Performance Analysis of Modular Multilevel Converter and Modular Multilevel Series Converter under Variable-Frequency Operation Regarding Submodule-Capacitor Voltage Ripple

The modular multilevel converter is capable to reach high-voltage levels with high flexibility, reliability, and power quality as it became the standard solution for high-power applications that operate fixed frequency. However, in machine-drive applications, shows critical problems since an extremely submodule-capacitor voltage ripple occurs machine start-up at low-speed operation, which can damage converter. Recently, a new named series was proposed promising alternative presented many important structural operational advantages relation such reduced number of submodule capacitors low frequencies. Even though capacitors, size these not analyzed. This paper presents detailed comparison analysis performance variable-frequency based on analytical description topologies. concludes be designed smaller if converters are used drive electrical machines within range low-frequency values. In other words, experiences very frequencies, means this operation.