Abstracts:Transformer winding hot-spot temperature (HST) is one of the important factors affecting transformer oil-paper insulation deterioration. This study presents a three-dimensional coupled electromagnetic-fluid-thermal analysis method for HST calculation in a 10 kV oil-immersed distribution transformer, the influence of the transformer internal metal structure parts on the HST of the winding is considered in the simulation. Combining electromagnetic-field calculation with no-load test and load test of the transformer provides a more accurate method to determine internal losses of the transformer. Taking those power losses as heat sources, the transformer fluid-thermal field analysis is conducted with the finite volume method. The variation of physical parameters of transformer oil with temperature is considered in the simulation. On the basis of the equivalent thermal resistance theory, the equivalent thermal conductivities of transformer windings are obtained. The simulation results deduced from the proposed method agree well with the experimental ones, which are obtained with fibre optic temperature sensors during the transformer temperature rise test, the maximum temperature difference is <;3°C. The results validated the validity and accuracy of the proposed transformer HST calculation method.

Abstracts:In order to widen the flux-weakening range of motors, this study proposed a DC-link voltage control strategy for high-speed permanent magnet motor drive systems powered by Z-source inverter. In this strategy, the DC-link voltage, also known as the output voltage of the impedance network, varies with the inverter output voltage and remains optimal at all times, whether in steady state or transient state. As for the shoot-through duty ratio and the modulation index, the two main control variables in the Z-source inverter are under unified control to ensure the stability of the system, while achieving fast tracking and reducing the loss. In addition, a new sliding mode control system based on the indirect control of the capacitor voltage is used to control the DC-link voltage to suppress the system fluctuation caused by the change of the given value or the motor load. Besides, various conventional voltage Z-source inverter pulse width modulation strategies can be applied to this technology. Simulations and experiments verified the effectiveness of the proposed strategy.

Abstracts:In this study, design optimisation of an axial-flux reluctance magnetic coupling is presented. The optimal design procedure is based on a two-dimensional (2D) semi-analytical model defined at the mean radius combined with a multi-objective genetic algorithm (NSGA-II). In order to take into account the end-effects in the radial direction, a correction factor is defined to improve the torque and the axial-force determination. The obtained results are compared with those of 3D non-linear finite element simulations and experimental results. It is shown that the proposed semi-analytical model is very accurate and requires very little computing time.

Abstracts:This study presents a general optimisation method for determining the dimensions of the magnetic levitation (maglev) actuator for rotary tables. Combined with an improved electromagnetic numerical model of the maglev rotary tables, the optimal thickness dimensions of coils and magnets are obtained by the evolutionary optimisation algorithm. Different from the existing magnetic force model built by the harmonic analysis method, the improved numerical model involves the clearances of the neighbouring magnets in the circular magnet array and applies the numerical integration method to solve the complex Lorentz integrals. According to the evaluation function based on the numerical force model, the optimal thickness dimensions are determined via an evolutionary optimisation algorithm. By this method, the size of coils and magnets in the rotary table with the circular Halbach magnet array can be determined accurately and directly, rather than obtaining a single structure dimension by an analytical approach. In this work, the method is applied to optimise the dimensions of a maglev rotary table, and a prototype is manufactured according to the obtained optimal parameters. The experimental and simulation results verify the accuracy and validity of the proposed optimisation design method.

Abstracts:In this study, the radial displacement of the stators is proposed to improve sensor-less speed control for dual-stator brush-less DC motor drives. The mechanical offset between stators leads to the double number of edges in the zero-crossing signal (ZCS) and thus, a more accurate speed estimation. Moreover, updating the speed in the control process will become faster that can decrease speed control error. As stators' axes are displaced 90° electrical, the distance between ZCS edges becomes symmetrical. Therefore, it would provide a uniform estimated speed updating, and can effectively decrease speed ripple. Also, asymmetrical stators displacement can decrease speed ripple compared to the aligned structure when the distance between adjacent zero-crossing points is appropriate. In addition, stators displacement is well known as an efficient technique to decrease torque ripple. This idea is verified via computer simulations and experimental results.

