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Axial flux and radial flux cycloidal permanent magnetic gears are characterized by high gear ratios and high torque densities; however, their rotors experience large unbalanced forces, which stress the bearings used in the gear. This paper presents a new cycloidal magnetic gear topology that combines the radial and axial flux topologies. The paper analyzes the forces and torques contributed by the axial and radial magnets in this topology using 3D finite element analysis. It was found that the perpendicular force is necessary to transfer torque to the high-speed shaft and, thus, cannot be cancelled out, but the eccentric component of the magnetic forces can be largely cancelled out, potentially reducing bearing losses and increasing the lifespan of the bearings used in the gear. A proof-of-concept prototype was constructed. Experimental slip torque results matched 3D finite element analysis (FEA) simulations to within 15%, and testing showed that no-load losses were reduced and the slip torque was increased by combining both axial and radial topologies, compared to using an axial configuration alone. [ABSTRACT FROM AUTHOR]

In this paper, the boundary discretization method is used to improve the traditional subdomain model. The improved model can be used to calculate the magnetic field distribution in the region containing non-orthogonal boundary, avoiding the influence of the simplified stator slot or permanent magnet shape on the results in calculating the motor magnetic field using the traditional subdomain model. In addition, the improved subdomain model can also be used to calculate the air-gap flux density when the rotor is eccentric, instead of segmenting the air-gap to an equivalent state without eccentricity. The calculation object of this paper is a surface-mount permanent magnet motor with a rectangular stator slot. The air-gap flux density under no-load and load conditions is calculated, respectively. Since the improved subdomain model does not need to simplify the stator slot shape, the magnetic potential in the stator slot is also calculated. Finally, the air-gap flux density under rotor eccentricity is calculated, and the influence of the calculating parameters on the results of the improved subdomain model is discussed. All the calculated results are compared with those obtained by the finite element method, which verifies the accuracy of the improved calculation model. [ABSTRACT FROM AUTHOR]

Connection of an LC filter to the output of voltage source inverter (VSI) in squirrel cage induction motor (SQIM) drive converts the pulse-width modulated (PWM) voltages into smooth sinusoidal voltages. However, this connection may lead to closed-loop instability in the rotor flux-oriented (RFO) vector-controlled (VC) SQIM system. The closed-loop stability of the combined SQIM + LC filter (SQLC) system is complex and has not been analyzed properly in the literature. In this paper, a detailed closed-loop stability analysis of the SQLC system has been presented based on stability region (SR) and accordingly the PI gains of VC has been designed. The SR method is adopted to derive the common stability regions for the SQIM system and SQLC system. Thereby, the paper proves that connecting an LC filter in-between the VSI and the SQIM system does not always destabilize the closed-loop system. Further, for an SQLC system, the complete range of current controller gains is obtained at various operating points. The frequency-domain specifications have been used to select a proper stabilizing set and the effect of parametric variation of LC filter on the stabilizing set has also been discussed. The experimental results are provided to validate the analysis. [ABSTRACT FROM AUTHOR]

This paper presents a fast analytical model for estimating the components of the PM flux density distribution in the air-gap for a number of interior permanent magnet synchronous machines (IPMSMs). Deriving the two-dimensional (2-D) analytical model for IPMSMs is more challenging compared to that of surface-mounted permanent magnet synchronous machines (SPMSMs) due to the inconsistent geometry of the rotor in polar coordinates. IPMSMs are usually modeled by using 0-D or 1-D methods such as the magnetic equivalent circuit (MEC); however, the MEC method is unable to take into account the tangential component of the magnetic flux density vector. In this paper, a 2-D analytical no-load electromagnetic model for five rotor topologies of IPMSMs is proposed. The effects of the stator slots on the radial component of the PM flux density distribution in the air-gap are then included by defining an air-gap function. The effects of the stator slots on the tangential components of the PM flux density distribution in the air-gap are also considered by injecting virtual surface currents (VSCs) or virtual permanent magnets (VPMs). For verification purposes, the analytical results are compared with those of the finite element method (FEM) and the experimental results of one of the cases. [ABSTRACT FROM AUTHOR]

The excitation system with a multi-phase annular brushless exciter (MPABE) is widely used in large-capacity nuclear power plants. It is of great significance to realize a reliable protection of the exciter for safe operation. Since the MPABE is adopted with rotary armature structure, the rotor winding short-circuit (RWSC) fault is very difficult to be diagnosed directly. However, it is an effective way to realize fault diagnosis through the characteristics reflected in the stator field winding. In this paper, based on the mutual induction relationship between stator current and rotor current, detailed theoretical analysis of the RWSC fault is conducted and the harmonic characteristics of the stator field current are obtained. Then, related experiments and simulations are carried out, verifying the correctness of the theoretical analysis. Finally, a diagnosis method based on the transient harmonic characteristics of the stator field current is proposed and its sensitivity is also analyzed. The diagnosis method proposed in this paper is simple and feasible, which helps to improve the safety and reliability of the MPABE system in nuclear power plants. [ABSTRACT FROM AUTHOR]

A variable reluctance electric machine with a two-degree of freedom rotor motion characterized by rotation around the center of the rotor and orbiting around the center of the stator is studied. One motivation for adopting such rotor motion would be to allow torque generation through both the radial and tangential components of the electromagnetic forces created in the airgap, as opposed to common rotary machines in which torque is a byproduct of only the tangential component of the airgap electromagnetic forces. Furthermore, the rotor motion provides a built-in gearing action similar to that of a cycloidal drive, which allows natural torque multiplication and the tight integration of the electromagnetic and mechanical systems. The two-degree of freedom rotor motion also results in a counter-intuitive inertia characteristic of this machine concept which is elaborated in this paper for the first time. Due to the reluctance nature of the torque, and because of the distinctive rotor motion profile which resembles the motion of a cycloid, the studied machine is called a cycloidal reluctance (CR) electric machine (CRM). In this paper, the principle of operation of the CRM is explained, and its performance is compared to a counterpart switched reluctance machine (SRM). A prototype is built, and the theoretical torque calculations are validated by experimental measurements. [ABSTRACT FROM AUTHOR]

