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Abstract To solve the problems of difficulty in speed measurement and low accuracy of speed measurement of induction motor (IM) during fast starting, the electromagnetic field coupling circuit (EFCC) and open‐loop control of IM considering rapid speed change are proposed. First, the EFCC of IM is established through the stator circuit, air gap magnetic field circuit and rotor circuit, and the stator voltage and electromagnetic torque of the fast starting process are deduced from the air gap magnetic density on the basis of constant slip angular velocity, and then the open‐loop control method based on the EFCC is given. Finally, compared with the open‐loop control based on the TEC, the results of simulation and experiment show that the open‐loop control based on the EFCC can follow the acceleration starting more quickly and the starting current is smaller, which is conducive to reducing the cost of the drive.

Abstract Aiming at the torque ripple caused by significant current ripple and non‐ideal back‐electromotive force (back‐EMF) of coreless brushless DC motor (BLDCM), an incremental predictive control strategy based on unipolar pulse width modulation (PWM) is proposed in the non‐commutation interval. Firstly, the unipolar PWM scheme is used to double the current ripple frequency, which can reduce the current ripple. On this basis, the current prediction equations of adjacent control periods are subtracted to obtain the incremental current prediction equation, and the influence of non‐ideal back‐EMF on torque ripple suppression is eliminated. Finally, combined with the author's previous research on the commutation torque ripple suppression strategy, an integrated suppression strategy for non‐commutation and commutation interval is proposed. The experimental results show that, compared with the PI control strategy, the total torque ripple of the proposed strategy is reduced to less than 35%, and the current ripple is reduced. Meanwhile, the commutation time is shortened, and the advantages of coreless motor rapid response are retained. The strategy is universal, not limited by motor parameters and operating conditions, and has theoretical and engineering value.

Abstract An analytical and optimisation method is presented to improve the air‐gap magnetic field of the surface‐mounted permanent magnet machine with multi‐level array magnets, which can reduce air‐gap magnetic field harmonics and torque ripple. Different from the conventional analytical method (AM) around the entire single‐magnet pole, the modelling method of multi‐level equal‐thickness ferrite magnets with different remanences for improving the air‐gap flux density is investigated. Considering the influence of air‐gap relative permeability by stator slots and multi‐level magnet remanences on the air‐gap flux density, the proposed AM for improving air‐gap flux density is derived by analysing the slotless air‐gap flux density and slotted air‐gap relative permeability. The cogging torque is predicted with energy method by analysing the tangential magnetic field distribution at stator slots. Then, the back electromotive force is predicted by analysing the winding distribution and radial air‐gap flux density. Based on the proposed AM, the simulated annealing particle swarm optimisation algorithm is used by optimising the widths and thicknesses of the multi‐level array magnets to further reduce torque ripple and increase output torque. Finally, the accuracy of the proposed AM is verified by comparing with the finite element method.

Abstract Large‐scale design optimisation techniques enable the design of high‐performance electric machines. Electromagnetic 3D finite element analysis (FEA) is typically employed in optimisation studies for accurate analysis of axial flux permanent magnet (AFPM) machines, which require extensive computational resources. To reduce the computational burden, a FEA‐based mathematical method relying on the geometric and magnetic symmetry of coreless AFPM machines is proposed to estimate the machine performance indicators using the least number of FEA solutions, thereby significantly lowering the running time. This method is generally applicable to AFPM machines with low saturation effects and cogging torque as exemplified for a printed circuit board (PCB) stator coreless AFPM machine. To further reduce the computation time, a systematically simplified equivalent 3D FEA model for planar PCB coils integrated with this machine is also proposed. The practical implementation of the introduced method is elaborated based on an example optimisation study, and an analytical method for fast design scaling is also discussed. The results of the proposed approach are compared with detailed transient FEA results, and a prototype 26‐pole PCB stator coreless AFPM machine was also used to validate the results experimentally.

Abstract This paper introduces a novel application of the inverse modelling method, which is designed to estimate core losses in both the stator and rotor regions of an electrical machine. The technique focuses on the use of short‐term transient temperature measurements obtained from the stator core of a slotless induction machine, with a focus on validating the measured temperature rise through a forward model. The measurement setup involves two primary approaches: (i) the use of thermal sensors embedded in a printed circuit board inside the stator core and (ii) surface sensors embedded on the stator yoke. Through the use of this innovative approach, the results indicate that the inverse modelling technique is highly effective in predicting core losses based on short‐time transient temperature rise measurements.

Abstract This paper investigates the optimal stator voltage angle in a rotor flux‐oriented system of an induction machine drive, aiming to maximise machine torque while operating in a deep field weakening region. Here, torque maximisation leads to maximum torque per voltage control, as only voltage constraints are relevant in this region due to high back‐electromotive force. Previous studies have predominantly focused on field‐weakening operation and torque maximisation, assuming a constant synchronous speed. However, for a given rotor speed, the variation in the dq voltage components impacts the slip speed, thereby influencing the synchronous speed. Therefore, this paper proposes enhanced analytical expressions to address this limitation. It is shown that after a linearisation around a suitable operating point, a closed‐form algebraic equation for calculating the speed and parameter‐dependent optimal voltage angle for torque maximisation can be obtained. The theoretical analysis is supported by numerical and experimental results. The presented linearised expression is proven to be an effective tool for the analytical calculation of the optimal voltage angle, making it suitable for real‐time control applications. It is shown that the proposed approach achieves higher drive torque and efficiency than the conventional voltage component distribution.

Abstract In this paper, counter rotating dual rotor wound field flux switching wind power generator is revisited to study the generating characteristics of the AC output power curves based on finite element analysis (FEA) and experimental study. Analysis are performed under dynamic conditions, such as variable resistance, field excitation and speed. Also, electromagnetic performance is studied under variation of the field and armature currents. Analysis reveals that outer port machines with higher power capability and better electromagnetic performance compared to the inner port counterparts, although with higher fluctuations exhibited on the torque profiles of the former due to higher slotting effects. From the power generation characteristics curves, it is clear that the developed wind generator is able to produce reliable performance over a wide operating range. The accuracy of the FEA predicted results are validated, experimentally. The cover image is based on the Research Article Generating characteristics and experimentation of counter rotating dual rotor wound field flux switching wind generator by Wasiq Ullah et al., https://doi.org/10.1049/elp2.12374.

