An overview of different strategies applied to enhance the fault Ride-Through (FRT) ability of the Doubly Fed Induction Generators (DFIGs)-based Wind Turbines (WTs) during transient state is introduced in the study. Different FRT strategies dependent on (a) additional protection circuit's establishment, (b) reactive power injecting devices installation, and (c) various control approaches have been proposed in the literature. Typically, during disturbance in the grid to restrict the generated rotor overcurrent and undesirable Direct Current (DC)-link overvoltage, the protection circuits or control structures are connected. Concurrently, to improve the transient performance of the DFIG-based WT, the reactive power injecting devices outperform any deficiency of the reactive power and consequently bound the DC-link voltage and current in the rotor. Actually, during the transient state without damaging its operating strategy, many research findings show a productive DFIG protection. Along these lines, this study centers around underscoring the present status of the rotor overcurrent and DC-link overvoltage protection solutions, for example, the crowbar and its related protection circuits, fault current limiter, the reactive power injecting devices, for example, the static synchronous compensators, static var compensator, and dynamic voltage restorer.

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The presence of nonlinear loads like brushless DC (BLDC) motor drives in the distribution system leads to poor power quality (PQ) indices like low power factor, high total harmonic distortion and creates electromagnetic interference. Passive filters and Power factor correction converters are often inserted between the utility and BLDC motor drives to improve the PQ parameters. This paper proposes the shunt active power filter (SAF) for the PQ improvement of medium and high power BLDC motor drives. In this paper, the design steps and control of an SAF for a 20 kW BLDC motor drive are presented. The control of SAF is realized by applying the instantaneous "p-q" theory with the sinusoidal current control strategy. The current control is realized by a hysteresis controller. In contrast to normal electrical loads, the motor drive loads are subjected to continuous speed and load variations. This will result in fluctuations in the DC-link voltage of the SAF capacitor. Hence, the sliding mode controller is used for DC-link voltage control. The proposed methodology is validated in simulations and the experimental prototype. The enhancement of various PQ parameters is analysed for different loading conditions of the motor in the distorted and non-distorted distribution system voltage conditions.

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