Transformer-less grid-connected 7-level inverter with model predictive control method suitable for PV application

This study presents a new single-phase transformer-less grid-connected inverter based on a six-phase interleaved dc/dc converter as a suitable topology for PV applications. The proposed topology consists of a dc input and multi-output in the dc-link side which results in production of six levels per half cycle. The voltage of the inverter at output side is 7-level that is injected into the network. The voltage of PV panels is low and this problem is solved by increasing the voltage level in the interleaved converter. Besides, the input current ripple of the interleaved dc/dc converter is very low which causes to improve the quality of the injected current into the grid through a PV panel. For control of the power switches and active/reactive power flows, the model predictive control (MPC) method is applied. The proposed system is capable of creating different voltage levels in step-up/down at the dc-link side and this will make it suitable for working in a wide range of power in the grid-tied. Besides, the total voltage blocking (TVB) of the power switches at the inverter side is greatly decreased. Consequently, the efficiency of the proposed system is high. To prove the accuracy of theoretical calculations, the proposed topology for a 900 W prototype at an operation of 50 Hz is built and tested in the laboratory.