Circulating Current Elimination Controller for Modular Multilevel Converter and Submodule Capacitor Voltage Analysis

摘要

this paper proposes a circulating current elimination controller based on the detailed analysis of sub module capacitor voltage ripple in modular multilevel converter (MMC). When a circulating current suppression controller is embedded in MMC overall controller, the switching function of arms consists of a second harmonic component. The magnitude and phase angle of the second harmonic switching function (SHSF) is dependent on various factors, like, output current, power factor, modulation index, submodule capacitor, average submodule capacitor voltage and submodule capacitance. This paper gives the mathematical analysis of determining the magnitude and phase angle of SHSF. Firstly, the voltage components of submodule capacitor at different frequencies are calculated using average model of MMC. Based on the derived voltages, the magnitude and phase angle of the SHSF is determined. The analytic expressions and proposed control scheme are validated with simulation study.