POD-PWM applied to circulating current control in HVDC-MMC based system

The Modular Multilevel Converter (MMC) control presents more technical challenges than the regular 2-level Voltage Sourced Converters (VSC) one. One of the most common type of control investigaded in literature is based on techniques such as the Phase Opposite Disposition PWM (POD-PWM), which include balancing capacitor voltages and circulating current control. This paper presents some details that are not clearly explored in the main references about this theme. The control system implementation is described and its performance is evaluated through an HVDC-MMC based system simulation using the Matlab Simulink software. The results show that the circulating current control is more effective if the total number of submodules connected at the same time (positive arm plus negative arm) is not constant, and most control techniques do not take advantage of this. Besides, the results show that the effect on the DC current is negligible.