Title: Simulation of ancillary services for the electrical grid from wind turbines

Abstract:

In the context of the energy transition coal and nuclear power plants will be replaced by renewable generation. For instance, the German government plans that 80 % of the electrical energy should come from renewable sources until 2030, to a substantial extent from wind and photovoltaic power plants. As a consequence, power quality from renewable sources has to be high and ancillary services to stabilize the grid have to be provided. As wind and photovoltaic plants are connected to the grid with inverters and the fuels, wind and sunlight, cannot be supplied to the generation process on demand one needs to make extra efforts to catch up with the conventional technology based on synchronous generators directly coupled to the grid and mechanical torque delivered by a steam turbine or diesel motor. In this paper we concentrate on two issues in this context. Firstly, we investigate the case of synthetic inertia or, more general, fast frequency response provided by wind turbines. With the help of general analytic modelling it is possible to discuss capabilities and limitations of wind turbines in this respect on a quantitative level. Then we set up a numerical model consisting of an aeroelastic simulation model (NREL FAST 8) for a wind turbine and a detailed converter model (with Matlab/Simulink). The torque is controlled at the generator-side converter and grid frequency variations are considered. The model allows us to obtain a detailed picture of the back-reaction of the wind turbine when fast-frequency response is introduced. Fast-frequency response is studied in different wind situations (steady wind and turbulent wind). Additional loads on the wind turbine and impact of energy production are analyzed for a maximum frequency drop and for continuous supply based on a frequency time series. In the next step we introduce a battery in the power generation system. The battery is integrated at DC link point such that at the grid-side the inverter has two sources. The battery storage system as a secondary source is a good approach for making wind turbines dispatchable. A controller is designed to control the power output to the grid depending upon the grid requirements and power production by charging or discharging the battery storage system while keeping a stable DC link voltage. The simulation results illustrate the control of DC-link integrated battery energy storage system in different wind conditions. What kind of ancillary service may be provided to the grid clearly depends on the battery capacity. With the right battery size such a system would be also suitable for a so-called minigrid.

Biography:

Uwe Ritschel was trained as a physicist and worked in wind industry since the year 2000 with focus on simulation and design of wind turbines. In 2014 he became Professor of Wind Energy Technology at the University of Rostock (Germany). Uwe Ritschel has worked on many R&D projects together with industry companies on various topics like for example floating wind turbines and grid integration of wind electricity. Since 2019 he is director of the IWEN Energy Institute, and he is teaching wind energy technology at the Southern Mediterranean University at Tunis