  It is well-established that a proportional current control gain emulates a
resistor in the converter output impedance. Even though this resistance can
provide additional damping to grid resonances, its effect for traditional
linear current controllers is known to be rather limited. Moreover, for
medium-voltage systems, high switching frequencies are not an option due to the
high switching losses. To meet the harmonic standards, it is expedient to use
optimized pulse patterns. This further exacerbates the problems with the
resistance of classical controllers, since an additional filtering would be
required so that the current controller acts only on the fundamental component
(and not on the ripple component). Such a design limits the damping effect not
only in its amplitude but also in the frequency range where it is active. This
paper shows that a high-bandwidth current-based model predictive pulse pattern
controller can alleviate these limitations. The pulse pattern control approach
can achieve a high gain even at low switching frequencies, while controlling
directly the instantaneous currents (i.e., the fundamental component and the
ripple together). With a fast implementation cycle, the frequency range where
this damping effect is active can be further extended. Numerical studies
showcase these benefits for a multi-phase medium-voltage wind power conversion
system.
