Using the Thermal Inertia of Trains for Contributing to Primary and Supplementary Frequency Control in Grids With High Penetration of Renewable Generation

Concerns about climate change have boosted the massive introduction of renewable energy into electric power systems. Renewable generators can mitigate pollution by replacing fuel-based energy with clean energy. However, these generators displace conventional synchronous ones. This changes power system dynamics and can lead to a less stable operation. To face this emerging problem, many approaches have been proposed in order to enable renewable generators and consumers to provide ancillary services. Nevertheless, if renewable generators adjust their production to support grid ancillary services, all the primary energy resources cannot be optimally used. This work proposes a way for railway systems to contribute to primary and supplementary frequency control and to relieve renewable generation from frequency control tasks. Furthermore, a tuning control method is introduced. Due to the high stochasticity of railway system operation, a method for selecting local optimum parameters is proposed. The frequency control scheme is set and tested in simulation, and experimentally validated by means of Hardware In the Loop tests with a real micro controller. The results demonstrate, first, the capacity of railway systems to manage a certain quantity of frequency deviations and, second, the feasibility of implementing the proposed control strategy in real time. This work broadens the framework of railway-based demand response approaches.