Neutral-Point-Clamped multilevel converters are nowadays a suitable solution to implement low-medium voltage and power applications, thanks to their intrinsic superior voltage and current quality. The conventional configurations of these converters present uneven power loss distribution, causing thermal stress in some power semiconductors, which weakens the power converter reliability. For overcoming it, an implementation of the Neutral-Point-Clamped multilevel converter based on a Switching-Cell Array is introduced, adding redundant conduction paths on one side and more options to distribute the switching losses on the other side. An active thermal control is proposed here to balance the temperature distribution in the converter. A four-level converter has been implemented to evaluate the proposed solution. Experimental results show that the proposed implementation and active thermal control present enhanced temperature distribution in the converter and therefore reduced thermal stress and better reliability.

The battery is at the heart of the electric vehicle and determines many of its key performance features. Hybrid batteries, combining two battery cell chemistries, benefit from the particular strengths of each battery cell technology, such as high specific energy or high specific power. This paper proposes a novel hybrid battery configuration where the interfacing between the two sets of cells is accomplished through a bidirectional multilevel neutral-point-clamped dc-dc converter. The novel topology is presented and a suitable power converter modulation and control are developed. The feasibility and benefits of such configuration are demonstrated and illustrated. In particular, the proposed battery system features a lossless intermodule battery state-of-charge balancing within both sets of battery cells. Simulation and experimental results are provided in the case of the three-level internal battery interfacing to verify the good performance of the proposed hybrid battery configuration, modulation, and control.

This paper presents detailed Markov models for the reliability assessment of multilevel neutral-point-clamped (NPC) converter leg topologies, incorporating their inherent fault-tolerance under open-circuit switch faults. The Markov models are generated and discussed in detail for the three-level and four-level active NPC (ANPC) cases, while the presented methodology can be applied to easily generate the models for higher number of levels and for other topology variants. In addition, this paper also proposes an extremely fast calculation method to obtain the precise value of the system mean time to failure from any given formulated system Markov model. This method is then applied to quantitatively compare the reliability of two-level, three-level, and four-level ANPC legs under switch open-circuit-guaranteed faults and varying degrees of device paralleling. The comparison reveals that multilevel ANPC leg topologies inherently present a potential for a higher reliability than the conventional two-level leg, questioning the suitability of the traditional search for topologies with the minimum number of devices in order to improve reliability. Experimental results are presented to validate the fault-tolerance assumptions upon which the presented reliability models for the three-level and four-level ANPC legs are based.

The present paper proposes a novel device defined as an intelligent electronic fuse (iFuse) meant to be connected in series with any current-bidirectional voltage-unidirectional active switch present in a given converter. The iFuse duty is to isolate its series- associated switch from the rest of the converter circuit immediately after detecting that said switch has failed in short circuit. Nonetheless, it maintains the reverse (free- wheeling) current path originally offered by the failed switch. The failure detection is performed when the failed switch causes a shoot-through event. Therefore, the iFuse is designed to be able to block the elevated current occurring in such event. The iFuse allows increasing the fault-tolerant capability and the reliability of power converters where such qualities are hindered by switch short-circuit failures, as in converters featuring parallelized switches, neutral-point-clamped multilevel topologies, or redundant legs. The feasibility of the iFuse device is verified through experimental tests, proving that the device is able to detect the failure of its associated switch and isolate it from the rest of the converter circuit in 6 μs, while stopping short-circuit currents of up to 1 kA without incurring in harmful di/dt values.