A multi-kilowatt high-frequency AC-link inverter for conversion of low-voltage DC to utility power voltages

In this paper the results from a prototype low voltage DC input (<30 VDC) kilowatt class high frequency parallel-loaded resonant AC-link inverter is described. This system delivers utility grade voltage-source power at electronically selectable 50, 60, or 400 Hz. Cycle-by-cycle bidirectional current flow reduces the need for intermediate energy storage and allows for operation in a wide range of power factor with passive stability. The high frequency AC link and voltage boost stage is comprised of a zero voltage, zero current switching full-bridge inverter. This soft switching high frequency inverter is well suited for handling the large currents expected from a low voltage source. The output inverter is connected directly to this high frequency AC-link and zero voltage switching is employed in the output inverter to eliminate switching loss. A discretized sinusoidal carrier wave modulation (DSCWM) algorithm is used to control the high frequency boost inverter. The switching frequency of the DSCWM algorithm is fixed in relation to the frequency of the resonant high frequency AC link. The discretization of the modulation algorithm allows for the high frequency link to be discontinuous thus improving the zero voltage switching of the inverter. The elimination of a rectifier stage and reduction of the intermediate energy storage delivers a high power density design when compared to conventional dc-dc-ac methods. While switching loss has been greatly minimized, AC resistance due to high frequency operation and large peak currents present must be addressed in the interconnections and magnetic design.