Model Predictive Control of a Four Level Quasi Nested Converter in 3-Phase 4-Wire Microgrid Islanded Operation

In this work, a Model Predictive Control (MPC strategy) is introduced for its application in a four-level quasinested topology, supplying three-phase loads on islanded microgrids. Additionally, a Hysteresis Multiband Control (HMB) is proposed to mitigate the fourth-wire neutral current. The proposed control strategy is capable to synthesize the required output space vectors to ensure perfect tracking of load currents under different loading conditions, while also ensuring voltage balance between the dc-link capacitors. The proposed converter topology is based on a reduced number of components compared to other mature converter topologies, such as the neutral-point clamped converter (NPC) or the active neutral-point clamped converter (ANPC) topologies, when compared in terms of the number of output voltage levels, since this quasi-nested topology does not require passive clamping devices such as diodes or active switches. Moreover, no floating dc-link capacitors with asymmetrical voltage levels are employed, thus simplifying the dc-link capacitor voltage balance mechanism. This work presents the switching operation principles, MPC control, and HMB control law when supplying an unbalanced three-phase fourwire RL load. Control law formulation and simulation results are presented.