Showing papers by "Vestas published in 2013"

Connecting wind power plant with weak grid - Challenges and solutions

Abstract: The size of individual wind power plant is continuously increasing, while sites with good wind conditions often are located far from electrical loads This often results in wind power plants connecting to weak transmission grids The short circuit ratios at the point of common coupling of wind power plant can be lower than 3 in many cases, and even lower than 2 in extreme cases This paper analyzes the problems of connecting wind power plant with a weak AC system through detailed voltage stability analysis, small signal stability analysis and transient stability analysis, using power flow, frequency domain and time domain simulation methods Among the technical challenges, the voltage stability is identified as most critical to the stable operation of wind power plant within weak grid If the wind power plant itself cannot provide sufficiently fast and extensive compensation, the typical solution for the voltage stability problem is to install dynamic reactive power compensation with fast voltage control capability, such as STATCOM or even Synchronous Condenser Such additions heavily increase investment cost In this paper, a coordinated control method of wind power plant is proposed, to minimize the size of any additional reactive power compensation, and it is compared to de facto voltage controllers The new method enables wind power plant to be controlled as an integral generation source to fulfill grid code requirements, configuring individual WTGs to work as stiff voltage sources However, with the increase of bandwidth of voltage controller and decrease of grid short circuit ratio, the system is susceptible to a shunt resonance between voltage controller and grid impedance, and its influence on the proposed method is discussed

Life cycle assessment of wind power: comprehensive results from a state-of-the-art approach

Abstract: The article presents the method and results of the life cycle assessments (LCAs) of the Vestas' 2-MW GridStreamer TM wind turbines and outlines the state-of-the-art approach adopted. For more than 10 years, Vestas has prepared LCAs of wind power. However, since 2010, a step change in comprehensiveness has been employed, for example, conducting the LCA to individually assess all components within a wind turbine (being composed of around 25,000 parts). Three LCAs have been conducted with the 2-MW GridStreamerTM turbines in accordance with ISO 14040/44 and critically reviewed by an expert. The goal was to evaluate potential environmental impacts and other non-impact indicators per kilowatt hour of electricity generated for a ‘typical’ 50-MW onshore wind plant. The LCAs assessed all life cycle stages and were built using GaBi DfX software. A significant quantity of primary data were gathered, for example, covering over 100 Vestas' sites for manufacturing, sales and servicing, as well as establishing turbine use-phase performance (i.e. electricity generation, servicing, etc.) based on over 20,000 monitored wind turbines around the world, covering around 20 % of the current worldwide installed capacity. The baseline results show that per kilowatt hour of electricity generated by the 2-MW GridStreamer™ turbines have the following baseline performance: ADP elements 0.44 to 0.58 mg Sb-e, ADP fossil 0.10 to 0.13 MJ; acidification potential 37 to 45 mg SO2-e, eutrophication potential 3.7 to 4.5 mg PO4-e, freshwater aquatic ecotoxicity 100 to 130 mg DCB-e, global warming potential 7 to 10 g CO2-e, human toxicity potential 1,150 to 1,400 mg DCB-e, marine aquatic ecotoxicity potential 1,100 to 1,300 g DCB-e, photochemical oxidant creation 4 to 5 mg ethene, terrestrial ecotoxicity potential 19 to 24 mg DCB-e, return-on energy 8 to 11 months and recyclability 81 to 85 % of turbine mass. Being equipped with extensive facts and comprehensive LCA models provides Vestas the basis to further integrate environmental considerations into product marketing, design and research, procurement and to deliver transparent information to stakeholders. Overall, the article presents a case study of the LCA approach used to assess the potential impacts of 2-MW GridStreamer™ turbines based upon comprehensive product knowledge and represents a state-of-the-art approach to LCA modelling of wind power. The article discusses further applications of LCA internally to direct product improvement and for external communications and also highlights the LCAs' aim to improve transparency and robustness of previous LCAs of wind power.

