Open-Circuit Fault-Tolerant Control Method for a Six-Phase PMSM with Double-Layer Concentrated Windings under Low Carrier Ratio Conditions

improve the performance of multi-phase PMSMs under open-circuit (OC) faults, OC fault-tolerant control (FTC) methods are extensively investigated under high carrier ratio conditions. However, due to the complexity of the fault-tolerant (FT) mathematical model, cross-coupling effects in signal flow between d- and q-axes and the digital delay from current sampling to voltage output in digital controller, the FTC performance may degrade under low carrier ratio (LCR) conditions. To address these issues, this paper proposes a novel FTC method for single phase open-circuit faults in a symmetrical six-phase PMSM with fractional-slot concentrated windings under LCR conditions. In this method, considering the distinctive inductance matrix of the investigated machine, an FT coordinate transformation method is developed. The transformation method simplifies the mathematical model of FT currents, back electromotive force (EMF), and inductance matrix in synchronous space. Further, a current control method based on discrete second-order rotational-decoupling control (DSRDC) is investigated. Through this control method, the cross-couplings in both d-q axis and d1-q1 axis are decoupled, and the FT current loop performance can be configured while sufficiently considering the digital delay. The proposed FTC method enables the FT operation on the investigated machine under LCR conditions with good stability and dynamic performance. Moreover, a smooth transformation method from OC fault to FT condition is investigated. The effectiveness is verified through experiments.