Review of Reduction of Leakage Current in Cascaded Multilevel Inverter

A primary goal of these systems is to increase the energy injected to the grid by keeping track of the maximum power point (MPP) of the panel, by reducing the switching frequency, and by providing high reliability. In the last years, multilevel converter topologies have been also considered in PV applications. Multilevel converter topologies can generate high-quality voltage waveforms with power semiconductor switches operating at a frequency near the fundamental. The cascaded multilevel converter constitutes a promising alternative, providing a modular design that can be extended to allow a transformerless connection to the grid. The cascaded multilevel topology has also disadvantages, as the strings of PV panels are not grounded and extra measures have to be taken in order to avoid currents due to stray capacitances between the panel and the earth. Pulse width modulated (PWM) multilevel inverters (MLIs) are gaining both popularity and applications, becoming an effective alternative to current inverter topologies. In their early stage, they were employed mainly in high-voltage high-power industrial and traction applications because they distribute the applied voltage among a number of cascaded power devices, thus overcoming their voltage limits and allowing the elimination of output transformers in medium–high voltage systems To avoid the common-mode leakage current, the conventional solution employs the half-bridge inverter or the full-bridge inverter with bipolar sinusoidal pulse width modulation (SPWM), because no variable common-mode voltage is generated. However, the half-bridge inverter requires a high input voltage which is greater than, approximately, 700 V for 220-Vac applications. Review of Reduction of Leakage Current in Cascaded Multilevel Inverter