It has been lately shown that, traditional diagnostic approaches for rotor electrical faults detection in induction motors can be dangerously misleading. That is due to many different fault cases that mask the fault signatures thus leading to false negative alarms, or a plethora of harmless conditions that generate signatures similar to the faulty ones leading to false positive alarms. Aiming for reliable fault detection, a new trend has appeared, that of the analysis of the stator current at start-up of the motor. This method proves to be reliable in many cases, however there are still cases where it can lead to false positive alarms especially when applied on motors by diagnostic engineers for the first time. Aiming for a more reliable approach, a new method is proposed in this paper. The proposed novel method consists of the analysis of the zero-sequence current under transient motor operation and specifically the start-up. The paper's findings demonstrate the method's reliability and superiority over the analysis of a single current. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control of a symmetrical six-phase induction generator based on a variable structure strategy is experimentally tested and compared with a classical proportional-integral controller. For this, we use a linear feedback sliding mode controller with switched feedback gains in such a way to control the inner current loops of this machine. One main drawback of the classical three-phase induction generator is that it is no longer possible to generate electrical power if only one phase is lost on the stator side. To overcome this issue, we will use a squirrel cage six-phase induction machine that can still operate when at least three phases remain on the stator side. This article proposes to use a variable structure control in order to cope with unbalanced currents and also maintain the generation of power when a loss of the stator's phases occurs. The proposed controller shows its robustness and good regulation performance in healthy and faulty modes. The simulation and experimental tests were carried out with a 24 kW induction machine that represents 1/100 of the electrical power of a real wind turbine. [ABSTRACT FROM AUTHOR]

The vibration characteristics of stator system of the interior permanent magnet synchronous motor for EV are deeply studied in this paper, the effectiveness of reducing the vibration by optimizing the vibro-inertance (acceleration admittance) of the stator system is validated. Firstly, the theory of the vibro-inertance matrix of stator system with single-point excitation and multi-point response is proposed, and the mathematical theory model of vibro-inertance matrix of prototype motor stator system is established. Secondly, a new method of 3D finite element method (FEM) be used to simulate and analysis the vibro-inertance's characteristics for the prototype's stator system. Then, the correctness of the theory and the FEM simulation is verified by the prototype source-path-contribution (SPC) experiment. And it is found that near some non-natural frequencies with large vibro-inertance amplitudes, although the amplitude of operating force is relatively small at these frequencies, the prototype still produces large vibrations. Finally, three methods for optimizing the vibro-inertance matrix of the stator system are further studied. These methods can effectively shift the inertance frequency band of the stator system and change the average value of the inertance's amplitude of the motor stator system in different frequency bands, thereby changing the vibration characteristics of the whole motor. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of stator/rotor pole number combinations and permanent magnet (PM) numbers on electromagnetic performance of consequent-pole hybrid excited flux reversal machines (CP-HEFRMs), which have different numbers of PM poles and iron poles and concentrated AC and DC windings on the stator and a salient pole rotor. PMs in the slots of one stator pole are magnetized radially in the same direction, while opposite on adjacent stator poles. Magnetic field paths of DC, PM, and hybrid excitations are investigated. The phenomenon of flux cancellation, i.e., PM and DC MMFs in CP-HEFRMs are of opposite polarities in the flux-enhancing operating mode, is revealed and verified, for the first time, as the key feature that makes CP-HEFRMs different from other hybrid excited machines. Consequently, the saturation in stator pole and yoke can be mitigated and hence the overload capability of DC excitation is enhanced, which is verified by finite element analysis (FEA). Global optimizations are utilized to obtain the optimal rotor and stator pole number combinations and PM numbers for each stator pole. Torque, torque ripple, inductance, unbalanced magnetic force, and flux regulation capability are compared for different PM numbers and rotor pole numbers. Comparisons are made on consequent-pole and non-consequent-pole topologies in terms of torque capacity, flux regulation capability, and PM consumption to further illustrate the advantages of consequent-pole topology. A prototype machine is built and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

In this paper, an interior permanent magnet (IPM) machine is presented and optimized for heavy-duty vehicle direct-drive applications. Since efficiency decrease and serious heating come along with excessive core loss under flux weakening control, a rotor topology with the combination of the eccentricity structure and magnetic barriers is proposed. The key is to achieve the comprehensive optimization of the proposed rotor topology to satisfy the different requirements under diverse operating points. Then, a multi-objective automatic parallel optimization method is applied, which simultaneously analyzes multi-condition operation without weight coefficients defined artificially. The 3D Pareto solution set is generated by using nature inspired evolutionary algorithm based on the high-precision metal-modals of optimal prognosis, which reduce the needed computation cost significantly. Moreover, the back electromotive force total harmonic distortion, torque and core loss of the optimal machine are analyzed at corresponding operating points. Finally, the finite-element results are validated by experiments based on a prototype machine. [ABSTRACT FROM AUTHOR]

In this paper, a dual-rotor slotless axial-flux permanent magnet (AFPM) motor with equidirectional toroidal winding (ED-TW) is proposed and compared with the AFPM motor with traditional toroidal winding (T-TW) with the same dimensions, number of coils and poles. Different from the T-TW, only the positive sides of coils of the ED-TW are left on one side of the stator core, the return sides of the coils are all removed to the other side of the stator core. Firstly, the structure and operation principle of the two motors are introduced and analyzed. To clarify the features of the ED-TW, the synthetic electromotive force (EMF) vector and armature reaction field of the ED-TW and T-TW are studied. Secondly, the main size equations of the AFPM motors with toroidal windings are presented. Subsequently, the electromagnetic characteristics of the AFPM motors with ED-TW and T-TW are analyzed and compared based on the three-dimensional finite element method (3D-FEM). The comparison results indicate that the AFPM motor with ED-TW has superiority in torque density and efficiency. Finally, a prototype of the AFPM motor with ED-TW is manufactured and tested, which validates the feasibility of the proposed motor and the correctness of the analysis of the 3D-FEM. [ABSTRACT FROM AUTHOR]

