Compensation of Arm Current Sensor Errors in Modular Multilevel Converter

The modular multilevel converter (MMC) is an attractive topology for medium- or high-power applications due to its high modularity, scalability, and high-power quality. Even if a direct modulated control algorithm guarantees a stable operation for the MMC system, it is unable to suppress the flow of a negative sequence second order leg current in the MMC. Mostly, for circulating current suppression, a PI controller in the double fundamental frequency rotating reference frame is adopted. The three-phase leg currents are calculated using the average of upper and lower arm currents of the respective phase after they are measured by arm current sensors. However, the previous circulating current suppression controllers do not consider the offset and scale error of the arm current sensors. This paper proposes an algorithm to compensate the offset and scale error of the arm current sensors. The proposed algorithm is easy to be implemented and effectively suppresses the leg current components caused by the current sensor errors. The validity of the proposed algorithm is verified through both simulation and experimental results.