Assessment of Virtual-Voltage-based Model Predictive Controllers in Six-phase Drives under Open-Phase Faults

Abstract

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 faulttolerant capability by maintaining the pre-fault control strategy after the fault occurrence. For this purpose, this work firstly 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 a next step, a version of the MPC that includes virtual voltage vectors (VVs) is tested for the first time in post-fault 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 ripplefree post-fault performance. This finding has two significant implications for industrial applications: the post-fault operation is highly simplified and, at the same time, the fault-tolerant multiphase drive becomes immune to fault detection errors and delays.