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No description available.

No description available.

No description available.

No description available.

Nanoscale mechanical resonators exhibit excellent sensitivity and therefore potential advantages for application as ultrasensitive mass sensors by comparison with micromachined cantilevers. We fabricated three dimensional vertical C-W-nanorods on silicon substrates by focussed ion beam induced deposition (FIB-CVD) and investigated the factors which affected the growth rate and smoothness of the nanorod sidewall, including the heating temperature of precursor gas and the ion beam current. We also discussed the effects on reducing the thickness of the nanorod with FIB milling, including the ion beam current, ion beam energy and ion incident angle. We fabricated a doubly-clamped beam and a singly-clamped beam by felling a vertical nanorod over a trench with FIB milling. We investigated the static mechanical properties (i.e. Young’s modulus) of doubly-clamped and singly-clamped nanorods by atomic force microscopy (AFM) with force displacement measurement. Since the optical signal reflected from a cantilever whose dimensions are sub-wavelength is very weak, it is difficult to measure the absolute nanoscale displacement of such cantilevers with an optical technique. We describe an electron microscope technique for measuring the absolute oscillation amplitude and resonance of nanomechanical resonators with a model-independent method. A piezo-actuator mounted in a field-emission scanning-electron microscope (SEM) is used to excite the nanomechanical resonator to vibrate. The secondary electron signal is recorded as the primary electron beam is scanned linearly over the resonator. An absolute oscillation amplitude as low as 5 nm can be resolved, this being comparable to the size (~1.5 nm) of the primary electron beam. The Q-factor of nanomechanical resonators was measured ranging 300 to 600. The mass resolution of the resonators was also estimated to the level of 1E-15 g.

The rising public awareness of climate change and urban air pollution has been one of the key drivers for transport electrification. Such trend drastically accelerates the quest for high-power-and-torque-density electric drive systems. The rare-earth permanent magnet synchronous machine, with its excellent steady-state and dynamic characteristics, has been the ideal candidate for these applications. Specifically, the fractional-slot and concentrated-winding configuration is widely adopted due to its distinctive merits such as short end winding, low torque pulsation, and high efficiency. The vibration and the associated acoustic noise become one of the main parasitic issues of high-performance permanent magnet synchronous drives. These undesirable features mainly arise from mechanical connection failure, imperfect assembly, torque pulsation, and electromagnetic radial and axial force density waves. The high-power-and-torque-density requirement will only be ultimately fulfilled by the reduction of both electromagnetic active material and passive support structure. This results in inflated electromagnetic force density inside the electric machine. Besides, the sti.ness of the machine parts can be compromised and the resultant natural frequencies are significantly brought down. Therefore, the vibration and acoustic noise that are associated with the electromagnetic radial and axial force density waves become a burden for large deployment of these drives. This study is mainly dedicated to the investigation of the electromagnetic radial forced density and its associated vibration and acoustic noise in radial-flux permanent magnet synchronous machines. These machines are usually powered by voltage source inverter with pulse width modulation techniques and various control strategies. Consequently, the vibration problem not only lies on the permanent magnet synchronous machine but also highly relates to its drive and controller. Generally, the electromagnetic radial force density and its relevant vibration can be divided into low-frequency and high-frequency components based on their origins. The low-frequency electromagnetic radial force density waves stem from the magnetic field components by the permanent magnets and armature reaction of fundamental and phase-belt current harmonic components, while the high-frequency ones are introduced by the interactions between the main low-frequency and sideband highfrequency magnetic field components. Both permanent magnets and armature reaction current are the main sources of magnetic field in electric machines. Various drive-level modeling techniques are first reviewed, explored, and developed to evaluate the current harmonic components of the permanent magnet synchronous machine drive. Meanwhile, a simple yet e.ective analytical model is derived to promptly estimate the sideband current harmonic components in the drive with both sinusoidal and space-vector pulse width modulation techniques. An improved analytical method is also proposed to predict the magnetic field from permanent magnets in interior permanent magnet synchronous machines. Moreover, a universal permeance model is analytically developed to obtain the corresponding armature-reaction magnetic field components. With the permanent magnet and armature-reaction magnetic field components, the main electromagnetic radial force density components can be identified and estimated based on Maxwell stress tensor theory. The stator tooth structure has large impacts on both electromagnetic radial force density components and mechanical vibration behaviors. The stator tooth modulation e.ect has been comprehensively demonstrated and explained by both finite element analysis and experimental results. Analytical models of such e.ect are developed for prompt evaluation and insightful revelation. Based on the proposed models, multi-physics approaches are proposed to accurately predict low-frequency and high-frequency electromagnetic radial vibration. Such method is quite versatile and applicable for both integral-slot and fractional-slot concentrated-winding permanent magnet synchronous machines. Comprehensive experimental results are provided to underpin the validity of the proposed models and methods. This study commences on the derivations of the drive parameters such as torque angle, modulation index, and current harmonic components from circuit perspective and further progresses to evaluate and decouple the air-gap magnetic field components from field perspective. It carries on to dwell on the analytical estimations of the main critical electromagnetic radial force density components and stator tooth modulation e.ect. Based on the stator mechanical structure, the corresponding electromagnetic radial vibration and acoustic noise can be accurately predicted. Various analytical models have been developed throughout this study to provide a systematic tool for quick and e.ective investigation of electromagnetic radial force density, the associated vibration and acoustic noise in permanent magnet synchronous machine drive. They have all been rigorously validated by finite element analysis and experimental results. Besides, this study reveals not only a universal approach for electromagnetic radial vibration analysis but also insightful correlations from both machine and drive perspectives.

