Large-scale Wind Energy Conversion Systems Research Articles

ANALYSIS OF PERFORMANCE COEFFICIENTS IN MAXIMUM ELECTRICAL POWER EXTRACTION FROM STAND-ALONE WIND ENERGY CONVERSION SYSTEM

Increasing performance and improving efficiency in maximum power extraction from Wind Energy Conversion Systems (WECS) is a quite important research topic. Today, in the large-scale WECS, it is widely aimed to extract the maximum mechanical power from the wind turbine using the Maximum Power Point Tracking (MPPT) unit. Similarly, it can also be targeted to achieve maximum mechanical power in small-scale WECS applications. However, losses occur in structural subsystems and electrical subunits located in WECS. Due to these losses, the overall system efficiency decreases and the characteristic of the system is also affected. The operation of these systems can also be performed via maximum electrical output power extraction, which is one of the most up-to-date ideas. Thus, the overall WECS rather than the wind turbine can be optimally controlled. Eventually, maximum electrical power tracking (MEPT) based designs can provide higher power extraction with higher efficiency than MPPT-based ones. In this paper, considering the system operating concepts with MPPT and MEPT for a stand-alone Permanent Magnet Synchronous Generator (PMSG) based WECS, the changes in performance coefficients at defined focus points in terms of system efficiency are evaluated. Technical and theoretical comparative analyzes are also made for each specific wind speed between 8m/s and 12m/s.

Modified demagnetisation control strategy for low‐voltage ride‐through enhancement in DFIG‐based wind systems

The large-scale wind energy conversion systems (WECSs) based on doubly-fed induction generators (DFIGs) are very popular in recent years due to the numerous technical and economic benefits. With the increasing penetration level of wind energy, the latest grid codes require the DFIG-based WECSs to remain connected to the grid under grid fault scenarios and deliver the required reactive power into the grid. However, the direct connection of the stator of the DFIG to the grid makes it prone to grid disturbances, especially to voltage sag. This study proposes a modified demagnetisation control strategy to enhance the low-voltage ride-through (LVRT) capability of the DFIG under grid faults. The proposed control strategy is implemented in a coordinated approach by using the existing demagnetisation control and the addition of an external resistance in the stator side of the DFIG. The demagnetisation control damps the direct current component of the stator flux and the external resistance accelerates the damping of the transient flux by decreasing the time constant and hence, enhancing the LVRT capability of DFIG. The effectiveness of the proposed control strategy is demonstrated under both symmetrical and asymmetrical grid faults simulated system through MATLAB/Simulink®. The comparative results justify the merits of the proposed methodology.

Wind energy potential and cost estimation of wind energy conversion systems (WECSs) for electricity generation in the eight selected locations of Tigray region (Ethiopia)

Wind energy is one of the most cost-effective forms of renewable energy source with significant increment in yearly installed capacities all around the world. In this study, three commercial wind turbines, namely POLARIS P15-50, POLARIS P50-500 and VESTAS V110-2.0, were chosen as large-scale wind energy conversion systems (WECSs) for technical assessment of electric power generation in eight selected locations spreading across the Tigray region of Ethiopia. The economic evaluations of these three WECSs for electric power generation in the selected locations were estimated using present value of cost (PVC) method. These results showed that the highest capacity factor is obtained as 7.873 % using VESTAS V110-2.0 at Mekele, while the lowest as 0.002 % using POLARIS P15-50 at Shire. Average minimum cost per kWh obtained at Mekele was 0.0011$/kWh using VESTAS V110-2.0, while the highest average cost was 7.3148$/kWh using POLARIS P15-50 at Shire. Furthermore, it can be suggested that Atsbi, Chercher, Mekele and Senkata were most profitable for electrical and mechanical applications than hydropower cost in the country.

Maximum Power Point Tracking Strategy for Large-Scale Wind Generation Systems Considering Wind Turbine Dynamics

Under the global trend of renewable energy development, various advanced techniques such as forecasting algorithm, intelligent computation, and optimal control are expected to make the complex and uncertain renewable energy system stable and profitable in the near future. This paper presents a new control strategy for large-scale wind energy conversion systems to achieve a balance between power output maximization and operating cost minimization. First, an intelligent maximum power point tracking (IMPPT) algorithm is proposed such that short-term wind speed prediction, wind turbine dynamics, and MPPT are collectively considered to improve system efficiency. Second, in view of a spatial and temporal distribution of wind speed disturbances, a box uncertainty set is embedded in the forecast wind speed, which is likely more realistic for practicing engineers. Then, the IMPPT and box uncertainties are applied to the wind energy conversion system (WECS) control strategy, which is formulated as a min-max optimization problem and efficiently solved with semi-definite programming (SDP). Finally, a comparison with the conventional MPPT control method demonstrates that the proposed approach can obtain higher efficiency, which validates this paper.

Grid matching of large-scale wind energy conversion systems, alone and in tandem with large-scale photovoltaic systems: An Israeli case study

This paper presents a grid matching analysis of wind energy conversion systems (WECSs) and photovoltaic (PV)–WECS hybrid systems. The study was carried out using hourly load data of the Israel Electric Corporation (IEC) for the year 2006 and the corresponding simulated hourly performance of large PV and WECS plants in the Negev Desert. Our major objective was to compare the grid-matching capabilities of wind with those of our previously published PV results, and to assess the extent to which the combined employment of WECS and PV can improve the grid matching capability of either technology when used on its own. We find that, due to the differences in diurnal and seasonal output profiles of WECS and PV, their tandem employment significantly improves grid penetration compared to their use individually.

