  The application of multilevel converters to renewable energy systems is a
growing topic due to their advantages in energy efficiency. Regarding its
control, model predictive control (MPC) has become very appealing due to its
natural consideration of discrete inputs, its optimization capability, and the
present-day availability of powerful processing hardware. The main drawback of
MPC compared to other control techniques in this field is that the control
input is held constant during the sampling period, and it is usually difficult
or even impossible to reduce this sampling period because of hardware
limitations. For this reason, a multirate MPC algorithm is proposed, which
allows to change the control input several times within the sampling period.
The optimization problem is simplified and made suboptimal to substantially
decrease computational burden. This approach is tested in simulation on a
three-phase, five-level diode-clamped converter (DCC) operating in inverted
mode with a three-phase resistive load. Results show significant reduction in
harmonic distortion at the cost of an increase in the number of commutations
with respect to a standard MPC operating at the same sampling period.
