A grid-connected multilevel converter for interfacing PV arrays and energy storage devices

This paper presents a design procedure and a control strategy for a grid-connected single-phase multilevel converter. The proposed system uses two series connected H-bridge modules, one fed by photovoltaic panels, the other by energy storage devices. The former switches at line frequency, while the latter operates in PWM. The system is designed to minimize the voltage stress on the switches, while the control strategy is such that a constant active power is delivered to the grid with high power factor, even if the energy produced by the photovoltaic panels is variable. The paper illustrates the power converter design procedure, the hybrid PWM method and the small signal modeling used to design the controllers of each inverter. In addition, the performance of the multilevel converter is verified by means of simulation and experimental results, which show the system ability to operate as expected.