Analytical Derivation of the DC-Side Input Admittance of the Direct-Voltage Controlled Modular Multilevel Converter

Journal article, 2017

The input admittance of a converter, connected to other dynamic subsystems, is a useful tool to investigate whether poorly damped oscillations or even unstable conditions might occur at certain frequencies. This is of interest in applications employing the modular multilevel converter (MMC), where the internal dynamics of the converter and the increased number of control loops greatly affect the MMC’s dynamic behaviour, compared to other types of converters. In this paper, the dc-side input admittance of the direct-voltage controlled MMC is derived analytically and verified via small-signal perturbation in a detailed nonlinear time-domain simulation model. The MMC’s input admittance is parametrically studied and compared to the dc-side input admittance of an equivalent two-level converter.