Forecasting abrupt variations in wind power generation (the so-called ramps) helps achieve large scale wind power integration. One of the main issues to be confronted when addressing wind power ramp forecasting is the way in which relevant information is identified from large datasets to optimally feed forecasting models. To this end, an innovative methodology oriented to systematically relate multivariate datasets to ramp events is presented. The methodology comprises two stages: the identification of relevant features in the data and the assessment of the dependence between these features and ramp occurrence. As a test case, the proposed methodology was employed to explore the relationships between atmospheric dynamics at the global/synoptic scales and ramp events experienced in two wind farms located in Spain. The achieved results suggested different connection degrees between these atmospheric scales and ramp occurrence. For one of the wind farms, it was found that ramp events could be partly explained from regional circulations and zonal pressure gradients. To perform a comprehensive analysis of ramp underlying causes, the proposed methodology could be applied to datasets related to other stages of the wind-to-power conversion chain.

This study presents a tool for solving optimal power flows (OPFs) in hybrid high-voltage direct current (HVDC) and high-voltage alternating current (HVAC) systems for grid integration of large wind power plants, located either offshore or onshore. The OPF departs from the assumption that the power being produced from the wind power plants is known, as well as the demand from the AC grid. To model the interaction between the DC and AC grids, the active power conservation is expressed between the AC side and DC side of each converter, taking into consideration converter losses (modelled as a second-order polynomial). The tool developed determines the voltages and the active and reactive power in each bus and branch that ensure the selected objective function. All the electrical variables are limited. Moreover, the currents flowing in each DC and AC branch are also limited. The maximum AC voltage that can be applied by the converters is also limited. To develop the tool, both HVDC and HVAC grids need to be represented appropriately through its impedances and admittances. The tool has been implemented through MATLAB^® optimisation toolbox and through a more specific optimisation software GAMS^®, leading to the same results for the study case presented.

Offshore wind farms connected to the mainland through high-voltage DC links based on voltage source converters (VSC-HVDC) are subject to grid code requirements, such as fault ride-through (FRT) capability and dynamic voltage support. To address the challenge of FRT capability, sophisticated control strategies are required, capable of handling the power imbalance between the two interconnection ends during onshore grid faults. Τhis study proposes an FRT method which combines a de-loading control strategy for the offshore wind turbines, utilising the communication infrastructure of the VSC-HVDC system, with a DC chopper to dissipate the power surplus that cannot be effectively curtailed via the communication link. The impact of communication system latency on the expected FRT response and the required rating of the DC chopper is investigated using a linearised small-signal model introduced in this study, whose results are validated against time-domain simulations using detailed electromagnetic transient-type models for the entire system. It is concluded that the required rating of chopper resistors can be substantially reduced when existing communication capabilities are exploited, even in the presence of relatively high communication delays.

This study discusses the life-cycle analysis of wind turbines through the processing of operational data from three modern European wind farms. A methodology for supervisory control and data acquisition data processing has been developed combining previous research findings and experience from operational wind farms followed by statistical analysis of the results. The analysis was performed by dividing the wind turbine into assemblies and the failures events in severity categories. Depending on the failure severity category a different statistical methodology was applied, examining the reliability growth and the applicability of the ‘bathtub curve’ concept for wind turbine reliability analysis.

The use of condition monitoring systems on offshore wind turbines has increased dramatically in recent times. However, their use is mostly restricted to vibration based monitoring systems for the gearbox, generator and drive train. A survey of commercially available condition monitoring systems and their associated costs has been completed for the blades, drive train, tower and foundation. This paper considers what value can be obtained from integrating these additional systems into the maintenance plan. This is achieved by running simulations on an operations and maintenance model for a wind farm over a 20 year life cycle. The model uses Hidden Markov Models to represent both the actual system state and the observed condition monitoring state. The CM systems are modelled to include reduced failure types, false alarms, detection rates and 6 month failure warnings. The costs for system failures are derived, as are possible reductions in costs due to early detection. The detection capabilities of the CM systems are investigated and the effects on operational costs are examined. Likewise, the number of failures detected 6 months in advance by the CM systems is modified and the costs reported.