The paper proposes a rotor speed observer for sensorless voltage and frequency control of a standalone doubly fed induction generator (DFIG) system. The proposed speed estimator is designed based on the sliding mode observer (SMO) technique, which makes the estimation algorithm robust under parametric variations and external disturbances. The position of the rotor is computed directly by the integration of the estimated speed by the designed observer. The proposed observer requires the measurements of stator voltage and current to estimate the speed. The design procedure of the observer does not require the mechanical parameters of the DFIG, which makes the observer design independent of the mechanical parameters. Lyapunov stability criteria are used to formulate the sliding gains for the observer. Simulation and experimental results are demonstrated to show the efficacy of the designed observer in terms of accuracy and convergence rate under different steady-state and dynamic conditions. The estimated rotor speed and position are utilized for controlling the magnitude of the stator voltage of a standalone DFIG system, which validates the performance of the observer. [ABSTRACT FROM AUTHOR]

To solve theproblems of an insufficient braking moment for the eddy current retarder at high speed, a small braking moment and slow response of the hydraulic retarder at low speed, and a low power density of the existing electromagnetic hydraulic retarder(EHR), a novel radially distributed electromagnetic-hydraulic retarder(R-EHR) was proposed. The R-EHR fully absorbs the advantages of the braking characteristics of hydraulic retarders and eddy current retarders. The cooling fluid is used to realize the braking of the hydraulic part. At the same time, it acts on the heating surfaces to improve the torque of the electromagnetic part. In this paper, finite element models of the flow field and electromagnetic field are established to predict braking performance. The braking performance of the R-EHR is obtained by bench test, the error between the simulation and experimental data is compared, and the experimental data are analyzed. The results show that the proportion of electromagnetic braking torque in the novel R-EHR is more reasonable. The braking torque increased by 26% and the power density increased by 37.5% at 2000 RPM compared to that of the EHR. The R-EHR can control the braking torque only by adjusting the current, thus simplifying the control system. [ABSTRACT FROM AUTHOR]

A comparative study of new partitioned stator hybrid excitation axial flux switching permanent magnet (HEAFSPM) motors with different partitioned excitation stator topologies for in-wheel traction applications is presented in this paper. The realization approaches of the partitioned stator HEAFSPM motor are discussed, and the motor topology with windings and permanent magnets (PMs) separately setting on different stators is selected in view of the advantageous structure for thermal management. On this basis, two partitioned excitation stator topologies including C-type tooth core and T-type tooth core stator configuration are proposed, and the air-gap flux modulation and flux regulation principle of the motors are analyzed. In addition, the design method of the partitioned stator HEAFSPM motor considering the effect of hybrid excitation sources is provided, and the two motors with different tooth cores are designed respectively. Meanwhile, for a fair comparison, the multiple objectives optimization method coupled with the sensitivity analysis is employed to optimize the two motors. The electromagnetic performances, anti-demagnetization capability, and flux regulation performance of the two motors are all investigated in detail. Finally, two prototype motors are fabricated and tested. Both the theoretical analysis and experimental results verify the effectiveness and reasonability of the motor. [ABSTRACT FROM AUTHOR]

A modified configuration for Permanent Magnet Assisted Synchronous Reluctance Motors (PMaSyRM) is studied in this paper. Conventionally, the PM materials are inserted in the flux barriers region of the rotor. Consequently, the PMs sizing parameters will be restricted to the available space that may limit the efficient use of PMs benefits. In this study, a portion of the rotor structure is replaced with an Interior PM (IPM) rotor so that an axially segmented integration of IPM and SyRM is obtained. Thus, the PMs design is performed specifically in the IPM segment independent of the SyRM scheme, while the SyRM segment remains PM-less. The main motivation of this concept is to improve the contribution of the PM material in the total torque as well as utilizing the special property of the proposed rotor configuration for pulsating torque reduction. A computationally cost-effective algorithm is proposed for the optimal design of IPM-SyRM motor by which a low-power design is carried out for a lightweight electric vehicle. The results for torque profile characteristics, PM volume, power-factor, and efficiency are compared with a conventional PMaSyRM that has been optimally designed as the reference case. Finally, a prototype is constructed to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a novel six-phase outer rotor induction motor equipped with pseudo-concentrated windings is introduced as a robust, reliable, and low-cost solution. Multiple aspects of the proposed motor structure have been investigated such as a design algorithm and an analytical modeling based on the modified winding function considering the skew effect. The effect of using variable number of turns for the coils has been examined on the pseudo-concentrated windings. An appropriate optimization problem has been also defined to maximize the power factor and efficiency and to minimize the output torque ripple. The designed motor has been fabricated to verify the accuracy of the design procedure with an analytical model and a finite element analysis. Experimental results show superior performances for the designed motor. [ABSTRACT FROM AUTHOR]

Rotor fault is a condition that may occur in induction motors due to high forces and stresses on rotor bars or end rings. When this occurs, the machine may lead to a forced outage in production lines. Several methods have been proposed in the literature for the detection of rotor faults; however, they cannot work under variable frequency conditions, and they are very sensitive to mechanical load oscillations. This paper presents a novel frequency normalization methodology for reliable rotor defect diagnosis in variable-frequency drive-fed systems. The normalization is implemented by demodulating the stator current signal with a time-variant factor. As a result, the fundamental component of the stator current is normalized in a constant frequency value, whereas avoiding spectral leakage and frequency smearing. This enables the transient stator current signature analysis to accurately locate targeted fault signatures. The effectiveness of the proposed frequency normalization approach is demonstrated by analyzing the stator current of motors under non-stationary conditions. Experimental results show that the proposed methodology can detect and distinguish between load oscillations and rotor fault signatures for avoiding false rotor fault alarms. [ABSTRACT FROM AUTHOR]

