The squirrel-cage induction motor with equivalent slot number may have starting problem due to synchronous locking torque. This study adopts dual skew rotor structure to solve that problem. First, the distribution of rotor slot harmonics is described. Second, the synchronous parasitic torque acting on the rotor is calculated. Eddy-current field simulation is implemented to calculate locking torque in three kinds of structure rotors squirrel-cage induction motor with equivalent slot. The induction motor with straight rotor hardly line starts in some rotor position, which illustrates that skew rotor can attenuate the synchronous parasitic torque, but cannot remove it. The dual skew rotor can remove the synchronous parasitic torque in which odd rotor slot harmonics interact with the unassociated stator harmonics, and also attenuate others. The validity of this rotor structure is verified by simulation study and also experiment.

This study introduces an optimisation-based procedure for characterising switched reluctance machine (SRM) performance and studies the optimisation to determine the conduction angles in SRM drives. The objectives employed in the optimisation cases are maximising average output torque, maximising the ratio of average torque over root mean square (RMS) value of phase current, and minimising RMS value of net torque ripple. Combinations of these objectives are used in four different cases, which are formulated either as single- or multi-objective problems. These cases are then compared in terms of output torque, torque ripple, and efficiency. One method of the four is selected and the performance of the motor over the entire operating range is characterised based on optimised turn-on and turn-off angles. Experimental results are used to verify the motor performance obtained from the optimisations for selected operating points.

The finite-control-set model predictive direct torque control (FCS-MPDTC) is a novel control scheme for permanent magnet synchronous motors (PMSMs). A key feature of FCS-MPDTC is that the eight possible voltage space vectors or switching combinations of the power converters are directly taken into account as the control input of the system. A cost function is used in FCS-MPDTC to evaluate each possible voltage space vector and the one with minimum cost is applied to the power converter. Due to the considerable torque and flux ripples, to improve the performance of FCS-MPDTC, this study presents an extended set of 20 modulated voltage space vectors with fixed duty ratio. For further improvement, a larger set size can be chosen, but this requires a larger computing power. To mitigate the computational burden caused by increased number of voltage space vectors, a pre-selective scheme is designed for the proposed FCS-MPDTC to filter out the impractical voltage vectors instead of evaluating all 20 voltage space vectors. The drive system efficiencies of conventional direct torque control, conventional FCS-MPDTC and proposed method are investigated. The theory and simulation are validated by experimental results on a PMSM prototype.

The self-inductance of doubly salient electro-magnetic motor (DSEM) varies with rotor position, so it's becoming an effective approach to estimate rotor position in DSEM sensorless drive system. Based on the feature that there must be a change in the magnitude relation of two phase self-inductances when the rotor goes from one sector to the other, this study proposes a novel rotor position estimation method for DSEM sensorless startup, it needs only one test pulse injection. The proposed method starts with injecting a test voltage pulse in all three-phase windings by turning on three proper transistors a certain time synchronously. Then at the end of the test pulse, the response currents of the two parallel-connected phases are sampled and compared for judging whether the rotor has reached the commutation instant. Moreover, the rotor position estimation error and output torque of the pulse-injection-based methods are theoretically analysed. Compared with the conventional rotor position estimating method which requires multiple test pulses, the proposed strategy has merits of less test time consuming, higher-accurate commutation, greater output torque and superior startup performance. Finally, the experiments on a 12/8-pole DSEM confirm the correctness and flexibility of the proposed method.

This study presents a new three-dimensional (3D) analytical method for no-load magnetic flux density computation of axial-flux permanent-magnet synchronous machines. In the method suggested, at first the machine's cylindrical coordinates are converted to the Cartesian coordinates using conformal mapping, and then Laplace's equation is solved in Cartesian coordinates in 3D to give the scalar magnetic potential. Finally, the magnetic flux density is computed using the scalar magnetic potential. Use of the analytical method takes much less computational time than 3D finite element method does, and is, thus, useful for designing and optimisation purposes. Validation of this method is performed through the 3D finite element analysis and experimental results.

In automotive testing systems such as chassis dynamometers and engine dynamometers, effective and efficient control strategies are required to control the induction motor drives, so that fast torque response and low-torque ripples can be obtained. The fast torque response can be obtained by using model predictive control (MPC) due to its high bandwidth over a wide-speed range; and the torque ripple can be reduced by using open-end winding induction motor (OEWIM). Since MPC can be current based or flux/torque based, and can be linear and non-linear, it is necessary to evaluate the effectiveness of different MPC methods on the open-end winding drives. In this study, linear and non-linear current-based MPC methods and flux/torque-based MPC methods for OEWIM drive are derived and evaluated. The transient and steady-state responses of MPC methods are compared through simulation and experiment. The results show that linear MPC methods require less computation time, and under the same sampling frequency, linear MPC methods provide lower current ripple and better zero-sequence-current suppression than non-linear MPC methods. This study provides practical perception for MPC used on multi-level converters and MPC used for unbalanced situations.