Abstract A modified non‐linear magnetic equivalent circuit (MEC) model is presented for double‐stator single‐rotor axial flux permanent magnet (AFPM) (DSSR‐AFPM) machine considering stator radial‐end flux‐leakage, which is severer under a heavier load. Compared to the conventional MEC model for DSSR‐AFPM machine, the proposed model can predict the electromagnetic performance more accurately when the machine operates under a heavy load. The proposed MEC model is verified by the finite element analysis (FEA) on a 24‐slot/20‐pole DSSR‐AFPM machine. The comparison results show that the relative error between the proposed MEC model and FEA is

Abstract Fractional slot concentrated winding (FSCW) permanent magnet (PM) machines are gaining more attention for low‐speed applications because of their great advantages. This paper proposes a new structure for an FSCW double rotor axial flux PM synchronous machine (DRAFPMSM) with counter‐rotating rotors. In addition, an analytical formula for the Back EMF waveform of the proposed structure is presented. The accuracy of the formula is investigated by designing a 40 W sample machine. The rotors of this machine rotate with speeds of 600 and 428 rpm in opposite directions. The Back EMF of the sample machine is calculated using the suggested formula. In addition, the finite element method (FEM) is used to determine the Back EMF waveform. Comparison of the obtained results confirms that the new formula yields the Back EMF precisely such that the results well match to those of FEM. The effect of the relative position of two rotors on the Back EMF waveform is investigated using the proposed formula. In addition, the optimum relative position of two rotors for minimizing the Back EMF THD of the case study machine is determined.

Abstract To suppress parameter mismatch and improve the output performance of model predictive control (MPC), a new robust virtual‐vector MPC strategy is proposed for a five‐phase permanent‐magnet motor in this study. Firstly, the incremental predictive model is applied to remove the impact of flux mismatch. Then the d‐q axis inductance parameter sensitivity of MPC is analysed, which produces the predictive current error between the normal parameter and mismatched parameter. Based on the current error, a new cost function is designed to select the voltage vector more accurately when the d‐q axis inductance parameter mismatch occurs. Thus, good robustness to the parameter's variation can be guaranteed. Afterwards, the duty cycle modulation technology is applied to allocate the duration time of two adjacent vector‐vectors and zero vector. So the motor current harmonics and torque ripple can be considerably suppressed. Finally, the experimental results are provided to show the effectiveness of this proposed method.

In order to effectively suppress rotor periodic synchronous vibration caused by the rotor mass eccentricity and sensor detection error of bearingless induction motor (BIM), a rotor vibration suppression control strategy with improved repetitive control is proposed based on the analysis of the problems existing in the traditional repetitive control. On the basis of the vector control model of the BIM system, a simplified suspension control model is derived. The fractional delay filter is used to optimize the repetitive control internal model. Furthermore, for enhancing the stability of the BIM control system, the design method of the repetitive control compensators in high-, middle- and low-frequency region is given in detail. The simulation and experimental results show that the vibration suppression control strategy with the improved repetitive control can effectively suppress the vibration of the rotor in steady state and improve the suspension accuracy of the BIM.

The reduction of the human environmental footprint can be achieved through the use of more efficient motors, such as synchronous reluctance motors (SynRMs). Known for their affordability, SynRMs are increasingly employed in sensorless AC drives. This paper presents a critical comparison of sensorless algorithms based on two nonlinear Kalman Filters (Unscented and Extended). The objective is to highlight the theoretical and practical advantages and drawbacks of each method when applied to the speed control of a SynRM, culminating in a definitive decision on the best choice. The magnetic model of the SynRM is much more nonlinear than that of induction motors, which are predominantly addressed in existing literature. This study aims to fill the gap by answering the question: “Is the extended Kalman filter still the best choice even in the case of nonlinear electric motors?” The answer comes through a large batch of experiments, including speed and load torque tests, zero-speed standstill starts, parameter sensitivity, and evaluation of computational burdens for both Kalman filter algorithms.

Bearings are the most vulnerable component in low-voltage induction motors from a maintenance standpoint. Vibration monitoring is the benchmark technique for identifying mechanical faults in rotating machinery, including the diagnosis of bearing defects. The study of different bearing fault phenomena under induction motor transient conditions offers interesting capabilities to enhance classic fault detection techniques. This study analyzes the low-frequency localized bearing fault signatures in both the inner and outer races during the start-up and steady-state operation of inverter-fed and line-started induction motors. For this aim, the classic vibration envelope spectrum technique is explored in the time–frequency domain by using a simple, resampling-free, Short Time Fourier Transform (STFT) and a band-pass filtering stage. The vibration data are acquired in the motor housing in the radial direction for different load points. In addition, two different localized defect sizes are considered to explore the influence of the defect width. The analysis of extracted low-frequency characteristic frequencies conducted in this study demonstrates the feasibility of detecting early-stage localized bearing defects in induction motors across various operating conditions and actuation modes.

There are numerous methods for detecting interturn faults (ITFs) in the field winding of synchronous machines (SMs). One effective approach is based on comparing theoretical and measured excitation currents. This method is unaffected by rotor temperature in static excitation SMs. However, this paper investigates the influence of rotor temperature in brushless synchronous machines (BSMs), where rotor temperature significantly impacts the exciter excitation current. Extensive experimental tests were conducted on a special BSM with measurable rotor temperature. Given the challenges of measuring rotor temperature in industrial machines, this paper explores the feasibility of using stator temperature in the exciter field current estimation model. The theoretical exciter field current is calculated using a deep neural network (DNN), which incorporates electrical brushless synchronous generator output values and stator temperature, and it is subsequently compared with the measured exciter field current. This method achieves an error rate below 0.5% under healthy conditions, demonstrating its potential for simple implementation in industrial BSMs for ITF detection.

