Predictive Control of a Grid-Tied Cascaded Full-Bridge NPC Inverter for Reducing High-Frequency Common-Mode Voltage Components

In this paper, a model predictive control (MPC) strategy for a grid-tied cascaded full-bridge inverter with neutral-point-clamped legs has been developed. Two strings of photovoltaic (PV) cells are interfaced to the grid by the inverter, while the controller ensures the operation at maximum power conditions. It is thus essential for the developed control method to be capable of independently regulating the two dc sources while balancing the dc-link voltages of the capacitors. In addition to these requirements, the proposed controller addresses the critical issue of the common-mode voltage (CMV) effects. By using the redundant switching states of the inverter topology, MPC reduces the high-frequency CMV components and consequently, the flow of the leakage currents from the PV system to earth ground. The developed control strategy is tested by conducting various experiments in an inverter prototype connected to two PV strings. Additionally, the system performance at steady-state conditions, during abrupt reference changes, and with grid voltage variations is compared with the traditional control strategy.