DISCRETE PREDICTIVE CONTROL OF A FLYWHEEL ENERGY STORAGE FOR TRANSIENT STABILITY AUGMENTATION

Hailiya Ahsan and Mairaj ud Din Mufti

Keywords

Flywheel energy storage (F-ES), doubly fed induction generator (DFIG), discrete predictive control (DPC), short circuits, intermittent renewable power

Abstract

A flywheel energy storage (F-ES) is characterized as a high-power density device with rapid full-depth discharge cycles. This makes it a viable solution as a high-power source/sink for small-time lengths. In this paper, transient stability augmentation of a power system is approached through a discrete predictively controlled (DPC) flywheel energy storage. Detailed modelling of F-ES is captured through mathematical equations concerning the flywheel in itself, the conjoining electric machine and the power conditioning support offered by successional converters and the intermedial DC link. A serial converter architecture is considered along the grid side and the machine side, where the former caters to bidirectional regulation of active–reactive power to the grid, while the latter controls the charge/discharge of the flywheel by switching the electric machine of the F-ES between motoring (charging) and generating (discharging) modes. The proposed DPC not only addresses the operational constraints on the power rating of the aforesaid power electronic interface but also regulates the state of the charge of the F-ES. A representative second-order system is employed to imitate the F-ES inner loop dynamics. Similarly, a dynamic constraint window (DCW), determined from the frequency variations, is issued for the reference F-ES power command for the next sampling instant. Studies are performed in MATLAB Mathworks platform on an upgraded Western System Coordinated Council model with exogenous uncertainties like faults and intermittent power from a 50-MW doubly fed induction generator (DFIG) wind plant. The effectiveness of the proposed scheme is evident from the simulations.

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