Design and development of a 4-kW/2-kHz dc-isolated power conditioner for utility-interactive photovoltaic applications

A utility-interactive inverter based on high-frequency isolation has been developed to provide a low-cost, compact, photovoltaic-to-utility interface at the residential power level of 4 kW. A single-quadrant, dc-isolated, push-pull buck converter switching at 20 kHz is used to generate a full-wave rectified sine wave that is subsequently unfolded by a low-speed, four-transistor bridge to result in a 60-Hz sine wave power output. A control strategy optimizing the output impedance of the inverter for the direct interface to the stiff utility voltage has been developed. A novel peak power tracking circuit based on the inherent 120-Hz input voltage ripple continuously follows the peak power without artificial operating point dither. Inverter shut-down after line disconnection is ensured, fully protecting the serviceman, even when the solar power available exactly matches a unity power factor load. Despite its low weight of only 17 kg, the inverter is 92% efficient. 5 refs., 60 figs., 7 tabs.