A fast dynamic unipolar switching control scheme for single phase inverters in DC microgrids

This paper presents the digital implementation of a boundary controller with unipolar switching characteristic for single phase voltage source full bridge inverters, which will be used as an interface between a low voltage DC microgrid and AC loads. This paper expands the second order switching surface control method for single phase inverters by unipolar switching with the use of a finite-state machine. Compared to bipolar switching, unipolar switching has the advantage of lower switching losses and filter size. Besides, the switching losses can be equally distributed among semiconductor switches compared to conventional three-level inverter switching scheme. The operating principles of proposed control scheme and mathematical derivation of the switching functions will be given. A 550 VA, 120 V, 60 Hz voltage source inverter (VSI) with a digital signal processor has been implemented to verify the theoretical predictions. Experimental results for steady state operation at different loading conditions show a tightly regulated output voltage, for large-signal disturbances the control is fast and precise