Flexible AC Phase Configurable NPC-based Converter Topology

The grid integration with distributed generators requires advanced power electronic converters capable to interconnect to different ac systems. This paper presents a flexible converter topology for phase configuration compatible to both single-phase two-wire and three-wire ac systems. The topology under investigation is comprised of two-leg three-level neutral-point clamped (3L-NPC) based with an integrated GaN-based neutral-point (NP) leg. The single-phase 3L-NPC based converter allows grid interconnect with different voltage phase displacement, for example $120 {V}_{L N}/240{V}_{L N}$ and $120V_{L N}/208V_{L L}$ ac systems. In ac voltage-controlled voltage source inverter mode, the new topology allows operation with different ac load-types, including half-wave rectified loads. Three controllers are designed to perform bi-directional power flow between dc and ac ports. The NP-controller compensates the dc power imbalance at the input dc port, as a reflection of unbalanced conditions of phase-a and -b. Thus, the converter allows full-quadrant operation with phase imbalance of active and reactive current components. Through the topological arrangement with direct bonding of neutral-point to grid-neutral advantageously eliminates the common-mode (leakage) current. The control strategy is presented along the phase configurable topology compatible to three-wire and two-wire ac grid systems. Simulation results, obtained using a 8kVA PV/EES phase configurable 3L-NPC based converter, are presented to validate the performance’s of proposed topology.