The torque ripple of a switched reluctance motor (SRM) should be taken into account, as it can have negative effects on a connected gearbox and/or load. In this paper a concept and two realization methods for the reduction of the torque ripple are presented. An optimized alignment of the active elements of the stator leads to a reduction of this torque ripple. The first method proposed here is a four-fold segmented motor, which can reduce the torque ripple by 37.3 %. This can be achieved by segmentation in combination with a clever arrangement of active elements. However, this increases the number of necessary inverters, which increases redundancy and therefore leads to more security. A second method of achieving an equal reduction can be obtained by using a “double stator” motor. In this configuration both stators can be powered together. With this concept, the number of converters is halved compared to the first mentioned solution. This saves electronic components and thus reduces the effort. All results referred to in this article are obtained by simulation, or measured on a prototype. [ABSTRACT FROM AUTHOR]

In this paper, a circulating-current-excited switched reluctance generator system with the diode rectifier is comparatively studied with a field-current-separated switched reluctance generator. By using a DC power source connected in series with the winding to provide the circulating current, a controllable excitation field is established in the proposed generator. To highlight the influence of this DC voltage source, the injected field current of the field-current-separated generator is kept the same as the circulating current of the circulating-current-excited generator. Then, both advantages and disadvantages of the generators are summarized. The circulating-current-excited switched reluctance generator system inherits both the advantages of good reliability of the separated-winding generator by using the diode rectifier and low copper loss of the integrated-winding machine by combining the AC and DC current in one set of windings. Furthermore, two more practically conventional field-current-separated generators are also compared with the proposed generator in terms of the external characteristics. These two conventional generators have different winding configurations. At last, the analysis is verified by experiments. [ABSTRACT FROM AUTHOR]

Motor current signature analysis (MCSA) has been widely used for fault diagnosis of induction motors (IMs) because of its non-invasiveness and comparatively low cost. However, the spectral leakage of the fundamental supply frequency can obscure the fault characteristic component when IMs operating at no-load or low-load conditions. In this paper, a broken rotor bar (BRB) fault diagnosis approach based on the third-order energy operator (TOEO) demodulated current signals is presented. The TOEO approach performs effectively in reducing the negative impact of the fundamental supply frequency spectral leakage and enhancing the BRB fault features. Theoretical and experimental results show that the TOEO approach can excellently reveal the fault characteristic frequency, instead of the sideband frequencies. Besides, the results are compared with the Teager-Kaiser energy operator (TKEO). The capability of the presented approach has several advantages over the TKEO, especially when the IMs are fed by an inverter. [ABSTRACT FROM AUTHOR]

Flux linkage estimation based on the voltage model has been widely employed in surface-mounted permanent magnet synchronous machine (SPMSM) sensorless drives due to its simple implementation. To deal with dc-offset and dc-drift problems, the pure integrator is modified as a programmable low pass filter (LPF)in practice. However, the estimation accuracy of the rotor position is affected by the adopted filter. Although the position deviation is compensated in steady-state based on the frequency characteristics of the filter, the compensation effect deteriorates during a dynamic process which severely degrades the sensorless control performance. In order to effectively tackle this problem, a novel compensation strategy based on the linear extended state observer (LESO) is proposed in this paper. With the constructed LESO in the estimated synchronous rotating reference frame, the position estimation error can be detected and compensated both in the steady and dynamic state. Moreover, the observer is enhanced to improve the estimation accuracy in linear acceleration and deceleration. Finally, the feasibility of the proposed method is verified under various operating conditions with a 5.5 kW SPMSM drive system. [ABSTRACT FROM AUTHOR]

This paper contributes to the characterisation of the brushless doubly fed induction machine (BDFIM), which is attractive as a variable speed generator in applications (off-shore wind turbine) with minimum maintenance requirements. The BDFIM has two three-phase stator windings of different pole numbers housed within the same stator slots and a short-circuited rotor winding capable of coupling fields of different pole numbers. The stator windings and rotor winding create a magnetic field distribution with a range of characteristics different to those of conventional induction machines. This paper presents an analysis to identify the field characteristics and discusses their impact on the analysis and design of the BDFIM. The characteristics are determined from an analysis of the sum of two rotating sinusoidal field waveforms and confirmed by comparison with time-stepping finite element results and measured magnetic flux density data. [ABSTRACT FROM AUTHOR]

A comparative study of five-phase outer-rotor flux-switching permanent magnet (FSPM) machines with different topologies for in-wheel traction applications is presented in this paper. Those topologies include double-layer winding, single-layer winding, C-core, and E-core configurations. The electromagnetic performance in the low-speed region, the flux-weakening capability in the high-speed region, and the fault-tolerance capability are all investigated in detail. The results indicate that the E-core FSPM machine has performance advantages. Furthermore, two kinds of E-core FSPM machines with different stator and rotor pole combinations are optimized, respectively. In order to reduce the computational burden during the large-scale optimization process, a mathematical technique is developed based on the concept of computationally efficient finite-element analysis. While a differential evolution algorithm serves as a global search engine to target optimized designs. Subsequently, multiobjective tradeoffs are presented based on a Pareto-set for 20 000 candidate designs. Finally, an optimal design is prototyped, and some experimental results are given to confirm the validity of the simulation results in this paper. [ABSTRACT FROM AUTHOR]

