Variable Ratio Gearbox Research Articles

Dynamic Modeling and Controller Design for a Novel Front-End Speed Regulation (FESR) Wind Turbine

Most existing wind turbine generation systems (WTGS) are based on double-fed induction generator (DFIG) and direct-drive synchronous generator (DDSG). In this paper, we investigate the modeling and controller design of a novel front-end speed regulation (FESR) wind turbine with differential variable ratio gearbox (VRG). For this wind turbine, a surface mount permanent magnet synchronous motor (SPMSM) unit is embedded to maintain the constant (i.e., synchronous) speed of the generator shaft over wide range of wind speed, which allows the conventional synchronous generator to be used to construct a grid-friendly WTGS. Compared with DFIG and DDSG, the novel FESR does not use converters for grid-connecting but adopt SPMSM to ensure the synchronous speed. A model-independent speed control algorithm for maximum power point tracking (MPPT) is developed based on a neuro-adaptive backstepping approach. Theoretical analysis and numerical simulations show that the proposed control scheme ensures more precise motor speed tracking in the presence of parameter uncertainties and external load disturbances.

A design methodology for selecting ratios for a variable ratio gearbox used in a wind turbine with active blades

Abstract This paper investigates the performance of a variable ratio gearbox (VRG) used in a small fixed-speed wind turbine with active blades. The major components of the VRG-enabled drivetrain are an automatic-manual gearbox and squirrel cage induction generator that connects directly to the grid. The simplicity of this system may be appealing for applications when cost and reliability are of concern. It is an alternative to variable speed systems, which necessitate a modified generator and power conditioning equipment. During partial load operation the VRG provides a discrete set of rotor speeds. This allows the controller to track the wind speed and to achieve a greater efficiency. This study suggests three VRG ratios are sufficient to improve performance when used with active blades. A case study is presented where the performance is simulated using three different wind data sets. The study suggests that the VRG can improve production between 7 and 8.5% in low wind areas. The design procedure also illustrates a technique for finding the lowest and highest gear ratios needed for VRG design. These ratios allow the system to achieve the lowest cut-in and rated speeds. The approach also has useful implications for the design of a continuously variable transmission.

A Methodology to Synthesize Gearbox and Control Design for Increased Power Production and Blade Root Stress Mitigation in a Small Wind Turbine1

Large wind turbines typically have variable rotor speed capability that increases power production. However, the cost of this technology is more significant for small turbines, which have the highest cost-per-watt of energy produced. This work presents a low-cost system for applications where cost and reliability are of concern. The configuration utilizes the fixed-speed squirrel cage induction generator. It is combined with a variable ratio gearbox (VRG) that is based on the automated-manual automotive transmission. The design is simple, low cost and implements reliable components. The VRG increases efficiency in lower wind speeds through three discrete rotor speeds. In this study, it is implemented with active blades. The contribution of this work is a methodology that synthesizes the selection of the gearbox ratios with the control design. The design objectives increase the power production while mitigating the blade stress. Top-down dynamic programming reduces the computational expense of evaluating the performance of multiple gearbox combinations. The procedure is customizable to the wind conditions at an installation site. A case study is presented to demonstrate the ability of the strategy. It employs a 300 kW wind turbine drivetrain model that simulates power production. Two sets of wind data representing low and high wind speed installation sites were used as the input. The results suggest a VRG can improve energy production by up to 10% when the system operates below the rated wind speed. This is also accompanied by a slight increase in the blade-root stress. When operating above the rated speed, the stress decreases through the optimal selection of gear combinations.

A Design Framework for Optimizing the Mechanical Performance, Cost, and Environmental Impact of a Wind Turbine Tower

The tower represents a significant portion of the materials and cost of the small wind turbine system. Optimization techniques typically maximize the tower loading capability while reducing material use and cost. Still, tower design focuses mainly on structural integrity and durability. Moreover, tower motion that intensifies drivetrain and structural loads is only rarely considered. The environmental impact of the wind turbine must also be considered since wind energy promotes sustainability. Trade-offs between the structural performance, cost, and environmental impact are examined to guide the designer toward a sustainable alternative. Ultimately, an optimal design technique can be implemented and used to automate tower design. In this study, nine tower designs with different materials and geometries are analyzed using finite element analysis (FEA). The optimal tower design is selected using a multilevel-decision-making procedure. The analysis suggests that steel towers of minimal wall thickness are preferred. This study is a continuation of the previous work that optimized energy production and component life of small wind systems (Hall et al., 2015, “An Integrated Control and Design Framework for Optimizing Energy Capture and Component Life for a Wind Turbine Variable Ratio Gearbox,” ASME J. Sol. Energy Eng., 137(2), p. 021022). The long-term goal is to develop a tool that performs optimization and automated design of small wind systems. In our future work, the tower and drivetrain designs will be merged and studied using higher fidelity models.

