Compensation method of arm current sensor scaling error in MMC system

The MMC is an emerging and highly attractive multilevel converter topology for medium and high voltage applications. Various modulation strategies are being used to control the MMC system. Balancing the cascaded submodule voltages and eliminating the second order circulating current in the leg of the MMC system are the main concerns of many researchers in the area of MMC system. Mostly, for circulating current suppression, a PI current controller in the double fundamental frequency rotating reference frame is adopted. Six current sensors are used to measure the six arm currents of the MMC system and the actual leg currents are calculated by taking the average value of the upper and lower arm currents of each leg. However, the scaling errors of the current sensors affect the operation of the circulating current suppressing controller and cause additional harmonic components in the leg currents. This paper proposes a scaling error compensation algorithm which can be easily implemented and eliminate the harmonics produced in the leg current due to the errors of the current sensors. The validity of the proposed algorithm is verified through both simulation and experimental results.