With the growing demand and projected shortage of rare earth elements in the near future, the urgent task of developing energy-efficient electrical equipment with less dependence on rare earth magnets has become paramount. The use of permanent magnet-assisted synchronous reluctance motors (PMaSynRMs), which reduce the consumption of rare earth magnets, can help solve this problem. This article presents a theoretical analysis of the characteristics of PMaSynRM in a subway train drive. Options with rare earth and ferrite magnets are considered. Optimization of the motor designs considering the train movement cycle is carried out using the Nelder-Mead method. Characteristics of the motors, such as losses, torque ripple, and inverter power rating, as well as the mass and cost of active materials, are compared.

Abstract Due to the application of only one voltage vector in a control period, conventional model predictive torque control (MPTC) suffers from relatively large steady‐state ripples. The‐state‐of‐the‐art double‐vector‐based MPTC (DVMPTC) was proposed to improve steady‐state performance. However, its duty cycle optimization method significantly affects the control performances. Thus, MPTC with hybrid mode duty cycle optimization is proposed, which realizes better performance than the universal DVMPTC, and obtains the appropriate average switching frequency, especially at high‐speed domain. The proposed method utilises the universal DVMPTC method, while it equips duty cycle optimization with discrete space vector modulation (DSVM) scheme as the additional constraint for further reducing the reference voltage tracking error that exists in DVMPTC. What's more, rotation module and pre‐selection strategies are involved in simplifying the design of vector selection methods. Comparative simulations and experiments verify the effectiveness of the proposed method.

Abstract In this article, a hybrid analytical model for a quasi‐regular polygon rotor (QPR) is proposed. It mainly uses the subdomain method and conformal mapping to solve a non‐circular boundary in the QPR. Firstly, the subdomain method combined with an equivalent surface current method is used to calculate the air‐gap magnetic field considering a slotted stator with a circular rotor. Secondly, by segmenting the non‐circular boundary in the QPR, the complex relative air‐gap permeance of the QPR can be calculated using the conformal mapping. Thirdly, this complex relative air‐gap permeance modifies the air‐gap magnetic field calculated in the first step to obtain the actual magnetic field distributions. Consequently, no‐load and loaded air‐gap flux densities, back‐electromotive force and torque can be obtained. A 12‐pole/3‐phase permanent magnet motor is modelled using the proposed hybrid analytical model, which is validated by finite‐element analysis and experiment. This proposed hybrid analytical model presents a new way of processing the QPR. Its calculation speed is nearly 50 times faster than the finite‐element analysis, which is of great help to the initial design and optimisation of machines with QPRs.

Abstract A computationally efficient time‐harmonic finite element model for the steady‐state analysis of a brushless doubly fed induction machine (BDFIM) is proposed. In the model, the electromagnetic couplings of the BDFIM are described by means of the sum of two complex magnetic vector potentials that represent the two fundamental harmonic time components of the magnetic flux density distribution in the rotor frame of reference. As in an ordinary induction motor, the non‐linearity of the magnetisation characteristic is accounted for using an effective magnetic permeability. For the BDFIM, this is derived by considering the features of modulated magnetic flux density waveform. The accuracy of the approach has been validated by comparing the characteristics of a D270 machine operating in the double‐feed mode with ones obtained from the experimentally verified time‐stepping model at various operating conditions. High accuracy of the results coming from the proposed model is demonstrated even under deep saturation conditions within the magnetic circuit.

Abstract Here, a modified magnetic equivalent circuit model which can accurately consider the air‐gap region is presented. The main defect of magnetic equivalent circuit model is in the modelling of air‐gap region. To solve this problem, a new approach based on conformal mappings is presented to accurately calculate the air‐gap permeances between the elements of stator and rotor while considering the real paths of flux tubes in air gap. The distributions of equivalent virtual currents on the both sides of air gap are obtained through modified magnetic equivalent circuit model, which represent the effects of slots, magneto motive force drops in iron parts, and magneto motive force sources. The conformal mapping method is then used to calculate the components of air‐gap magnetic field for every operating point under starting conditions and different loads. One typical cage‐rotor induction motor, which is used in electric submersible pumps, is considered to investigate the accuracy of modified magnetic equivalent circuit model. Some of the analytical results obtained through modified magnetic equivalent circuit model are verified by comparing with the corresponding results obtained from finite element method and experiment set up.

Abstract An analytical method is proposed to model the magnetic field distribution across a slotless tubular interior permanent magnet machine. In order to consider the permeability of both permanent magnets and iron poles of the slider, in the proposed approach, instead of choosing each one as an individual sub‐domain, they are taken as an integrated sub‐domain. Therefore, the governing partial differential equation alters from Poisson equation to the governing magnetostatics equation for inhomogeneous (space‐dependent permeability) materials. The solution is derived through separation of variables method in which a Sturm‐Liouville problem is encountered. The solution and its important mathematical properties, such as the orthogonality and generalised Fourier series, are fully addressed. These properties are very helpful for creating linear interface equations in terms of the integral coefficients. In addition, since the number of sub‐domains is decreased, the total number of the unknowns of the final matrix of equations is reduced effectively. To validate the proposed method, a case study is simulated by the aid of computer software and its results are compared with those of finite element method. It has been observed that the results are in good agreement.

Abstract A permanent magnet synchronous machine (PMSM) temperature estimation method fusing the classic lumped‐parameter thermal network (LPTN) and the stator sensor temperature information is investigated. With respect to the industrial servo applications, it is important to monitor the rotor magnet temperature to extend the machine thermal utilisation. A simple LPTN is developed and the quadratic programming is applied to identify the model parameters. The research work shows that the rotor temperature is sensitive to the rotor speed even at low speeds, and this simple estimation network can provide an accurate estimation. The winding sensor information can further improve the performance. A compound mechanism is built, by which the winding temperature estimation error is used as feedback to suppress the model‐based temperature estimation error accumulation. The estimation performance is compared with a regular constant LPTN‐based method. Experimental results based on a PMSM are presented to validate the proposed method.

