Zhenfei Chen

In response to the structural characteristics of hydro-generators, such as multiple pole-slots and salient rotor poles, and their differences between healthy and rotor out-of-roundness fault conditions, this paper proposes an analytical modeling method that considers pole-slot coupling effects under rotor out-of-roundness fault conditions. First, the independent influences of stator slots and rotor salient poles on the air-gap length distribution are solved separately. The influence of the stator slots is subdivided into contributions from the slot openings and the teeth, while the effect of the rotor salient poles is derived based on geometric structure. This establishes an analytical magnetic field model for the healthy state that accounts for pole-slot coupling. Building upon this foundation, the impact of the rotor out-of-roundness fault on the air-gap length is incorporated to further construct an analytical magnetic field model for the faulty state. A comparison of key electromagnetic performance parameters calculated by the model, such as air-gap flux density, electromagnetic force, back electromotive force (back-EMF), and torque, with finite element analysis results demonstrates close agreement. This outcome validates both the feasibility and the accuracy of the proposed analytical modeling method.

This paper proposes an efficient analytical modeling method for the air-gap flux density in hydro-generators under eccentricity faults. The method specifically addresses the multi-factor coupling characteristics induced by the combined effects of stator slotting, salient-pole rotor structure, and eccentricity. Based on geometric analytical derivation, individual models for air-gap length considering stator slotting, rotor salient-pole structure, and eccentricity are established, and an analytical expression for the air-gap length under coupled conditions is derived. By incorporating the spatial distribution characteristics of the magnetomotive force, a mathematical model for no-load air-gap flux density is constructed, enabling the rapid calculation of air-gap magnetic field distribution. Finite element verification conducted on an 84-slot, 10-pole hydro-generator demonstrates that the proposed method accurately reflects the periodic fluctuations and amplitude variations in the magnetic flux density under both normal and eccentric conditions. Compared with the finite element method (FEM), the analytical approach significantly enhances computational efficiency while maintaining high accuracy, providing effective theoretical support for the structural optimization and eccentricity fault diagnosis of hydro-generators.

Background: Multi-branch parallel permanent magnet synchronous motors (PMSM) are prone to parallel branch open-circuit faults (PBOCF), which may result in winding overheating, insulation damage, and other reliability issues. Objective: This study aims to propose an effective fault diagnosis method that can distinguish between open-circuited faults (OCF) and PBOCF in PMSMs, while maintaining robustness under varying operating conditions. Methods: The winding function method is employed to analyze the inductance matrix differences between healthy and faulty states. Based on this analysis, mathematical models of PMSM under both conditions are established. Fault diagnosis is realized by comparing the zero-sequence current (ZSC) AC components before and after the fault, and the faulty phase is identified by analyzing the root mean square (RMS) values of the three-phase currents. Results: Simulation results verify the effectiveness of the proposed method. The approach successfully distinguishes between OCF and PBOCF without the need for additional hardware. Conclusions: The proposed method provides a reliable and robust solution for diagnosing PBOCF in PMSM, demonstrating strong resistance to variations in torque and speed.

Fractional slot concentrated winding permanent magnet motors (FSCW-PMMs) with star-delta (Y-△) connection windings are increasingly used in industrial applications due to their high efficiency and precise control. However, inter-turn short circuit fault (ITSCF) poses challenges to their reliability and operation, requiring comprehensive analysis. This paper investigates the effects of ITSCF in FSCW-PMMs, focusing on contact capacitance and resistance variations. A mathematical model, rooted in electromagnetic principles, is developed to predict motor behavior under various fault scenarios in both star and delta windings. The study analyzes torque, three-phase currents, and losses, revealing significant impacts of fault position and contact capacitance on motor performance. ITSCF amplifies peak currents, torque fluctuations, and core losses, particularly with increased contact capacitance. These insights emphasize the importance of considering contact capacitance and fault position in motor design to improve reliability and efficiency.

