Illustration of Modern Wind Turbine Ancillary Services – Wind Power System Security

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[tweetmeme Ioannis D. Margaris (National Technical University of Athens ); Anca D. Hansen, Poul Sørensen (Risø National Laboratory for Sustainable Energy, Technical University of Denmark); Nikolaos D. Hatziargyriou (Public Power Corporation S.A. Athens, Greece) have published a paper titled „Illustration of Modern Wind Turbine Ancillary Services.“  Increasing levels of wind power penetration in modern power systems has set intensively high standards with respect to wind turbine technology during the last years. Security issues have become rather critical and operation of wind farms as conventional power plants is becoming a necessity as wind turbines replace conventional units on the production side. This article includes a review of the basic control issues regarding the capability of the Doubly Fed Induction Generator (DFIG) wind turbine configuration to fulfill the basic technical requirements set by the system operators and contribute to power system security. An overview of ancillary services provided by wind turbine technology nowadays is provided, i.e., fault ride-through capability, reactive power supply and frequency-active power control.

The introduction to this article reads:

A decade ago, most grid codes considered wind farms as small size dispersed generation and therefore did not require wind turbines to support the power system during transients following grid disturbances. Wind turbines could be disconnected when abnormal grid voltage behavior was detected. The constantly increasing penetration of wind power in the power systems over the last years has posed serious concerns regarding the sudden loss of power during grid faults, which could be caused by wind turbines´ disconnection, leading possibly to further severe frequency and/or voltage instability. These concerns have led to detailed review of national grid codes, which nowadays include a wide range of technical requirements that wind farms must fulfill. The operational behavior of wind farms has to follow today the basic guidelines, which have been up to now traditionally only referred to conventional power stations. In this article the capability of the DFIG configuration to fulfill the main technical requirements, common to most national grid codes, will be presented. The following wind turbine ancillary services are addressed and discussed in the article:

  • Capability to regulate their power production during normal operation—According to several national grid codes, wind farms must be able to regulate their power production to an imposed reference value, set remotely or locally. The capability of the DFIG wind turbine to independently control active and reactive power and provide the corresponding service is assessed and emphasized in normal operation conditions by means of simulations.
  • Fault ride through (FRT) capability—The ability of modern wind turbines to withstand low voltage conditions, which mostly appear during short circuit faults in the grid, stay connected during the fault and resume their pre-fault normal operation shortly after the fault clearance is essential. Advanced design of the wind turbine controller and/or development of new equipment in wind turbines are necessary to enable the wind turbine to fulfill this requirement, which is usually described in grid codes through definitions of the duration and the depth of a voltage drop at which the wind turbines are not allowed to disconnect.
  • Voltage-reactive power control capability—In most grid codes wind farms are asked to support the voltage of the power system in normal operation, by providing or absorbing reactive power. The reactive power supply capability largely depends on the specific wind turbine technology. Variable speed wind turbine schemes, like the DFIG studied here, are nowadays able to provide additional reactive power through advanced control of their power electronics. Some particular grid codes, such as E-ON Netz and the Spanish one, require voltage support through reactive current injection during fault operation as well. The present paper reveals for instance how a DFIG wind turbine equipped with a co-ordinated voltage control system can enhance the grid support, even during abnormal voltage conditions.
  • Frequency-active power control capability—A crucial aspect related to system stability is active power balance in the system. Frequency stability is often seriously threatened during events, i.e., sudden load change, tripping of a production unit due to protection reasons. As wind farms tend to substitute conventional units in the power system, they are often required to remain connected during frequency variations while in the future they should also contribute actively to the generation control of the system. The wind turbines have to adjust their power output according to frequency deviations although the fluctuating nature of wind poses serious constraints regarding the availability of active power. This feature becomes vital for non interconnected power systems, like island systems, whose inertia is restricted and frequency variations often lead to severe load shedding.

Read the full article in PDF format by clicking here.

Citation: Margaris, Ioannis D.; Hansen, Anca D.; Sørensen, Poul; Hatziargyriou, Nikolaos D. 2010. “Illustration of Modern Wind Turbine Ancillary Services.” Energies 3, no. 6: 1290-1302.

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