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Doubly fed induction machine (DFIM) is increasingly being preferred in large rated variable speed pumped storage power plants (PSPP), because it provides better energy efficiency due to optimization of pump/turbine efficiency. Increased efficiency results from the flexibility of operating speed at different hydraulic heads. In doubly fed configuration, partial rated power converters feed the rotor circuit. Parallel-connected back-to-back voltage-source converter on rotor side is responsible for starting, braking (dynamic/regenerative), and speed (real power) control of the unit. This paper presents smooth starting and regenerative braking, and assesses performance under power converter and sensor faults of a 250-MW DFIM pump turbine unit to be commissioned in Tehri PSPP, India. Survivability of the unit during faults is analyzed based on current, speed, and dc-link voltage. Further, this paper investigates fault-tolerant operation of 250-MW DFIM unit at open-circuit fault in converters. A 2.2-kW DFIM is tested in the laboratory to corroborate the simulation. [ABSTRACT FROM AUTHOR]

Reliable operation of multichannel power electronic converters in a large pumped storage power plant (PSPP) is a main concern among policymakers and/or hydropower project developers. This paper aims to design a two-stage protection circuit operation strategy for a large-rated doubly fed induction machine (DFIM) employed for variable-speed PSPPs. This paper initially studies the dynamic behavior of DFIM under symmetrical short-circuit faults in both the 400-kV power system and at stator terminal of the generating unit. Based on the fault analysis, a two-stage protection circuit (dc-link braking chopper circuit and crowbar protection circuit) operation strategy is designed in consideration of practical limitations. The designed operation strategy ensures the continuous operation of large-rated DFIM under marginal grid disturbances. To investigate the effective operation of a two-stage protection circuit, a 250-MW DFIM with multichannel power converters is implemented in MATLAB/Simulink tool. An experimental test is carried in a 2.2-kW DFIM laboratory prototype. [ABSTRACT FROM AUTHOR]