Two improvements to the dynamic wake meandering model: including the effects of atmospheric shear on wake turbulence and incorporating turbulence build‐up in a row of wind turbines

Abstract: The dynamic wake meandering (DWM) model is an engineering wake model designed to physically model the wake deficit evolution and the unsteady meandering that occurs in wind turbine wakes. The present study aims at improving two features of the model: The effect of the atmospheric boundary layer shear on the wake deficit evolution by including a strain-rate contribution in the wake turbulence calculation. The method to account for the increased turbulence at a wake-affected turbine by basing the wake-added turbulence directly on the Reynolds stresses of the oncoming wake. This also allows the model to simulate the build-up of turbulence over a row of turbines in a physically consistent manner. The performance of the modified model is validated against actuator line (AL) model results and field data from the Lillgrund offshore wind farm. Qualitatively, the modified DWM model is in fair agreement with the reference data. A quantitative comparison between the mean flow field of the DWM model with and without the suggested improvements, to that of the AL model, shows that the root-mean-square difference in terms of wind speed and turbulence intensity is reduced on the order of 30% and 40%, respectively, by including the proposed corrections for a row of eight turbines. Furthermore, it is found that the root-mean-square difference between the AL model and the modified DWM model in terms of wind speed and turbulence intensity does not increase over a row of turbines compared with the root-mean-square difference of a single turbine. Copyright © 2013 John Wiley & Sons, Ltd.

Wind-power-plant control upon low-voltage grid faults

Abstract: A wind power plant connected to an electric grid A central plant controller is configured to carry out a method of controlling an electric output of the wind power plant in the event of a transient low-voltage fault of the electric grid The central plant controller is configured, after a fault stage in response to detection of a low-voltage fault during which the wind turbines ride through the grid fault, to control the wind power plant during a post-fault-support stage to provide only real power, or perform voltage control The central plant controller is configured to resume control of the wind power plant according to the nominal-grid operation mode, which prevailed before the low-voltage fault, in a nominal-grid operation stage

Field tests experience from 1.6MW/400kWh Li-ion battery energy storage system providing primary frequency regulation service

Abstract: Lithium-ion battery energy storage systems (BESSs) represent suitable alternatives to conventional generating units for providing primary frequency regulation on the Danish market This paper presents aspects concerning the operation of the BESSs in the Danish energy market while providing upwards primary frequency regulation Moreover, the paper presents the experience form field tests dedicated to the evaluation of the BESSs' performance degradation For this purpose, capacity measurements, Hybrid Pulse Power Characterization (HPPC) measurements, and AC impedance measurements were performed on the BESS demonstrator located in Western Denmark and initial results are introduced and discussed These measurements can be used to validate models for battery ageing during realistic operation or to develop the diagnostic tools for the BESS

Power plant & energy storage system for provision of grid ancillary services

Abstract: The present invention relates to method for operating a power plant, with at least one wind turbine generator arranged for supplying power to an electrical grid, at least one energy storage device arranged for supplying power to the electrical grid, and a power plant controller, the method comprises, measuring repetitively measurement sets of at least one electrical parameter from the electrical grid, and calculating, in respect the measurement sets of the at least one electrical parameter, a change in active and/or a required change in reactive power at a point of common coupling, and calculating and dispatching of a first control reference signal to the at least one wind turbine generator and a second control reference signal to the at least one energy storage device,for providing ancillary service functionalities to the electrical grid. The invention also relates to a power plant with at least one wind turbine generator for supplying power to an electrical grid, at least one energy storage device for supplying power to the electrical grid, and a power plant controller for providing ancillary service functionalities to the electrical grid.

A method of determining individual set points in a power plant controller, and a power plant controller

Abstract: This invention relates to a method and a power plant controller arranged to carry out the method. The method is on an intelligent dispatching of the power production to wind turbines and optional compensation equipment of a wind power plant, as the power producing units of a wind power plant. The invention relates to a case where the requested produced power is less than the total capacity of the power plant, and the invention relates to utilizing this situation to dispatch set points to the wind turbines and the compensation equipment in a flexible way. This flexibility may increase the wind turbines' life time, help in scheduling maintenance and expand the electrical operating range of the wind power plant. The determination of the set points on active and reactive power is a combined determination of both set points for each of the energy producing units of the wind power plant.

Frequency-Weighted Model Predictive Control of Trailing Edge Flaps on a Wind Turbine Blade

Abstract: This paper presents the load reduction achieved with trailing edge flaps during a full-scale test on a Vestas V27 wind turbine. The trailing edge flap controller is a frequency-weighted linear model predictive control (MPC) where the quadratic cost consists of costs on the zero-phase filtered flapwise blade root moment and trailing edge flap deflection. Frequency-weighted MPC is chosen for its ability to handle constraints on the trailing edge flaps deflection, and to target at loads with given frequencies only. The controller is first tested in servo-aeroelastic simulations, before being implemented on a Vestas V27 wind turbine. Consistent load reduction is achieved during the full-scale test. An average of 13.8% flapwise blade root fatigue load reduction is measured.

