Analysis and comparative evaluation of a three-phase three-level unity power factor y-rectifier

The basic principle of operation of a three-phase PWM rectifier system formed by star-connection of three single-phase three-level PWM rectifier modules (three-level y-rectifier) is discussed based on space vector calculus. The mains current ripple resulting for synchronized operation of the phase modules is calculated and comparatively evaluated against a direct three-phase PWM (Vienna) rectifier realization. The current stresses on the power semiconductors and on the passive power components are calculated analytically in order to provide a basis for the system dimensioning. A novel concept for controlling the y-rectifier is proposed which guarantees a symmetric loading of the phase modules and allows to continue the system operation also in case of heavily unbalanced mains voltage and/or for a failure of a mains phase. Finally, the advantages and drawbacks of the y-rectifier concept are summarized and topics of further research are identified.