This study proposes a new dual-mode flux-switching doubly salient DC-field (FS-DSDC) machine for the wind power harvesting applications. The key distinction of the proposed machine is to artfully incorporate the design concepts of two machines, namely, the flux-switching DC-field (FSDC) and the DSDC machines together. By regulating the winding configurations, the proposed machine can behave similarly as the corresponding machines do and hence achieving the dual-mode operations, namely, the FSDC mode and DSDC mode, to offer higher flexibility and stability for different wind situations. The proposed machine can utilise its external DC-field winding to tune its flux density effectively, hence providing the constant-voltage charging function at various wind speeds and loads. The corresponding performances of the proposed machine are analysed by using the finite element method and verified by experimental results.

In this study, two control strategies involving ‘continuous’ and ‘ON/OFF’ operation of the diesel generator in the solar photovoltaic (PV)-wind-diesel-battery hybrid systems are modelled. The main purpose of these developed models is to minimise the hybrid system's operation cost while finding the optimal power flow considering the intermittent solar and wind resources, the battery state of charge and the fluctuating load demand . The non-linearity of the load demand, the non-linearity of the diesel generator fuel consumption curve as well as the battery operation limits have been considered in the development of the models. The simulations have been performed using ‘fmincon’ for the continuous operation and ‘intlinprog’ for the ON/OFF operation strategy implemented in Matlab. These models have been applied to two test examples; the simulation results are analysed and compared with the case where the diesel generator is used alone to supply the given load demand. The results show that using the developed PV-diesel-battery optimal operation control models, significant fuel saving can be achieved compared with the case where the diesel is used alone to supply the same load requirements.

This study presents a control design for a grid connected wind energy conversion system based on a gearless PMSG. The generation system structure comprises a three blade turbine, a 2 MW multi-pole PMSG and a full-scale back-to-back frequency converter linked to the utility grid. The proposed control scheme allows following dynamical specifications taking into account operational requirements and ancillary services imposed by the recent grid connection codes, that is, reactive power regulation and fault ride-through (FRT) capabilities. The control actions to be applied during normal grid operation are designed through second-order sliding mode techniques using a two-stage cascade structure. The multi-variable controller designed attains to regulate the active and reactive powers delivered to the grid, minimising the resistive losses into the generator and maintaining important internal variables into the desired range. This controller presents attractive advantages such as robustness against unmodelled dynamics and external perturbations, finite time convergence to the sliding surfaces and chattering mitigation. To endorse the controlled system with FRT capabilities, a switching control scheme based on voltage grid measurements is also proposed. The performance of the whole control approach is analysed through representative simulations which include parameter variations, external perturbations and three-phase voltage dips.

Photovoltaic (PV) systems, especially the ones installed in urban and suburban areas, operate often under non-uniform distribution of solar irradiance and PV cells temperature over the PV array. At this purpose, an architecture of the PV system based on distributed DC–DC converters, that performs the maximum power point tracking algorithm (DMPPT) can effectively counteract the reduction of power efficiency because of electrical, thermal and irradiance mismatch phenomena. Aim of this study is to experimentally assess the effect of the use of DC–DC boost converters with MPPT capability, directly applied at the substring level of a single PV module. The novelty of the approach here proposed with respect to the state-of-the-art is that the outputs of the converters are connected in parallel. Comparing the power efficiency of a conventional PV module with that of the considered prototype where the three substrings are connected to a dedicated DC–DC converter, a remarkable improvement of the extracted power ranging from 11 to 25% under non-uniform solar radiation was found.

This study presents an operation of custom power park (CPP) with wind turbine system (WTS). The classical power system stability, changes and challenges in the power system with installation of wind energy sources are given. The CPP is composed by static transfer switch (STS) for WTS. An electromagnetic transient model of a system is composed by WTS and STS in power system computer aided design/electromagnetic transient including DC (PSCAD/EMTDC) programme. The entire model of the proposed system is developed and simulating results are verified in PSCAD/EMTDC programme at different fault types. The system responses of the different fault types are given and obtained results are evaluated in detail for power quality problems. Moreover, of the different type faults are implemented to the WT feeder and the response of the proposed system is observed for all cases. Then, the simulating results are evaluated. The currents and voltages of all systems are investigated during normal, transfer and post-transfer periods and also these simulating results are evaluated.

