In recent years, doubly fed induction machine (DFIM) is increasingly being preferred in variable speed pumped storage power plants due to its merits like partial-rated excitation system (cost factor), unity power factor, real and reactive power controls. In large-rated DFIM (250 MW), parallel-connected three-level neutral-point clamped (3L-NPC) back-to-back converter systems are employed as rotor excitation circuit to handle slip power requirements (-10% to +8.33% in Tehri PSPP, India). The power semiconductor device failure in the rotor excitation circuit may cause serious concerns in grid stability and system reliability. To ensure the continuous operation of a generating unit, this paper aims to design a redundant parallel leg configuration with six antiparallel IGBTs for a 3L-NPC back-to-back converter structure to acquire fault tolerant operation under power semiconductor device failure. Furthermore, an efficient active current sharing control strategy with fault tolerant operation is implemented for each converter to obtain better performance of the drive system. In fault tolerant operation, fault identification is computed based on a normalized phase currents average method with less computational effort and timely identification of open switch faults in both grid side converter and rotor side converter. The circuit reconfiguration under postfault operation is performed by antiparallel IGBTs with the help of fault tolerant control scheme. The effectiveness of a designed fault tolerant control scheme is validated through MATLAB/Simulink environment for a 250-MW DFIM system with 25 MW (5-channel) power converters. To ensure the trustworthiness of the simulation, an experimental demonstration is performed through a 2.2-kW DFIM laboratory prototype with a 2-channel 3L-NPC back-to-back converter structure.

A stealthy cyberattack (SCA) aims to gradually drive the system toward instability. Although research is continuing in attack detection algorithms, a resilient control strategy is vital if SCAs go undetected for a considerable time. Especially for a controller involved in automatic generation control (AGC), resiliency becomes more crucial as the controller has to sometimes work under abnormal conditions considering that shutdown of operation is not an option. This paper introduces an innovative approach to support dual-area thermal power systems in the face of network-related challenges such as transference latency (TL) and SCAs. We propose a new tri-parametric fractional controller (TFC) that merges the advantages of proportional-integral and proportional-derivative operations, eliminating the need for additional control loops and enhancing system efficiency. The TFC's efficacy in mitigating random and step load disturbances is established, outperforming existing controllers. We employ the complex root boundary method to define the optimal parameter search space, with an improved equilibrium optimizer algorithm determining the best controller settings. The inclusion of renewable energy sources, including solar and wind, is considered, and the robustness of the system is evaluated using uncertainty norms and complementary sensitivity functions. Our approach is validated through hardware-in-loop real-time verification on the OPAL-RT platform, demonstrating superior performance in maintaining frequency stability under SCAs and TL challenges.

Power electronic converter plays a significant role in hydropower generating systems of both fixed and variable speed types. These converters are used in the form of simple rectifier for static dc excitation in fixed speed system and in the form of ac excitation (AC-AC or AC-DC-AC) in variable speed system. Parallel connected multiple three-level neutral-point-clamped (3L-NPC) megawatt back-to-back (BTB) converters have been adopted in recently commissioned variable speed pumped storage units (VSPSU). For such configurations, reliability and efficiency are considered to be prominent. This paper proposes a methodology for effective utilization of parallel-connected BTB power converter for VSPSU of large capacity by performing load dependent activation /deactivation of converters. Vector control strategy for active and reactive power deliveries of VSPSU is formulated. This paper also focusses on losses and thermal behavior of converters at different speeds of generator in accordance with water head variations. The proposed control system is designed in such a way to decrease overall losses in power converter system. The effectiveness of proposed method is explained on a real scale of 250 MW doubly fed induction machine (DFIM) with 5x5 MW power converters using MATLAB/PLECS software and experimental validation is performed through a downscaled 2.2 kW laboratory prototype.

Doubly fed Induction machine (DFIM) is increasingly being preferred in large rated variable speed pumped storage power plants (PSPP) since 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 (VSC) on rotor side is responsible for starting, braking (dynamic/regenerative) and speed (real power) control of the unit. This paper presents the 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: (i) current, (ii) speed, (iii) 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.