Accommodating High Levels of Variable Generation - NERC

Characteristics of Power Systems & Variable Generation
Much work has been done, particularly in recent years, 44 to clearly define and explain the
various variable generation technologies and how they should be modeled for system studies.
International cooperation to develop generic wind turbine models, initiated by the Western
Electricity Coordinating Council (WECC) is a positive step. This WECC-led effort considered
the four major turbine topologies in current commercial applications. In the very near term, best
representations of specific commercial turbine models with the current generic structures must be
provided. This effort will require significant collaboration between the power engineering
community and the wind turbine manufacturers and vendors, since these entities generally
privately hold the measurement data or detailed simulation results that provide the best
opportunities for validation of the behavior and adjusting the parameters of the generic models.
In contrast to wind generation, simulation models for CSP steam turbine generator sets are fully
developed, though the models for dish-Stirling engines are considered proprietary. It is not
known if simulation models have been validated against performance of commercially-available
PV inverter modules.
The modeling of variable generation should continue to be advanced by the IEEE Power and
Energy Society’s Power System Dynamics Committee in order to provide a broader forum for
the needed work and refinements in this area. Variable generation models are required to
comply with existing NERC Modeling, Data and Analysis Standards (MOD) and this
requirement should be clearly understood. There are challenges that need to be addressed over
time to improve model standardization and industry experience similar to conventional generator
models. Steps that should be taken in this regard include:
• Variable generator owners and operators must comply with appropriate NERC MOD
Standards, and a timetable should be set for compliance;
• Existing standards should be assessed to determine what modifications to modeling
standards (if any) are necessary to properly consider the unique aspects of variable
generation; and
44 (a) WECC Wind Generator Power Flow Modeling Guide
(b) Nevada Power Company, Renewable Energy Department
(c) ESB National grid, “Dynamic modeling of wind generation in Ireland”, January 2008
(d) Coughlan, Y., Smith, P., Mullane, A. and O’Malley, M.J., “Wind turbine modelling for power system
stability analysis - a system operator perspective”, IEEE Transactions on Power Systems, Vol. 22, pp. 929 –
936, 2007.
(e) CIGRE Technical Brochure 328, Modeling and Dynamic Behavior of Wind Generation as it Relates to Power
System Control and Dynamic Performance, Prepared by CIGRE WG C4.601, August 2007 (available on-line
at: www.e-cigre.org)
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