Active power control of multi-rotor turbines for fast frequency reserve

Abstract

Fast frequency reserve is a dynamic ancillary service for the power grid. In previous grids, this was provided by power plants with synchronous machines and dispatchable primary sources. In systems of the near future, this must be provided as far as possible by converter-based regenerative resources. The requirements for wind energy systems are high. According to existing grid codes, output must be reduced by 60–80% within 1–2 seconds to provide so-called negative inertia. Positive inertia, i.e., an increase in power to emulate the inertia of conventional synchronous machines, results from the power reserve of a derated wind energy system. To be able to provide this with a multi-rotor wind turbine, i.e., the primary energy system of a wind energy system, the established control concepts must be significantly modified. This article presents a decentralised control concept in which each rotor contributes to the active power fed into the grid. A theoretical and systematic controller design method is proposed, which allows the dynamic adaptation of the power generated by wind power plants. The focus is on the dynamic tracking control of the primary power. Finally, simulation results are presented, along with a concept that enables active power generation also by turbine rotors without pitch control via stall operation.