Capacitor voltage control in single-phase three-level PWM converters

The authors describe the circuit topology of the three-level single-phase pulse converter, and list its advantages over two-level converters. Different modulation schemes which achieve PWM switching of the converter are described. A preferred scheme is selected on the basis of simplicity and symmetry. For this scheme the effect of odd and even modulation ratios is discussed in detail. The effect of unbalanced circuit conditions on the capacitor voltage sharing is described. An algorithm to maintain equal capacitor voltage even under unbalanced conditions is proposed. The results are obtained using the Saber mixed-mode simulator