T03.7 - Single-Stage Bidirectional High-Frequency Link DC to Three-Phase AC (4-Wire) Grid-Tied Microinverter

This work introduces a novel, single-stage, inertia-less isolated converter (IIC) designed to interface low-voltage PV and battery storage with the AC grid at 480 VAC. The IIC addresses challenges in traditional multi-stage DC/AC topologies by eliminating intermediate energy storage elements, enhancing power density, reliability, and reducing system costs. 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, and eliminating PWM dead-time and dwell-time compensation loops. The proposed PDM scheme simultaneously manages volt-second and amp-second balance on the transformer, mitigating injection of DC flux on both the primary and secondary windings. This work provides a detailed analysis of the DC to 3-phase AC IIC topology, including analysis of critical parasitic elements and zero-voltage switching (ZVS) of the AC bridge devices. A 2 kW, 125 VDC to 480 VAC unit has demonstrated full ZVS operation in single-phase operation. The final paper will provide results from three-phase operation, with projected system efficiency over 97.7%.