Submodule Capacitance Dimensioning for Cascaded H-bridge STATCOM with Film Capacitors

The capacitance value is designed in this paper to increase system's power density while maintaining converter performance for cascaded H-bridge (CHB) STATCOM in delta connection. The capacitance design rules are proposed for power quality and system safety. With the application of trigonometric transformation, the capacitance design rules can be represented as a series of nonnegative univariate polynomials, whose coefficients are associated with the capacitance value. The sum of squares (SOS) program is applied to obtain the minimal required capacitance. Simulations and experiments are conducted to validate the optimal capacitance design strategy.