The double-stator configuration of the switched reluctance machine (SRM) aims to maximise the energy conversion efficiency by optimising the ratio of motional force to the total magnetic force. Maintaining the attractive features of SRM, the double-stator switched reluctance machine (DSSRM) proves to have higher torque/power density than the conventional SRM, which is a crucial feature for traction applications. The original winding configuration used in DSSRM is the full-pitch winding, which yields high-power density but causes significant heat within the machine's end windings. As end windings do not take part in torque generation, concentrated windings were proposed to reduce the heat as well as to reduce the size, cost, and weight of the machine. This study provides a detailed comparative analysis of the effects that the winding configuration has on the performance of a 100 kW DSSRM, with emphasis on flux density distribution, efficiency, and heat generation. It is concluded that the concentrated windings are a better alternative to the full-pitch windings in DSSRM.

This study investigates how to improve the fault tolerance or availability of an electrical drive containing a three-phase 12 stator teeth/10 rotor poles (12/10) the flux-switching permanent magnet machine. In this respect, space-vector modulation and space-phasor modulation will be analysed in this type of machine for control scheme design under three-phase operation. While for safety critical applications, availability requires that during faults, such as loss of one inverter phase leg or open circuit of one machine phase winding, the electrical drive system remains partly operational. Therefore, initial research is given in this study on the implementation of control algorithms that drives the machine under normal condition and preserves the electromagnetic torque under phase open-circuit faults.

Since the three-dimensional (3D) analysis of linear induction motor (LIM) needs to consider the transverse end effect, the transverse magnetomotive force (m.m.f.) distribution model becomes significantly important. This study investigates the influences of different transverse m.m.f. models on operating characteristics of double-sided LIMs, and it also develops a novel m.m.f. model. First, four types of hypothetical distribution models are put into a 3D analytical method that considers the longitudinal and transverse end effects. Second, variations of the thrust, lateral and vertical forces with the models are comprehensively investigated in the possible operating regions. Besides, the calculated results are validated by finite elements method results and measurements in a prototype double-sided linear induction motor (DLIM). Finally, the model presented in this study can be considered as a kind of optimal model for analysing DLIMs, and comparisons with other models in each operating region are mentioned.

Wind energy (WE) as an environment-friendly resource is green, clean, and innovative solution for the globe energy dilemma. For the blade pitch control (BPC) of the WE, the gain scheduling of the BPC becomes important to cope with the wind intermittency. The innovative idea of this study is to employ the novel advanced MOTs for enhancing the dynamic behaviour of the wind power plant. For this purpose, the genetic algorithm (GA), artificial bee colony (ABC) algorithm and grey Wolf optimiser (GWO) are used for the optimal tuning of the BPC system parameters. A comprehensive comparative study is presented to verify the effectiveness of the proposed MOTs over different conventional methods such as the conventional Zeigler–Nichols, and the simplex algorithm). This comparative analysis is based on the time response specifications such as maximum overshoot, settling time and steady-state error. The proportional-integral-differential (PID) controller is applied to the multivariable BPC for a wind turbine generating system connected to a large power system. The simulation results show that the GWO-PID is more effective than the ABC, GA and the conventional methods. Moreover,the GWO-PID controller robustness is verified in the presence of system parameter variations, an abrupt change in the mechanical torque and the wind speed variation.

This study proposes a novel control scheme for doubly-fed induction generator (DFIG) in DC-grid where its stator and rotor are connected to DC-bus via insulated-gate bipolar transistor (IGBT)-based converters, namely rotor side converter and stator side converter (SSC). Maximum slip frequency strategy is proposed to determine stator frequency and improve stator voltage at low-rotor speed, which could lower the design difficulty of SSC. Stator voltage decreases with stator frequency at low-rotor speed, and keeps its rated value at normal rotor speed. The control strategy of constant stator voltage and constant rotor exciting current is adopted to make DFIG operate at normal and low-rotor speed, respectively, and low-speed wind energy is utilised accordingly. Furthermore hysteresis control strategy is adopted to avoid frequent switching in the strategy switching process. Experiment results validate the feasibility and effectiveness of the proposed control scheme.

The doubly salient electromagnetic machine (DSEM) is a kind of variable reluctance machine, which is different from the conventional AC electric machines. The standard angle control and the three-state angle-advanced control are traditional control strategies for DSEM, with dead zone existing. Six-SAA (SSAA) control is a newly proposed control strategy with no dead zone. Compared to traditional control strategies, it can increase output torque, and reduce the torque ripple. However, it is hard to select proper advanced angles in SSAA control. In this study, a 12/8-pole DSEM has been studied. Then, several control strategies for DSEM are presented, and the operating principles are analysed in detail. After that, a new control strategy is proposed, and its characteristic during commutation stage is analysed. Besides, the optimal advanced angles are deduced, with its variation characteristics, and the comparison of these control strategies are conducted by finite element simulation. With the proposed control strategy, a higher-output torque can be acquired in a wide-speed range, and meanwhile, the selection of advanced angles is simplified. Finally, the theoretical analysis is verified by simulations and experimental results.

