On the Analysis of a Back-to-Back Converter Connecting a Microgrid Under Unbalanced Voltages

In this paper, a comprehensive analysis of the implications of operating Back-to-Back (BTB) systems with conventional dq control under unbalanced voltage conditions is presented. BTB converters can be highly useful for interconnecting a microgrid (MG) to a distribution grid (DG). Simulation results of four study cases in which a voltage unbalance in either of the interconnected grids results in highly unbalanced AC currents with significant Total Harmonic Distortion (THD) are presented. The simulation results indicate that these effects depend on critical factors such as which of the two voltage source converters (VSC) in the BTB system regulates the DC link voltage, the time response used for DC voltage regulation, and whether the VSC experiencing the unbalance operates in rectifier or inverter mode. The findings presented here are particularly valuable for improving the operation of BTB systems employing conventional dq control under unbalanced voltage conditions, offering insights to mitigate adverse effects and enhance system performance.