A four-legged three-phase PFC rectifier is proposed to handle unbalanced source voltage and to provide fault tolerant operation. The four-legged PFC rectifier is controlled by a three-dimensional space vector modulation (3D SVM) scheme, and runs in the overmodulation region when the source is unbalanced and/or a leg failure occurs. Modeling and control of the four-legged PFC rectifier are presented. Under unbalanced source, operation of the four-legged rectifier with three control strategies-equal current, equal resistance and constant power are analyzed. Two rectifier failure modes are studied: (1) entire leg fails; (2) active switches fail with the anti-parallel diodes still functional. It turns out that in both failure modes, the PFC rectifier can have an equal or higher than 2/3 of the rated output power level. The operation of the four-legged rectifier with 3D SVM is demonstrated by experimental results. The simulation results show that the proposed four-legged rectifier is advantageous over directly coupled three single-phase PFC rectifier and three-legged three-phase PFC rectifier.
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