On the flywheel/battery hybrid energy storage system for DC microgrid

This paper presents a hybrid energy storage system (ESS) consisting of flywheel and battery for wind generator based DC microgrid. In the studied DC microgrid, a wind permanent-magnet synchronous generator (PMSG) is connected to its DC bus via a three-phase Vienna switch-mode rectifier (SMR). And a single-phase three-wire (1P3W) bidirectional load inverter is developed to serve as the load of microgrid and the interface from microgrid to utility grid. Good 220V/110V 60Hz AC output voltages are generated for local loads via the proposed simple robust control scheme. As to the established ESS, while the battery bank is connected to the microgrid DC bus via a half-bridge bidirectional interface DC/DC converter, the developed permanent-magnet synchronous motor (PMSM) driven flywheel employs a bidirectional three-phase inverter as the interface. Good charging and discharging performances of these two ESS devices are achieved by the properly designed control schemes. The energy balanced transfer between wind PMSG, battery, load, dump load and mains can be automatically accomplished. During the flywheel charging operation, the insufficient power provided from the wind generator can be supported by the battery automatically. Some measured results are provided to verify the performances of the established system.