Impact of wind power plant reactive current injection during asymmetrical grid faults

Abstract: As more renewable energy sources, especially more wind turbines (WTs) are installed in the power system; grid codes for wind power integration are being generated to sustain stable power system operation with non-synchronous generation. Common to most of the grid codes, wind power plants (WPPs) are requested to stay connected and inject positive-sequence reactive current in order to boost positive-sequence grid voltage during short-circuit grid faults, irrespective of the fault type; symmetrical or asymmetrical. However, as shown in this study, when WPPs inject pure positive-sequence reactive current in case of asymmetrical faults, as a conventional method (CM) in accordance with the grid code requirement, positive-sequence grid voltage is boosted, but also higher negative sequence voltage in the grid and higher overvoltages at the non-faulty phases occur. In this study, an alternative injection method, where WTs are injecting both positive and negative sequence currents during asymmetrical faults, providing improved grid support, is given and compared with the CM. In addition, effect of coupling between positive, negative and zero sequences when WPPs are injecting currents during asymmetrical faults, is investigated, which was not considered in the wind power impact studies before.

Generic 12-bus test system for wind power integration studies

Abstract: High wind power penetration levels into power systems requires an appropriate power system model when assessing impact on the overall system stability. The model should capture the wide range of dynamics related to the wind integration studies, such as voltage control, synchronizing power control, inertial response, frequency control, damping of electromechanical oscillations, balanced and unbalanced fault management, etc. Hence, the power system components: conventional power plants with controls, transmission lines, transformers and loads should be represented accurately to achieve realistic power system characteristics. Additionally, the power system model should be simple and computationally manageable in order to simulate multiple scenarios with different control parameters in a reasonable time. In this paper, a generic power system model is presented in order to comprehend the wind integration studies with different penetration scenarios.

Fiber-optical grating sensors for wind turbine blades: a review

Abstract: With the rapid growth of wind turbines and focus on maintenance costs structural measurements are becoming essential. Fiber-optical sensors have physical properties that make them suitable for embedding in wind turbine blades, such as small size and immunity to electrical interferences. Fiber-optical grating sensors can be utilized to provide important information regarding strain, temperature, and curvature of the blades, which can be applied in condition-monitoring to detect fatigue failure and furthermore for optimization of the production from the wind turbine. We provide an overview of the current status and a discussion on research and implementation of fiber Bragg gratings and long-period gratings in wind turbine blade sensors.

Method of de-icing a wind turbine blade

Abstract: A method of de-icing a wind turbine blade (5) comprises the steps of: generating heated air using heating means (10) provided in the root portion of the blade; and continuously circulating the heated air around the interior of the blade through at least a portion of two more longitudinal blade cavities (24, 26, 28) defined within the blade. The circulating step includes: channelling the heated air from an outlet (32a) of the heating means at least part way through a first longitudinal blade cavity (26), towards the tip end (18) of the blade; at a position along the length of the blade, diverting the heated air from the first longitudinal blade cavity (26) into a second longitudinal blade cavity (24); and channelling the diverted air at least part way through the second longitudinal blade cavity (24) back to an inlet (34) of the heating means (10). The heated air is circulated through at least a central cavity (24) and a leading edge cavity (26) defined between longitudinal webs (22) within the blade.

Dynamic thermal modelling and analysis of press-pack IGBTs both at component-level and chip-level

Abstract: Thermal models are needed when designing power converters for Wind Turbines (WTs) in order to carry out thermal and reliability assessment of certain designs. Usually the thermal models of Insulated Gate Bipolar Transistors (IGBTs) are given in the datasheet in various forms at component-level, not taking into account the thermal distribution among the chips. This is especially relevant in the case of Press-Pack (PP) IGBTs because any non-uniformity of the clamping pressure can affect the chip-level thermal impedances. This happens because the contact thermal resistances in the thermal impedance chains are clamping pressure dependent. In this paper both component-level and chip-level dynamic thermal models for the PP IGBT under investigation are developed. Both models are developed using geometric parameters and material properties of the device. Using the thermal models, the thermal impedance curves under various mechanical clamping conditions are derived. Moreover, the deformation of the internal components of the PP IGBT under operating-like conditions is investigated with the help of the thermal models and the coefficient of thermal expansion (CTE) information.

