IEEE Power Electronics Magazine - September 2022 - 54

real-life yearly mission profile. The reliability was evaluated
under a yearly mission profile of solar irradiance and
ambient temperature adopted from Aalborg, Denmark
[29]. Figure 5a shows the predicted random failure rate
for the considered FT PV microconverter. In the pre-fault
conditions, the PV microconverter experiences a moderate
failure rate. After a fault appears, the control system
curtails the maximum input power.
Preliminary calculations showed
that this PV microconverter would
experience new faults next time it
attempts to process the rated power
of 300 W. If the input power is curtailed
at the level of 250 W, the converter
can continue operation after
the topology reconfiguration but
with much increased yearly random
failure rate. The curtailment level
should be reduced to 200 W to retain
the random failure rate of a healthy
microconverter. A further reduction
of the curtailment level to 150 and
100 W shows a further reduction in
the failure rate.
On the other hand, the PV microconverter with a low
and the shorted faulty switch as a current path in the postfault
topology.
As a result, post-fault maintenance can be delayed at
The main obstacle in
designing zero redundancy
systems is in
achieving a trade-off
between the cost of
the converter and the
level of post-fault
power curtailment.
curtailment level cannot efficiently utilize the available
PV energy, as predicted in Figure 5b. A healthy FT
PV microinverter is predicted to deliver total energy of
309 kWh/year at the output terminals during the normal
operation before the fault occurrence. The case
of no power curtailment during the post-fault operation
is avoided in Figure 5 as these conditions lead
to a guaranteed catastrophic failure anytime the PV
microconverter attempts to process powers close to
the rated power. When the maximum operating power
of 250 W is used, the PV microconverter loses only 9%
of its energy yield estimated for the output side of the
converter. Hence, it can continue its operation without
catastrophic failures. For the power curtailment level
of 100 W, the PV microconverter can still provide a little
over 60% of the initial energy yield. It is worth mentioning
that the dependence between the curtailment
power level and energy yield loss would be much more
substantial in southern climates, where more energy is
produced at higher power levels compared to the reference
case from Northern Europe.
Conclusions and Discussion
The article has discussed three FT approaches to overcoming
semiconductor faults in galvanically isolated
dc-dc converters using SRC as the reference topology.
Among them, the zero redundancy FT approach shows
the lowest implementation cost but requires some degree
of power curtailment after a fault. This approach is based
on the topology morphing control principle that allows
converter topology reconfiguration using healthy switches
54 IEEE POWER ELECTRONICS MAGAZINE z September 2022
no extra cost compared to the other two FT approaches.
The most reasonable approach could be keeping the maintenance
schedule after a fault occurred and was remedied
to avoid costly urgent maintenance events. This helps
avoid power outages and allows for
a faster return on investment. The
main obstacle in designing zero
redundancy systems is in achieving
a trade-off between the cost of
the converter and the level of postfault
power curtailment. The power
curtailment reduces post-fault thermal
loading of the critical converter
components and even avoids catastrophic
failure. Depending on the
application and climate conditions,
power curtailment after a fault does
not necessarily penalize the generated
energy. It may be needed just
to avoid catastrophic failure during
rare moments of peak power generation
or processing. Therefore, the zero-redundancy fault
tolerance approach suits the best for numerous emerging
applications where the cost of implementation is essential
while the performance of the post-fault operation is
allowed to deteriorate reasonably.
Acknowledgments
This research was supported by the Estonian Research
Council grants: PSG206 - literature review and classification
of methods, and PRG1086 - fault-tolerant PV microconverter
related research.
About the Authors
Abualkasim Bakeer received the B.Sc. and M.Sc.
degrees in electrical engineering from Aswan University,
Aswan, Egypt, in 2012 and 2017, respectively. He is currently
pursuing the Ph.D. degree with the Department of
Electrical Power Engineering and Mechatronics, Tallinn
University of Technology, Estonia. In 2014, he joined the
Electrical Engineering Department, Faculty of Engineering,
Aswan University, as a Demonstrator, and then
became an Assistant Lecturer in 2017. His main research
topics are dc-dc converters, fault diagnosis and fault tolerance,
impedance-source power converters, and model
predictive control.
Andrii Chub received the B.Sc. and M.Sc. degrees in
electronic systems from Chernihiv State Technological
University, Ukraine, in 2008 and 2009, respectively, and
the Ph.D. degree in electrical engineering from the Tallinn
University of Technology, Estonia, in 2016. He was
with Kiel University in 2017 and Federico Santa Maria
Technical University from 2018 to 2019. He is currently
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