Abstracts:A doubly-salient relative permeance method is presented herein to predict the magnetic field of bearingless flux-switching permanent-magnet machines (BFSPMMs). Firstly, the subdomain model method is used to compute the magnetic field of slotless BFSPMMs. Then, the slotting effect of the stator and rotor is obtained by the doubly-salient relative permeance method. By combining the two above, the air-gap magnetic field of slotted BFSPMMs can be obtained. The doubly-salient relative permeance method is based on the theory of the subdomain model method. The whole doubly-salient structure is divided into several subdomains, and the Laplace equations for subdomains are established. Then, according to the boundary conditions between subdomains and the core, and the continuity conditions between adjacent subdomains, the equations are solved to calculate the slotting effect. Based on the proposed analytical model, the flux density and electromagnetic performances including back-electromotive force (EMF), torque, and suspension force are predicted and compared with the finite element method results. Furthermore, the back-EMF of the prototype motor is measured and the suspension experiments are carried out based on the analytical method. The comparison results and experiment results verify the validity of the analytical method.

Abstracts:Electrical machines are widely used as a driving source for various applications because of their wide speed range, high efficiency, and torque density. Similar to any other machine, manufacturing tolerances occur when mass producing the motors. In particular, the tolerances of the shape of the motor or the residual flux density in the permanent magnet significantly affect the back-electromotive force (EMF), inductance etc. When the magnitude of the back-EMF is changed, the armature current must be changed to obtain the same torque. This consequently affects the loss of the motor, and hence leads to changes in efficiency. In particular, the loss changes cause thermal problems such as irreversible demagnetisation of the magnets and dielectric breakdown due to the increase in the temperature of the coils. Therefore, to reduce the inevitable manufacturing tolerance, a robust methodology should be assured. Here, the Taguchi's robust design is applied to an integrated starter-generator motor by using the signal-to-noise ratio to consider the coil temperature.

Abstracts:This study proposes a modified structure of the E-core permanent magnet (PM) assist switched reluctance motor by relocating the PM blades inside the stator core. For this purpose, the PMs are removed from the stator poles and placed slantwise inside the yoke. The proposed yoke-PM assist structure is characterised with higher average torque and a lower torque ripple with respect to the conventional pole-PM assist structure. An analytical approach based on the magnetic equivalent circuit is applied at the preliminary design stage to predict the performance of the motor. Based on the presented analytical modelling, the physical dimensions of the motor are optimised via a genetic algorithm to maximise the motor torque and the overall steady state performance. For further verifications, the finite-element analysis simulation results are verified by the experimental tests on the motor prototype.

Abstracts:The hardware-in-the-loop (HIL) real-time simulation for high-speed train electrical traction system aims to reduce the design cost and speed up control verification process of algorithms in the developmental stage of the traction control unit. In this study, based on the dSPACE real-time simulator, the multiple-simulator, multiple-simulation step of HIL real-time simulation system is first built. Second, for the associated discrete circuit modelling method, an optimisation method is proposed to minimise the switching loss and improve the simulation accuracy by selecting the optimal discrete-time switch admittance parameter, <i>G</i>_S. To decrease the computational burden for field-programmable gate array (FPGA), a decoupling method without simulation latency is presented to reduce the matrix dimension of the system model. Finally, the real-time simulation models of electrical traction system are realised by CPU + FPGA-based simulator, in which the power electronics converter models are computed in FPGA with a fixed 100 ns time-step. The validity and reliability of the real-time simulation system is verified by the HIL simulation and experimental results, which indicate that the real-time HIL simulation at the nanosecond level improves the accuracy essentially.

Abstracts:In this study, the identification and control scheme of the motor-drive servo turntable are researched to achieve accurate tracking. Firstly, the input-output identification experiments are designed and realised for the global model of motor-drive servo turntable. The order of the global controlled auto-regressive model is determined by the Akaike information criterion, and the parameters are estimated by a particle swarm optimisation-cuckoo search algorithm. Secondly, the switched friction model is built combining the LuGre structure and the Stribeck curve. The switching conditions and the parameters of the switched friction model are determined though the input-output and the friction experiments. A constrained multi-objective optimisation problem is constructed for the parameter identification of the switched friction model. It is solved via a fuzzy comprehensive evaluation. Finally, the composite control strategy, in which the proportional-integral-derivative controller and model-based friction observer are combined, is proposed in the azimuth angle system of the motor-drive servo turntable. The trajectory tracking results in simulation and experiment illustrate the effectiveness of the proposed switched model, identification method, and composite control strategy.