Wind turbine blades and method of manufacturing the same

Abstract: Method of making a spar cap (146) for a wind turbine blade, the method comprising: (a) providing a plurality of elongate pultruded fibrous composite strips (100), each strip being of substantially constant cross section defined by first and second mutually opposed and longitudinally extending sides (102. 104) and by first and second longitudinal edges (110, 112), the first and second sides comprising, respectively, first and second planar abutment surfaces (118), the strip being of substantially uniform thickness between the first and second abutment surfaces, a first edge region (120) of the strip comprising a first edge of the strip being of relatively reduced thickness, the first side of the strip comprising an edge surface (122) adjacent the first abutment surface in the first edge region of the strip, and the strip having a first peel ply layer (114) at least partially covering the first abutment surface and at least partially covering the edge surface; (b) removing the first peel ply layers from the respective strips; (c) stacking the strips in a mould such that the first abutment surface of each strip abuts an abutment surface of an adjacent strip in the stack to define an interface region (142) between the strips, and such that a clearance region (144) is defined between the first edge region of each strip and an edge region of an adjacent strip in the stack; (d) supplying resin to the respective clearance regions and causing the resin to infiltrate into the interface regions between adjacent strips; and (e) curing the resin to bond the strips together.

A method of operating a wind turbine plant

Abstract: A method of operating a wind turbine plant is provided. Such a wind turbine plant comprises at least one transmission branch comprising a plurality of wind turbine generators and coupled to an electrical grid at a point of common coupling through at least one circuit breaker comprising a breaking capacity. The method comprises monitoring the electrical grid for a low voltage fault event; and if a low voltage fault event is detected: calculating a grid short circuit strength, determining a short circuit current limit if the grid short circuit strength requires an initial fault current contribution which exceeds the breaking capacity of the circuit breaker to be passed through the circuit breaker, determining a maximum fault current contribution based on the short circuit current limit and operating the wind turbine generators to provide to the electrical grid the maximum fault current contribution.

Wind turbine blade vibration detection and radar calibration

Abstract: A wind turbine (1) is provided, having a wind turbine tower (2) and at least one rotatable blade (5), and further comprising a system for measuring rotor blade vibration of said wind turbine. The system comprises at least one Doppler radar unit (7) operatively configured to emit and receive radar signals, the radar unit being mounted on the wind turbine tower at a position above the lowest position of the at least one blade, the radar unit being positioned so as to measure reflections of an emitted radar signal from the turbine blade. A processing unit is configured to receive measurement data from the radar unit and to determine, by analysis of Doppler shift in received radar signals relative to transmitted signals due to movement of the blade towards or away from the turbine tower, the velocity of the blade in the direction towards or away from the turbine tower. Using a radar unit to measure blade velocity allows a determination to be made of the vibrations occurring in the blade without needing an internal sensor in the blade. This reduces manufacturing and maintenance costs of the blades since sensors in the blades will not need to be replaced, and sensors positioned on the tower are easier to replace in the field.

Control of wind turbines

Abstract: A method of controlling a wind turbine is described. The method involves forecasting the temperature evolution of a component of the wind turbine based upon the current operating parameters of the wind turbine and upon a required power output; predicting from the temperature forecast a future alarm event caused by the temperature of the component exceeding a first threshold level or falling below a second threshold level; and adjusting the operating parameters of the wind turbine to control the temperature evolution of the component thereby to avoid or delay the predicted alarm event.

Ancillary services provided from wind power plant augmented with energy storage

Abstract: This paper presents a scheme to augment a wind power plant with energy storage and apply combined controls for provision of frequency support, inertial response and power oscillation damping Practical experience from a power plant configured with 12MW wind generation and 16MW energy storage is discussed, including sample results from tests of the ancillary services functionality

Gain-scheduled model predictive control of wind turbines using Laguerre functions

Abstract: This paper presents a systematic approach to design gain-scheduled predictive controllers for wind turbines. The predictive control law is based on Laguerre functions to parameterize control signals and a parameter-dependent cost function that is analytically determined from turbine data. These properties facilitate the design of speed controllers by placement of the closed-loop poles (when constraints are not active) and systematic adaptation towards changes in the operating point. Vibration control of undamped modes is achieved by imposing a certain degree of stability to the closed-loop system. The approach can be utilized to the design of new controllers and to represent existing gain-scheduled controllers as predictive controllers. The numerical example and simulations illustrate the design of a speed controller augmented with active damping of the tower fore-aft displacement.

