Effects of voltage sag on Doubly fed induction machine at hyper-synchronous motoring mode

Load-frequency match is mandatory requirement for interconnected power system stability. Any unscheduled change in load or intermittent power injection from Renewable Energy Sources (RES) leads to system instability by changing the frequency. Therefore, energy storage devices are essential as they can provide quick response for any change in system frequency. Pumped Storage Plants (PSP) serves the dual purpose, either by storing surplus power or by generating hydro power during peak requirements. The use of Doubly-Fed Induction Machine (DFIM) with power electronics in rotor circuit is significant in both motoring and generating modes in PSP. This paper investigates the effect of symmetrical voltage sag on the performance of DFIM at motoring mode. Various motor parameters, namely peaks in total power taken from grid, torque and current (stator and rotor current), and speed loss were investigated. With the aid of both simulation and experimental results, symmetrical voltage sag effects on a 2.2kW three-phase DFIM are analyzed. In steady-state operation of DFIM, the voltage sag produces motor instability which depends on sag depth and duration.