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The auxiliary resonant commutated pole (ARCP) multiceLl converter is a soft-switched variant of the multicell converter. It is shown in this paper that the ARCP technique can be very efficiently used in multicell flying capacitor converters. The main properties of the resulting soft switching multicell converter are very similar to those of the hard-switched version. They are presented and validated by simulations as well as experimental results. In practice, due to the damping, the ARCP multicell converter can suffer from switching faults as in two-level ARCP inverters, but in the case of a multicell converter failures can occur in different cells. So, the main control strategies are evaluated and the switching process is discussed step by step, taking account of the main imperfections of actual control circuits. When they can occur, the switching faults are described and analyzed. Finally, an original quasisoft switching control that should give a high safety of operation is proposed. Experimental results obtained with a 900 V-100 A ARCP multicell inverter leg are given and the performances are compared with those of a hard-switched multicell inverter leg of the same rating. Index Terms--ARCP, dual-thyristor, multicell flying capacitor inverter, safe control, soft-switching, switching faults.

Efficiency of high-power uninterruptible power supplies (UPSs) is a fundamental criterion regarding the permanent use of such a device. A state of the art on soft switching over constraint of UPS application has been made. The principle of auxiliary resonant commutated pole using autotransformer has been identified as the most interesting way to increase efficiency or switching frequency. Its application for multilevel converters has been studied. A simplified resonant pole has been proposed for a three-level rectifier used as power factor corrector. The design criteria have been discussed. A single phase of a 200-kVA three-level rectifier has been realized and qualified in switching mode. To assess the gain of this principle, the switching losses have been measured on the prototype in both hard and soft switching. The switching losses have been divided by two. [ABSTRACT FROM AUTHOR]