Abstract Wind energy as the cleanest source of renewable energy requires a highly efficient lightweight generator that provides maximum power density while having the least vibration noise and maintenance. In this study, an axial air gap transverse flux machine is presented, and all excitation sources are located in the stator. This structure provides lower core loss, weight and cost due to the full utilisation of the permanent magnets, SMC‐free structure and short magnetic flux path. In fact, by combining the features of a flux‐switching machine into a transverse flux generator with an axial air gap, it is possible to improve the performance of a direct‐drive wind turbine generator by overcoming traditional structures' challenges. To analyse the axial transverse flux switching permanent magnet generator performance characteristics, 3D finite element simulations have been performed, which have been validated by comparing them to the practical results of a single‐phase prototype. The results are in agreement with an acceptable error that is caused by manufacturing uncertainties.

Motors with rare earth permanent magnets are the most compact and energy efficient in most applications. However, their use as traction motors for off-highway vehicles, such as mining dump trucks, is challenging not only because of the high cost of the magnets, but also because of the difficulty of providing a wide range of constant power speed control due to the unregulated permanent magnet flux. For this reason, induction motors remain the most popular type of motor for hybrid and all-electric mining dump trucks. However, the use of an induction motor results in increased power loss, increased current, and high temperature ripple of the power switches of the solid-state inverter when stopping on a slope with an electric brake. In this article, a theoretical comparison between an induction motor (IM) and a magnet-free wound rotor synchronous motor (WRSM) with a rotor DC-excitation in a mining dump truck drive is presented. Both motors have an identical stator outer diameter, and their geometry is optimized using the Nelder-Mead method. 2D finite element analysis in the time domain is used to calculate the IM characteristics. Steady-state characteristics of the motors such as efficiency, losses, torque ripple, required inverter power, dimensions, weight and cost of active materials are compared. In addition, losses and temperature ripples in the power modules of the semiconductor inverter, which affect the reliability of the drive, are compared when using the considered motors. The study demonstrates that the WRSM offers significant benefits such as reduced power loss, inverter power requirement, cost and mass of active materials, making it promising for use in mining trucks.

Abstract To pursue high‐performance motor drive, the current regulators are designed directly in the discrete domain. However, few kinds of research are developed to achieve arbitrary poles placement simply. To fill this gap, the authors propose a discrete‐time current regulator consisting of two parts: the main regulator used to obtain decoupling control of dq axes currents, and the bi‐proper compensator applied to realise arbitrary poles placement. To strengthen the anti‐disturbance ability of the current regulator, the active resistance is added to the inner feedback path. Combining the active resistance, a new zero‐order‐hold equivalent motor model is developed, based on which the main regulator is designed using the zero‐pole cancellation method. Furthermore, in this way, decoupling control for the two control objectives of reference tracking and anti‐disturbance is realised. To achieve fast tracking response and negligible overshoot, an easy‐to‐implement scheme that simplifies the tuning of the current regulator is proposed based on the arbitrary poles placement. Moreover, the current regulator can be treated as a two‐degree‐of‐freedom controller with this scheme. Finally, the effectiveness and reliability of the proposed current regulator are validated by the simulation results and experimental results in an alternating current machine drive platform.

Principle of sequential excitation for stator windings of switched reluctance motor (SRM) causes many problems including torque ripples and substantial requirement for rotor position sensing. This paper presents an online torque sharing function (TSF) to minimize the undesirable torque ripples in SRM which operates under sensorless drive system. In classical TSF, variance between incoming and outgoing motor torque responses makes tracking of motor torque to reference torque cannot be achieved. Moreover, the TSFs are mainly designed for operating at rated speed. As motor speed changes, the torque ripples increase because the commutation period (CP) becomes inappropriate for commutation process. The proposed TSF is designed to guarantee the good matching between the motor torque response and TSF reference. So, a linear function is chosen as a torque reference for the incoming phase while an exponential function is selected for the outgoing phase. Additionally, the online tuning of commutation period is employed in the proposed hybrid TSF. The sliding mode observer (SMO) based model is formulated for rotor position and speed estimations purpose. The performance of the modified TSF is validated throughout computer simulations and experimental results. Furthermore, the comparisons between the proposed TSF and conventional TSF are carried out.

Abstract The phenomenon of imbalance is a variation of voltage and current waveforms from a perfect sinusoidal waveform, which is considered a crucial challenge in power systems. Uneven loads and disturbances result in three‐phase voltage/current unbalance that leads to a temperature rise and low output curves at synchronous machines. Thus, the unbalance/fault must be recognized and avoided. This article suggests a methodology to detect and evaluate three‐phase voltage and current unbalance/fault using a coherence algorithm. The suggested scheme develops integrated protection functions that can be divided into three modules: voltage unbalance, current unbalance, and power factor unbalance. Therefore, it can be useful in mitigation techniques applied to compensate the voltage unbalance effects. The present protection introduces a new proposal of closed‐tripping curves based on the values range of nine coherence factors. To investigate the protection performance, a segment of power grid with real parameters’ information is simulated utilizing ATP platform. Several fault types, such as shunt and series faults, are conducted on the simulated system to analyze the results and monitor the system status using the coherence statistic processed in MATLAB software. The results show that the approach is smart, swift, precise, reliable and stable. Moreover, the algorithm can be practically implemented, and represents a base for digital unbalance/fault detectors and relays because its performance is superior in detecting Power Quality Disturbances (PQDs).

Abstract The twisted structure of strand is ignored and the resistance of all parallel copper strands is assumed to be at the same temperature in existing temperature estimation method of water cooling stator windings. However, the twisted structure leads to the changing of thermal source and cooling structure, the uneven thermal distribution of parallel copper strands leads to uneven resistance distribution, both of which will influence thermal distribution of stator windings and should be considered in the temperature estimation method. In this study, the temperature estimation method considering twisted structure and uneven resistance distribution is first proposed, called three‐dimensional (3‐D) network method, in which the nodes of circuit network and thermal network are completely consistent. Then, the water cooling stator winding of a 1240‐MW turbo generator is taken as an example, the thermal distribution of which are calculated by the proposed method and validated by both short‐circuit type test data and 3‐D finite element method (FEM). Finally, the influence of twisted structure and resistance distribution on the thermal distribution is analysed in detail. The results show that the twisted structure has a great effect on thermal distribution, which cannot be ignored, while the resistance distribution has little effect on thermal distribution.