This study deals with the problem of voltage security in microgrids. In general, voltage security is an issue for power systems, where the lack of reactive power is a concern. For microgrids a complexity is imposed, since frequency and voltage level deviations may take place by the operation of droop-controlled inverters. This study incorporates the load margin calculation into a microgrid structure. For this purpose, a special power flow program is developed in order to consider the effects of the droop-controlled inverters. Simulation results are obtained with the help of an islanded distribution system with only generators coupled by droop-controlled inverters, so the proposed methodology may be tested and discussed.

This study presents the design of a robust active disturbance rejection (ADR) controller in order to improve low-voltage ride-through (LVRT) capability of wind farms connected with doubly fed induction generator (DFIG). The ADR controller is particularly effective in real-time estimation and mitigation of the total effect of various uncertainties against a wide range of parameter variations, model uncertainties and large disturbances. The performance evaluation of the designed controller is performed on an IEEE system under different test cases. The simulation results show that the proposed controller is robust against uncertainties in operating conditions and successfully improves the damping and voltage stability and thus the LVRT capability of DFIGs.

From the perspective of output voltage control stability, this study investigates the stable operating area of photovoltaic (PV) cells feeding the DC–DC converter in output voltage regulation (OVR) mode. In this study, the boost interface converter is taken as an example, and its control system arrangements, small-signal model including the dynamic equivalent circuit of PV cells and the closed-loop transfer functions with different control loop formation are deduced at first. After that, according to the Hurwitz criterion, the essential condition for output voltage control stability is analysed and the relations between control loop formation of the interface converter in OVR mode and the stable operating area are obtained. The validity of the theoretical analysis has been verified by the experiment and simulation results of a 150 W prototype. The investigation shows that: (i) no matter what kind of control loop formation is adopted, the PV cells cannot output the maximum power when the PV interface converter operates in OVR mode; (ii) when the interface converter operates in OVR mode, PV cells can only operate stably in voltage area or current area. Moreover, the type of operating area entirely depends on the converter's output voltage control loop formation.

Microgrid (MG) could allow renewable and clean resources to penetrate into a controllable utility and achieve maximum utilisation of existing energy and demand-side management. This study proposes a new paradigm for distribution system operation considering MG conception. This study is focused on probabilistic analysis of optimal power dispatch considering economic aspects in MGs environment with technical constraints. In this study the economic operation of small scale energy zones is formulated and solved as an optimisation problem. A typical MG consists wind turbine (WT), photo voltaic (PV), micro turbine, fuel cell, combined heat and power and electric loads. Fluctuation behaviour of loads and generated power by WTs and PVs are caused complexity in proposed problem. Cost function includes generated powers by units, power transaction between MGs and main grid, operation and maintenance cost of resources and cost of pollutants emission. Considering MG concept in smart grids, the balance between supply-demand is secured through power exchanging between MGs and main grid, so that the value of objective function be minimised. The imperialist competitive algorithm is applied to solve proposed problem and obtained results are compared with Monte Carlo simulation method.

Considering the influence of slow response characteristic of a high-power proton exchange membrane fuel cell (PEMFC) on a grid-connected system adequately, a 150 kW PEMFC grid-connected system, including a PEMFC power unit based on a Ballard Stack Modules-FCvelocity™ HD6 is developed in this study. Moreover, then an active control strategy with vector-proportion integration controller is proposed to regulate the cascade system actively and improve the performance of compensating low-order harmonics. The comparisons with conventional active/reactive power (PQ) control are carried out to verify the validity of the proposed method under different conditional tests. The results demonstrate that the proposed strategy can not only track the grid power demand quickly, but also prevent the unsteady phenomena which are aroused by PQ control method from the relatively slow response of high-power PEMFC power unit. Furthermore, the total harmonic distortion of grid-connected current is measured by means of the criterion of IEEE Std1547-2003 and the result of fast Fourier transform analysis testifies that the proposed strategy can decrease the total harmonic content of currents better. Therefore, this proposed method will be an optional effective technique for the design of advanced high-power PEMFC grid-connected control system.

