September 25, 2017

CoE Site Index  |  
WESEP: Wind Energy Science, Engineering, and Policy

Wind Energy Conversion System and Grid Operations

Thrust Goal and Connection to Project Objectives

The goal of this thrust is to identify the extent to which interdependencies between (a) the choice of wind farm locations in terms of terrain, wind resource, and grid interconnection location, (b) the mechanical, electrical and control design of individual wind turbines and wind power plants, and (c) power system operational attributes including fast-ramping generation, load control, system-level energy storage, new transmission, and market structure, can be coordinated to maximize electric energy production and optimize electric system performance. This thrust will address RO2 and RO3 by developing design principles, models, and simulation software to perform integrated design and analysis of wind energy conversion systems, the wind farm physical layout and electric collection system, and the electric grid.

Background and Need for Research

Recently, researchers have concluded that the entire wind-to-wire electromechanical energy conversion system, which consists of the blades and hub, the gearbox (when present), the electric generator, the power electronics converter, a transformer, the wind plant collection system, and the rest of the power system, ideally must be viewed as a single system whose efficiency and reliability should be analyzed together by identifying and taking into account interactions between the various subsystems. For example, efficiency gains obtained by improving the design of the generator or the transformer can be lost due to the effect of the power electronics converter. Increases in blade efficiency can be lost due to increased dynamic effects on the gear box.

Current research objectives in this area include designing novel high-power-density low- or medium-speed drive trains which are light weight, reliable and easy to transport and assemble. Research is needed to explore the many options of providing energy conversion including permanent magnet generators (for direct-drive or medium-speed drive trains); continuously-variable drive trains; direct drive systems; integrated drive trains; and multi-drive path gearboxes. Other areas of research include efficient and reliable power electronic converter topologies; alternative wind power plant distribution system architectures; condition monitoring systems; advanced controls (of yaw, pitch, and converter) to maximize power extraction from the wind while minimizing mechanical stress on the mechanical components of the drive train during normal operation and during power system faults; controls that ensure the turbine’s proper behavior during faults at the power system side; and inter-turbine intra-plant adaptive controls that maximize power production by accounting for the interactions between wind turbines. For low-power applications where vertical axis wind turbines are more suitable (e.g., for residential applications), axial-flux permanent magnet generators hold significant advantages and could enable higher penetration of distributed renewable energy resources.

Current design methods which model only one or a limited number of subsystems at a time are not proficient in detecting wind-to-wire effects which can result from interactions between subsystems. Integrated design platforms are in their infancy, with partial progress towards this end being made by only a few European organizations. Our objective is to develop methodologies and a suite of software design tools to address the issue of integrated wind power plant design. To initiate this effort, we will assemble state-of-the-art commercial and research grade software, and make it available to our students on an internet platform. This will enable our students to immediately engage in a complete wind turbine/power plant design at the beginning of the project.

Dissertation Project Examples

Generator condition monitoring and sensor-fault-tolerant operation: The dissertation will develop new condition monitoring techniques for the electromechanical energy conversion system (this topic intersects with Thrust 4). In addition, we will investigate advanced sensor-fault-tolerant techniques to enable the operation of the turbine after the failure of sensors used in the control system (thus leading to increased energy yields and reduced maintenance requirements).

MIMO adaptive control of wind turbines: It is now common to provide individual pitch actuators at each blade so that the number of control inputs available to the system designer is increased above the traditional generator torque control. In addition, force/moment sensing or accelerometers can be installed at each blade individually as well as on the nacelle and tower. These additional inputs and outputs, and the fact that the turbine structural modes couple with the drive train and pitch actuation through torque and bending moments, make the wind turbine an inherently multi-input-multi-output (MIMO) system. Sensors used for the turbine health monitoring could be integrated in the control systems to provide robustness and adaptation mechanisms to wearing and faults. Modeling the stochastic nature of the change in wind profile as it travels and optimizing feed-forward control for operation in the presence of the resulting measurement errors will help to realize performance improvement.

