Design and Implementation of a Single-Source 17-Level Inverter for a Single-Phase Transformer-Less Grid-Connected Photovoltaic Systems

Abstract

Transformer-less multilevel inverters (MLIs) based on switched capacitors are gaining importance due to the voltage boosting ability from a single-input DC source and inherent capacitor voltage balancing capability. Most of the grid-connected transformer-less inverters are five-level and are commonly grounded so that their leakage current is zero. However, some major challenges like higher total standing voltage (TSV), more losses due to capacitor voltage ripples, higher charging current, and peak VA rating of the switches are comparatively higher. The motivation of the proposed work is to reduce the voltage ripple across the capacitors, minimum TSV, higher efficiency close to 98% at 1 kW, and lower cost. By using a modified sinusoidal pulse width modulation (SPWM) technique for the proposed single-phase 17-level inverter, a transformer-less grid-interfacing can be realized as the leakage current is (≈22 mA) well within the acceptable value (<300 mA) and is independent of the switching frequency. To validate the performance of the proposed structure, its performances are compared with the recently developed transformer-less inverters. The experimental prototype of a 1-kW single-phase 17-level inverter is designed and tested for grid-connected and standalone mode, and the corresponding results are verified.