A terminal Voltage Source Converter Control Connected to an Unbalanced grid

Abstract

This study deals with analysis and control of shunt-connected Voltage Source Converters (VSC) feeding a variable DC load through an output DC-bus capacitor when the three-phase network voltages are suddenly affected by typical voltages dips causing a momentary asymmetry to the considered grid voltages. Under these conditions, the use of vector control technique under its conventional form to regulate the DC-bus voltage will confront some troubles relative to negative sequence apparition. The main reason for these issues is that the line currents present a dangerous transient value during the period of voltage drop considered. Therefore, an enhanced form of vector control must be applied in order to cover both positive and negative sequences characterizing the unbalanced system voltages. The effectiveness and ability of the proposed control scheme have been verified by both simulation and experimental results.