Optimal control of wind farms: This work will develop optimal control strategies to regulate wind farm power production to the reference power ordered by the system operators. In this situation, operating each wind turbine at its own maximum power extraction point is not globally efficient due to aerodynamic interactions between the turbines. Rather, turbines should be orchestrated so that the wind farm achieves maximal power extraction compatible accounting for system operator demands and wind conditions.

Aerodynamic and aeroelastic loads: Aerodynamic and aeroelastic loads expected on future wind turbine systems must be considered for optimum design and in the development of new materials and processes necessary to achieve efficiency in these systems. We will use both time and frequency domain models for predicting the aerodynamic and aeroelastic loads on blades and towers to understand the aerodynamic drag/lift, stall and flutter characteristics of blades as well as vortex-induced/buffeting response of towers as influenced by surrounding terrain and wind turbines in a typical wind farm. Accurate dynamic modeling of wind turbine and its components based on realistic wind loads with parameters measured in the Aerodynamic/Atmospheric Boundary Layer (AABL) Wind and Gust Tunnel in an atmospheric boundary layer flow will help provide a more robust and reliable design of wind turbines to produce higher energy yields.

Electromechanical energy conversion systems: This topic involves analysis, modeling, and design of integrated multi-MW drive train systems that satisfy several (usually conflicting) design objectives related to parameters such as weight, cost, reliability, efficiency, maintenance requirements, mechanical stress, thermal losses, and operating characteristics, including the turbine’s dynamic behavior during grid disturbances. An approach that treats the energy conversion system as an integral component of the entire wind turbine is needed. A detailed analysis of dynamic effects of wind loading and overall operation will be coupled with a complete system design, which will lead to advances in drive trains. This effort will involve the modeling of continuously variable drives, medium speed hybrid drives, semi-integrated drive systems, and unique combinations of gearing and generators.

Wind power variability: At high wind penetration levels, grid integration requirements for maintaining power balance require increased regulation (time frame of seconds), load following (minutes), and dispatch (hour) capabilities. We will develop inter-farm control methods to address this, comparing it in terms of cost and performance to other proposed solutions, including individual turbine control, increased levels of fast-response reserves, and use of energy storage.

Collection circuit design: A central factor in any wind plant is the local lower-voltage collection system used to move energy from individual turbines to transmission substations while considering turbine placement for maximum energy extraction and agricultural constraints such as location of field drainage systems. We will explore various collection circuit technologies, including high phase order, high surge impedance loading and high temperature conductors, dynamic loading equipment, and direct 34.5 kV to 345 kV and 765 kV connections to obtain more capacity for a given right of way.

Increased transmission: Much of the nation’s best wind resources are in regions of low population densities, constraining wind penetration levels due to long distance interstate high-voltage transmission necessary to move energy to the load centers. Although transmission is a relatively small fraction of the cost to produce electric energy, it is essential. For example, it was found that without significant additional investments, the Eastern U.S. Interconnection would not be able to reach even a 6% wind penetration level (by energy), much less than DOE’s desired 20% by 2030. Conductor materials, the electric circuit design, and their deployment raise research issues related to the cost of circuit capacity, and interaction with rail and highway right of way (for transmission). Policy questions are key for transmission cost allocation, federal versus local power to force or block right of way access, and wind plant interaction with day ahead and real-time electricity markets.

Key Faculty

  • James D. McCalley, Harpole Professor in Electrical Engineering – Electrical and Computer Engineering (Lead)
  • Dionysios Aliprantis, Assistant Professor – Electrical and Computer Engineering
  • Nicola Elia, Associate Professor – Electrical and Computer Engineering
  • Agustín A. Irizarry-Rivera, Professor – Electrical Engineering (University of Puerto Rico – Mayagüez)
  • Partha Sarkar, Professor – Aerospace Engineering
  • Judy Vance, Joseph C. and Elizabeth A. Anderlik Professor of Engineering – Mechanical Engineering