Direct power control of three-phase three-level neutral-point-clamped converters with control input saturation

The phenomenon of control input saturation due to limitations in the duty cycles of the gate pulses of the power switches is an important issue in the performance of power electronic converters. This paper formulates and analyzes the control input saturation effects in a three-phase three-level neutral-point-clamped converter connected to the grid. Particularly, the phenomenon is studied when a direct power control strategy is implemented as an indirect control through a space vector modulation technique. The discrete set of values of the gating signals defines the power converter control region. Due to the modulation strategy, which is introduced to generate the switching sequence, any point located inside the control region is physically implementable. However, the points situated out of this area can not be generated because they represent duty cycles higher than 100%, leading to a saturation scenario. In this paper, several strategies are studied in order to cope with the saturation problem and obtain the final gating signals. The performance of the power converter under these different approaches is evaluated by means of simulation results in PSCAD^© environment.