This paper incorporates the idea of integrated field and armature windings into the design of novel hybrid excited machines with bi-directional flux modulating effect, which results in a new hybrid-excited machine concept that is referred as dual-electrical-port dc-coil-free hybrid-excited machine (DEP-DCF-HEM). In the proposed design, dc field windings are eliminated and dc bias currents are injected into the windings to generate dc excitation field. In addition, the armature windings are divided into dual electrical ports, and zero-sequence current flows between these two ports can adjust the air-gap field effectively. Compared with existing HEMs with additional dc coils, the proposed machines can achieve both higher torque density and wider flux weakening range. The presented design principle can be utilized in a variety of configurations of DEP-DCF-HEMs. Topologies with stator permanent magnet (PM), rotor PM, and dual PM are possible designs, which are all investigated in this paper. A dual PM DEP-DCF-HEM prototype is manufactured, and experimental measurements are conducted to verify its performances. [ABSTRACT FROM AUTHOR]

When the permanent magnet synchronous motor (PMSM) works in the high-speed region with low carrier ratios, the performance of the rotor flux observer has a great influence on the loading capacity and stability of the speed sensorless vector control system. The problem of the adaptive compensation flux observer (ACFO) of the PMSM at low carrier ratios is analyzed in this paper, and an ACFO with a feedback delay component is presented. After retuning the PI regulator parameters, the new expression related to carrier ratio is obtained, which can improve the performance of the flux observer at low carrier ratios and make the torque and current loop response faster. Meanwhile, the stability of different Euler approaches of the integrator for ACFO in the discrete domain is analyzed, and a new Euler with a coefficient is proposed to combine the merits of the backward Euler and the trapezoid Euler. It shows better performance at low carrier ratios. Finally, the effectiveness of the discrete ACFO is verified by experiments. [ABSTRACT FROM AUTHOR]

Switched reluctance motors (SRMs) have attracted much attention in industry due to the advantages of low cost, robust structure, high fault tolerance and high torque density. However, several disadvantages like high torque ripples and coil temperatures hinder their industrialization for some applications requiring high dynamic performance, like electric vehicles (EVs). In this paper, a multiobjective and multiphysics design optimization method considering both thermal and electromagnetic performance is presented for a 12/10 SRM. First, the topology of the SRM is introduced and the optimal parameters are defined. Then, the electromagnetic finite element model (FEM) is introduced and the 3D transient lumped-parameter thermal model (TLPTM), considering both axial and radial heat transfer for the SRM, is proposed. Second, the objectives and constraints of the optimization are determined. To improve the optimization efficiency, the sequential subspace optimization strategy is employed to find the optimal solution of this high-dimensional design optimization problem. Finally, to validate the effectiveness of the proposed method, both simulation and experimental results are given and discussed. Compared with the initial design, the optimal solution exhibits lower temperature, higher torque, lower torque ripple and less loss. [ABSTRACT FROM AUTHOR]

This paper proposes a direct speed and flux control system for Dual Stator Winding Induction Machines (DSWIMs) based on Super Twisting Sliding Mode Control (STSMC). The proposed nonlinear controller which has finite time convergence of error to zero, is designed such that the Lyapunov stability condition is satisfied. Furthermore, a novel torque-sharing algorithm is introduced for DSWIMs. This algorithm enables them to operate in a wide speed region, including zero speed, such that the required electromagnetic torque is supplied by two winding sets based on their power ratings. In addition, a Sliding Mode Control (SMC) based full order observer is proposed for DSWIMs. This observer, which is able to estimate the winding fluxes, flux angles and rotor speed with high-accuracy, guarantees the optimal flux condition. The functionality of the proposed sensor-less DSWIM drive scheme is evaluated through some experimental tests performed on a 3.3 kW DSP-based DSWIM drive system. The experimental results confirm the effectiveness of the proposed control method, torque sharing algorithm and the full order observer in various speed regions. [ABSTRACT FROM AUTHOR]

In this paper, superposition methods including the superposition of a single stator tooth and the superposition of a single rotor tooth, are proposed to predict the open-circuit performances of flux-reversal permanent magnet (FRPM) machines. By the proposed superposition methods, the electromagnetic performances, such as air-gap flux density, electromotive force, cogging torque, and unbalanced magnetic pull (UMP) are investigated and verified by 2D finite element analysis (FEA). Further, according to the superposition methods, cogging torque reduction techniques can be acquired from both stator side and rotor side. In addition, the influence of stator-slot/rotor-pole-pairs (slot/pole) combination on UMP is also studied, and consequently, a reasonable slot/pole combination rule is suggested to avoid UMP. Then, an improved configuration for UMP reduction is also investigated and verified by FEA. Finally, the prototype machines are manufactured and tested to further verify the theoretical analysis and FEA predictions. [ABSTRACT FROM AUTHOR]

For a marine electrical machine, its high power density and large electromagnetic (EM) load tend to bring high saturation to the magnetic circuit. When the non-linearity of ferromagnetic material is not taken into consideration, large errors will appear in the calculation of air-gap flux density and EM force wave. Considering the radial and tangential EM force waves that cause the stator core to vibrate and deform are the primary sources of EM vibration of a non-salient pole synchronous generator (NSPSG), this paper introduces a semi-analytical method of calculating the radial and tangential EM force waves, with the non-linearity of ferromagnetic material taken into account. The method includes the distributed magnetic circuit method (DMCM), the separation variable method (SVM) and the complex variable conformal transformation method (CVCTM). First of all, the radial air-gap flux density is obtained by using the DMCM to calculate the no-load magnetic circuit of the NSPSG and dealing with the non-linearity of ferromagnetic material by B-H curve. Then, the tangential air-gap flux density is calculated by the SVM and the complex relative air-gap permeance is calculated by the CVCTM to determine the effect of slotting. Finally, the radial and tangential EM force waves are obtained by Maxwell stress tensor method. The proposed semi-analytical method is verified through measuring vibration acceleration of the NSPSG. [ABSTRACT FROM AUTHOR]