In this paper a novel Inset Permanent Magnet Consequent Pole Synchronous Machine (IPMCPSM) with H-type modular stator core for higher average torque ( $T_{a}$ ), torque density ( $T_{d}$ ), power density ( $P_{d}$ ) and efficiency ( $\eta$ ) with features of reduced torque ripple ratio ( $T_{r}$ ) and harmonics content in back-EMF ( ${\mathrm {EMF}}_{THD}$ ) are proposed. Detailed static analysis of the proposed IPMCPSM under variable flux gaps at all and alternate stator teeth is investigated. Performance analyses disclose that with variable flux gaps in proposed IPMCPSM, beside improved flux weakening capability due to flux focusing effects, electromagnetic performance is greatly improved. Additionally, due to physical isolation of the adjacent phase modules with modular topology, mutual flux influence is de-coupled that improve phase self-inductance to mitigate the short-circuited current under fault condition whereas mutual flux decoupling mitigates mutual inductance that ultimately improves overall machine fault-tolerant capability. Furthermore, effectiveness of the proposed IPMCPSM with H-type modular stator is elaborated with comparative study of conventional E-core and C-core topologies. Detailed comparative analysis reveals that proposed IPMCPSM suppresses ${EMF}_{THD}$ , improve $\eta $ by 18.9%, diminish $T_{r}$ up to 55% and boost $T_{a}$ and $P_{d}$ maximum up to 2.66, 2.59 times, respectively with enhanced flux focusing effects and fault tolerant capability.

Abstract There is an urgent need to develop a robust capacitor charge power supply (CCPS) system to meet the requirement of pulsed load in all‐weather mobile occasions such as vehicle, ship and aircraft. Brushless doubly fed alternator (BDFA) works through the rotor's pole pairs' transformation to get excitation indirectly, without magnets, brushes and slip rings. Both DC and AC excitation can be used. Therefore, it has high reliability and a good application prospect in the CCPS system. However, the existing research studies lack analysis of the parameters that affect charging performance, and have no experimental analysis of the prototype. To solve this problem, a comprehensive design method and experimental procedure of the pulsed BDFA are proposed and investigated. First, the operation principle of the pulsed BDFA is illustrated. Then, the charging performances under different design schemes are comparatively analysed through the finite element analysis (FEA). Finally, a prototype of the pulsed BDFA is manufactured, and the related experiments are carried out. The results verify the feasibility of the experimental procedure and the accuracy of FEA. The comprehensive design method and experimental procedure in this work provide a straightforward reference for the subsequent applications in the CCPS system.

This article proposes a compensation method for gain and offset errors in the current sensing of three-phase AC machine drives with three current sensor measurements during exact or close to standstill conditions. Errors are treated sequentially based on the elliptical trajectory method, a mathematical manipulation by demodulating faulted time-varying $d,q$ currents using the machine position. As three current sensors are used, a correction factor through measured neutral current is proposed such that the impact of machine resistance deviation and inverter non-idealities are minimized. The method does not incorporate any additional hardware, making it low-cost and straightforward in its implementation. It is proposed as a tool for initial commissioning before the machine runs. It is robust to rotor position perturbations and does not need a mechanical lock for compensation in standstill conditions. The effectiveness of the suggested approach is shown by analysis, modelling, and experimental findings acquired from a hardware prototype by mimicking the actual use of high-precision mechatronics.

Permanent Magnet Linear Flux Switching Machines (PMLFSMs) are potential candidates when higher thrust force ( $\boldsymbol {T}_{ \boldsymbol {F}}$ ) and low cost are the primal requirements. However, conventional PMLFSMs shows flux leakages and utilizes high Permanent Magnet (PM) volume ( $\boldsymbol {V}_{ \boldsymbol {PM}}$ ) that increase overall expense. Therefore, this paper proposed novel Segmented PM Consequent Pole Linear Flux Switching Machine (SPMCPLFSM) with flux bridges. In comparison with PMLFSM, the proposed SPMCPLFSM diminish detent force by $\boldsymbol {20.41\%}$ , suppress thrust force ripples by 27.68%, reduces ripple ratio by 1.77 times, improve $\boldsymbol {T}_{ \boldsymbol {F}}$ to 2 times and boost $\boldsymbol {T}_{ \boldsymbol {F}}$ density to 2.64 times utilizing 75% PM volume and reducing PM cost by 24.16%. Moreover, to overcome computational complexity and computation time, analytical model uniting Lumped Parametric Magnetic Equivalent Circuits, vector potential and Maxwell Stress Tensor method are utilized for open circuit flux linkages, magnetic flux density, detent force and thrust force. Finally, analytical model is validated with finite element analysis (FEA) that show good agreement with FEA. Thus, authors are assured to suggest analytical techniques for early design purpose and proposed SPMCPLFSM for roller coaster application.

The converter switching in variable-frequency drives can generate high frequency common mode voltage between the machine winding and the converter ground, leading to high frequency parasitic currents which can flow through the machine bearings unless precautions are taken in design and installation. These parasitic and unintended currents in the bearings cause deterioration of the lubrication film and surface damage to the rolling elements of the bearings. These problems will be exacerbated as wide-bandgap semiconductors with faster switching rise times start becoming more widespread in variable-frequency drives. This paper reviews the modelling and mitigation techniques of high frequency bearing currents in inverter fed AC drives. It aims to provide a solid base for the research community to further understanding the bearing currents phenomenon and helping to find novel improved technique for their mitigation and measurement.

