Single-Stage Bidirectional Inertia-less Isolated DC/AC Converter

This paper presents a novel (patent pending) single-stage inertia-less isolated converter (IIC), which overcomes key challenges with low-power two-stage DC/AC microinverters that are commonly used in grid-connected PV solar and energy storage applications. Elimination of the intermediate DC capacitor improves power density and reliability, while also reducing cost. Single stage operation poses several challenges that drive the need for ultra-low leakage inductance in the transformer, control that ensures no DC flux in the transformer core, and the use of discrete pulse modulation strategies. Given the cost sensitivity of typical low-cost inverters, a simple high-bandwidth control strategy is developed that achieves high performance without excessive computation or delays. In this digest, the detailed operation of IIC is discussed with the proposed control scheme. Further, a brief discussion on the design of the transformer is presented with the investigation of converter losses. The presented simulation results demonstrate the operations of the IIC topology for DC to AC conversion with the proposed control scheme. A dedicated 1kVA (2 kW peak) prototype that switches at 40 kHz has been constructed that achieves high power density and high efficiency at low cost.