Control of a grid connected modular multilevel converter under pulsed DC load

This paper analyses the behaviour of grid connected modular multilevel converter, under pulsed load at the DC side. The goal is to achieve minimum AC power fluctuation despite high power fluctuation on the DC side. Pulsed load causes imbalances of cell capacitor voltages, and this effect is analytically described. The control methodology, together with an algorithm for capacitor voltage balancing is presented. The simulation proves the success of the algorithm in the majority of the cases, but its operation is dependant on the pulse position with respect to grid voltages. The limitations of the algorithm are analysed in detail.