Electrical machines with rare-earth permanent-magnets (PMs) exhibit high torque density and good efficiency over a wide operation range. However, the high cost and limited reserves of the rare-earth material makes it less sustainable to develop this machine technology for electric vehicle (EV) traction. To improve machine performance and reduce PM usage, this thesis investigates a number of issues pertinent to modelling and design of PM machines for EV traction applications. A four-wheel vehicle dynamic model is established to quantify the influence of tyre slip on machine sizing, and thus an optimum control for torque split ratio of distributed front-rear drives is realised by minimising the loss resulting from tyre slip. PM-assisted synchronous reluctance machines with fractional-slot windings are proposed to reduce PM usage whilst exploiting advantages of fractional-slot windings. To more accurately evaluate reluctance torque and thus maximise torque production of an interior PM (IPM) machine in design stage, a torque model allowing for torque component separation via frozen permeability is presented. A generic approach to magneto-motive force harmonics reduction using multiple 3-phase windings is proposed to reduce rotor iron loss and torque ripple whilst improve reluctance torque and machine efficiency. A 9- phase 18-slot 14-pole IPM machine is subsequently designed based on the proposed multiple 3-phase windings and its performance validated on a 10kW prototype. In order to accurately assess the performance of an IPM machine drive, a high-fidelity and computationally efficient machine model is proposed by considering magnetic saturation, spatial harmonics, iron loss and temperature effects. Furthermore, an electro-thermally coupled model is established by integrating the temperature-dependent electromagnetic model with a state-space lumped parameter thermal model. Both models are experimentally validated. An analytical mechanical stress model is proposed to incorporate mechanical strength constraints into machine global optimisation process. Thus, unfeasible designs whose mechanical strength cannot meet the requirement can be avoided.

This thesis is concerned with the digital computer prediction of the performance of a 125MVA synchronous compensator during starting and synchronising to a power transmission system. Little work has been conducted in the past on synchronising problems, and the few studies reported discuss either synchronous motors or generators. Although basically similar machines, synchronous compensators have different design parameters to synchronous motors because of the duty that they are required to perform, and the starting and synchronising conditions can be quite different from those of synchronous motors. Therefore, application of studies of synchronous motors to synchronous, compensators may produce results of doubtful value. In the study described in this thesis, digital computer programs are developed to simulate the performance of a synchronous compensator using methods of analysis first developed by Park.