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The main purpose of this paper is to select appropriate voltage vectors in the switching techniques and, by selecting the proper voltage vectors, be able to achieve a DC link with the same outputs and a symmetric multi-level inverter.

The proposed structure, a two-stage DC–AC symmetric multi-level inverter with modified Model Predictive Control (MMPC) method, is presented for Photovoltaic (PV) applications. The voltage of DC-link capacitors of the boost converter is controlled by MMPC control method to select appropriate switching vectors for the multi-level inverter. The proposed structure is provided for single-phase power system, which increases 65 V input voltage to 220 V/50 Hz output voltage, with 400 V DC link. Simulation results of proposed structure with MMPC method are carried out by PSCAD/EMTDC software.

Based on the proposed structure and control method, total harmonic distortion (THD) reduces, which leads to lower power losses and higher circuit reliability. In addition, reducing the number of active switches in current path causes to lower voltage stress on the switches, lower PV leakage current and higher overall efficiency.

In the proposed structure, a new control method is presented that can make a symmetric five-level voltage with lower THD by selecting proper switching for PV applications.

This paper aims to propose a new transformer-less inverter structure to reduce the common-mode leakage current in grid-connected photovoltaic (PV) systems.

The proposed circuit structure is the same as the conventional full-bridge inverter with three additional power switches in a triangular structure. These three power switches are between the bridge and the output filter, and they mitigate the common-mode leakage current flowing toward the PV panels’ capacitors. The common-mode leakage current mitigation is done through the three-direction clamping cell (TDCC) concept. By clamping the common-mode voltage to the middle voltage of the DC-link capacitors, the leakage current and the total harmonic distortion (THD) of the injected current to the grid is effectively reduced. Therefore, the efficiency is improved.

The switching modes and the control method are introduced. A comparison is carried out between the proposed structure and other solutions in the literature. The proposed topology and its respective control method are simulated by PSCAD/EMTDC software. The simulation results validate the advantages of the presented structure such as clamping the common-mode voltage and reducing leakage current and THD of injected current to the grid.

Presenting a single phase-improved inverter structure with low-leakage current for grid-connected PV power systems represents a significant original contribution to this work. The proposed structure can inject a sinusoidal current with low THD to the AC grid, and the power factor is unity on the AC side. In the half positive cycle, one of the switches in the TDCC is turned off under zero current. Besides, one of the other switches in TDCC is turned on with zero voltage and, therefore, its turn-on switching losses are zero. The efficiency of the proposed topology is high because of the reduction of leakage current and power losses. Accordingly, the presented topology can be a good solution to the leakage current elimination.