Buck-boost DC-AC inverter: proposal for a new control strategy

The buck-boost DC-AC inverter is a special topology consisting of two buck-boost DC-DC converters that generate an AC output voltage in a single stage. This is achieved by means of driving both buck-boost DC-DC converters with two 180° phase-shifted DC-biased sinusoidal references. The differential output voltage is therefore an AC output voltage whose peak value is independent of the DC input voltage. The advantageous configuration of the buck-boost DC-AC inverter (AC voltage generated in a single stage, reduced number of semiconductors, small losses, output voltage naturally filtered, no dependence on the input voltage level, etc.) has a drawback related to the control of both buck-boost, as they are required to work in a variable operating point condition. This paper proposes a new double-loop control strategy for both buck-boost DC-DC converters that includes different compensations and feed-forward loops that make possible a fast and accurate control of both converters in a variable operating point condition. In addition, the proposed strategy achieves a high immunity to external perturbations such as input voltage and output load disturbances. Simulation tests show the robust performance in these situations as well as in case of transient short circuits and nonlinear loads connection.