Renewable power plants (RPPs) are different from conventional power plants (CPPs) in several ways. While a 300-megawatt (MW) CPP may consist of one or two large generators (e.g., two 150-MW synchronous generators), an RPP may consist of hundreds of 1.5-MW solar photovoltaic (PV) inverters or wind turbine generators. In addition, many RPPs have a power-electronics-based interface with the grid; thus, the time constant of a RPP system is a lot faster than that of the mechanical-based CPP. Power system planning is concerned with the representation of the RPP at the point of interconnection with the grid. Thus, in an RPP, the collective behavior of hundreds of generators is more important than the behavior of a single generator, and this must be represented properly in dynamic models.
NREL works with the solar and wind industries to provide utilities and grid operators with generator models to help them analyze the impact of variable generation on power system performance and reliability. As the amount of variable generation increases, the need for such models increases. Ensuring the models are as generic as possible allows for ease of use, model validation, data exchange, and analysis. To address this need, NREL researchers are developing generic dynamic models of wind and solar power plants.
NREL's dynamic modeling efforts include (generator, power converter, control, protection) at the generator level and at the plant level:
Monitoring, collecting, and analyzing RPP output data with corresponding resource data (wind speed, direction, air density, solar irradiance) from meteorological towers and performing multivariate analysis of the data to develop an equivalent RPP power curve and/or model representation
Developing and validating RPP dynamic models (including generator, control system, and protection) in open source architecture
Development of average as well as detailed dynamic models in three-phase, cycle-by-cycle electromagnetic transient program
Examining the short-circuit behavior of RPPs
Performing wide-area power system modeling by inclusion of synchrophasor measurements and available FACTS devices (e.g., HVDC, SVC, STATCOM) in the surrounding power system network
Equivalency of dynamic modeling at the plant level by aggregation without losing the important characteristics of the renewable generators, both for onshore and offshore plants
Developing control algorithms for the generator to allow ancillary service implementation in anticipation of future rules and regulations that may be imposed upon the incoming RPP fleet as the level of variable generation increases to a sufficiently high level both for offshore and onshore application
Dynamic modeling of generators for other renewables beyond wind and solar PV (e.g., variable-speed pumped storage hydro, tidal, wave, solar thermal).
These efforts contribute to a better understanding of how RPPs interacts with the larger system and how this impacts grid stability and reliability.
For More Information
For more information about wind generator modeling, see the following resources. Additional publications can be found in the NREL Publications Database.
Variable-Speed Wind Power Plant Operating With Reserve Power Capability
This paper explores several ways to control wind turbine output to enable reserve-holding capability.
Variable Frequency Operations of an Offshore Wind Power Plant with HVDC-VSC
This paper investigates the control strategies and the operation of offshore wind power plants connected to an onshore substation using high-voltage direct current (HVDC) transmission.
Understanding Inertial and Frequency Response of Wind Power Plants
This paper analyzes and quantifies the inertia and frequency responses of wind power plants with different wind turbine technologies.
Symmetrical and Unsymmetrical Fault Currents of a Wind Power Plant
This paper investigates the short-circuit behavior of a wind power plant for different types of wind turbines. Both symmetrical faults and unsymmetrical faults are investigated.
Dynamic Model Validation of PV Inverters Under Short-Circuit Conditions
This paper validates a PV inverter dynamic model against benchtesting under short-circuit conditions. The equivalent circuits and results are given in three-phase quantities and also in positive, negative, and zero sequence quantities.