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A general analytical model is developed in a concise block matrix form for surface‐mounted permanent magnet (SPM) machines with series‐parallel coil connections under inter‐turn short circuit (ITSC) fault. In the model, branch currents are used as state variables and inductances of different series‐parallel coil connections are calculated using an analytical method, namely winding function approach (WFA) together with slot permeance method. Based on the characteristics of the calculated inductances and the developed fault model, the multiphase Clarke transformation has been proposed to simplify the fault model. In the process of model simplification, the healthy machine model using branch currents as state variables have been proven to be equivalent to that using 3‐phase currents as state variables. The proposed fault models of a 3kW 96‐slot 32‐pole SPM machine with different series‐parallel coil connections have been built in Matlab/Simulink and validated by time‐stepping 2D FE simulations. Simulation results show that different series‐parallel coil connections have little influence on the amplitude of the ITSC current. Finally, a small scale 24‐slot 8‐pole SPM machine prototype has been built to further validate the accuracy of the proposed fault model. [ABSTRACT FROM AUTHOR]

This paper proposes a general analytical model for large-power surface-mounted permanent magnet (SPM) wind generators under inter-turn short-circuit (ITSC) faults. In the model, branch currents rather than phase currents are used as state variables to describe the electromagnetic behavior of the faulty machine. In addition, it is found that the multiphase Clarke transformation can be used to simplify the proposed fault model with the inductances calculated analytically or numerically using finite element analysis. With the latter, both linear and nonlinear inductances can be obtained, and the non-linear inductances are used for the fault modelling of large power rating machines due to larger electrical loading and heavier magnetic saturation. With the developed fault model, studies of scaling effects (different power ratings such as 3 kW, 500 kW and 3 MW) and the influence of fault location on the electromagnetic performance of SPM generators with series-parallel coil connections have been carried out. The simulation results show that large-power SPM wind generators are vulnerable to ITSC faults when a relatively small number of turns are short-circuited and a single-turn short-circuit fault at the top of the slot is found to be the worst case. [ABSTRACT FROM AUTHOR]

This article investigates the effect of airgap length on the electromagnetic performance of direct-drive surface mounted permanent magnet Vernier (SPM-V) machines with different power ratings. Using 3 kW machine as an example, its performance is comprehensively compared with a conventional SPM machine with the same airgap lengths using two-dimensional finite-element analysis. For each airgap length, the slot/pole number combination for the SPM-V machine is investigated to achieve the optimal performance compared to the conventional SPM machine. In order to make the study more generic, the slot/pole number and the airgap length variations are expressed as normalized pole pitch, i.e., $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ (ratio of rotor pole pitch to electromagnetic airgap length). The results show that for 3 kW machines, $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 is a good design criterion for the SPM-V machines to achieve higher average torque and efficiency than the conventional SPM machines. In addition, a reasonably good power factor (>0.9 in this case) can be achieved. Although the power factor of SPM-V machines drops significantly at multi-MW power level, i.e., 3 and 10 MW, the criterion $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 still results in achieving a performance closest to their optimal capability. However, when $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2, special consideration should be paid to avoid potential irreversible magnet demagnetization at multi-MW power levels. [ABSTRACT FROM AUTHOR]

Electrical machines with high-temperature superconducting (HTS) armature windings can benefit from high power density and efficiency. Furthermore, by using permanent magnets (PM) on the rotor, the cryogenic system can be significantly simplified compared with the fully superconducting (SC) machines or the machines with SC field windings. Compared with the conventional electrical machines, the performance of machines with HTS armature windings can be more sensitive to the design parameters due to the interaction between the operating current and the flux density. In this article, the influence of stator geometry on the machine with HTS armature windings and PM rotor is investigated. By considering the interaction between the operating current and the flux density, an iteration procedure for calculating the operating current of the HTS armature windings is proposed. A 10-MW surface-mounted PM wind power generator with HTS armature windings is studied by the finite element analysis. It is found that machines with different coil angle have different behaviors when changing the tooth width and the dimensions of tooth tips, which is different from conventional electrical machines. A new design and optimization method is then developed. Finally, the optimal design is identified with global optimization. [ABSTRACT FROM AUTHOR]

In this article, the operating current and torque of surface-mounted permanent magnet (SPM) wind power generators with high-temperature superconducting (HTS) armature windings are analyzed. The influence of coil location and current angle on the electromagnetic performance is investigated systematically. The results show that the location of the HTS coils significantly affects the operating current and torque. Furthermore, the maximum torque current angle of SPM wind power generators with HTS armature windings can be different from 180° due to the interaction between the armature and magnet fields. A design optimization method for wind power generators with HTS armature windings is developed in this article. The optimal design is then identified with consideration of the coupling influence of coil location and current angle. [ABSTRACT FROM AUTHOR]

The effect of tooth tips on the performance variations due to using grain-oriented electrical steel (GOES) stator laminations in permanent magnet fractional-slot modular machines is studied in this work. It is concluded that the electromagnetic performance is further improved using GOES in machines with tooth tips compared to machines without tooth tips. This is due to a higher increment on the flux density in the airgap. The acoustic behaviour variations due to using GOES are predicted by analysing several mechanical- and acoustic-related parameters. It is predicted that implementing GOES improves the acoustic behaviour in machines without tooth tips. Furthermore, the effects of GOES in machines with tooth tips are slightly improved compared to machines without tooth tips. However, in order to determine the real mechanical and acoustic behaviours, further analysis is needed. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of torque–speed characteristics and cogging torque of the fractional-slot interior permanent magnet brushless ac machines having different slot openings, viz. open slot, closed slot, and hybrid slot (sandwiched open and closed slots), and unskewed and step skewed rotors. The influence of such alternate slot openings on the magnetic cross-coupling and cogging torque is particularly emphasized. Furthermore, the repercussion of the manufacturing limitations and tolerances on the cogging torque of machines having these alternate slot openings is also investigated. The magnetic cross-coupling level and the sensitivity of cogging torque to manufacturing limitations and tolerances strongly depend on the slot opening materials. The finite-element analyses are experimentally validated. [ABSTRACT FROM PUBLISHER]