Winding faults are the most commonly occurring type of fault in offshore doubly-fed generator units. Such faults are difficult to detect and repair, and therefore higher fault identification accuracy is required. Most of the existing research analyzes stator and rotor winding faults separately, but due to the coupling characteristics between windings, it is necessary to analyze doubly-fed induction generator (DFIG) winding faults in a unified way. This paper proposes a general fault diagnosis method that can be applied to both the stator and rotor winding faults of DFIGs. First, a general mathematical model of a windings short circuit of a doubly-fed generator is established. Then, according to the mechanism of a turn-to-turn short circuit fault of a DFIG and the expression of a bilateral flux linkage between stator winding and rotor winding, a new fault feature-bilateral flux linkage difference vector (FLDV) is obtained by mathematical derivation. Finally, the recommended value for an experimental motor of feature quantity is set. The proposed method for inter-turn fault (ITF) diagnosis of stator and rotor windings provides technical support for the sustainable development of offshore wind power. A simulation and experiment prove that FLDV has high sensitivity and high reliability for windings ITF diagnosis. [ABSTRACT FROM AUTHOR]

This paper proposes a monolayer Halbach array based permanent magnet spherical motor (PMSpM) using cubic permanent magnets (PM). The research aims to provide a fast computing model to calculate the magnetic field for this PMSpM, which helps for future PMSpM optimization and control study. Three thickness equivalence principles are provided and compared for cubic PMs. The magnetic scalar potential is introduced, and the spherical harmonics expansion is implemented for rotor magnetic field analysis. Engineering revision is used to reduce the Legendre function deviation in polar angle direction. Torques and forces are deduced using the Lorentz force law, and relatively simple models of this PMSpM for both magnetic fields and torques are acquired. In addition, a prototype motor has been developed, and the analytic results of air-gap flux density and torque are compared with their finite element simulation and experimental results, which are proved consistent. It is concluded that the fundamental component of the spherical harmonics can be used to present the magnetic field model, which uses fewer integrals than the Biot-Savart law based solution, and the modeling results of the magnetic field flux density, forces and torques are in line with the expectations. The analytic models are proved correct. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual-armature (DA) flux reversal permanent magnet (PM) machine with halbach array magnets in the stator slot opening is proposed, which is abbreviated as DA-Halbach machine. Besides the stator armature windings, another set of windings is added in the rotor slots to further enhance torque performance via fully utilizing the rotor space. The influences of major geometric parameters on torque performance are investigated. Both DA-Halbach machine and conventional Halbach machine are optimized with the goal of maximum torque under the same copper loss using finite element (FE) method. The electromagnetic performance of two optimized machines are compared, the results show that the proposed DA-Halbach has larger torque and smaller torque ripple than conventional Halbach machine. When compared with surface-mounted PM machines, the proposed DA-Halbach machine still show better torque performance. [ABSTRACT FROM AUTHOR]

A feasible online test procedure is proposed in this paper to estimate the full set parameters of synchronous generators (SG). The recommended test procedure involves applying step perturbations to one of the power system stabilizer (PSS) inputs like active power or rotor speed, such that the stator and field winding signals change considerably, which makes them suitable for parameter estimation purposes. Furthermore, an accurate approach is suggested to estimate SG's parameters by utilizing the recorded data from the proposed test procedure. The effect of magnetic saturation, which can influence the estimation results, is also taken into account continuously during the parameter estimation. Finally, the proposed test is applied to a 200 MVA gas unit SG, and the parameters are estimated using a Genetic algorithm (GA) from the measurement data. The results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Torque ripple reduction has become an active research area for permanent magnet synchronous machine (PMSM) drives. This paper presents a novel torque ripple reduction method based on harmonic current control. In the proposed method, the optimal harmonic current solution based on the torque ripple model with minimum stator resistive loss is derived in the rotor reference frame (RRF). The optimal harmonic currents are injected by the proposed harmonic current controller (HCC), wherein the magnitude of harmonic currents are defined as controller variables. To estimate the harmonic currents, the proposed method also utilizes the least mean square (LMS) based adaptive filter (AF), wherein the coefficients are defined as feedback to the proposed HCC. The proposed methodology is demonstrated using both simulations and experiments and is verified to reduce torque ripples of PMSM drives over a wide range of speeds. [ABSTRACT FROM AUTHOR]

The brushless excitation structure characteristics of the aviation wound-rotor synchronous starter/generator (WRSSG) put forward the requirement on the brushless exciter (BE) model that both the stator and rotor windings can be interfaced with the external circuit directly. In this paper, a double-side variable-parameter voltage-behind-reactance (DS-VP-VBR) model of the BE considering magnetic saturation was established firstly to realize the direct connection between the stator and rotor windings with external circuits. Then, a double-side constant-parameter VBR (DS-CP-VBR) model with completely decoupled RL circuit was developed through the algebraic transformation and numerical approximation from the DS-VP-VBR model. In order to further improve the model accuracy, the leakage inductance variation of the stator and rotor windings were also considered. Computer studies under steady-state and transient operating conditions verified the validity and accuracy of the proposed BE DS-VBR models. [ABSTRACT FROM AUTHOR]

The thermal modeling and design process of highly utilized electric machines is a complex task. The main heat paths within an electric drive are influenced by a variety of different thermal interfaces, that can mainly be described by thermal conduction and convection. The proper selection and estimation of these design parameters is challenging especially in the early design stage. This paper provides a systematic investigation evaluating inaccuracies and design influences of single thermal resistances, such as the convective heat transfer in the rotor-stator annulus, in the cooling jacket or interfaces between different machine components. Within the study, electromagnetic finite element models and thermal lumped parameter models of two traction drives are developed and validated using test bench measurements. The thermal design parameters are varied in a range resulting from intensive literature research and own laboratory experience. The influence of the design parameters in different operational points of the drives are studied in a sensitivity analysis. [ABSTRACT FROM AUTHOR]

