Assessment of Virtual-Voltage-Based Model Predictive Controllers in Six-Phase Drives Under Open-Phase Faults

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.