In this paper a novel outer-rotor consequent pole permanent magnet machine (OR-CPPMM) with H-type modular stator core is proposed for higher average torque ( $T_{avg}$ ), flux linkage ( $\Phi$ ) and efficiency ( $\eta$ ) whereas low cogging torque ( $T_{cog}$ ), torque ripple ( $T_{rip}$ ) and harmonics content in flux linkage ( $\Phi _{THD}$ ) and back-EMF ( ${\mathrm {EMF}}_{THD}$ ). The proposed OR-CPPMM is investigated with different stator flux gaps width for static and dynamics electromagnetic performances. Analysis reveals that flux gaps in H-type stator core not only improve electromagnetic performance i.e., $\Phi $ is enhanced by 10.23%, $\Phi _{THD}$ is suppressed by 80.65%, diminished ${\mathrm {EMF}}_{THD}$ by 59.37%, truncate $T_{rip}$ by 44.37% and improve $T_{avg}$ by 15.99% but also exhibits better flux focusing effect to enhance flux linkage and diminish harmonic contents. In addition, H-type modular stator structure provide physical isolation of adjacent phase that de-couple the adjacent phase coupling flux which enhance self-inductance and weaken mutual-inductance and hence improve fault tolerant capability. In addition, to elaborate effectiveness of the proposed design and justification of OR-CPPMM novelty with H-type modular stator, electromagnetic performance is extensively compared with existing state of the art including E-core and C-core structure. Analysis and comparison with state-of-the-art reveals that proposed OR-CPPMM enhanced $\Phi $ by 65.35%, diminish $\Phi _{THD}$ by 67.24%, truncate $T_{cog}$ by 96.72%, suppresses ${EMF}_{THD}$ by 44.40%, diminish $T_{rip}$ by 77.23% whereas $T_{avg}$ is enhanced by 91.69%. Furthermore, the proposed design novelty is justified with comparison of OR-CPPMM with inner rotor and dual rotor permanent magnet flux switching machines. Comparison and analysis unveil that OR-CPPMM exhibits $T_{avg}$ higher up to 35.16%, truncate $T_{rip}$ up to 32.88%, enhanced $\Phi $ up to 22.13% and boost $T_{den}$ to 3.41 times at the cost of 2.58% increase in $T_{rip}$ .

This paper deals with medium frequency resonance effects in electrical machine windings, which can be excited by harmonic components of voltage source converters. The topic is getting more and more relevant with steadily increasing switching frequencies. For squirrel-cage induction machines with form-wound coils an algorithm is presented, which allows the prediction of first machine differential mode resonance frequencies already at design stage. Examples of the experimental model verification and interpretation of resonance frequencies complete the article.

A robust design in electrified powertrains substantially helps to enhance the vehicle's overall efficiency. Robustness analyses come with complexity and computational costs at the vehicle level. The use of sensitivity analysis (SA) methods in the design phase has gained popularity in recent years to improve the performance of road vehicles while optimizing the resources, reducing the costs, and shortening the development time. Designers have started to utilize the SA methods to explore: i) how the component and vehicle level design options affect the main outputs i.e. energy efficiency and energy consumption; ii) observing sub-dependent parameters, which might be influenced by the variation of the targeted controllable (i.e. magnet thickness) and uncontrollable (i.e. magnet temperature) variables, in nonlinear dynamic systems; and iii) evaluating the interactions, of both dependent, and sub-dependent controllable/uncontrollable variables, under transient conditions. Hence the aim of this study is to succinctly review recent utilization of SA methods in the design of AC electric machines (EM)s used in vehicle powertrains, to evaluate and discuss the findings presented in recent research papers while summarizing the current state of knowledge. By systematically reviewing the literature on applied SAs in electrified powertrains, we offer a bibliometric analysis of the trends of application-oriented SA studies in the last and next decades. Finally, a numerical-based case study on a third-generation TOYOTA Prius EM will be given, to verify the SA-related findings of this article, alongside future works recommendations.

An optimally designed line-start permanent magnet synchronous machine may require a different squirrel-cage design than traditional induction machines. The objective of this paper is to apply topology optimization based on the normalized Gaussian network in order to find the optimal shape of the rotor bars for a line-start permanent magnet synchronous machine. This approach facilitates optimizing the shape of the bar, without the limitation of a predefined bar geometry and arrangement, as is usually considered for classic induction machine design. For this study, a previously designed four-pole line-start permanent magnet synchronous machine with a rated power of 1.5kW is used as an initial design. To verify the accuracy of performance evaluation by utilizing finite-element methods, a prototype of this machine was built and tested. Then, verified model of line-start permanent magnet machine is used for topology optimization of its rotor cage area. The outcome of the optimization is the Pareto front, from which three optimized designs are selected. Finally, these designs are analyzed and proved to have better steady-state performance than the initial machine. The results provide new insights for the design of squirrel-cage bars for line-start permanent magnet synchronous machines.

Computational complexity, magnetic saturation, complex stator structure and time consumption due to repeated iteration compels researchers to adopt alternate analytical model for initial design of electric machines especially Switched Flux Machine (SFM). To overcomes the abovesaid demerits, In this article alternate analytical sub-domain model (SDM) for magnetic field computation in Segmented PM switched flux consequent pole machine (SPMSFCPM) with flux bridge and flux barriers accounting boundary and interface conditions, radial magnetized PMs (RM-PMs) and circumferential magnetized PMs (CM-PMs), interaction between stator slots and inner/outer rotor topologies is proposed. Overall field domain is divided into air gap, stator slots and Permanent Magnet (PM) accounting influence of CM/RM-PMs under no-load and on-load conditions. Analytical expression of field domain is obtained by solving magnetic vector potential utilizing Maxwell’s equations. Based on the magnetic field computation especially no-load and on-load condition, Magnetic Flux Density (MFD) components, open-circuit flux linkage, mechanical torque and cogging torque are computed utilizing Maxwell Stress Tensor (MST) method. Moreover, developed analytical SDM is validated with globally accepted Finite Element Analysis (FEA) utilizing JMAG Commercial FEA Package v. 18.1 which shows good agreement with accuracy of ~98%. Hence, authors are confident to propose analytical SDM for initial design of SPMSFCPM to suppress computation time and complexity and eliminate requirements of expensive hardware and software tools.

