This paper provides the switching angles that mitigate
the dominant low-order line-to-line voltage harmonics in a cascaded H-bridge
power converter with a single faulty switch. In this paper, first the firing
angles for 5-level and 7-level converters are calculated by solving a set of
nonlinear equations. Then, in the faulty condition, a set of switching angles
for each phase that results in balanced line-to-line voltages is derived. Finally,
the provided solutions are used to simulate the faulty operation of a
multilevel inverter.
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM
Fig.
1. The seven-level cascaded H-bridge converter.
Fig.
2. Inverter output voltages in the event of a fault at phase ‘a’. (a) Inverter
phase voltages: VaN is the blue waveform (b) Inverter line voltages (c)
Inverter load voltages and (d) Harmonic spectrum of the Phase, Line and Load
voltages.
CONCLUSION
This
paper provided a method to deal with a single fault in a 7-level CHB converter
based on SHM method. Using the proposed strategy, the inverter generates
balanced line to line voltages in fault condition while the low order harmonics
of the load voltages are limited within the acceptable industrial limits (EN
50160 and CIGREWG 36–05). Using the conventional SHM algorithm the maximum
achievable line voltage for a seven-level CHB inverter reduces to about 33% in
the event of a single fault. While the decrement of output voltage with the
proposed fault–tolerant strategy is about 10%. Therefore, the proposed approach
improves the maximum achievable fundamental voltage. This strategy can be
easily extended and implemented for inverters with more voltage levels.
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