An Integrated Control and Design Framework for Optimizing Energy Capture and Component Life for a Wind Turbine Variable Ratio Gearbox

Small wind turbines are a promising technology that can provide renewable power to rural and remote communities. In order to increase the efficiency and competitiveness of small wind technology, it is necessary to maximize the wind energy capture and to prolong the turbine system life. Accordingly, this paper presents an integrated development framework that optimizes component design goals, including durability and minimal gearbox mass, with the control objective of producing maximum energy over the turbine system’s 20-yr life. This study focuses on the wind turbine gearbox, which plays a critical role in achieving high efficiency and extended system life. A variable ratio gearbox (VRG) previously developed by the authors is used as an example to demonstrate the methodology. In this paper, an algorithm developed for optimizing the VRG gear ratio is integrated with the design selection of commercially available gears, which will be used to construct the VRG gearbox. The proposed multi-objective framework is capable of identifying the optimal gearsets based on a trade-off between selecting gearsets that maximize wind turbine efficiency and choosing gearsets that best meet the design requirements.

Modeling of a Hydraulic Wind Power Transfer Utilizing a Proportional Valve

Hydraulic circuits can transfer remarkable amounts of energy in the desired direction without taking large space. To implement this technology for harvesting the energy of wind appropriately, models of the system are required. Hydraulic wind power technology has the benefits of eliminating expensive and bulky variable ratio gearbox and its costly maintenance, while enabling the integration of multiple wind turbines in a single generation unit. In this paper, the dynamics of different hydraulic elements are studied, nonlinearities are taken into account, pressure dynamics in different parts of the system are studied, and the motor load effects are considered. Based on these considerations, a novel nonlinear state-space representation of the system is introduced. Results of the mathematical model and the experimental data are compared to verify the proposed model. The comparison demonstrated that the mathematical model captures all major characteristics of the hydraulic circuit and can model the system behavior under different operating conditions.

Optimal Control of a Wind Turbine With a Variable Ratio Gearbox for Maximum Energy Capture and Prolonged Gear Life

An optimal control approach for a wind turbine drivetrain with a variable ratio gearbox is presented. The objective is to find the optimum shifting sequence of the variable ratio gearbox in order to maximize power generation and extend gear life. The employment of a variable ratio gearbox enhances the capabilities of the wind turbine to cope with wind speed variations. Based on the authors' preliminary study, the gear ratios of the variable ratio gearbox were carefully selected to maximize the wind energy capture. In this paper, a new control approach is proposed to achieve both extended gear service life and optimal energy harvesting. This new approach finds the gear shifting sequence that will minimize the tangential force on the gear tooth while maximizing the wind energy capture. The wind turbine drivetrain with a variable ratio gearbox is modeled and simulation results based on recorded wind data of different wind classes are presented and compared.

Performance Analysis of Hybrid and Full Electrical Vehicles Equipped with Continuously Variable Transmissions

The main aim of this paper is to study the potential impacts in hybrid and full electrical vehicles performance by utilising continuously variable transmissions. This is achieved by two stages. First, for Electrical Vehicles (EVs), modelling and analysing the powertrain of a generic electric vehicle is developed using Matlab/Simulink-QSS Toolkit, with and without a transmission system of varying levels of complexity. Predicted results are compared for a typical electrical vehicle in three cases: without a gearbox, with a Continuously Variable Transmission (CVT), and with a conventional stepped gearbox. Second, for Hybrid Electrical Vehicles (HEVs), a twin epicyclic power split transmission model is used. Computer programmes for the analysis of epicyclic transmission based on a matrix method are developed and used. Two vehicle models are built-up; namely: traditional ICE vehicle, and HEV with a twin epicyclic gearbox. Predictions for both stages are made over the New European Driving Cycle (NEDC).The simulations show that the twin epicyclic offers substantial improvements of reduction in energy consumption in HEVs. The results also show that it is possible to improve overall performance and energy consumption levels using a continuously variable ratio gearbox in EVs.

Dynamic Optimization of Drivetrain Gear Ratio to Maximize Wind Turbine Power Generation—Part 2: Control Design

The cost of electrical power produced by small wind turbines impedes the use of this technology, which can otherwise provide power to millions of homes in rural regions worldwide. To encourage their use, small wind turbines must capture wind energy more effectively while avoiding increased equipment costs. A variable ratio gearbox (VRG) can provide this capability to the simple fixed-speed wind turbine through discrete operating speeds. This is the second of a two-part publication that focuses on the control of a VRG-enabled wind turbine. The first part presented a 100 kW fixed speed, wind turbine model, and a method for manipulating the VRG and mechanical brake to achieve full load operation. In this study, an optimal control algorithm is developed to maximize the power production in light of the limited brake pad life. Recorded wind data are used to develop a customized control design that is specific to a given site. Three decision-making modules interact with the wind turbine model developed in Part 1 to create possible VRG gear ratio (GR) combinations. Dynamic programming is applied to select the optimal combination and establish the operating protocol. The technique is performed on 20 different wind profiles. The results suggest an increase in wind energy production of nearly 10%.