Unique double salient structure of Permanent Magnet Flux Switching Machines (PMFSM) with both Concentrated Armature Winding (CAW) and Permanent Magnet (PM) on stator attract researcher's interest for high speed brushless application when high torque density (T den ) and power density (P den ) are the primal requirements. However, despite of stator leakage flux, high rare-earth PM usage, PMFSM is subjected to slot effects due to presence of both PM and CAW in stator and partial saturation due to double salient structure which generates cogging torque (T cog ), torque ripples (T rip ) and lower average torque (T avg ). To overcome aforesaid demerits, this paper presents Partitioned PM (PPM) Consequent Pole Flux Switching Machine (PPM-CPFSM) with flux barriers to enhance flux modulation, curtail PM usage and diminish stator leakage flux which reduces slotting effects and partial saturation to ultimately reduces T cog and T rlp . In comparison with the existing state of the art, proposed PPM-CPFSM reduces 46.53% of the total PM volume and offer T avg higher up to 88.8%, suppress T rlp maximum up to 24.8%, diminish T cog up to 22.74% and offer 2.45 times T den and P den . Furthermore, torque characteristics of proposed PPM-CPFSM is investigated utilizing space harmonics injection i.e. inverse cosine, inverse cosine with 3 rd harmonics and rotor pole shaping techniques i.e., eccentric circle, chamfering and notching. Detailed electromagnetic performance analysis reveals that harmonics injection suppressed T cog maximum up to 83.5%, T rip up to 40.72% at the cost of 4.71% T avg . Finally, rotor mechanical stress analysis is utilized for rotor withstand capability and 3D-FEA based Coupled Electromagnetic-Thermal Analysis (CETA) for thermal behavior of the developed PPM-CPFSM. CETA reveals that open space along PPM act as cooling duct that improve heat dissipation.

This paper proposes an adaptive flux observer for a sensorless switched reluctance motor. The observer adaptive gains are designed using the Lyapunov theory to guarantee both the accuracy and stability of the sensorless control of a switched reluctance motor. A nonlinear inductance model is developed based on a finite element analysis data and used in the estimation algorithms for rotor position and speed. The adaptive flux observer estimates the rotor position at low, medium, and high speeds. A low-frequency ramp method is proposed to excite the switched reluctance motor during standstill where the voltage and current signals are unobservable. The proposed hybrid method is characterized by simplicity, accuracy, ease of implementation, and low real-time computation burden. Therefore, the sensorless control technique depends only on active phase measurements without extra hardware and memory storage for real-time implementation. Complete sensorless control of a three-phase 6/4-pole switched reluctance motor drive system is carried out using Matlab/Simulink. Also, it is implemented experimentally in real-time using the digital signal processor-DS1102 control board. The simulation and experimental results of the proposed sensorless scheme demonstrate the accurate estimation of both the speed and rotor position during the transient and steady states.

In this paper, a fault-tolerant three-phase induction drive based on field-oriented control is studied, and an analytical approach is proposed to elucidate the limitations of FOC in flux-torque regulation from the controller perspective. With an open-phase fault, the disturbance terms appear in the controller reference frame and degrade the controller performance when operating in a d-q plane with DC quantities. In addition, the hardware reconfiguration, which is essential to operate faulted three-phase drives, causes substantial change in the way the control parameters vd, vq are reflected onto the machine terminals. An accurate understanding of the feedforward term, by considering the open-phase fault and the hardware modifications, is provided to re-enable the FOC in presence of an open-phase fault. Furthermore, the concept of feedforward term derivation is generically extended to cover multiphase induction drives encountering an open-phase fault whereby no hardware reconfiguration is intended. The proposed method is explained based on a symmetrical six-phase induction and can be extended to drives with a higher number of phases. The effectiveness of the proposed derivation method, which is required to form a feedforward fault-tolerant controller, is verified and compared through the simulation and experiment, ensuring smooth operation in postfault mode.

This paper presents a practical thermal model of a synchronous generator for high-power applications. This model couples the lumped parameter thermal network and coolant network together to utilize the impact of the coolant’s temperature rising over the machine. Furthermore, the advanced multi-planes technique provides a more precise and higher resolution temperature distribution of various machine sections. Therefore, the machines are divided into five planes; three belong to the active part, and two are added to model the machine’s drive and non-drive end-regions. Furthermore, the paper pays special attention to describing the challenges and providing solutions to them during the heat transfer modeling and analysis. Finally, the analytical model is verified using experimental results on a synchronous generator with a salient pole rotor and an open self-ventilation (OSV) cooling system by comparing the analytical and experimental results. As a result, good correspondence between the estimated and measurement results is achieved.

Synchronous homopolar motors (SHMs) have been attracting the attention of researchers for many decades. Various mathematical models of SHM have been proposed to deal with its complicated magnetic circuit. Among them, there are time-consuming 3D finite element models (FEM), equivalent circuit models neglecting some significant features of the machine design, and 2D FEM models with virtual excitation winding distorting its magnetic field picture. This paper proposes a novel 2D FEM of SHM and shows that since there are no sources of excitation in the cross-sections of the rotor and stator stacks, no virtual elements are required. This model uses the general solution of the Gauss's law for magnetism containing excitation flux. The model is based on a set of magnetostatic boundary value problems for various rotor positions. The set of boundary problems is completed with the excitation equivalent circuit. The losses in the armature and field windings and the stator and rotor magnetic cores are computed in postprocessing. All these computations are carried out for a single combination of stator and rotor stack. A symmetrization algorithm is proposed to extend the obtained results to the whole SHM. A comparison of the theoretical and experimental data for a nine-phase three-section 320 kW SHM is carried out. These SHMs were used in a mining truck with a carrying capacity of 90 tons.

