Experimental evaluation of PWM-methods for modular multilevel converters

Five sorting-based methods for the modulation of modular multilevel converters are implemented on a test bench and evaluated regarding their switching frequency, voltage balancing capability, harmonics, voltage error, and computation time. In contrast to already published methods, the cells considered here can omit additional switch transitions when entering PWM mode. This reduces the switching frequency but complicates harmonic cancellation. One method is able to reduce the rms ripple of the dc current by increasing the likelihood of suitable duty cycles, eliminating the need for fixed carrier signal assignment.