Analysis of Capacitor Current Stress in Five-Level Active Neutral Point Clamped Converter

This paper derives analytical expression for current stress on capacitors of Five-Level Active Neutral Point clamped Converter (5L-ANPC) connected on load side. In hybrid multilevel structure, semiconductor devices operate at different switching frequencies and may not conduct even when they are gated on. Therefore, the duty ratio expressions used to evaluate current stress in DC-link capacitors may not result a correct expression. Also there is a flying capacitor in the circuit. Expressions are obtained using conduction functions (G). Conduction function is obtained by combination of switching functions (S) of appropriate switches. Results of derived expressions are compared with MATLAB Simulink results to validate the expressions. Difference in current stress on flying capacitor and DC-link capacitor in the same converter leg over sizing, lifetime expectancy and voltage ripple is discussed.