Modular multilevel converter modelling, control and analysis under grid frequency deviations

Abstract: A tool for component sizing for MMCs has been developed and tested through simulations in PLECS. The steady-state behaviour under grid frequency deviations - interesting for offshore wind farm connections - has been analysed, providing insights in MMC characteristics and further testing the proposed tool.

A consistent turbulence formulation for the dynamic wake meandering model in the atmospheric boundary layer

Abstract: This thesis describes the further development and validation of the dynamic meandering wake model for simulating the flow field and power production of wind farms operating in the atmospheric boundary layer (ABL). The overall objective of the conducted research is to improve the modelling capability of the dynamics wake meandering model to a level where it is sufficiently mature to be applied in industrial applications and for an augmentation of the IEC-standard for wind turbine wake modelling. Based on a comparison of capabilities of the dynamic wake meandering model to the requirement of the wind industry, four areas were identified as high prioritizations for further research: 1. the turbulence distribution in a single wake 2. multiple wake deficits and build-up of turbulence over a row of turbines 3. the effect of the atmospheric boundary layer on wake turbulence and wake deficit evolution 4. atmospheric stability effects on wake deficit evolution and meandering The conducted research is to a large extent based on detailed wake investigations and reference data generated through computational fluid dynamics simulations, where the wind turbine rotor has been represented by an actuator line model. As a consequence, part of the research also targets the performance of the actuator line model when generating wind turbine wakes in the atmospheric boundary layer. Highlights of the conducted research: 1. A description is given for using the dynamic wake meandering model as a standalone flow-solver for the velocity and turbulence distribution, and power production in a wind farm. The performance of the standalone implementation is validated against field data, higher-order computational fluid dynamics models, as well as the most common engineering wake models in the wind industry. 2. The EllipSys3D actuator line model, including the synthetic methods used to model atmospheric boundary layer shear and turbulence, is verified for modelling the evolution of wind turbine wake turbulence by comparison to field data and wind tunnel experiments. 3. A two-dimensional eddy viscosity model is implemented to govern the distribution of turbulent stresses in the wake deficit. The modified eddy viscosity model improves the least-square fit of the velocity field in the wake by ~13% when compared to higher-order models. 4. A method is proposed to couple the increased turbulence level experienced by a turbine operating in waked conditions, to the downstream wake evolution of the wake-affected turbine. The intraturbine turbulence coupling improved the fit of the turbulence distribution by ~40% and the wind speed distribution by ~30% over a row of eight turbines. 5. The effect of the atmospheric shear on the turbulent stresses in the wake is captured by including a local strain-rate contribution for the ambient shear gradient. This results in more realistic turbulent stress levels in regions of small wake deficit gradients; this is particularly important in the far-wake region where atmospheric shear gradients are an important contribution to the local strain-rate. 6. A method to include the effect of atmospheric stability on the wake deficit evolution and wake meandering is described. Including the atmospheric stability effects improved the model prediction of the mean velocity field by ~19% and of turbulence distribution by ~28% in unstable atmospheric conditions compared to actuator line results. The power production by a row of wind turbines aligned with the wind direction is reduced by ~10% in very stable conditions compared to very unstable conditions at the same turbulence intensity. This power drop is comparable to measurements from the North Hoyle and OWEZ wind farms.

A power system and method for operating a wind power system with a dispatching algorithm

Abstract: The present invention relates to a power system having a plurality wind turbine generators and a power plant controller arranged to communicate with the plurality of wind turbines generators, where each of the plurality of wind turbine generator being related to a wind turbine controller, the wind turbine controller being arranged to control an active power output in its related wind turbine generator according to an active power set point received from the wind power plant controller; a first subset of wind turbine generators operating at an active power output unrestricted of the active power set point; and a second subset of wind turbine generators operating according to an active power set point; and wherein the wind power plant controller communicates the active power set point, in accordance with the active power output of the first subset of the plurality of wind turbines generators, so as to reduce active power fluctuation of the aggregated active power output of the first and second subset of the plurality of wind turbines generators. The present invention also relates to method accordingly.

