Authors: Reza Barzegarkhoo, Yam. P. Siwakoti, Naser Vosoughi, and Frede Blaabjerg
Photovoltaic (PV) string inverters with transformerless grid-connected architecture are the most commonly used solar converters owing to their appliance-friendly and cost-effective benefits. A novel circuit configuration for these converters is presented in this study, which seeks to address the shortcomings of most of the conventional topologies such as the problem of leakage current, voltage ratio transformations, and power quality. The proposed structure is based on the series-parallel switching conversion of the switched-capacitor (SC) cell and is comprised of only six unidirectional power switches with a common-grounded (CG) feature.
Through the use of the SC cell and the CG connection of active and passive used elements, not only is the number of output voltage level enhanced by up to five but also a two times voltage boosting feature with a single stage operation as well as elimination of the leakage current is acquired. Herein, to inject a tightly controlled current into the grid, a peak current controller approach has been used which can handle both the active and reactive power supports modes. Details of the proposed CGSC-based 5L inverter and its closed-loop control diagram with the typical waveforms of the gate switching pulses, output 5L PWM voltage, and the injected grid current have been illustrated in Fig. 1. Theoretical analysis, design guidelines, comparative study, and some experimental results are also given to corroborate the feasibility and accurate performance of the proposed topology.