Fractional-slot winding configurations have attracted much attention due to the availability of concentrated windings and low cogging torque in permanent magnet brushless motors. For the design of the winding configurations, many design parameters must be determined. The winding factor provides a useful index for the optimal design. However, no general expressions of the winding factor have been derived for all the winding configurations. This study performs the general formulation of the winding factor for the fractional-slot concentrated windings. The winding factor is redefined for stator windings without any information of the numbers of poles. For given stator windings, the optimal numbers of poles are determined from the obtained winding factors. The design strategy for the winding configurations is validated through a finite element method analysis.

This paper proposes an adaptive controller with an improved high-frequency injection method for sensorless synchronous reluctance drive systems. A mathematical model is presented to show that the use of a high-frequency injection method that takes into account the effects of unequal mutual-inductances and the influence of speed reduces the rotor position estimation error. The adaptive speed control algorithm offers improved transient performance in comparison to typical proportional–integral (PI) controllers that are employed in sensorless drive systems. To demonstrate the viability, the proposed adaptive controller and the modified high-frequency injection method are implemented using a TMS-320F-28335A digital signal processor to control a 500 W prototype synchronous reluctance motor drive. Experimental results are presented to show that the transient, load disturbance, and tracking responses of the proposed drive system are superior in comparison to a drive that uses a PI controller. Both experimental and theoretical analyses clearly indicate that the proposed high-frequency injection method with an adaptive speed-loop controller offers improved performance in adjustable speed synchronous reluctance drive systems.

Analyses of transformer electromagnetic vibration noise are presented in this study. A finite element model is established which combines transient electromagnetic field analysis, mechanical field analysis and acoustic analysis to calculate the sound pressure level of the radiated noise around the transformer. Transient electromagnetic field analysis is performed to get the Lorentz, reluctance magnetic forces and magnetostriction according to Maxwell theory and virtual displacement principle. Mutual influence of strain and magnetisation has been considered. The main frequency components of harmonic electromagnetic excitations are analysed by Fourier transformation so as to carry out the harmonic response analysis and obtain the nodes displacements of the windings and core. The noise distribution is further calculated by acoustic analysis based on the achieved vibration data. Comparison of calculated results and measured data verifies that the combined noise calculating model is applicable for transformer noise prediction.

This paper proposes a novel integrated brushless excitation method (IBEM) for a rotor-excited generator. IBEM is applied to a rotor-excited hybrid excitation synchronous generator (HESG) to realise brushless excitation while the key features of the rotor-excited generator are maintained. The new generator is referred as IBE HESG here. The stator excitation windings are buried in the stator slots. The static excitation field is established in the air gap when there is dc excitation current in the stator excitation windings. The three-phase armature coils of the rotor induce the static excitation field and provide the dc excitation current for the rotor excitation windings via a rotating rectifier. The operating principles are discussed theoretically. The magnetic field distribution and the operating characteristics are studied by finite-element analysis. The no-load, external, regulation and excitation characteristics are analysed. Compared with the brush excitation HESG, the rotor excitation current is able to meet the requirement and the output voltage is conveniently regulated by the stator excitation current. Finally, a 1.5 kVA prototype is fabricated to test the operating characteristics of IBE HESG. It demonstrates that the brushless excitation is realised and the output voltage is regulated by the stator excitation current.

This study proposes a high-speed permanent magnet actuator (HSPMA) for high-voltage vacuum circuit breaker (VCB). The HSPMA comprises mainly of an eddy current repulsion force actuator and a permanent magnet (PM) actuator. The structural saliency of HSPMA is described and its control principle is elaborated in details. Finite element method is used and the eddy current is included in the computation of the electro-magnet fields of the HSPMA. The system equations, which couples the magnet field to circuit and mechanical equations, are built in ANSOFT Maxwell and Circuit Editor in this study of the making and breaking procedures of the HSPMA. The simulated characteristics show the design meets the requirement of the high-voltage VCB. The optimal thickness of the eddy current plate is 10 mm. The capacitor also has an economic optimal value of 10,000 µF. The simulated results indicate that the HSPMA has a sound characteristic when compared with circuit breakers with only PM actuator.

In this paper, the authors present a novel compact structure of an integrated radial/thrust magnetic bearing (IRTMB) without thrust disk. The structure without thrust disk can further reduce the frictional and windage loss for a high-speed driving system. At the same time the rotor supported by the two IRTMBs can further reduce its axial size, and improve rotor dynamic performance. The axially magnetised magnet forms a cylindrical magnet sandwiched between a four-leg laminated radial stator and a solid return pole piece. On the basis of the return pole, a novel air gap, called the return air gap, is constructed between the rotor and the return pole. The bias flux produced by the permanent magnet and the control flux produced by the thrust magnetic bearing (TMB) unit are conducted by this return pole. The magnet produces the bias flux for radial and TMB units, and separates the control flux loops of radial and TMB units. The IRTMB structure and its analytical models are deduced using equivalent magnetic circuit method. To study the performances of the IRTMB, another IRTMB with thrust disk used in a high-speed motor with power of 45 kW at 60,000 rev/min has been fabricated and is chosen as the comparison target.

This paper evaluates the capability of saliency tracking to assess the health condition of permanent magnet synchronous motor (PMSM) drives operating under non-stationary conditions. The evaluated scheme is based on saliency tracking methods, which are associated to the accurate sensorless control of AC drives without zero speed limitations. In this work two representative saliency tracking architectures are evaluated: high frequency (HF) injection, and PWM transient excitation. Although a monitoring approach based on HF injection was previously reported, a comparative study to evaluate the most representative saliency tracking schemes to assess health condition in drives was still missing. The aim of this work is to fill out this gap by evaluating and comparing two saliency-based monitoring schemes (one based on HF-injection and the other based on PWM transient excitation) to evaluate their performance in the presence of inter-turn winding faults. Simulation and experimental results are presented which confirm that both schemes offer excellent detection capabilities and that are suitable for drives operating under nonstationary conditions including standstill operation.

Flux weakening is an inevitable requirement in the operation of variable speed permanent magnet (PM) machines for high-speed applications due to inverter voltage limits. A new winding switching technique is experimentally validated in this study that can extend the speed range of such PM machines. A drive topology is proposed that utilises two current regulated voltage source inverters to control the machine in a dual inverter fed configuration before transitioning into an open winding configuration after winding switching. The proposed drive topology extends the constant torque region of the machine and boosts its maximum output power capability. Complete experimental results are provided to demonstrate the effectiveness of the proposed machine drive system for continuous operation over the entire speed range.

This paper presents a finite simulation model of the hybrid excitation synchronous machine taking into consideration the saturation effect, the iron losses and including higher-order electromagnetic force harmonics. Simulation and experimental testing prove that the advanced model represents more accurately the machine especially when compared with the basic Park model built with sinusoidal waveform assumption. The main contribution of the work is that only few experimental measurements are needed in order to implement the advanced model.