Medium-voltage cables in hydropower plants are typically arranged in multi-circuit configurations to ensure reliability, yet their exposure to harsh operational conditions accelerates insulation degradation and increases partial discharge risks. Traditional fault localization methods, such as the traveling wave method using wavelet transform to process fault signals, suffer from wavefront distortion due to inter-line reflections and noise interference in multi-circuit systems, because wavelet-based techniques are limited by preset basis functions and environmental noise. To address these challenges, a fault localization method for multi-circuit parallel cables based on the Teager–Kaiser Energy Operator (TKEO) is proposed in this paper. First, the fault signal is decoupled using Clarke transformation to suppress common-mode interference, obtaining the α component. Subsequently, the α component is subjected to wavelet transform to obtain the high-frequency components, which are then optimized using the TKEO. The TKEO is applied to optimize the wavelet-transformed signal, enhancing transient energy variations to precisely identify the arrival time of the fault wavefront at measurement points, thereby enabling accurate fault localization. The results of the four types of fault experiments indicate that the use of the TKEO to optimize the wavelet transform of the traveling wave method improved the accuracy of fault localization.

The rotor eccentricity fault will cause the electric vehicle (EV) drive machine to generate unbalanced magnetic pull (UMP) and torque fluctuation. It may induce more complex rotor dynamics behavior and endanger the safe and reliable operation of the drive system. In this article, three spoke-type interior permanent magnet synchronous machines (IPMSMs) with different armature winding structures, which are integer-slot double-layer distributed winding, fractional-slot double-layer concentrated winding, and fractional-slot four-layer concentrated winding with star–delta (Y– $\Delta$ ) connection, are introduced. The armature magnetomotive force (MMF) analytical models of the three IPMSMs are built. Also, the air-gap permeability is analyzed when static eccentricity, dynamic eccentricity, and mixed eccentricity faults occur in IPMSMs. Furthermore, electromagnetic characteristics of the three IPMSMs under different rotor eccentricity faults are studied. Effects of static eccentricity and dynamic eccentricity faults on cogging torque, back electromotive force (EMF), radial electromagnetic force, electromagnetic torque, loss, and efficiency of the IPMSMs with three different winding structures are compared and analyzed. Research shows that the IPMSMs with integer-slot distributed winding and fractional-slot concentrated winding have different performances under rotor eccentricity faults.

The design and analysis of a novel salient-pole surface-mounted permanent magnet synchronous machine (SSPMSM) are presented in this paper for wide-speed range applications. In this machine, iron teeth are placed in the d-axis on the surface of rotor core to increase armature inductance and enhance the effect of d-axis armature reaction. But torque ripple is also increased since the rotor teeth increase the saliency of the machine. So segmented Halbach magnetization is applied to reduce the electromagnetic torque ripple. In order to investigate the characteristics of SSPMSM, four finite element (FE) models with different rotor cores and magnetizations are built. Flux-weakening/enhancing characteristics, no-load characteristics and load characteristics are obtained and compared. The results show that SSPMSM has better magnetic field adjustment ability than traditional surface-mounted permanent magnet synchronous machine (SPMSM).

Electromagnetic torque model is built in this paper for permanent-magnet synchronous machine (PMSM) with non-sinusoidal back electromotive force (back-EMF) and current. Electromagnetic torque is divided into four parts depending on the different combinations of fundamental and harmonic component. Effects of current harmonic order, amplitude and initial angle on average torque and torque ripple are investigated based on the mathematic model. Desired harmonic parameters are obtained from the analysis, in order to suppress the torque ripple as much as possible. Further, a method for reducing the 5^th and 7^th harmonic components of torque ripple is proposed, according to the characteristics of back-EMF harmonic distribution. The proposed method is greatly simplified and more feasible by only injecting 5^th and 7^th harmonic currents. The theoretical analysis validity has been proved by finite element (FE) simulation, and the FE results show that torque ripple would be more effectively reduced by injecting proper harmonic current than weakening it merely.