This paper studies the unbalanced magnetic pull in the brushless doubly fed machine (BDFM) caused by both static and dynamic rotor eccentricities. Several parallel winding designs for the two stator windings are proposed, and the practicality of such designs is discussed with respect to direct coupling between the stator windings and with rotor undesirable harmonic fields. Once practical parallel winding designs are established, their effects on reducing deflection as a result of static and dynamic eccentricities are shown and compared with series wound stator. This study has been carried out on a prototype D400 250-kW BDFM.

This paper investigates the fundamental trade-offs involved in designing energy-regenerative suspensions, in particular, focusing on efficiency of power extraction and its effect on vehicle dynamics and control. It is shown that typical regenerative devices making use of linear-to-rotational elements can be modelled as a parallel arrangement of an inerter and a dissipative admittance. Taking account of typical adjustable parameters of the generator, it is shown, for a given suspension damping coefficient, that the power efficiency ratio scales with inertance. For a typical passenger vehicle, it is shown that there is a feasible compromise, namely that good efficiency is achievable with an inertance value that is not detrimental to vehicle performance. A prototype is designed and tested with a resistive termination and experimental results show good agreement between ideal and experimental admittances. The possibility to use dynamic (rather than purely resistive) loads to improve vehicle control without limiting the energy recovery is discussed.

The brushless doubly-fed machine (BDFM) has two stator windings with different pole numbers, supplied with different frequencies. Therefore, the distribution of magnetic fields in stator and rotor iron is complex. In addition, the stator flux density distribution is non-sinusoidal and has a DC offset at the natural speed. This makes the use of conventional hysteresis models utilised for sinusoidal fields impractical for the BDFM. In this paper a new hysteresis model is proposed for the BDFM stator iron based on the scalar Preisach model. The rotational characteristics of the magnetic fields in the BDFM are also considered and their effects in generating iron losses are assessed. 2-D time-stepping finite element (FE) models are developed for a prototype D160 BDFM to estimate iron losses and are validated by experiments.

In this work, an analytical study has been performed on the Brushless Doubly Fed Machine's (BDFM) vibration due to the interaction of its fundamental magnetic fields, exerting bending forces in the back iron. The effects of rotor eccentricity on exacerbating the machine's vibration have been considered by assessing the stator back iron displacement function in the presence of rotor eccentricity. Finite element analysis is carried out for a 250 kW BDFM built in frame size D400 to validate the analytical methods. The stator back iron displacement is determined for an ideally-constructed machine as well as when the rotor has static and dynamic eccentricity. In addition, the prototype BDFM was tested at different operating conditions in order to examine its noise and vibration levels. A set of measurements was conducted to assess the main vibration component frequencies developed by the machine at different rotor speeds. It is shown that the main vibration components are created by bending set-up in the back iron, rotor eccentricity, and the components with time and space harmonic natures. The results obtained from finite element analysis and experimentally agree with the analytical assessment of BDFM vibration.

A correct understanding of fluid flow and heat transfer characteristics in oil injection cooling for hairpin end winding is crucial for accurate thermal analysis. This article utilizes a meshless computational fluid dynamics (CFD) approach, based on moving particle simulation (MPS), to develop a simplified numerical model. The model provides qualitative insights into fluid dynamics and heat transfer mechanism in hairpin end winding. Experimental validation is conducted to compare the numerical data and identify key factors influencing oil coverage rate (OCR) and heat transfer coefficient (HTC), including the number and placement of inlets, coolant flow rate and temperature, and rotation speed. The results indicate that increasing the number of inlets and optimizing their placement enhances cooling uniformity. Furthermore, the HTC is strongly influenced by the coolant flow rate and temperature, with an average HTC of 130 W/m²/K achieved at an inlet temperature of $40~^{\circ }$ C and a flow rate of 8 L/min. The highest HTC values are found in the lower winding layers due to the downward flow of oil. Rotation also improves the OCR and HTC by approximately 20% and 37%, respectively, at 1000 r/min, as oil droplets are sprayed onto the winding surfaces, particularly near the rotor. However, at higher rotational speeds, the cooling efficiency stabilizes, and the effect of rotation becomes less significant.