Performance Evaluation of a New Transformerless Grid-Connected Six-Level Inverter with Integrated Voltage Boosting

This paper presents a new six-level switched-capacitor multilevel inverter, which can generate six output voltage levels with 2.5 times voltage gain from a single dc source. The design is motivated by the need for an overall compact and efficient inverter with a smaller line filter without an additional boost converter and line transformer. The capacitor voltages remain balanced as the constant dc input voltage source directly charges them. The suppression of inrush capacitor charging current using charging inductors and voltage boosting capability make this inverter a significant contender for a transformerless grid-connected photovoltaic system. The closed-loop dq current control and dc-link voltage control have been discussed theoretically to control the active power fed to the grid and voltage across the dc-link capacitors. The hardware implementation demonstrates lower harmonics and reactive power handling capability. The simulation and experimental results are analyzed and presented for the grid-connected mode of operation. The maximum measured efficiency is 95.79% at 448.8 W of output power. The ability of multiphase expansion from a single dc source and 2.5 times voltage gain makes the proposed MLI suitable for interfacing distributed energy generation systems with the electrical grid.