Dynamic Optimization of Drivetrain Gear Ratio to Maximize Wind Turbine Power Generation—Part 1: System Model and Control Framework

Wind is considered to be one of the most promising resources in the renewable energy portfolio. Still, to make wind energy conversion more economically viable, it is necessary to extract greater power from the wind while minimizing the cost associated with the technology. This is particularly important for small wind turbines, which have the highest cost per kilowatt of energy produced. One solution would be a variable ratio gearbox (VRG) that can be integrated into the simple and low-cost fixed-speed induction generator. Through discrete variable rotor speed operation, the VRG-enabled system affects the wind speed ratio, the power coefficient, and ultimately the power produced. To maximize electrical production, mechanical braking is applied during the normal operation of the wind turbine. A strategy is used to select gear ratios (GRs) that produce torque slightly above the maximum amount the generator can accept while simultaneously applying the mechanical brake, so that full load production may be realized over greater ranges of the wind speed. To characterize the performance of the system, a 100 kW, fixed speed, stall-regulated wind turbine, has been developed for this study. The VRG-enabled wind turbine control system is presented in two papers. Part 1 focuses on the turbine simulation model, which includes the rotor, VRG-enabled drivetrain, disk brake, and electric generator. A technique for estimating the performance of a disk brake, in the wind turbine context, is also presented. Part 2 of the research will present a dynamic optimization algorithm that is used to establish the control protocol for competing performance objectives.

Performance of a 100 kW wind turbine with a Variable Ratio Gearbox

A Variable Ratio Gearbox (VRG) can be used in the drivetrain of a small to medium-size wind turbine to improve aerodynamic efficiency. Currently, all commercially-available wind turbines operate using a fixed-gear ratio between the turbine rotor and electrical generator. A VRG allows wind turbines, with a constant-speed generator, to discretely vary rotor speed and to achieve greater aerodynamic efficiency. The authors’ previous results demonstrate the viability of the VRG design. This research quantifies the gain in efficiency for a VRG-enabled wind turbine based on wind data from representing all seven wind classifications. A method is also presented to identify turbine sites that provide the VRG with the greatest opportunities to increase production. The overall findings suggest that the VRG can benefit all wind turbines, irrespective of wind class, with some wind profiles in the study experiencing gains greater than 10%.

Wind energy conversion with a variable-ratio gearbox: design and analysis

Variable-speed wind turbines are able to adapt to low wind speeds and therefore have greater efficiency than fixed-speed turbines during partial-load operation. Unfortunately, the high cost and low reliability of the electronics that enable variation in speed have discouraged this mode of operation for distributed wind turbines. Alternatively, a Variable-Ratio Gearbox (VRG) can be integrated into the fixed-speed wind turbine to facilitate operation with a discrete set of variable speeds that boost efficiency. The VRG concept is based upon mature technology taken from the automotive industry and is characterized by low cost and high reliability. In this paper, a model-based design methodology is introduced to study the performance gain of integrating a VRG into a fixed-speed stall-regulated wind turbine system. The results demonstrate how this device can improve the efficiency of the fixed-speed turbine in the partial-load region and the potential to use the VRG to limit power in the full-load region where pitch control is often used.

Control Strategy of PWM Inverter Drive System for Electric Vehicles

This paper presents an advanced ac drive system used in electric vehicles (EV's). The system consists of an induction motor, a PWM transistorized inverter, a variable ratio gear box and a controller. The special features of the drive system are discussed, with emphasis on the control strategy which can optimize the performance of the EV.

The Performance Potential of Limited Cooled Diesel Engines

A mathematical model is used to predict the performance of a turbocharged diesel engine with a partially insulated combustion chamber. The model is briefly described, with emphasis on heat transfer aspects and prediction of combustion chamber surface temperatures. First the trade-off between performance improvement (efficiency) degree of insulation, combustion chamber surface temperature and exhaust gas energy is examined. It is shown that the high surface temperatures in the cylinder, due to insulation, cause volumetric efficiency to fall. However, this reduction is offset by increased boost pressure from the turbocharger due to greater exhaust gas energy. The contribution to overall reduction in heat loss from cylinder head, piston and liner and their effect on engine efficiency are presented and discussed. Various turbo-compound systems are examined and it is shown that most systems become unmatched when working over the wide speed and load range necessary for vehicle application, unless a variable geometry turbine or a variable ratio gearbox (this maintains compound power at part load) are used. Furthermore, substantial overall performance benefits can only be obtained with very efficient turbomachinery. Rankine bottoming cycles are more effective than fixed geometry turbo-compounding at low load, but their normal efficiency is limited by high condenser temperature, and they would be difficult to install in a compact European truck. It is concluded that the ultimate improvement in engine specific fuel consumption of an adiabatic turbo-compound engine is 20 per cent (excluding the savings from fan and water pump). However, drastically new design concepts are necessary, if engines are to be built that approach this degree of insulation. Meanwhile redesigned conventional engine types will offer substantial reduction in cooling system requirements with more modest thermal efficiency benefits.

A Volterra series-derived describing function for a motor/variable gearbox/load combination

A solution to the speed variations of a load driven via a variable ratio gearbox from a non constant speed drive is obtained as a Volterra series. A particular solution is found when the gear ratio is varied sinusoidally. This leads to a simple transfer function, with coefficients varying with input amplitude, which is shown to adequately model the overall dynamics.