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At present, the disturbances like the voltage fluctuations, resulting from the grid's complexities and unbalanced load conditions, create severe power quality concerns like total harmonic distortion (THD) and voltage unbalance factor (VUF) of the grid voltage. Though the custom power devices such as distribution-static compensators (D-STATCOMs) improve these power quality concerns, however, the accompanying controller plays the substantial role. Therefore, this paper proposes a fractional-order sliding mode control (FOSMC) for a D-STATCOM to compensate the low power distribution system by injecting/absorbing a specific extent of the reactive power under disturbances. FOSMC is a non-linear robust control in which the sliding surface is designed by using the Riemann-Liouville (RL) function and the chattering phenomenon is minimized by using the exponential reaching law. The stability of FOSMC is evidenced by employing the Lyapunov stability criteria. Moreover, the performance of the proposed FOSMC is further accessed while doing its parametric variations. The complete system is demonstrated with a model of 400V, 180kVA radial distributor along with D-STATCOM under two test scenarios in MATLAB/Simulink environment. The results of the proposed controller are compared with the fixed frequency sliding mode control (FFSMC) and conventional proportional-integral (PI) control. The results validate the superiority of the proposed controller in terms of rapid tracking, fast convergence, and overall damping with very low THD and VUF.

Microgrid is an ideal solution to many problems that exist in conventional electrical grids mainly electrical power reliability concerns. Power quality disturbances are of equal concern as power reliability since they have a direct impact on load's life and performance. Microgrid is unable to tackle power quality-related problems in electrical grids without additional support. A unified power quality conditioner (UPQC) is top-ranked power quality compensation device; it minimizes the vulnerability toward power quality problems through its series and shunt compensators, which are connected via two voltage source converters (VSCs). However, the performance of UPQC mainly depends on the controllers directing the VSCs. In this article, the authors have proposed a new controller for microgrid connected UPQC, which controls the switching of VSCs of UPQC by taking the derivative of error at three different stages and then integrates it over time, while being supplemented by three gains, to improve its stability and performance toward power quality problems. The authors have also used fuzzy logic-based sensing to trigger the switching of series or shunt compensators to condition any voltage sag/swell, voltage transients, current harmonics, current unbalance, and voltage unbalance problem. The stability assessment of proposed controller has been carried out by using Lyapunov stability criteria and bode plots. The performance has been

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