Most studies involving the use of hydropower in an electric power system tend to consider the point of view of the system operator even though under liberalized markets in Europe, the operation of hydro units is set by the owner to maximize their profits. Such studies also often neglect uncertainties related to hydropower operation and instead assume perfect knowledge of the system conditions over the simulation horizon. This paper presents a methodology to overcome the aforementioned limitations. We optimize the operational choices of a hydropower cascade owner with multiple linked hydro assets and the ability to participate in several energy and reserve markets while also accounting for the impact of market price uncertainties on the owner’s operating decisions. The versatile optimization model created includes a detailed representation of any selected hydro cascade’s topology, constraints to reflect the machinery characteristics, and a rolling horizon approach to account for the price uncertainties in the daily operating schedule. The model is first validated using historical data for a hydro cascade in Switzerland and a perfect-knowledge approach. Next, price uncertainty is added to improve the historical simulation results and find a trade-off between accuracy and computational time.

This paper introduces a novel type of direct-drive electric generator, suitable for producing high-power at low rpm in wind applications. The proposed patented design eliminates the magnetic core based on the concept of circular flux and characteristics of Halbach Array. By using circular flux crossing through patented Folded Electromagnetic Coils (FECs) on the stator, an optimal design with maximum use of space will be gained. Furthermore, through special configuration of diametric and axial magnets on the rotor, a pattern of circular flux can be produced, which is magnified only on the side of the stator (where needed), based on characteristics of the Halbach array. By using such design, the need for using magnets on both sides of armature windings (devised in certain designs such as the Yokeless and Segmented Armature (YASA) topology), will be eliminated, resulting in further reduction of the magnetic materials in the machine design. In the paper, we show how the proposed design results in better no-load voltage per kg by a factor of 1.52 when compared to a YASA design of the same physical size. Furthermore, we show how our calculations are based on experimental results verified through tests on a prototype of the proposed design.

Based on a real-world scenario in Central America, this work is to plan and design a solar-powered microgrid for the rural communities who have had no access to electric power due to their distance from the grid as well as the mountainous terrain. The minimum spanning tree method is used to generate the initial grid topology and the difference between the results with and without the consideration of actual terrain effects is shown. The design of solar generation and energy storage has 3 options: a centralized solar park powering all communities, each community with a solar plant, and distributed generation at household level. Using dc power flow, we develop optimization algorithm to improve the solutions and compare the designs in terms of feasibility and resilience (against power congestion) or robustness (against structural damage). Through this case, it is demonstrated that our methodology can inform and assist the planning of solar-powered microgrids for remote communities.

In recent years, there has been a growing demand for high-power-density direct-drive generators in the wind industry owing to their high reliability, torque per unit volume, and conversion efficiencies. However, direct-drive wind turbine generators are very large, low-speed electric machines, which pose remarkable design and manufacturing issues that challenge their upscaling potential and cost of implementation. With air-gap tolerance as the main design driver, the need for high stiffness shifts the focus toward support-structure design that forms a significant portion of the generator’s total mass. Existing manufacturing processes allow the use of segmented-steel-weldment disk or spoke-arm assemblies that yield stiffer structures per unit mass but tend to be heavier and more expensive to build. As a result, there is a need for a transformative approach to realize lightweight designs that can also facilitate series production at competitive costs. Inspired by recent developments in metal additive manufacturing (AM), we explore a new freedom in the structural design space with a high potential for weight savings in direct-drive generators. This includes the feasibility of using nonconventional complex geometries, such as lattice-based structures as structurally efficient options. Powder-binder jetting of a sand-cast mold was identified as the most feasible AM technology to produce large-scale generator rotor structures with complex geometry. A parametric optimization study was performed and optimized results within deformation and mass constraints were found for each design. The response to the maximum Maxwell stress due to unbalanced magnetic pull was also explored for each design. Further, a topology optimization was applied for each parameter-optimized design to validate results and provide insights into further mass reduction. These novel designs catered for AM are compared in both deflection and mass to conventional rotor designs using NREL’s systems engineering design tool, GeneratorSE. The optimized lattice design with a U-beam truss resulted in a 24% reduction in structural mass of the rotor and 60% reduction in radial deflection. It is demonstrated that additive manufacturing shifts the focus from manufacturability constraints toward lower mass.

