Center-Point Voltage Balancing of Hysteresis Current Controlled Three-Level PWM Rectifiers

Abstract—The output center-point voltage of a hysteresis cur-rent-controlled three-level, unidirectional PWM rectifier is not nat-urally stable. This paper shows that the balancing of the center-point voltage can be realized by adding an offset to the input cur-rent-reference and that this offset results in a change of the rela-tive on-times of the redundant switching states. The space-vector representation of the input rectifier voltage and current is used to help explain the effect of the current-offset injection on the output center-point voltage. The influence of the offset-current injection on the mains currents as well as the control and center-point char-acteristics are analyzed and verified by measurements. Finally, the design of the center-point controller is presented and its dynamic performance experimentally demonstrated. Index Terms—Center point voltage control, hysteresis current control, three-phase three-level rectifiers. I