A Current-Mode Controller For an HB-NPC Inverter Using the Virtual-Ground Trajectory for Power Injection in PV Systems

This paper presents the analysis and control design for an HB-NPC power converter which is used in a transformerless photovoltaic systems, and is aimed to guarantee active power injection to the grid. The system includes a Virtual-Ground connection to mitigate the leakage-ground currents, which are produced by the effect of common-mode voltage variations across the stray capacitances. The latter arise between the photovoltaic cells and their grounded frame. The system considers an LCL output filter with split capacitors to allow the virtual ground connection. Moreover, the proposed controller provides active damping of the typical third-order response presented by LCL filters. The proposed control scheme consists on a proportional-plus-resonant controller acting on the inverter-side current error. Finally, experimental results are provided to demonstrate the benefits of the proposed solution in the leakage-ground current mitigation as well as in the active power injection to the grid.