Stability assessment and performance analysis of new controller for power quality conditioning in microgrids

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 analyzed through simulations in MATLAB/Simulink environment on a 400 V, 5.63 kVA LV distribution system. The results have been compared with the classical PI controller and validate that the proposed controller gives a better performance in terms of considered power quality problems like voltage sag/swell, transients and current unbalances and harmonics. The total harmonic distortion with the proposed controller has been reduced to 3.32%. Furthermore, as compared to other standard controllers, the proposed controller ends up in less complexity, fast response time, and stable performance.