UNIVERSAL BIDIRECTIONAL DC-AC CONVERTER

Abstract

The paper presents a schematic solution and a description of the operation of a bidirectional
DC-AC converter with transformer isolation. The topology is based on the principles used in
resonant LLC converters and dual active bridges (DAB), but the proposed design uses bipolar
inverter topology on the AC voltage side, as well as combined frequency and pulse width control.
This makes it possible to implement a number of functions in a single converter using a small
number of commutations in the power circuit. So, it is possible to implement the following operating
modes: an uninterruptible power supply (conversion of a battery DC voltage to a 220 V 50 Hz
AC); a grid-tie inverter for alternative sources (solar panels); a battery charger (operating both
from the mains and from solar panels); a welding inverter for semi-automatic welding (and welding
can be carried out both from mains, and from the battery); an AC voltage regulator; a DC/DC
voltage converter (for “cranking up” batteries with different voltages or state-of-charge). A device
with the listed set of functions can be used, for example, in the field – for organizing power supply
of various loads, charging batteries, as well as performing minor welding operations. The circuit
topology of the converter allows, when using appropriate control algorithms, to work with a power
factor close to unity on the AC voltage side. This makes it possible to ensure operation in a
"weak" grid – from an autonomous generator, with a large length of the power cord, etc.