A modified reduced frequency capacitor voltage balancing strategy with reduced number of sensors for modular multilevel converters

The balancing of sub-module capacitor voltages of modular multi-level converters (MMC) is considered to be an essential process for keeping the quality of the output power at considerable limits. This paper presents a new capacitor voltage estimation technique which feeds the capacitor voltage balancing control. This strategy not only eliminates the need for measuring the sub-module capacitor voltages but also it removes the communication channels needed to transmit the readings of these measurements. The proposed strategy is tested using PSCAD/EMTDC software package and simulation results showed a robust behavior during normal as well as abnormal operating conditions.