Multilevel converters have received increased interest
recently as a result of their ability to generate high quality
output waveforms with a low switching frequency. This makes
them very attractive for high power applications. A Cascaded HBridge
converter is a multilevel topology which is formed from
the series connection of H-Bridge cells. Optimized pulse width
modulation techniques such as Selective Harmonic Elimination
(SHE-PWM) or Selective Harmonic Mitigation (SHM-PWM) are
capable of pre-programming the harmonic profile of the output
waveform over a range of modulation indices. Such modulation
methods may however not perform optimally if the DC links of
the Cascaded H-Bridge Converter are not balanced. This paper
presents a new SHM-PWM control strategy which is capable of
meeting grid codes even under non-equal DC link voltages. The
method is based on the interpolation of different sets of angles
obtained for specific situations of imbalance. Both simulation
and experimental results are presented to validate the proposed
control method