In this paper, the fault-tolerant capability in terms of inductance profile of a dual-stator permanent magnet brushless AC machine is presented. Similarly, its power-speed and torque-speed characteristics are also predicted. Special reference is made to the impact of different rotor pole numbers. A 2D-finite element analysis (FEA) procedure is adopted in this work, and the cross-coupling effect of the machine inductances owing to the influence of direct-axis and quadrature-axis currents is also taken into consideration. The results show that, the investigated machine having odd number of rotor poles would exhibit better fault-tolerant capability compared to their counterparts with even number of rotor poles. Further, the machine having 6-stator slots and 13-rotor poles i.e. 6Slots-13P machine has the greatest field-weakening potential owing to its high full-speed to rated speed relation. The studies also show that, the investigated machines have negligible reluctance torque due to their basically unity saliency ratios obtained from the machines’ almost similar quadrature-axis inductance, Lq, and direct-axis inductance, Ld, values.

This paper proposes a variable width reduced rib rotor structure for Synchronous Reluctance (SynRel) Motor. In convention supporting iron ribs are introduced in transversally laminated anisotropic (TLA) type rotors of SynRel motor to increase the robustness of the rotor structure for high speed operations. However, the presence of these ribs degrades the electromagnetic performance of the motor such as saliency ratio and average output torque due to the flux path oriented along q-axis, through the rib area. Hence, the selection of appropriate shape and number of support ribs are essential to ensure the robustness of the rotor without much affecting the required torque density. Present paper uses Finite Element Analysis (FEA) to study electromagnetic as well as mechanical performance of SynRel motor. Rotor structure employing variable width for radial ribs is proposed. The use of variable width in radial ribs decrease the inductance oriented along q-axis, thus improving the saliency ratio and average output torque of SynRel motor. A 1 kW prototype is fabricated for the proposed rotor structure. A detailed comparison between the conventional and proposed rotor structure is also presented to demonstrate the advantages of the latter for high speed and high torque density applications.

In this paper, two well-known topologies of proposed Double Sided Field Excited Linear Flux Switching Machine with Segmented Secondary (FELFSMSS) i.e. Dual Stator and Dual Mover are quantitatively compared with a valid decision of selecting Dual Stator FELFSMSS (DSFELFSMSS) based on low numerical values of detent force, thrust force ripples, and normal force, and high values of open circuit flux linkage, average thrust force, and thrust force density. In order to uplift overall thrust force profile of selected DSFELFSMSS at the rate of minimum thrust force ripple ratio, geometry based deterministic optimization and appropriate selection of AC and DC current density approach is adopted. Finally, a novel technique of auxiliary end tooth DC winding is applied to limit thrust force ripple ratio less than 10 percent.

In order to approximately obtain sinusoidal air-gap magnetic field and get larger radial levitation force of the bearingless permanent magnet synchronous motor (BPMSM), a novel BPMSM with Halbach magnetized rotor is proposed. Firstly, the suspension and rotation mechanisms of the BPMSM are introduced. The control mechanism of producing the radial levitation force in single direction and arbitrary direction is analyzed in detail. The mathematical models of the radial suspension force are given. Secondly, the comparative research on the BPMSMs with the Halbach magnetized rotor and parallel magnetized rotor is carried out. The air-gap magnetic field, back electromotive force (EMF), radial suspension force, and torque are calculated and compared. Finally, the prototype motor equipped with the Halbach magnetized rotor is constructed. Some experimental results are tested and the stable suspension operation of the proposed motor is realized.

In order to effectively suppress rotor periodic synchronous vibration caused by the rotor mass eccentricity and sensor detection error of bearingless induction motor (BIM), a rotor vibration suppression control strategy with improved repetitive control is proposed based on the analysis of the problems existing in traditional repetitive control. On the basis of the vector control model of the BIM system, a simplified suspension control model is derived. The fractional delay filter is used to optimize the repetitive control internal model. Based on the stability conditions of the control system, the design method of repetitive control compensation function in high, middle and low frequency region is given in detail, and the simulation and experimental system of BIM is built. The results show that the vibration suppression control strategy with the improved repetitive control can effectively suppress the vibration of the rotor in steady state and improve the suspension accuracy of the BIM.

This paper proposes a novel combinatorial approach for the optimization design of the asymmetric-paths winding, to solve the design contradiction between the asymmetric degree and the tidiness of end connections. In the proposed approach, the combinatorial models for the arrangement and the connection are built. In addition, some grouping strategies are applied into the combinatorial models, and some matching strategies are provided to deal with the combination of coils among groups for the optimized arrangement. At last, the winding design of a large hydro-generator combing with the electromagnetic analysis is provide for the validation. The results show that the optimized design presents a low asymmetric degree between parallel paths as well as a tidy connection of end windings simultaneously, which are better than the existing designs. This approach provides a novel idea for the modeling and optimization design for the ac windings, especially for the asymmetric-paths windings.

This paper analyses how the type of winding affects the current distribution and power losses in armature winding. Using finite element method, four different types of winding used in large asynchronous motors are analyzed: form-wound concentric, with and without transposition, and form-wound barrel, with and without transposition, for the stationary state. In two cases, the calculation shows clear differences between maximum currents in strands, a shift in their phases, and a resulting increase of AC resistance. In two other cases, minor deviations, smaller phase shift and smaller increase of AC resistance, are detected. It indicates that in certain types of armature winding of large motors the strands transposition leads to significant positive effects in terms of motor power, while in other cases it leads to unnecessary complications making the manufacture of large asynchronous machines more difficult, with relatively small positive effect on the motor power losses.

This paper discusses two methods of altering the harmonic content of the spatial air-gap flux density waveform in synchronous machines (generators and motors). First, fractional-conductor windings are analysed for adoption as a replacement for a conventional distributed winding arrangement, their advantages and disadvantages briefly discussed and an example design scenario presented. Second, analysis and discussion regarding the use of semi-magnetic slot wedges as a replacement for glass-fibre type wedges is presented to complement the choice of winding in synchronous machines. Both methods are shown to benefit machine performance under certain circumstances.