In this study an analytical model based on solving Maxwell equations in the machine layers is presented for linear resolver (LR). Anisotropy, field harmonics, slot effects, number of slots per pole per phase and the effect of tooth skewing are considered in the model. The proposed method is a design oriented technique that can be used for performance prediction and design optimisation of the LR due to its acceptable accuracy and fast computation time. Two- and three-dimensional time stepping finite element method (FEM) is employed to validate the results of the proposed model. Good correlations between the results obtained by the proposed method and the FEM confirm the superiority of the proposed method over the FEM due to its much lower computational time. Finally, the prototype of the proposed sensor is built and tested. The results of the experimental tests verify the accuracy of the simulations.

An overall six-sigma process (SSP) that includes a novel process capability control (PCC) procedure is presented for satisfying a six-sigma level for a Z-value as well as a mean value of target performance. An example of this process is present for the efficiency and torque ripple in a spoke-type permanent magnet motor considering the manufacturing tolerances of five rotor dimensions. In this context, six-sigma means that the probability of failure of the product or system is 0.00034%. A novel SSP with a PCC procedure is suggested for designing electrical machines. In this procedure, three possible PCC methods were determined based on the definition of the Z-value. Next, each method was carried out to achieve the target Z-value and to illustrate the advantages and possible issues associated with each method. Finally, the authors showed that the suggested PCC procedure effectively achieves the target Z-value of the motor and can be widely used for the design of electrical machines.

Timely and accurate detection of the rotor winding inter-turn short-circuit fault of a synchronous generator can reduce the more serious damages caused by fault deterioration and economic losses, so developing online detection methods with high sensitivity is necessary. On the basis of the structural characteristics of the synchronous generator, this study proposes a sensorless online detection method for rotor winding inter-turn short-circuit faults, respectively, taking a 300 MW turbo generator and a 550 MW hydro-generator as the objects of finite-element simulation. The results show that the new fault diagnosis method of the rotor winding inter-turn short circuit for the sensorless synchronous generator has high sensitivity and can realise real-time monitoring of the faults.

The study presents the direct flux and current vector control of an induction motor (IM) drive, which is a relatively newer and promising control strategy, through the use of model predictive control (MPC) techniques. The results highlight that the fast flux control nature of direct flux control strategy is further enhanced by MPC. Predictive control is applied in two of its variants, namely the finite control set and modulated MPC, and the advantages and limitations of the two are underlined. This work also highlights, through experimental results, the importance of prioritising the flux part of the cost function which is particularly significant in the case of an IM drive. The performance of the MPC-based approach is compared with the proportional–integral controller, which also prioritises the flux control loop, under various operating regions of the drive such as in the flux-weakening regime. Simulations show the performance expected with different control strategies which is then verified through experiments.

In this paper, the 117 kW, 60,000 r/min super high-speed permanent magnet generator (SHSPMG) under unbalanced load condition is studied. First, the influence mechanism of the unbalanced load on the generator was revealed, and by using field-circuit coupling method and at rated load, the current unbalance factor (CUF) was determined. Second, through the time-stepping finite element method, the generator air-gap flux was obtained and decomposed in virtue of the principle of Fourier transform. The influence of the unbalanced load on air-gap flux was studied, and the eddy current loss and torque ripple with different CUFs were calculated and analysed. Finally, based on the calculation results of two-dimensional transient electromagnetic field, the negative sequence current was extracted by using the symmetrical component method. The research showed that the harmonic content of air-gap flux density increases when the generator is connected to unbalanced load, and the eddy current loss and the torque ripple increases with the increase of the load unbalance degree. The experimental platform was established and the test data were in good agreement with the model calculated results, which verified the correctness of the model. The research could provide some useful conclusions for the research of the SHSPMG.

This study investigates the experimental validation of finite control set–predictive current control (FCS-PCC) of a multi-level four-leg voltage-source inverter (VSI) operating under balanced and unbalanced conditions. The proposed topology is a combination of conventional four-leg VSI with an additional four switches circuit serving as dc voltage synthesiser. Unification of both circuits can supply energy to unbalanced three-phase loads by providing the path for a zero-sequence load while maintaining appropriate load voltage to the system. The proposed control strategy takes advantage of the discrete nature of the power converter system to predict the future behaviour of the output current. FCS-PCC is based on an optimal approach that selects the most accurate switching signals among 48 valid switching states by computing cost function and applying switching state that minimises the tracking error to the next sampling time. The proposed control has been experimentally verified to assert the robustness of the control. The prominent outcomes of the experiments confirm the ability of independent load current reference tracking with harmonics distortion lower than the conventional eight switches VSI.