Tower Vibration Control of Active Stall Wind Turbines

Abstract: Negative aerodynamic damping amplifies tower vibrations on turbines with stall rotors. Under certain conditions, these vibrations may rise to a level that causes a shutdown. Active stall turbines have a pitch system, and the objective of the work was to develop pitch control algorithms, which would minimize the probability of tower vibrations rising to the shutdown level. The results of a root cause analysis show that vibrations are largest when coherence of the wind across the rotor is high, and turbulence intensity is low. High magnitude tower vibrations are found to occur if all blades have similar angles of attack and these are in the narrow region in which aerodynamic damping is negative. The first control algorithm uses individual pitch control to ensure that all three blades do not have the same angle of attack. The second algorithm uses de-rating to eliminate the forcing function that causes the instability. The algorithms are described and simulation results are presented. Measured data from thousands of V82-1.65 MW turbines with the software in operation are presented. The control algorithms are found to reduce substantially the number of vibration shutdown events. The tower vibration control software is now in operation on more than 5 GW of installed wind turbines. The fact that high fatigue loads occur under conditions of unusually low turbulence and high coherence is the opposite from the normal wind turbine design situation. This provides a different perspective on wind turbine loads and control.

Compensating electrical harmonics on the electrical grid

Abstract: The invention relates to a control system for compensating undesired electrical harmonics on an electrical grid. Part of the control system referred to as a harmonic compensator is operatively connected with a power inverter of a power producing unit supplying power to the grid. Another part of the control system, referred to as an impedance detector, is operatively connected to a point of coupling to which point one or more power producing units are connected. The impedance detector is configured to scan impedances as a function of frequency to identify frequencies of impedance peaks which peaks are indicative of resonance frequencies. The determined resonance frequencies are supplied to one or more the harmonic compensators. A compensator determines control signals to the inverter which causes the inverter to inject compensation currents to the grid which currents will damp currents oscillating at or close to the determined resonance frequency.

Wind Turbine Blades

Abstract: A method of making a wind turbine blade incorporating a lightning protection system, the method comprising: providing a wind turbine blade mould; arranging a protruding element in the mould; arranging an electrically conductive layer over the protruding element in the mould; arranging one or more structural layers and/or structural components over the electrically conductive layer; consolidating the layers under vacuum to form a blade shell having an integrated electrically conductive layer proximate an outer surface of the shell; separating the protruding element from the blade shell to define a recess in the outer surface of the shell, with the electrically conductive layer extending into the recess; providing an electrical component of the lightning protection system adjacent an inner surface of the shell; and electrically connecting the electrically conductive layer to the electrical component via a connecting member; wherein an end portion of the connecting member is housed in the recess such that a surface of the connecting member abuts the electrically conductive layer across an interface region inside the recess, and such that the end portion does not substantially protrude from the outer surface of the shell.

Wind power plant frequency control

Abstract: The present invention relates to a method of operating a wind power plant, with at least one wind turbine generator connected to an electrical grid, wherein the method comprises the steps of, monitoring a frequency parameter and comparing it with a frequency set point, as to select a low or high frequency event and determining a power reference to the a least one wind turbine generator, based on the frequency parameter, In case a high frequency event is detected, the power reference is determined as a minimum of a selection of at least a first and a second minimum power reference And in case a low frequency event is detected, the power reference is determined as a maximum of a selection of at least a first and a second maximum power reference, dispatching the power reference to the at least one wind turbine generator The invention also relates to a wind power plant operating according to the method

A method of operating a wind turbine as well as a system suitable therefore

Abstract: A method of operating a wind turbine is provided. The wind turbine comprises a turbine rotor with at least two blades, each blade having a variable pitch angle. The method comprises determining mechanical loads on the blades, determining an asymmetric load moment experienced by the turbine rotor based on the mechanical loads on the blades, determining high order harmonics from the asymmetric load moment, and determining an individual pitch control signal for each of the blades for varying the pitch angle of each blade to compensate for the asymmetric load moment. The individual pitch control signal for each blade is determined at least based on the high order harmonics.

Node structures for lattice frames

Abstract: A node structure for connecting a member of a lattice frame to one or more other members of the frame comprises a hollow brace having opposed walls that converge outwardly at an acute angle in cross-section toward a central plane to connect at an outer edge. At least one root portion has a central longitudinal axis extending outwardly in the central plane of the brace for alignment with a member of the frame. The root portion has an inner end cut away at opposite sides around the central plane to leave a joining surface that intersects the converging walls of the brace while embracing an outer region of the brace extending inwardly from the outer edge.