Operation and control of a high performance inverter consisting of a buck-boost and a zero switching losses H-bridge for photovoltaic systems

This paper analyses the control of a especial inverter topology consisting of a buck-boost and a H-bridge in which the first one generates a rectified output voltage and the second one inverts one of each two half cycles. As a consequence, the H-bridge commutates at twice the line frequency and, what is more important, at zero voltage. Switching losses are therefore zero, and global losses of the inverter topology are very small achieving thus a high performance. In addition, the AC output voltage can be lower or greater than the DC input voltage. Both properties make this topology very interesting for photovoltaic systems. The main drawback of the structure is that the buck-boost has to be controlled in a variable operating point condition. This paper proposes two new control loops for the inductor current and the output voltage that include different compensations and feed-forward loops. This control strategy makes possible a fast and accurate control of the inverter output voltage. In addition, it 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.