Seamless Mode Transitions for Triple-Loop Controlled Interlinking Converters

Interlinking converters interface microgrids with the ac main grid and are expected to operate both grid-connected and islanded. The capability of transition between the two modes of operation is therefore an important functionality. However, significant current and voltage spikes can easily occur across the transitions, which makes the mode transition control a challenging task. A flexible feed-forward solution is proposed herein to achieve seamless operation modes transitions, by exploiting an underlying large-bandwidth triple-loop controller for interlinking converters. Thanks to the advantages brought by the triple-loop controller and the flexible feed-forward strategy, the proposed solution achieves i) in grid-tied operation, robustness against various types of grid anomalies (e.g., amplitude or frequency variations, grid voltage harmonics), ii) in islanded operation, continuous, high-quality supply of the local loads, iii) smooth transitions between the two operation modes. These features are verified experimentally on a 3kVA single-phase inverter.