Analysis of Capacitor Voltage Ripple Minimization in Modular Multilevel Converter Based on Average Model
In this paper, the particle swarm optimization (PSO) algorithm is used to calculate the optimal magnitude and phase angle of the circulating current components in order to minimize the voltage ripple across the capacitors. The 2nd and 4th harmonic components of the circulating current are considered to minimize the voltage ripple. The approach is based on an average model derived for the converter. For different magnitudes of arm inductance (representing different applications such as motor drives and AFEs.) the capacitor voltage waveforms are compared with the natural circulating current, eliminating the circulating current and when injecting an optimal magnitude of the circulating current. Also, the effect of the circulating current on the efficiency of the converter is investigated by calculating the semiconductor losses.