This study aims to define an online reactive power control scheme for a wind energy harvesting network such that it regulates the voltage at the transmission level in a manner comparable to a conventional synchronous plant and hence could be integrated in an existing transmission network hierarchical voltage control scheme. For that purpose, all decentralised elements within the network (wind farms and on load tap changing (OLTC) transformers) should be coordinated. In that sense, a central controller needs to be implemented. Unwanted controller interactions may then arise as the various decentralised controllers dynamically respond to the changing set-points received from a central controller. To mitigate these interactions, this study proposes a novel offline optimisation approach for tuning the dynamic settings (i.e. settings that affect the central controller temporal evolution such as time constant, time delays or dead bands). These settings ensure that the centrally determined set-points can actually be achieved in practice, and unlocking such performance is the principle research contribution of the present study.

For adaptive hill climbing method, variable stepping is achieved by sizing the change of power over the change of voltage (dP _PV/dV _PV) and change of power over change of D (dP _PV/dD) to appropriate step size using a properly tuned scaling factor. However, the photovoltaic (PV) power versus voltage curve has two different slopes which are the left-hand side of the maximum power point (MPP), and right-hand side of MPP (ROM). The fine-tuned scaling factor for the left-hand side PV slope has good performance at left-hand side of MPP (LOM) but can cause overshoot when system operates at the ROM; while scaling factor properly tuned for the right-hand side PV slope has good performance at ROM but slow voltage response when the system operates at LOM. Dual scaling factor technique is proposed to achieve good performance at LOM and ROM. Besides that, the drawback of implementing hill climbing method on buck converter is discussed, where using constant step size, the hill climbing method has small voltage response at point far from MPP but large voltage response at point near MPP. Based on the results obtained from a lab-scale prototype, it is proven that the proposed method is simple and effective.

The conversion efficiency of a crystalline silicon photovoltaic (PV) module increases as its temperature decreases. Considering this characteristic of the PV technology, in this study the authors analyse the use of cooled floating PV modules in a fraction of the area occupied by three reservoirs – Castanhão, Orós and Banabuiú – in the Brazilian semi-arid region. Comparing with conventional ground-mounted PV modules, an average conversion efficiency increase of 12.5% was measured for floating PV modules under the local weather conditions. In a second phase, measurements are used as input data in the PVSYST software in conjunction with a spreadsheet for the construction of electricity production scenarios. According to these scenarios, the potential PV production in the mentioned reservoirs would supply 7.4 and 18.8% of the electricity demand of Brazil's Ceará state (8.84 million inhabitants) and its largest city Fortaleza (2.6 million inhabitants), respectively.

In recent years, frequent accidents due to lightning have occurred in wind power plants, resulting in damages to electrical equipments in the power collection system, especially in the cable power collection system (CPCS) and the nacelle step-up transformer. In this study, electromagnetic transient simulation of lightning overvoltage in a 35 kV CPCS with the nacelle step-up transformer was carried out. Influencing factors including the location of the step-up transformer, the lightning current, the grounding resistance of wind turbine generator (WTG) and distance between WTGs are taken into consideration. The simulation results show that, in the case of 30 Ω grounding resistance for the WTG, the current flowing through the arrester installed at the high voltage winding side of the step-up transformer will reach up to 27.1 kA when subjected to a 200 kA lightning current, which reveals the damage mechanism of arrester blasting. Based on the calculation results, recommended nominal discharge current value for the arrester as well as the optimal lightning overvoltage protection method are proposed here.

