Operating MicroGrid Energy Storage Control during Network Faults

A MicroGrid is expected to operate both as a sub system connected to the main grid or as an islanded system. However the provision of fault currents, in an islanded MicroGrid consisting only of micro-generation interfaced with relatively low-current power electronics, is a serious system protection issue. This paper presents the novel concept of using the central energy storage system (flywheel) as the main fault current source in islanded mode. The three-phase MicroGrid test rig used at University of Manchester, and the flywheel control system are described. The importance of accurate systems modeling of the whole microgrid and energy storage unit is shown. A fault study is carried out on the test rig and in PSCAD. The flywheel inverter system is shown to contribute enough fault current for a sufficient duration to cause the system protective device to clear the fault.