Fast and reliable detection of stator faults is of key importance for fail-safe and fault-tolerant machine drives in order to immediately trigger appropriate fault mitigation actions. The paper presents a detailed analytical and experimental analysis of the behavior of a closed-loop controlled permanent magnet machine drive under interturn fault conditions. It is shown that significant second harmonic components in the dq voltages, currents, instantaneous active power (IAP), and instantaneous reactive power (IRP) are generated during turn fault conditions. The analyses further show that the increase of the second harmonic in IAP and IRP during fault conditions is comparatively higher than that of voltage and current, making them ideal candidates as turn fault indicators. A turn fault detection technique based on second harmonic in IAP and IRP is implemented and demonstrated for a triple-redundant, fault-tolerant permanent magnet assisted synchronous reluctance machine drive. The effectiveness of the proposed detection technique over the whole operation region is assessed, demonstrating fast and reliable detection over most of the operating region under both motoring and generating mode.

The flux-switching permanent magnet (FSPM) machine has aroused wide interest recently due to high-power density, favorable PM cooling capability, and essentially sinusoidal electromotive-force (EMF) waveform per phase. Previously, the phase back-EMF generation mechanism of FSPM machines is exposed from a flux-switching perspective, however, which is rethought from the viewpoint of air-gap modulation magnetic field in Part I as in this article, and electromagnetic torque generation mechanism of FSPM machines will be reported in Part II as another sister paper. With the aid of magnetic field modulation theory, the air-gap PM magnetic field and back-EMF of the FSPM machine are modeled based on modulation and winding functions. Their characteristics are analyzed in detail and consequently, principles concerning FSPM machines on arbitrary stator-slot/ rotor-pole combinations can be obtained, including the basic feature of FSPM machines, the principle and necessary conditions for the back-EMF generation, the fundamental reason of sinusoidal back-EMF waveform, and the contributions of modulation harmonics to phase back-EMF. Finally, experimental verification on a 12s/10p prototyped machine is conducted.

A fault-tolerant machine drive based on permanent magnet-assisted synchronous reluctance machine is proposed and investigated for aerospace applications where reliability and safety are crucial. In order to achieve enhanced fault-tolerant capability, the risk of permanent magnet field that cannot be turned off under fault conditions is minimized without compromise in torque density and efficiency. This is achieved by employing a synchronous reluctance rotor topology with embedded permanent magnets. Three independent segregated three-phase windings are configured to ensure isolation and nonoverlapping between the three 3-phase winding sets. Each three-phase winding set is driven by a standard three-phase inverter to facilitate fast integration and cost reduction. The machine behavior under various fault conditions has been evaluated by finite element simulations. A 40 kW prototype was designed, constructed, and tested. The test results demonstrate the performance and excellent fault-tolerant capability of the proposed drive system under various faults, including open-circuit and short-circuit conditions.

Based on the back electromotive force generation principle in part I of the series papers, the electromagnetic torque generation mechanism of flux-switching permanent magnet (FSPM) machines is rethought in this article as part II from the perspective of air-gap modulation magnetic field. By magnetic field modulation theory, the air-gap armature magnetic field due to winding currents is modeled. Considering the unipolarity of the stator core, a novel concept of ‘fictitious modulation reluctance (FMR) rotor’ for FSPM machines is proposed. Then, by combining with the air-gap permanent magnet (PM) field and the FMR rotor, generation mechanisms of harmonic PM torque and reluctance torque are investigated. The requirements for FSPM machines to produce a stable electromagnetic torque are determined, i.e., |mP_w ± vP_r | = P _pm , m_rvM_fm ≠0, and ω_e = P_rω_r . Besides, the harmonics operation states and harmonic torque characteristics of FSPM machines are analyzed and calculated based on the Maxwell stress tensor method. Further, the average torque versus current density predicted by finite element is validated by testing on an exampled 12s/10p FSPM one.

In this paper, a deadbeat predictive current control based fault-tolerant scheme is proposed and developed for dual three-phase PMSM drives. For open-phase fault of dualthree phase PMSM, the current references are derived without low-order components for minimum stator copper loss. The utilization of deadbeat predictive current control guarantees high control bandwidth for the current references under faulttolerant operation. Then, a fault-tolerant control scheme is proposed for open-switch fault based on hybrid current references, which can fully utilize the remaining one health switch in the faulty inverter leg and minimize the stator copper loss. The additional copper loss caused by the open-switch fault can be reduced by around half with the proposed fault-tolerant control compared to previous remedial strategies. Thus, the ultimate torque output under open-switch fault can be increased by around 20%. The machine model, the space vector diagram, and the control structure of motor systems remain unchanged with the proposed fault-tolerant control scheme. The validity of the proposed fault-tolerant control schemes is verified by experiments.

Fault-tolerant machine drives are key enabling technologies in safety critical applications. The machine drives are expected to exhibit high performance in healthy conditions and accommodate as many faults as possible, namely open circuit or short circuit in the machine and inverter or even an interturn short circuit. This paper aims to assess a triple redundant nine-phase (3 × 3-phase) permanent magnet assisted synchronous reluctance machine (PMASynRM) drive by comprehensive experimental tests under both healthy and fault conditions on a 35 kW machine drive prototype. The healthy performance, fault behavior, fault detection, and mitigation strategy are presented and assessed by extensive tests which demonstrate that the machine drive exhibits high performance and excellent fault tolerance with simple and cost-effective implementation. Therefore, the proposed machine drive has proven to be a practical candidate for safety critical applications.