Penetration levels of distributed wind power park modules (WPPMs) reach such high levels in parts of the world, for example, Germany, that reverse power flows (RPFs) from distribution to transmission level occur regularly in certain areas of the power system. This study compares the impact of normal and RPFs on the network fault response of WPPMs in distribution systems that are prone to fault-induced delayed voltage recovery issues for a fault in the transmission system. The study contributes to the ongoing discussion on grid connection requirements for WPPMs and raises awareness of a prolonged low-voltage ride-through (LVRT) operation of WPPMs when these are set to ride-through faults in ‘blocking mode’, during which the set-points for the active and reactive currents are set to zero. For RPFs such LVRT operation causes a substantial sustained active power deficit in power system areas with high penetration of distributed WPPMs and potentially leads to a stability risk.

Recent researches oriented to photovoltaic (PV) systems feature booming interest in current decade. For efficiency improvement, maximum power point tracking (MPPT) of PV array output power is mandatory. Although classical MPPT techniques offer simplified structure and implementation, their performance is degraded when compared with artificial intelligence-based techniques especially during partial shading and rapidly changing environmental conditions. Artificial neural network (ANN) algorithms feature several capabilities such as: (i) off-line training, (ii) nonlinear mapping, (iii) high-speed response, (iv) robust operation, (v) less computational effort and (vi) compact solution for multiple-variable problems. Hence, ANN algorithms have been widely applied as PV MPPT techniques. Among various available ANN-based PV MPPT techniques, very limited references gather those techniques as a survey. Neither classification nor comparisons between those competitors exist. Moreover, no detailed analysis of the system performance under those techniques has been previously discussed. This study presents a detailed survey for ANN based PV MPPT techniques. The authors propose new categorisation for ANN PV MPPT techniques based on controller structure and input variables. In addition, a detailed comparison between those techniques from several points of view, such as ANN structure, experimental verification and transient/steady-state performance is presented. Recent references are taken into consideration for update purpose.

To better cope with the challenges posed by the world today, the transition of systems engineering principles to complex, large scale, integrated and evolutionary system of systems (SoSs) has occurred. On the other hand, distributed generation has made its mark in the power distribution system, as a consequence of economic and environmental considerations. With the exponential advancement of technology, unconventional sources of generation, storage and microturbines have been enhanced. The microgrid has paved its way into distributed generation and looks promising for future prospects. A review of microgrid architectures and models is presented in this study. Various control schemes devised for microgrids are also reviewed. The concept of SoSs is introduced and its applications are discussed. A framework is proposed for microgrids from an SoS perspective and control paradigms based on SoS are explained in terms of microgrid control.

This study gives a selective overview of the technological status and comparison of selected thin-film solar cells. In the first part of this study, the development of thin-film solar cells is assessed, followed by comparison of the design structure among those thin-film solar cells and the current status of thin-film solar cells efficiency. The advantages and disadvantages of thin-film solar cells are also discussed. In the second part of this study, a comprehensive review is done on research upon copper–indium–gallium–diselenide (CIGS) thin-film solar cell in Southeast Asia countries. As compared with other regions of the world, Southeast Asia has not started the large manufacturing of CIGS yet, however, the research on it has been started.

The increasing share of distributed energy resources (DER) in electricity production requires new sources and techniques in grid support services to keep the quality and reliability of power supply high. Addressing this matter, DER systems are required to follow technical grid connection requirements determined by distribution system operators (DSOs). Currently, these requirements widely differ from country to country. Recent studies suggest developing unified grid connection requirements for DER on the international level. This unification currently is the main activity for DSOs and standardisation organisations in the field of grid-connected DER. To support this activity, the present article (i) offers a status report on recent studies relevant to the harmonisation of DER grid connection requirements, and (ii) identifies and discusses current DER grid connection guides, namely standards of international and European standardisation organisations, as well as regulations of national DSOs from Austria, Germany, Ireland, Latvia, Switzerland (German-speaking part) and the United Kingdom. The guides are collected and grouped according to the technical area and technology in a database: http://dergridrequirements.net. The database is a tool for finding relevant DER grid connection guides for a specific region, technical area and/or technology. The target audience of the database is DER system developers.