Hybrid excited machines, with synergies of permanent magnet (PM) and wound field (WF) excitations, exhibit high torque density as well as controllable flux and are perceived as promising candidate for variable speed application. A novel doubly salient hybrid excited (DSHE) machine with non-overlapped field winding is presented in this paper. It inherits simple structure of conventional doubly salient PM (DSPM) machine and facilitates the regulation of magnetic field by field winding. The electromagnetic performances of the proposed machine with different stator and rotor pole number combinations are investigated by finite element method (FEM), confirming these advantages. Furthermore, the effect of iron bridge on the hybridization between PM and WF excitations is analyzed to obtain a trade-off between high torque density and wide flux regulation range with the frozen permeability method (FPM). It is revealed that the proposed DSHE machine possesses higher power and fault tolerance at flux weakening region compared with the DSPM machine, albeit with sacrificed torque density and efficiency with introduction of field winding. Finally, a prototype is fabricated and tested to validate the theoretical analyses. [ABSTRACT FROM AUTHOR]

In this paper, the mathematical model of a novel 12-stator-pole/10-rotor-tooth doubly-fed flux-switching permanent magnet (DF-FSPM) machine employing 3-phase stator winding and 5-phase rotor winding is established and analyzed. Firstly, the stator and rotor winding inductance waveforms are analyzed in stator reference frame and modeled as the functions of rotor position considering major harmonic contents. Then, the inductances are transformed from the stator reference frame into the rotor reference frame using two Park transformation matrices, all of which become constants after the transformation. Thereafter, the voltage equation, power equation, torque equation are derived step by step. It shows that the magnetic coupling between stator and rotor windings causes the phase voltages to be affected by both stator and rotor currents. However, the reluctance torque and the torque produced by the magnetic coupling between stator and rotor windings are negligible. Further, the flux weakening capability of the machine is predicted from the voltage and torque equations. The power factors are analytically calculated and compared with the finite-element analysis, which indicates that both the stator and rotor of DF-FSPM machine exhibit high power factors. Finally, experimental validation is carried out on a prototype machine. [ABSTRACT FROM AUTHOR]

In this paper, a novel and non-invasive stator inter-turn short circuit (ITSC) online detection method is presented for an induction machine (IM), driven by a two-level voltage source inverter (2L-VSI) via finite control set model predictive control (FCS-MPC). The main idea of the proposed method is to utilize the controller itself as an observer: under the presence of a fault, the distribution of inverter switching states significantly deviates from the original balanced case. Therefore, by inspecting the inverter switching vectors, which are the outcomes of the FCS-MPC routine's online optimization procedure, a stator fault can be detected efficiently. It is observed that both the zero-vector allocation over the complex plane and the allocation among the active vectors are influenced by the presence of a stator short-circuit fault. The proposed fault detection strategy introduces little to no extra burden for processor and memory. Experimental results verify the proposed method, and inter-turn short circuits of two and three turns are confidently detected and located for a 500 W, two-pole IM. [ABSTRACT FROM AUTHOR]

This paper presents a new control strategy using model-based predictive current control (MB-PCC) for a doubly fed induction machine (DFIM) driven by an indirect matrix converter (IMC). This strategy proposes the control of rotor currents, whose references are calculated from active and reactive stator power set points and the dynamic model of the DFIM. The control strategy works well in the four P-Q operating regions of the DFIM. The grid synchronization process is carried out by setting the P-Q power set points to zero. The results include the DFIM synchronization procedure as well as the active and reactive power control at variable shaft speed to validate the feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

Fractional-slot slot harmonic only windings (SHOW), featured by multi-layer and varied coil turn ratios, contain only the torque-generating component and its slot harmonics in stator magnetomotive force (MMF), which makes them attractive. This paper establishes general design principles of SHOW considering different slot/pole combinations and makes detailed comparisons between SHOW and double layer (DL) windings for surface-mounted permanent magnet (SPM) machines. Firstly, fractional slot windings are classified into several categories. Similarity in distribution factors of MMF harmonics is illustrated, based on which, harmonics elimination principle of SHOW is explained. Then, general equations for calculating optimal coil turn ratios for SHOW are derived. Practical ratios approximating the optimal ones are also presented and evaluated. Furthermore, in order to show the superiorities of SHOW, 12-slot/10-pole (12s10p) and 24S10P SPM machines with SHOW are comprehensively studied and compared with their DL counterparts in terms of torque ripple, overload capability, rotor magnet loss, stator iron loss and radial electromagnetic force harmonics. Finally, 12S10P and 24S10P prototypes with SHOW are fabricated and tested for verifications. [ABSTRACT FROM AUTHOR]

Squirrel cage induction motor is the most widely adopted electrical machine in applications directly fed by the main grid. The analysis, design, and optimization of this machine topology has been addressed by a considerable amount of literature over the last century. Although its wide adoption, the induction motor design, especially when carried out in an automatic fashion, still presents significant challenges because the accurate prediction of the performance requires time-consuming finite element analysis. This work proposes a systematic approach to perform the design optimization of a squirrel cage induction motor focusing on the rotor slot geometry, being this the major player in defining the torque-speed characteristic. Structured as a two-parts companion papers, this first part presents an innovative performance evaluation methodology which allows a very fast estimation of the torque, and efficiency behaviour preserving the results’ accuracy. The proposed performance estimation technique is assessed against experimental tests carried out on an off-the-shelf induction motor. The selection of the performance indexes to be optimized is justified in detail along with the description of a generalized rotor parametrization which allows a comprehensive exploration of the research space. The presented optimization procedure is then applied to a case study, and the preliminary results are commented, highlighting benefits, and drawbacks of the proposed methodology. [ABSTRACT FROM AUTHOR]

