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Eccentricity is a critical fault in permanent magnet synchronous machines (PMSMs), and can be generally classified into static eccentricity (SE), dynamic eccentricity (DE) and mixed eccentricity (ME). In this article, the fault diagnosis method based on zero-sequence voltage component (ZSVC) is proposed for detecting eccentricity in PMSMs with rotational asymmetric winding configurations. Different types of eccentricity can be classified with different fault characteristic harmonics in the measured ZSVC, which is extracted by Fast Fourier Transform (FFT). Specifically, the fundamental component and sideband harmonics appear under SE and DE, respectively. Both the fault characteristic components show up in case of ME. Notably, the ZSVC difference between two sets of three-phase windings obtains higher sensitivity for detection in dual three-phase PMSMs with rotational asymmetric winding configurations. Furthermore, the influence of eccentricity condition, load condition as well as other faults is investigated. Especially, the effect of d-axis current on fault indicators is revealed from armature flux linkage and PM flux linkage due to different degree of core saturation under eccentricity fault. Finally, the experiment is carried out on 10-pole/9-slot and 10-pole/12-slot surface-mounted single three-phase PMSMs, and the latter one is also connected as different dual three-phase winding configurations for verification.

In dual three-phase surface-mounted permanent magnet (PM) machines, three-phase short circuit (3PSC) fault is usually assumed to happen in only one winding group whilst the remaining one can be normally supplied. This article investigates the influence of healthy winding group (HWG) current on 3PSC of faulty winding group (FWG) and the resulting demagnetization. Firstly, the article develops the analytical model of 3PSC current component caused by HWG current. Based on this, the influence of HWG current is analyzed. It is found that, for symmetrical winding configurations, the d- and q-axis peak 3PSC current can be reduced to their minimum values when HWG current angles are about 90 and 135 electrical degrees, respectively. In addition, the suppression is more effective when HWG current amplitude increases. However, for asymmetric winding configurations, the suppression effect heavily depends on 3PSC start rotor position. The optimal HWG current angles are given for different start rotor positions, which maximumly reduces the d-axis peak current and demagnetization. Then, this article investigates the influence of forcing HWG into 3PSC on peak short-circuit current. It is found that an additional inductance component is added in FWG when forcing HWG into 3PSC, which reduces the peak current. However, since 3PSC current in HWG can also lead to demagnetization, the overall demagnetization level can be mitigated only at relatively low PM temperatures. Finally, experiments are conducted to validate the theoretical analysis.

This article investigates the classification of magnetomotive force (MMF) harmonics in multi-m-phase fractional-slot machines when arbitrary m-phase channels are disconnected due to faults. By employing a universal Q-set m-phase winding arrangement, this study reveals the intrinsic relationships between MMF harmonics generated by different winding sets. Through analytical derivation, the results show that harmonics of the same order from different winding sets share the same amplitude but differ in phase shifts. For harmonics of different orders, certain symmetries and similarities are found in their phasor diagrams. Based on the discovered rules, all composite MMF harmonics can be classified into at least (Q/ $2+1$ ) groups when Q is even and ( ${Q} +1$ )/2 groups when Q is odd. The MMF harmonics within the same group vary synchronously as the faulty condition changes. The findings are validated by the finite-element (FE) simulations on machines with even and odd Q, respectively.

In wind power generation, generators with multiple independent three-phase winding sets grow in popularity owing to their fault-tolerant capability. Nevertheless, when one three-phase channel malfunctions and is disconnected, it is found in this article that unbalanced voltages and output power occur under such a faulty condition in triple three-phase (TTP) generators. The reason is revealed to be the magnetic coupling between winding sets (WSs). By analogy with the transformer effect, an equivalent circuit model is built to investigate the coupling effect. Furthermore, the influence of factors such as the current angle, electric loading, and mutual inductances are discussed. When all three WSs operate, the currents of each WS can be regarded as shifted by a leading and lagging angle, respectively. Due to symmetry, these two effects cancel out in healthy operation. However, under faulty condition, only the leading effect still exists for one WS and the lagging effect for the other WS, resulting in the stated imbalance. Finally, experiments on a TTP machine validate the theoretical analysis.

A novel Π-core dual-armature doubly salient PM machine (Π-core DADSPMM) is presented, in which an auxiliary armature winding is recommended to be wrapped on rotor teeth. Since this machine benefits from better space utilization compared to the existing Π-core doubly salient PM machine (Π-core DSPMM), it exhibits higher torque density. Moreover, when any one of both armature windings cannot work, this machine still can produce electromagnetic torque and thus has an inherent fault-tolerant feature. Firstly, machine structure and operation principles are investigated. Further, based on the finite element (FE) technique, both Π-core DADSPMM and Π-core DSPMM are optimized for high output torque in case of the same stator diameter, active axial length, and rated copper loss, followed by electromagnetic performance comparison. It is shown that compared to Π-core DSPMM, the proposed Π-core DADSPMM has about 67.4% higher average torque while retaining a comparable torque ripple. Furthermore, if one set of armature winding fails, Π-core DADSPMM halves its output torque, which is still about 84.2% of that in the Π-core DSPMM. Finally, a prototype is made and verified that the experimental results agree well with the simulation results.

