This study compares the impact of drivetrain configuration on the mass and capital cost of a series of wind turbines ranging from 1.5 MW to 5.0 MW power ratings for both land-based and offshore applications. The analysis is performed with a new physics-based drivetrain analysis and sizing tool, Drive Systems Engineering (DriveSE), which is part of the Wind-Plant Integrated System Design & Engineering Model. DriveSE uses physics-based relationships to size all major drivetrain components according to given rotor loads simulated based on International Electrotechnical Commission design load cases. The model's sensitivity to input loads that contain a high degree of variability was analyzed. Aeroelastic simulations are used to calculate the rotor forces and moments imposed on the drivetrain for each turbine design. DriveSE is then used to size all of the major drivetrain components for each turbine for both three-point and four-point configurations. The simulation results quantify the trade-offs in mass and component costs for the different configurations. On average, a 16.7% decrease in total nacelle mass can be achieved when using a three-point drivetrain configuration, resulting in a 3.5% reduction in turbine capital cost. This analysis is driven by extreme loads and does not consider fatigue. Thus, the effects of configuration choices on reliability and serviceability are not captured. However, a first order estimate of the sizing, dimensioning and costing of major drivetrain components are made which can be used in larger system studies which consider trade-offs between subsystems such as the rotor, drivetrain and tower. INTRODUCTIONThree-point and four-point suspensions, which refer to wind turbine drivetrain configurations with either one or two main bearings, respectively, are the most common wind turbine drivetrain architectures. In the three-point suspension configuration, the rotor is rigidly connected to the main shaft, which is supported by a single main bearing near the rotor. A shrink disk typically connects the downwind side of the shaft to the low-speed stage of the gearbox. The gearbox is supported by two torque arms that are connected to the bedplate elastically. These two torque arms, along with the single main bearing, provide a total of three points of support. Commercial wind turbines that utilize this configuration include the General Electric GE 1.5 MW, Siemens SWT108 2.3 MW, Nordex N117 2.4 MW and Vestas V112 3 MW. 1 Four-point suspension configurations, sometimes referred as two-main-bearing suspension configuration, place an additional main bearing near the down-wind side of the main shaft with the intent of isolating any non-torque rotor loads upwind of the gearbox. Non-torque rotor loads are the non-torsional loads transmitted from the rotor blades to the drivetrain. These non-torque loads can affect gearbox reliability significantly by causing uneven loads among planetary gears and reducing bearing life. 2 The design protects the gearbox from non-torque loads but, at the same time, suc...

This report summarizes the theory, verification, and validation of a new sizing tool for wind turbine drivetrain com ponents, the Drivetrain Systems Engineering (DriveSE) tool. DriveSE calculates the dimensions and mass properties of the hub, main shaft, main bearing(s), gearbox, bedplate, transformer if up-tower, and yaw system. The level of fi delity for each component varies depending on whether semiempirical parametric or physics-based models are used. The physics-based models have internal iteration schemes based on system constraints and design criteria. Every model is validated against available industry data or finite-element analysis. The verification and validation results show that the models reasonably capture primary drivers for the sizing and design of major drivetrain components. iii This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications-continued from previous page Nomenclature Meaning GB Gearbox gbx Gearbox gc Gear coupling GE Generator gen Generator hb Hub hs High-speed shaft/coupling mb1, mb2 Upwind and downwind main bearing for four-point suspension mb Main bearing for three-point suspension ms Main shaft ms, i Inner main shaft norm Normal stress range p Planet r Rotor ra Radial rb Rotor-main bearing RNA Rotor-nacelle assembly s Sun rg Ring t Transformer T F Transformer TW Tower Superscript Meaning x, y, z Coordinates de, mean, ult, max Load type (deterministic, mean, ultimate, maximum) st stochastic vi This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications

This study investigates the effect of tip-speed constraints on system levelized cost-of-energy (LCOE). The results indicated that a change in maximum tip-speed from 80 to 100 meters per second (m/s) could produce a 32% decrease in gearbox weight (a 33% reduction in cost), which would result in an overall reduction of 1%-9% in system LCOE depending on the design approach. Three 100-m/s design cases were considered: a low tip-speed ratio/high-solidity rotor design, a high tip-speed ratio/low-solidity rotor design, and a flexible blade design in which a high tip-speed ratio was used along with removing the tip-deflection constraint on the rotor design. In all three cases, the significant reduction in gearbox weight caused by the higher tip-speed and lower overall gear ratio was counterbalanced by increased weights for the rotor and/or other drivetrain components and tower. As a result, the increased costs of either the rotor or drivetrain components offset the overall reduction in turbine costs from downsizing the gearbox. Other system costs were not significantly affected, whereas energy production was slightly reduced in the 100-m/s high-solidity case and increased in the low-solidity case. This situation resulted in system cost-of-energy reductions moving from the 80-m/s design to the 100-m/s designs of 1.5% for the high tip-speed ratio and 5.5% for the final flexible case (the latter result is optimistic because the impact of deflection of the flexible blade on power production was not modeled). The low tip-speed ratio case actually resulted in a cost of energy increase of 2.1%. Overall, the results demonstrated that there is a trade-off in system design between the maximum tip-speed and the overall wind plant cost-of-energy but also that there are several design trade-offs and design constraints that can limit the benefits of higher tip-speed designs. Scope Land-based wind project development has historically limited turbine designs to operate at blade-tip-velocities in the range of 75-80-m/s. The constraint arises from blade-tip aero-acoustic noise generation. The turbine system sound power levels are usually dominated by blade-tip noise when appropriate measures have been taken to mitigate sound emissions and audible tones from the tower head machinery within the nacelle and the power electronic converters often located within the tower base. The study looks at five overall turbine configurations: 1. A baseline 5-megawatt (MW) reference turbine Jonkman et al. (Feb 2009) with maximum tip-speed of 80-m/s 2. An optimized version with the same 80-m/s tip-speed design constraint 3. An optimized design at 100-m/s maximum tip-speed with a high-solidity rotor 4. An optimized design at 100-m/s maximum tip-speed with a low-solidity rotor 5. An optimized design at 100-m/s maximum tip-speed with a low-solidity rotor where the tip-deflection con straint has been removed (as a proxy for a machine that would operate downwind). In each of the design cases, a sequential optimization was performed to design the turbine. The ro...

With the proliferation of alternate power sources such as fuel cells and photovoltaic systems in the distributed power system architecture it is important to design inverters to support seamless bi-directional power flow between the inverter and the grid. For this the inverter should work in voltage control mode in stand alone operation; current control mode in grid connected operation and when power is drawn from the grid the inverter should, typically, operate in power factor correction mode. This paper deals with the modeling and analysis of grid connected inverters to address control issues in the above modes together with seamless transfer between modes. It is shown that the filter network configuration changes between modes and greatly impacts overall system dynamics. Based on small signal modeling, new control strategies that ensure near unity power factor in bidirectional power flow and smooth transition between modes is presented. The control scheme is implemented on a DSP platform using state-space filtering techniques.