The most serious and recent competitor to the standard field oriented control (FOC) for induction motors (IM) is the finite control set model predictive control (FCS-MPC). Nevertheless, the extension to multiphase drives faces the impossibility to simultaneously regulate the flux/torque and the secondary current components (typically termed 𝒙-𝒚 in literature). The application of a single switching state during the whole sampling period inevitably implies the appearance of 𝒙-𝒚 voltage/currents that increase the system losses and deteriorate the power quality. These circulating currents become intolerably high as the per unit 𝒙-𝒚 impedance and the switching frequency diminish. Aiming to overcome this limitation, this work suggests the integration of virtual voltage vectors (VVs) into the FCS-MPC structure. The VVs ensure null 𝒙-𝒚 voltages on average during the sampling period and the MPC approach selects the most suitable VV to fulfill the flux/torque requirements. The experimental results for a six-phase case study compare the standard FCS-MPC with the suggested method, confirming that the VVbased MPC maintains the flux/torque regulation and successfully improves the power quality and efficiency.

Achieving a self-reconfigurable fault-tolerant control in multiphase machines requires a fast fault detection and localization. Most fault detection techniques inherit the three-phase approach by defining fault indices in a per-phase basis. A recent approach suggests an alternative fault detection mechanism based on vector space decomposition (VSD) variables, but the study is limited to open-phase faults (OPFs) for a sixphase drive that is regulated under field oriented control (FOC). It is known however that i) the open-switch faults (OSFs) in the converter are more likely than the OPF in the machine and ii) the drive performance in the event of an open-circuit fault is more critical when model predictive control (MPC) is used. This work extends the study of the VSD fault detection method to multiphase machines with different number of phases (five), control strategy (MPC) and type of faults (OPF and OSF). Although experimental results show that MPC misbehaves after the fault occurrence, the fast detection provided by the VSD approach allows a satisfactory transition to post-fault mode of operation.

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The inherent fault-tolerant capability of multiphase machines is highly appreciated, but it requires fault detection and localization together with a reconfiguration of the control scheme. When the multiphase machine is regulated using finite-control set model predictive control (MPC) strategies, the reconfiguration involves the use of different transformation matrices, cost functions, and current references for each of the multiple open-phase fault (OPF) scenarios. Aiming to simplify this procedure and add further robustness, this paper explores the possibility to achieve a natural fault-tolerant capability by maintaining the prefault control strategy after the fault occurrence. For this purpose, this paper first analyzes the two main reasons why MPC-regulated multiphase drives misbehave in the event of an OPF: the voltage vector shifting and the search for incompatible goals. In the next step, a version of the MPC that includes virtual-voltage vectors (VVs) is tested for the first time in postfault situation and it is compared to conventional MPC technique. Extensive experimental results reveal that, while MPC misbehaves in the event of an OPF, the VV-MPC provides a satisfactory ripple-free postfault performance. This finding has two significant implications for industrial applications: the postfault operation is highly simplified and, at the same time, the fault-tolerant multiphase drive becomes immune to fault detection errors and delays.

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