Ocean and wind energy require reliable, efficient electric conversion systems to be viable resources. Direct drive electric generators offer both benefits; however, it is difficult to generate the required torque at the low speeds typical of these resources. In this DOE sponsored project, ABB US Corporate Research partnered with Resolute Marine Energy (RME) and Texas A&M University to investigate the suitability of direct drive electric power generation for a paddle-type wave energy converter (WEC). This WEC provides high torque in a relatively chaotic, oscillating manner and requires a machine capable of handling high peak torques of approximately 40,000 N·m at speeds typically not exceeding 3 rpm. The baseline concept uses a hydraulic power take-off coupled with a generator and convertor; a direct drive electric solution may be beneficial. As a first step in designing a suitable direct drive generator for this application, we have begun with a smaller scale prototype targeting one tenth of the speed and torque, and we investigated a machine topology that may be promising in the operating regime of the full-scale machine. To this end, we designed and tested an integral generator and magnetic gear which is rated at 3,800 N·m at 30 rpm and completed a paper design for a machine of the required scale. This paper describes the mechanical design and testing of the prototype machine and provides some reflection on necessary design changes for the full-scale machine.

The world of intelligent microgrids and smart grids is rapidly evolving, with new technologies frequently emerging. Integrating “smart” controls into tactical or mobile grids is critical for remote locations that may not have access to utility power. This paper describes research on a process by which a power network topology can be automatically mapped, allowing the control system to identify which equipment is powered by a specific generator. Called the power beacon, this technology is designed to be used in cases where electric subgrids can be joined or split to accommodate power sharing for tactical or emergency power grids. The power beacon operates by issuing a brief current that can be measured at the generation source. Each load in the power grid is retrofitted with the simple and inexpensive circuitry to create this signal. If the grid configuration changes, an iterative process is used so that the location of each load with respect to its power source can be automatically and rapidly determined. Research and development of the power beacon evaluated various methods for generating the current pulses. Initial testing of the concept included shaping of the pulse to reduce noise, as well as testing open and closed loop pulse generation with and without feedback. The development also addressed pulse frequency to help mitigate the negative effect the load inductance will have on power beacon operations. The design process and results from initial testing acted as a proof of concept. Based on the initial results of system testing, modifications were made to handle electrical “noise” coming from the sample power distribution system. The new design integrated a digital filter for noise rejection and increased the current pulse amplitude. These adjustments were tested and indicated significant improvement. The updated power beacon has been installed in a demonstration power distribution system to continue evaluation of viability.

For Boiling Water Reactors (BWR) and steam generators, the water level is a safety-relevant process variable. The most commonly applied measuring method is based on the calculation of the liquid level from geodetic pressure differences to a reference column of defined height and density. However, transition processes occurring under operational and accident conditions may lead to dynamic changes in the reference level and therefore to fluctuations in the differential pressure signal. This paper presents experiments and numerical simulations on the steady-state and transient behavior of gas/liquid phase boundaries in “Zero Chamber Level Vessels” (ZCLV). In these slightly inclined miniature tubes, the constant reference level is provided by surface tension forces and the capillary effect, respectively. To investigate the basic topology of gas/liquid interfaces under simplified conditions (environmental parameters, no heat transfer), a test facility with optical access was developed. The construction allows for variations of the inner tube diameter, inclination angle and liquid mass flow rate, respectively. By this means, experiments on phase boundaries were carried out for ethanol/air and water/air. The results provide information about the impact of geometry parameters and their interactions on the interface topology. In addition, the dynamic draining of excess liquid mass at the free end of the tube and at artificial weld seams, which is supposed to be the reason for temperature fluctuations observed in ZCLV during power operation of BWR, was experimentally analyzed. The measurements represent the basis for an experimental validation and optimizations of the numerical flow code ANSYS CFX 12.0. In the next step, water/vapor phase boundaries at 286 °C and 70 bar will be investigated by applying x-ray radiography to a scale model. The results will be discussed in context with the hydrostatic level measurement in BWR.

Natural weathering and wear of structural materials in service nearly always generate surface roughness, and follow the Central Limit Theorem prediction for surface topology. This study couples experimental and statistical theory, to extend knowledge of life of materials from initial service surface conditions through surface damage accumulation. Statistical moments and other parameters were correlated with fracture locations probability ( H/N ), versus auto correlation length, and depth. As the surface grows to a full Gaussian, H/N increases its dependence on profile’s average and RMS roughness, and derived parameters. This dependence shows an asymptotic limit behavior that approaches agreeably Griffith’s crack criterion, though with multiple fracture locations. Importantly, a Transitional Region was observed, below which the probable location of fracture is uncorrelated to the parameters studied. This is because introduced roughness is insufficient to compete with impurities, internal and external manufacturing flaws, and scratches, due to handling and machining, on the samples.