Composite System Adequacy Assessment Incorporating Large-Scale Wind Energy Conversion Systems Considering Wind Speed Correlation

This paper investigates the reliability effects on a composite generation and transmission system associated with the addition of large-scale wind energy conversion systems (WECS) using the state sampling Monte Carlo simulation technique. Three types of composite system were developed to represent the general conditions that exist in practical systems and used to conduct the studies presented in this paper. Load point and system indices for the three types of test systems are presented to illustrate the impact of adding wind farms in various system locations and the effect of varying the degree of wind speed correlation. The contributions of large-scale wind farms considering different degrees of wind speed correlation to the reliability performance of an electric power system are quantified in this paper.

Feasibility analysis of renewable energy supply options for a grid-connected large hotel

This study presents an analysis of the technical and financial viability of grid-only, RES-only and grid/RES hybrid power supply configurations for a large-scale grid-connected hotel (over 100 beds). Assessment criteria comprised net present cost (NPC), renewable fraction (RF) and payback time. The RES software HOMER (National Renewable Energy Laboratory, US) was utilised as the assessment tool with modeling performed with hourly load data input from a hotel located in a subtropical coastal area of Queensland, Australia. The results demonstrate that RES, in principle, has the potential to supply significant power for a large-scale tourist accommodation, in conjunction with the grid-electricity supply. Optimisation modeling demonstrated that, at 2004 prices, the NPC of the grid/RES hybrid configuration is comparable with the grid-only supply and resulted in a RF of 73%, a payback time of 14 years and a reduction in greenhouse gas emissions of 65%. Optimisation modeling also showed that whilst a RES-only configuration can potentially supply 100% of power demand, such a configuration is presently uneconomical given current electricity costs. Results indicate that wind energy conversion systems (WECS), rather than photovoltaics, are the most economically viable RES technology for large-scale grid-connected operations. Specifically, large-scale WECS (over 1000 kW) are more efficient and more economical than multiple small-scale WECS (0.1–100 kW). Hydrogen fuel cells and storage are presently uneconomical in grid-connected configurations. Sensitivity analysis demonstrated that operations that rely on grid-only supply are more economically susceptible to escalations in electricity costs and the imposition of carbon taxes, in comparison to grid/RES hybrids. Indeed, at present electricity prices, which have nearly quadrupled since 2004, the grid/RES hybrid is more economical over a 20-year span than the grid-only system, with a NPC which is 50% lower, and a payback time of 4.5 years. The analysis demonstrates that RES is both technically feasible and economically viable as an addition to grid-connected supply for large-scale tourist operations, and should become more attractive as costs of conventional supplies increase.

Feasibility analysis of stand-alone renewable energy supply options for a large hotel

This paper provides a feasibility analysis of renewable energy supply (RES) for a stand-alone supply large-scale tourist operation (with over 100 beds). The analysis utilises the power load data from a hotel located in a subtropical coastal area of Queensland, Australia. The assessment criteria of the analysis are net present cost, renewable factor and payback time. Due to the limited number of RES case studies in tourist operations and the absence of studies for large resorts, requiring facilities with a higher degree of comfort such as air-conditioning, it is not possible to establish with confidence the viability of RES in this industry. The specific operational characteristics of the tourism accommodation sector, such as 24-h operation, comfort provision and low tolerance for failure necessitates a separate assessment of RES viability for this sector, rather than relying on similar assessments from other commercial sectors. This study uses RES assessment software tools, HOMER (National Renewable Energy Laboratory, US) and HYBRIDS (Solaris Homes, Queensland, Australia), in order to compare diesel generator-only, RES-only and RES/diesel hybrid technologies. HOMER uses hourly load data, whilst HYBRIDS uses average daily energy demand for each month. The modelling results demonstrate that RES, in principle, has the potential to adequately and reliably meet power demand for a stand-alone large-scale tourist accommodation. Optimisation modelling demonstrates that 100% of power demand can be supplied by a RES-only configuration. A hybrid diesel/RES configuration provides the lowest NPC result with a resultant RF of 76%. In comparison to the diesel generator-only configuration, NPC is reduced by 50% and Greenhouse Gas (GHG) emissions by 65%. The payback time of the hybrid RES scenario is 4.3 years. Results indicate that wind energy conversion systems (WECS), rather than photovoltaics, are the most economically viable RES for large-scale operations. Large-scale WECS (over 1000 kW) are more efficient and economical than multiple small-scale WECS (0.1–100 kW). Both modelling tools produced similar results, with HYBRIDS producing on average slightly higher NPC results than HOMER. The modelling and resulting data from the analysis indicate that RES is technically feasible and economically viable as a replacement for conventional thermal energy supply for large-scale tourist operations dependent on stand-alone power supplies.

Determination of optimum arrays of wind energy conversion devices

This paper discusses the use of large-scale wind energy conversion systems consisting of arrays of individual wind machines. The arrays have been analyzed in some detail with the aid of a rough boundary-layer velocity profile model. The analyis indicates intermachine spacings that will provide for maximum output from either the total array or individual machines within the array. These arrangements are not coincident. Using the results obtained, detailed optimization and economic analyses may be made for large-scale wind systems. Nomenclature A — swept area of wind energy conversion system A1 = variable representing value of velocity model with discrete roughness on surface in the power ratio equation B — constant for turbulent boundary-layer velocity profile