A Single-Sensor-Based Circulating Current Controller for a Modified Three-level Modular Multilevel Converter

A voltage controller for the middle capacitor of a modified modular multilevel converter (MMC) is proposed in this paper. This controller is utilized as an alternative solution to the existing circulating current controller. Unlike the circulating current controller, the second-order harmonic component of the circulating current is regulated indirectly by controlling the second-order component of the middle capacitor voltage. Using this approach, only one voltage sensor per phase is needed instead of two current sensors. The validity of the proposed control is proved by simulation and experimental results.