Sandia National Laboratories (Sandia) researchers, collaborating with Group NIRE and Baylor University, demonstrated that modulating the rotation speed of wind turbine rotors can offer two important grid services—load balancing and stability management—among other potential benefits to provide flexibility and resilience on the grid.
A typical generator in a power plant has the ability to respond to sudden increases in power demand by sensing that more energy is being pulled from the plant than what is being produced. This response is triggered by detecting the reduction of rotating kinetic energy of the generator's turbine. In other words, when the turbine slows down instead of remaining at its usual speed, the plant controls recognize that the plant needs to produce more power.
Wind turbines also have the ability to balance loads and support grid stability despite fluctuating energy demands. Sandia, Group NIRE, and Baylor demonstrated that by modulating the power output of a Vestas V27 wind turbine at the Scaled Wind Farm Technology (SWiFT) facility, they could provide up to six times the stored energy of a conventional synchronous generator (per MW nameplate) with only a 0.12% drop in aerodynamic efficiency. This research may help identify operating practices that could allow turbines to run at higher efficiencies while still being able to respond to surges in demand.
The research also demonstrated that controlled power modulation of a wind turbine can mitigate oscillations in the grid. Oscillations occur as power is transmitted across long transmission lines, such as region to region. If oscillations are poorly damped, they can jeopardize grid stability and can lead to widespread outages during stressed grid conditions.
Using a modified control algorithm from a prior test of the Pacific DC intertie—a power transmission line spanning the Pacific Northwest to Los Angeles—Sandia, Baylor, and Group NIRE simultaneously tested whether it would be feasible to use the same rotor modulation technique to dampen inter-area oscillations. Using a grid-connected Vestas V27 Wind turbine at SWiFT, a control system at Sandia's Control and Optimization of Networked Energy Technologies Laboratory, and phasor measurement units on the grid, the team successfully tested the ability to use a wind turbine to supply load balancing reserve energy and stabilize a wide-area grid.
Although additional research is needed into the operations and maintenance costs of turbine modulation, initial results indicate that wind turbines could be a significant source of flexibility and resilience on the grid, in addition to contributing valuable grid services and a new, potential source of revenue for wind plant operators.
The results are publicly available from Sandia National Laboratories in the report, "Use of Wind Turbine Kinetic Energy to Supply Transmission Level Services."