Single-Stage Bidirectional High-Frequency Link DC to Three-Phase AC (4-Wire) Grid-Tied Microinverter

This work presents a novel, single-stage, inertialess isolated converter (IIC) designed to interface low-voltage PV and battery storage to the three-phase AC grid at 480 VAC. This approach addresses key challenges with multi-stage DC/AC topologies conventionally used in grid-connected PV and energy storage applications. Specifically, elimination of the intermediate DC capacitor improves power density, reliability, and system cost. Further, single stage operation enabled by the proposed pulse density modulation (PDM) scheme simplifies plant control, providing high-bandwidth, closed loop control of the inverter output voltages without PWM dead-time and dwell-time compensation loops. The proposed PDM scheme manages volt-second and amp-second balance on the transformer, mitigating injection of DC flux on both the primary and secondary windings. Transformer parasitic elements are utilized to enable zero voltage switching (ZVS) of the AC bridge devices. This work provides a detailed analysis of the DC to 3-phase AC IIC topology, exploring the impact of critical parasitic elements and commutation of the AC bridge devices. A 3-phase, 2 kW 125 VDC to 480 VAC unit has been built and tested, validating ZVS operation of the AC bridge devices. Projected system efficiency at full load is >97.3%.