Design guidelines of circuit parameters for modular multilevel converter with H-bridge cell

Abstract

This paper presents theoretical formulae for circuit parameter design as design guidelines in a step-down rectifier in a power system connected to a 6.6-kV AC power grid, where a modular multilevel converter (MMC) is applied. In particular, this paper focuses on the design of heat sinks, capacitors, and arm inductors. In addition, the worst case for each component design is shown as the first step of the converter design. First, the formula for the ripple current in the electrolytic capacitor is derived in order to evaluate the capacitor lifetime. Second, the formulae for the semiconductor losses are clarified on the basis of the analysis of the arm current. Third, the formula for the ripple current in the arm inductor is derived on the basis of the ripple current model of a chopper circuit. Finally, all formulae are verified by experiments with a miniature model. It is confirmed that theoretical values from formulae agree with the measured values with the errors lower than 12%.