High-gain observer-based sensorless control of a flywheel energy storage system for integration with a grid-connected variable-speed wind generator

This paper introduces an induction machine-based flywheel energy storage system (FESS) for direct integration with a variable-speed wind generator (VSWG). The aim is to connect the FESS at the DC bus level of a permanent magnet synchronous generator-based VSWG in order to stabilize the DC bus voltage as well as the power flowing into the grid. A rotor flux-oriented control strategy is proposed for the FESS converter based on the actual speed of the flywheel rotor. Since mechanical speed sensors are prone to failure and increase the maintenance cost of the system, a sensorless technique is proposed to estimate the rotor speed through a specially synthesized high-gain observer (HGO). The proposed observer achieves accurate tracking of the flywheel speed and flux and reduces the adverse effects of variations in the rated rotor resistance. Simulation results obtained using the MATLAB-Simulink environment are presented to illustrate the theoretical synthesis and analysis of the proposed FOC and sensorless HGO control strategies.