators

Voltage rise issues have become a major limiting factor to greater penetration of wind generators in weak distribution networks. A complete decentralised approach to voltage control (VC) that fully utilises the reactive power capabilities of distribution wind generators is an emerging technology and one that has not yet been investigated extensively. This study explores the potentials of modern wind turbine technology integration to address the problem. It assesses such potentials on a realistic 289-node UK generic 11 kV distribution network using time-series optimal power flow simulations under constraint conditions. This study examines the power factor control and VC modes of operation of typical generators and proposes practical techniques that enhance greater connection capacities. The study successfully reveals that, operating the wind generators within a flexible reactive power capability limits effectively mitigates the voltage rise problem and maximises generation levels