A ZVS imbricated cell multilevel inverter with auxiliary resonant commutated poles

The imbricated-cell multilevel converter is well suited to high power applications. It allows the series connection of n switches with natural voltage sharing between these switches enabled through the connection of n-1 flying capacitors. This paper deals with the application of soft-switching on this topology; to date, only the hard-switching mode has been studied. The use of soft switching enables an increase of the switching frequency (resulting in the size reduction of the flying capacitors) without a decrease of the converter efficiency. Of the soft switching methods considered, the Auxiliary Resonant Commutated Pole (ARCP) technique was chosen due to the relative ease in which it can be incorporated into the converter topology. Furthermore, this technique offers numerous advantages: loss reduction, no added stress to the switches and compatibility with PWM control. The main properties of the ARCP multicell converter are the same as the hard-switched topology: an increase of the apparent output switching frequency and natural self-balancing of the flying-capacitor voltages. This paper presents the results of both simulations performed and measurements taken from an experimental set-up in order to study the viable system functioning. The introduction of soft-switching strongly complicates the theoretical study of the balancing mechanisms, however. As a result, the authors depend on simulations to validate the natural balancing effect during soft switching. Lastly, a general method of loss measurement is presented. Results show that the converter losses are reduced by at least 30%.