A New Circuit Performance of Modular Multilevel Inverter Suitable for Photovoltaic Conversion Plants

This paper investigates a new circuit topology of the modular multilevel converter (MMC) for deploying in photovoltaic (PV) distributed generation systems. In the conventional MMC, two arm inductors are placed in each phase to limit the circulating current. In the proposed topology, the inductors are replaced by a transformer. The proposed circuit gives a 50% reduction in the voltage rating of the power devices and the capacitor size in comparison with the basic MMC topology. The required dc-link voltage that is directly fed by PV panels is also reduced by half. In addition, the transformer helps to limit the fault current in the dc bus. This paper presents a pulsewidth modulation method to control the solar inverter output voltage, in which there is no need to calculate the duty cycle of individual cells. A brief description of the charging process for the capacitors is also included. The converter behavior is evaluated by numerical simulation to validate the concept. Experimental verification is achieved through a downscaled real test bench.