Fast Reliability Assessment of Neutral-Point-Clamped Topologies through
Markov Models
Abstract
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.