Reliability is critical to the design, operation, maintenance, and performance assessment and improvement of wind turbines (WTs). This paper systematically reviews publicly available reliability data for both onshore and offshore WTs and investigates the impacts of reliability on the cost of energy. WT failure rates and downtimes, broken down by subassembly, are collated from 18 publicly available databases including over 18 000 WTs, corresponding to over 90 000 turbine‐years. The data are classified based on the types of data collected (failure rate and stop rate) and by onshore and offshore populations. A comprehensive analysis is performed to investigate WT subassembly reliability data variations, identify critical subassemblies, compare onshore and offshore WT reliability, and understand possible sources of uncertainty. Large variations in both failure rates and downtimes are observed, and the skew in failure rate distribution implies that large databases with low failure rates, despite their diverse populations, are less uncertain than more targeted surveys, which are easily skewed by WT type failures. A model is presented to evaluate the levelised cost of energy as a function of WT failure rates and downtimes. A numerical study proves a strong and nonlinear relationship between WT reliability and operation and maintenance expenditure as well as annual energy production. Together with the cost analysis model, the findings can help WT operators identify the optimal degree of reliability improvement to minimise the levelised cost of energy.

The paper presents a new model of the VSC-HVDC aimed at power flow solutions using the Newton-Raphson method. Each converter station is made up of the series connection of a Voltage Source Converter (VSC) and its connecting transformer which is assumed to be a tap-changing (LTC) transformer. The new model represents a paradigm shift in the way the fundamental frequency, positive sequence modeling of VSC-HVDC links are represented, where the VSCs are not treated as idealized, controllable voltage sources but rather as compound transformer devices to which certain control properties of PWM-based inverters may be linked-just as DC-to-DC converters have been linked, conceptually speaking, to step-up and step-down transformers. The VSC model and by extension that of the VSC-HVDC, takes into account, in aggregated form, the phase-shifting and scaling nature of the PWM control. It also takes into account the VSC inductive and capacitive reactive power design limits, switching losses and ohmic losses.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.

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In this paper, a centralised control framework is introduced for day-ahead operational planning of active distribution networks which accommodate high levels of distributed generation resources. The purpose of the framework is to plan network operation in order to minimise power curtailment from distributed generation and maintaining acceptable levels of voltage regulation throughout the network. For this purpose, both power flow control and rapid network reconfiguration have been considered as various acceptable levels of control available to the network operator to provide required levels of operational flexibility. The power flow control within the network is promised by the application of fully controlled back-back voltage source converters placed in key points (both normally-open and normally-close) in the network. Meanwhile, the network reconfiguration constraints guarantee that radial topology is always maintained in order to avoid tremendous changes in the protection system coordination. The operation of a modified 33-bus system exemplar is analysed in three case studies namely, passive network (base case), active network using remote-controlled switches and active network using intelligent power converters. Results show a significant saving in terms of operational costs as well as transmission losses in active cases despite the radial constraint condition in place.

This paper presents, with a live field experiment, the potential of increasing wind farm power generation by optimally yawing upstream wind turbine for reducing wake effects as a part of the SmartEOLE project. Two 2MW turbines from the Le Sole de Moulin Vieux (SMV) wind farm are used for this purpose. The upstream turbine (SMV6) is operated with a yaw offset ( α ) in a range of − 12 ° to 8° for analysing the impact on the downstream turbine (SMV5). Simulations are performed with intelligent control strategies for estimating optimum α settings. Simulations show that optimal α can increase net production of the two turbines by more than 5%. The impact of α on SMV6 is quantified using the data obtained during the experiment. A comparison of the data obtained during the experiment is carried out with data obtained during normal operations in similar wind conditions. This comparison show that an optimum or near-optimum α increases net production by more than 5% in wake affected wind conditions, which is in confirmation with the simulated results.

2019) 'A simplied algorithm to solve optimal power ows in hybrid VSC-based AC/DC systems.', International journal of electrical power and energy systems, 110 . pp. 781-794.The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractHigh Voltage Direct Current systems based on Voltage Source Converters (VSC-HVDC) are increasingly being considered as a viable technology with advantages, above all when using underground or submarine cables for bulk power transmission. In order to fully understand how VSC-HVDC systems can be best used within existing power systems, it is necessary to adapt conventional tools to carry out system-wide studies including this technology. Along this line, this paper proposes a simplified algorithm to solve optimal power flows (OPFs) in hybrid VSCbased Alternating Current / Direct Current (AC/DC) grids with multi-terminal VSC-HVDC systems. The proposed algorithm makes it possible to seamlessly extend a previous large-scale AC case to which several multi-terminal VSC-HVDC systems must be added. The proposed approach combines two ideas used previously in two different modelling approaches: each VSC is modelled as two generators with a coupling constraint; and DC grids are modelled as notional AC grids, since, in per unit, the equations for the former are a particular case of the latter with resistive lines and no reactive-power injections. In the proposed approach, the hybrid VSC-based AC/DC system is transformed into an equivalent only-AC system. Therefore, the OPF solution of the AC/DC system can be found with the same tool used for the previous AC problem and a simple extension of the original case.Index Terms VSC HVDC, HVDC transmission, multi-terminal, optimal power flow, power systems. NOMENCLATUREA G , A bus , A branch , A slacks : Sets of the generators, buses, branches and slack buses of the AC grids, respectively. A vsc , A dcbus , A dcbranch : Sets of the VSC stations, buses and branches of the multi-terminal VSC-HVDC systems. V i = V i ∠θ i : Voltage at AC bus ī S G,i = P G,i + jQ G,i : Active-(P) and reactive-power (Q) generation (bus i) S D,i = P D,i + jQ D,i : P/Q consumed by the loads (bus i) S i = P i + jQ i : P/Q injections into the AC grid at bus ī Y bus,ik = G ik + jB ik : Admittance matrix of AC line (i, k) I ik : Current through AC branch (i, k) (leaving bus i) (magnitude) S ik = P ac,ik + jQ ac,ik : P and Q flows through AC branch (i, k) (leaving AC bus i) Z ac,ik = R ac,ik + jX ac,ik : Series impedance of AC branch (i, k) B ac,sh,ik : Shunt susceptance of AC branch (i, k) V s,i = V s,i ∠δ s,i ...