A Flying-Capacitor Modular Multilevel Inverter based Dynamic Voltage Restorer for Voltage Quality Improvement in Electrical Distribution Grids

Abstract

This paper proposes the mitigation of grid voltage disturbances using a flying-capacitor modular multilevel Inverter (FC-MMI) based dynamic voltage restorer (DVR) solution. Which regulates the injection of the compensation voltage in series and synchronism with the grid during the voltage disturbance events, the auxiliary capacitor voltage, while controlling the FC-MMI output current. this paper presents a flying-capacitor modular multilevel converter (FC-MMI) based on series-connected sub-modules. The proposed FC-MMI circuit is characterized by the cross connection of upper and lower arm middle taps through a flying capacitor in per phase leg. By properly controlling the AC current flowing through the flying capacitor, the power balance between upper and lower arms is achieved, leading to very small voltage ripples on sub-module DC capacitors . that the proposed FC-MMI along with the proposed control method performs satisfactorily in dynamic and static state . This feature enables the structure to be used to compensate for the power quality of power distribution networks. Modified Phase Modified Pulse Width Modulation (MPSPWM) in the inverter is used to create the desired waveform. The  In-Phase control method is selected to control the proposed DVR and use the synchronous reference frame (SRF) method to detect the network voltage fluctuations. To verify and validate the proposed DVR performance, simulations are carried out in the MATLAB / SIMULINK software environment, and the results indicate the optimal performance and desirability of the proposed DVR to compensate for the voltage sag, swell and flicker power distribution grids. Theoretical analysis and simulation results are given to show the high performance of the proposed solution.