This article delves into the post-demagnetization torque ripple of fractional-slot surface-mounted PM wind power generators after short circuit faults. Firstly, demagnetizing magnetomotive force from three-phase short circuit (3PSC) currents is modelled and demagnetization distribution pattern is analyzed. Then, this article investigates the post-demagnetization cogging torque. It is shown that the period of cogging torque becomes 360Np/Ns electrical degrees, where Ns and Np are the slot and pole pair numbers of unit generator, respectively. In addition, the amplitude increases when the overall demagnetization level increases with 3PSC rotor speed. Following this, this article analyzes the post-demagnetization back-EMF and load torque ripple. It is found that the demagnetization adds low-order harmonics in the back-EMF and leads to additional torque ripple component under the same stator current, which also increases with demagnetization level. Although the harmonic torque ripple offsets the cogging torque, it has smaller amplitude and thus the total torque ripple still increases with demagnetization level. Most importantly, it is also found that the demagnetization distribution pattern heavily depends on the 3PSC start rotor position. Specifically, when 3PSC starts at the rotor position kπ/3 (k = 0, 1, 2…), the demagnetization distribution is the most uneven in different PMs, which results in the largest post-demagnetization load torque ripple and the smallest average torque. Conversely, the opposite condition occurs around the 3PSC start rotor position π/6+kπ/3. In addition, the influence of 3PSC and single-phase short circuit are compared. Finally, the theoretical analysis is verified by experimental evidence.

Nowadays, various analytical models (AMs) have been developed to analyze SPM machines with magnet shaping technique consideration, but their mechanism are all based on division and superposition theory, and numerous repetitive model calculations are required, which greatly attenuates the inherent speed superiority of AMs. In this article, a new fast AM is proposed, which can analytically solve the magnetic field generated from an arbitrary number of currents to obtain the magnetic field solution for shaping PM without any repetitive model calculation. Besides, five existing typical AMs considering shaping PMs are implemented and compared with the new model, viz., radial and tangential PM segmented method, traditional equivalent current method, and conformal mapping models. The comparison study investigates the adjustable model parameters, the dimension of the stiffness matrix, the number of repetitive model calculations, and the actual time consumption. Then, by finite element model validation, the new proposed model can maintain high accuracy and breakneck computational speed simultaneously. Ultimately, the broad application scope and rich added value of new AM are also expounded.

Interturn short-circuit (ITSC) is one of the most common faults in permanent-magnet synchronous machines (PMSMs), and ITSCs in PMSMs with parallel-connected winding (PCW) are generally more difficult to detect than those in PMSMs with series-connected winding. In this article, the mathematical model of PCW PMSM with ITSC is established first, and the main fault features of ITSC such as the third harmonics in phase currents, negative sequence of phase voltages and circulating current are also modeled. Then, the reasons for the weak fault features in PMSMs with PCW are analyzed. Furthermore, the effects of ITSC modes, including single-branch ITSC and branch–branch ITSC, and short-circuit position on these fault features are investigated. It is shown that branch–branch ITSCs are more difficult to detect, especially when the short-circuit position is close to the midpoint of phase winding. Experimental tests are carried out on a PCW PMSM with ITSC, and the experimental results agree well with the theoretical analysis.

This article presents an accurate and efficient quasi-3-D analytical method for the yokeless and segmented armature (YASA) axial flux permanent magnet (AFPM) machine. The proposed method takes into account the 3-D magnetic flux distribution, slotted effect, and end effect simultaneously. To facilitate the modeling of the YASA machine, the quasi-3-D method is utilized to transform it into a multislice linear machine. The linear machine is then modeled by the exact subdomain method considering the slotted effect, which eases the numerical computation using the elimination method compared with the conventional subdomain method. The scalar magnetic potential of the above subdomains is solved by applying boundary conditions, and the flux density distribution in the air gap is derived accordingly. To compensate for the flux density variation at the inner and outer radii owing to the end effect, the virtual equivalent linear model is adopted to construct an end-effect compensation function considering the slotted effect. Besides, the electromagnetic characteristics, in terms of flux linkage, back electromotive force, and cogging force, are derived based on the compensated flux density distribution in the air gap. Finite element analysis validates the accuracy and efficiency of the proposed analytical method. The proposed analytical method is generic and can be applied to other AFPM machines.