Control and simulation of a flywheel energy storage for a wind diesel power system

Wind diesel power systems (WDPSs) are isolated microgrids which combine wind diesel generators with wind turbine generators. If the WDPS includes a short-term energy storage system (ESS) both the logistic and the dynamic operation are improved. Flywheel based energy storage systems (FESSs) have characteristics that make them very appropriate to be used as short-term ESS in WDPS, so that a FESS, is added to the WDPS. The FESS main components: electrical machine, flywheel, grid converter and electrical machine converter are described. As the main aim of the FESS in the present article is power quality improvement, a robust low cost low-speed FESS (LS-FESS) is selected. The LS-FESS which includes an asynchronous machine (ASM) and a steel flywheel is sized for a particular WDPS. The FESS power converters and ASM can be controlled as if they were a servo but, in order to attain more robustness, it is better to control the ASM converter to maintain a constant DC-voltage in the DC-link and to control the grid converter to exchange the necessary power references with the isolated grid. Finally, in order to verify the proposed low speed FESS, it is simulated along with the WDPS. Simulation results with graphs for the isolated power system frequency and voltage, active powers generated/consumed by the WDPS elements, the FESS-ASM direct and quadrature currents and FESS-flywheel speed are presented for load and wind speed steps. The simulations show a power quality improvement of the isolated microgrid due to the use of the FESS.