Output Filter Design for Grid-tied Cascaded Multi-level Inverters Based on Novel Mathematical Expressions

Renewable energy resources, which are widely used in modern power systems, require power electronic-based converters to couple with the external grid. The main impact of utilizing power electronic converters on the grid power quality is harmonic generation produced by their switching process. Multi-level inverters are outstanding solutions to significantly reduce the voltage stress and harmonics. In this paper, novel mathematical expressions are derived to calculate the maximum ripple of the inverter output current, which are used to size the inverter-side inductor for an output filter. Moreover, new analytical and simplified formulas are proposed to calculate the damping losses, which lead to optimum selection of the damping resistor of the output filter. Ultimately, a mathematical expression for the grid-side inductor is attained considering compatibility level for harmonics within the range of 2-150 kHz to cover electrical and electronics equipment, which currently are the most important issues in the international standardization committee (IEC, TC77A). The efficiency of the proposed approach is finally validated by the experimental and simulation results.