Analysis of doubly-fed induction machine operating at motoring mode subjected to voltage sag

Variable Speed (VS) Pumped Storage Plants (PSP) equipped with large asynchronous (Doubly-Fed Induction) machines are emerging now in hydropower applications. Motoring mode of operation of Doubly-Fed Induction Machine (DFIM) is essential and techno-economical in this application due to: (1) its uniqueness in active power controllability, (2) bulk power handing capability with less rated power converters in rotor circuit, and (3) integrating Renewable Energy Sources (RES). This paper investigates the performance of two DFIMs at different power ratings (2.2 kW and 2 MW) under voltage sag with different attribute. The test results are analyzed in terms of the peaks in torque, speed, power taken and transient currents in rotor and stator circuits. During sag, stable region for DFIM operation along with speed and stator side reactive power input control is also illustrated. The negative effects of voltage sag are briefly discussed. MATLAB simulation is validated with experimentation. The various observations during simulation and experimental analysis are also supported by the theoretical explanations.