This paper presents a technique for estimating the rotor resistance of an induction machine over the machine's entire speed and torque range. This technique is based on injecting a relatively low-frequency carrier signal into the reference of the rotor flux linkage magnitude and extracting the induction machine's response to the carrier signal, which is then used in a model reference adaptive system. This paper also presents a technique to minimize the torque ripple generated by the carrier signal. This technique utilizes the rotor flux linkage reference in conjunction with a proportional-integral-resonant feedback plus feedforward control to generate references for the direct and quadrature axis stator currents. This paper also improves tracking of the torque and rotor flux linkage in direct field-oriented control of the induction machine through employing electromotive force and resistive compensation methods for tracking q-axis and d-axis reference stator currents, respectively. Simulation and experimental results demonstrate the effectiveness of the technique over the entire operating range. [ABSTRACT FROM AUTHOR]

Inaccurate machine parameters can cause orientation errors and instability in field-oriented control schemes relying on model-based estimations. This paper analyzes the accuracy and stability of two field-oriented control schemes for a stand-alone doubly fed induction generator (DFIG), where the field orientation is affected by the stator inductance and stator/mutual inductance ratio. After deriving a reduced-order model accounting for parameter mismatch, the paper deduces a formula to calculate the field orientation error as a function of the inductance mismatch, revealing parameter sensitivities. A stability analysis is then carried out proving that overestimating the stator/magnetizing inductance ratio may trigger instabilities in case of a high load level, whereas underestimation allows always stable operation. The theoretical insight is supported with simulation and test results on a laboratory rig. [ABSTRACT FROM AUTHOR]

Vibration and acoustic noise in switched reluctance motor (SRM) drives have been investigated and addressed frequently. However, the focus of most the paper is on vibration of the stator frame due to radial electromagnetic forces acting on the stator teeth. In this paper, a comprehensive vibration analysis for a SRM assembly using finite element (FE) method is conducted, which considers the stator and rotor vibrations due to radial electromagnetic force as well as the effect of mechanical coupling on the vibration between the stator and rotor. First, an experimental modal test was performed to extract modal parameters and to observe the coupling effect. The parameters were then used to adjust and validate the FE model that was used to obtain transfer functions for vibration characterization. Using the frequency domain representation of the radial magnetic force vector and the calculated transfer functions, radial and tangential vibration components have been predicted. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive extended Kalman filter (AEKF) algorithm estimating the stator stationary axis components of stator currents, the stator stationary axis components of rotor fluxes, the rotor mechanical speed, and the load torque for speed-sensorless control applications of induction motors (IMs). The performance of a standard extended Kalman filter (SEKF) algorithm depends on the correct selection of system and measurement noise covariance matrices. In SEKF algorithms, these matrices are generally assumed as constant and determined by the trial-and-error method. However, they are affected by the operating conditions of IM and should be updated considering the operating conditions. For this purpose, instead of the time-consuming trial-and-error method for determining these matrices, an innovation-based adaptive estimation approach having the capability of online update is used in this paper. Finally, in order to verify the superiority of the AEKF algorithm, estimation performances of AEKF and SEKF algorithms are compared under challenging scenarios for a wide speed range considering computational burdens and parameter variations. [ABSTRACT FROM AUTHOR]

This paper investigates the accurate loss calculation and thermal analysis for a nine-phase flux switching permanent magnet (FSPM) machine. First, the 3 D finite element method (FEM) model is developed to calculate the PM eddy current loss, in which magnet axial segmentation is taken into account. In order to calculate the iron loss quickly and precisely, the magnetic flux leakage coefficient is proposed in this paper to modify the 2 D calculation model of iron loss. Both the dc-biased magnetic induction and the rotational magnetization are taken into account. Then, the key parameters for thermal modeling, such as the convective heat-transfer coefficient between external frame and ambient, and the coefficient of convection heat transfer in the end region, are derived, based on which a dissymmetric 3 D FEM are used for thermal calculation of nine-phase FSPM machine. Finally, experiments on a prototype machine at the rated generation operation condition are carried out to verify the effectiveness of the developed model. [ABSTRACT FROM AUTHOR]

As an auxiliary brake element, the eddy current brake is widely used to ensure safe driving in heavy vehicles due to its noncontact braking characteristics. It is important to increase the power density of the eddy current brake and suppress the thermal derating of its braking performance. According to the principle of the eddy current braking and current skin effect, a decline in temperature can greatly increase the eddy current density of the low-frequency electromagnetic device. In this paper, a new heat dissipation method is proposed to cool the heating surface of the eddy current brake directly. The electromagnetic field model and the flow-heat coupling model are established to predict and analyze the steady-state temperature distribution and braking torque. A new type of internal liquid cooling eddy current brake prototype was manufactured for a bench test. The experimental data prove that the computational model is effective. The calculation results show that the new internal liquid cooling eddy current brake has improved heat dissipation advantages. [ABSTRACT FROM AUTHOR]

The stator-PM variable reluctance (VR) resolver has been proposed as a new position sensor for a wide speed range. The high-frequency (HF) signal injection is only required to measure the rotor position at low-speeds. Alternatively, at higher speeds, without requiring the HF excitation, the position measurement can be achieved by the back-EMF generated by the stator-PM. This novel resolver has a simple rotor structure and the analog signals can be efficiently decoded at high-speeds. In the first proposed stator-PM VR resolver, the prototype must have even number of rotor salient poles. However, the resolvers with odd number of rotor poles are also useful in many scenarios. To complete the design scheme of this resolver category, this article practices a solution on the basis of the theory of field modulation. The design issue and solution are illustrated and addressed in this paper. The winding function approach is applied to analyze the signals. With the low-cost materials, the proposed resolver measurement system is prototyped. [ABSTRACT FROM AUTHOR]