Wind energy is a fast-growing interdisciplinary field that encompasses multiple branches of engineering and science. Despite the growth in the installed capacity of wind turbines in recent years, larger wind turbines have energy capture and economic advantages, the typical size of utility scale wind turbines has grown by two orders of magnitude. Since modern wind turbines are large, flexible structures operating in uncertain environments, advanced control technology can improve their performance.The goal of this article is to describe the technical challenges in the wind industry relating to control engineering.

Control of Wind Turbines

As wind energy becomes a larger portion of the world's energy portfolio and wind turbines become larger and more expensive, wind turbine control systems play an ever more prominent role in the design and deployment of wind turbines. The goals of traditional wind turbine control systems are maximizing energy production while protecting the wind turbine components. As more wind generation is installed there is an increasing interest in wind turbines actively controlling their power output in order to meet power setpoints and to participate in frequency regulation for the utility grid. This capability will be beneficial for grid operators, as it seems possible that wind turbines can be more effective at providing some of these services than traditional power plants. Furthermore, establishing an ancillary market for such regulation can be beneficial for wind plant owner/operators and manufacturers that provide such services. In this tutorial paper we provide an overview of basic wind turbine control systems and highlight recent industry trends and research in wind turbine control systems for grid integration and frequency stability.

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A tutorial of wind turbine control for supporting grid frequency through active power control

With an increasing penetration of wind power in the modern electrical grid, the increasing replacement of large conventional synchronous generators by wind power plants will potentially result in deteriorated frequency regulation performance due to the reduced system inertia and primary frequency response. A series of challenging issues arise from the aspects of power system planning, operation, control and protection. Therefore, it is valuable to develop variable speed wind turbines (VSWTs) equipped with frequency regulation capabilities that allow them to effectively participate in addressing severe frequency contingencies. This paper provides a comprehensive survey on frequency regulation methods for VSWTs. It fully describes the concepts, principles and control strategies of prevailing frequency controls of VSWTs, including future development trends. It concludes with a performance comparison of frequency regulation by the four main types of wind power plants.

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State-of-the-art review on frequency response of wind power plants in power systems

This paper details a comprehensive study undertaken by the National Renewable Energy Laboratory, Electric Power Research Institute, and the University of Colorado to understand how the contribution of wind power providing active power control (APC) can benefit the total power system economics, increase revenue streams, improve the reliability and security of the power system, and provide superior and efficient response while reducing any structural and loading impacts that may reduce the life of the wind turbine or its components. The study includes power system simulations, control simulations, and actual field tests using turbines at NREL's National Wind Technology Center (NWTC). The study focuses on synthetic inertial control, primary frequency control, and automatic generation control, and analyzes timeframes ranging from milliseconds to minutes to the lifetime of wind turbines, locational scope ranging from components of turbines to large wind plants to entire synchronous interconnections, and additional topics ranging from economics to power system engineering to control design.

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Active Power Controls from Wind Power: Bridging the Gaps

As wind penetration levels on power systems increase worldwide and synchronous generation is displaced, the dynamic characteristics of these systems, and hence the protocols for how they are operated, are changing One issue, of particular concern, is the resulting reduction in system inertia since modern variable speed wind turbines do not inherently contribute to the inertial response of the system Such devices can, however, be fitted with a control loop which provides an active power response to significant frequency deviations, similar to the inertial response of fixed speed wind turbines and synchronous generation Unlike conventional machines, however, the response of variable speed turbines is dependent on local wind speeds and so cannot be quantified deterministically by system operators As a result, it is likely that uncertainty will exist over the inertial response capability of the system at high wind penetration levels In this paper, the frequency response capability is assessed on a test system and the effectiveness of wind turbines' contribution to system inertial response is evaluated in the context of future system requirements

Frequency Response of Power Systems With Variable Speed Wind Turbines

The invention relates to a method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, where a pitch reference value for the wind turbine blades is determined, and an operational parameter representing a loading on the wind turbine rotor exerted by the wind is measured at time intervals. A variation parameter reflecting a variation of the operational parameter over time is determined and used in the determination of a minimum pitch limit value of the pitch reference value. The wind turbine is then controlled according to the pitch reference value only if the pitch reference value is above or equal to the minimum pitch limit value, and otherwise according to the minimum pitch limit value. The invention further relates to a method of controlling the change in the operational parameter as measured in two successive time steps is determined and the turbine then being controlled according to a safety control strategy if the difference between the operational parameter change and the variation parameter is above a certain alert threshold. The invention further relates to a control system configured to perform the above control method, and a wind turbine comprising such system.

Control method for a wind turbine

Wind speed variability generates the main challenges for grid integration of wind power. Worldwide, requirements governing generator connection to the transmission grid evolve as the modern energy industry continues to develop. With increased wind power penetration, wind power plants are required to provide grid support and control actions similar to conventional power plants. Dedicated control systems for wind power plants employing variable-speed wind turbines can provide advanced control features for the transmission network operator. The paper summarizes the control characteristics of a modern wind power plant. It identifies the capability of modern wind power plants to offer fast regulation and frequency response services. Advanced functionalities for regulation and response to grid disturbances are also addressed.

Regulation and frequency response service capability of modern wind power plants

The present invention relates to a method for curtailing electrical power supplied from a wind turbine or a group of wind turbines to an associated power supply grid, the method comprising the steps of determining an available electrical power level from the wind turbine facility and setting a wind speed independent curtailment level. The curtailment level may be a percentage of an actual available electrical power level or a fixed power level. The method further comprises the step of operating the wind turbine facility in such a way that the generated electrical power supplied from the wind turbine facility equals the difference between an actual available electrical power level and the curtailment level. The present invention further relates to a wind turbine facility and a curtailing controller for carrying out the invention.

Power curtailment of wind turbines

The invention relates to a method for controlling a wind power plant comprising a plurality of wind turbines being operatively connected to a plant collector grid, the method comprising the steps of providing a desired power reference signal; determining the power production of the wind power plant, and generating an actual power reference signal in response thereto; comparing the desired power reference signal with the actual power reference signal, and performing one of the following steps: 1) applying a first filter characteristic as part of a generation of a wind turbine power reference if the desired power reference signal exceeds the actual power reference signal; or 2) applying a second filter characteristic as part of the generation of the wind turbine power reference if the actual power reference signal exceeds the desired power reference signal, wherein the first filter characteristic is different from the second filter characteristic. The invention also relates to a power plant controller, a wind power plant and a computer program product.

Control of a wind power plant

The invention relates to a method, system and computer readable code for diagnosis of pitch and/or load defects of e.g. wind turbines as well as wind turbines using said diagnosis method and/or comprising said diagnosis system.

Søren Dalsgaard

Papers

Control method for a wind turbine

Regulation and frequency response service capability of modern wind power plants

Power curtailment of wind turbines

Control of a wind power plant

Diagnosis of pitch and load defects