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Accurate and timely fault diagnosis of the rotating rectifier for a wound-rotor synchronous starter/generator is of great importance to improve system reliability. In the generation mode of the system, there is one idle stator winding of the main exciter. The terminal voltage characteristic of the idle stator winding is analyzed, and a novel fault diagnosis method for the rotating rectifier in the generation mode of the system is proposed. In this method, two feature voltages, namely, the maximum peak voltage and any other peak voltage of the idle stator winding terminal voltage are extracted through voltage sequence reconstruction to calculate the feature ratio for fault detection. The corresponding rotor position obtained by an inherent position sensor where the maximum peak voltage occurs is collected to determine the faulty diode location. The experimental results verify the feasibility and effectiveness of the proposed fault diagnosis method.

Wound rotor induction motors (WRIM) are widely used in a vast number of high output power industrial applications due to their capability of reaching high start torques while maintaining low inrush currents. Nonetheless, these machines are very prone to require early maintenance, and the possibility of presenting rotor winding asymmetry failures is high due to their more complex rotor circuit. Although some recent works have proposed techniques that overcome the drawbacks of conventional methods, an additional research effort for the development of alternative approaches able to enhance their performance and reliability is desirable. In this work, a new method for the diagnosis of rotor asymmetries in WRIM is presented. The proposed methodology is based on a feed-forward neural network (FFNN) feed by suitable fault severity indicators, which rely on the maximum energy density of higher order harmonics (amplified by the failure) at strategic regions of the time-frequency maps obtained from stray flux signals under startup transient. Experimental results for three different levels of rotor asymmetries in a 11 KW WRIM prove the reliability of the enhanced proposed system in comparison to conventional approaches that only rely on the main sideband fault-harmonic amplitudes.

The brushless doubly fed motor (BDFM) shows great potential for use in large medium-voltage adjustable-speed drive (ASD) systems due to its high reliability and cost benefits of a partially rated low-voltage power electronics converter. However, undesired performance caused by rich useless space-harmonics restrict the application of the BDFM in medium-voltage high-power ASD systems. In this paper, a medium-voltage wound rotor BDFM consisting of specially designed stator and rotor windings is developed. Firstly, the wound rotor with unequal turns and unequal pitches is designed and then compared with a nested loop counterpart. In addition, a 10 kV single-layer winding with shifted slot number in the stator is proposed to further reduce the space-harmonics by equivalent pitched effect. The finite element model of the BDFM is established to analyze electromagnetic performance and the influence of magnetic slot wedges. A lumped parameter thermal model is developed to quickly evaluate the average temperature rise of the proposed prototype. Field tests of driving a circulation water pump in a steel rolling mill were conducted to validate the feasibility of the proposed scheme.

Wound Rotor Induction Machine (WRIM) connected to stator and rotor Voltage Source Converters (VSCs), known as the Double-Inverter-fed WRIM drive, can be viewed as two virtual Squirrel Cage Induction Machine (SQIM) drives, when seen from air-gap. In this article, this feature of WRIM is explored to develop an improved Dual Direct Torque Control (DDTC) technique such that, two individual and independent conventional DTC controllers can be directly employed to control the stator and rotor VSCs. The improved technique is inculcated with all the benefits of conventional DTC controller, especially the benefit of zero dependency on rotor position. Furthermore, the increased torque ripple with the conventional DTC controllers is mitigated by modifying the Switching Tables (STs) such that, the Voltage Vectors (VVs) emulated in the air-gap are equivalent to a 3-Level Neutral Point Clamped (3L-NPC) VSC. The STs are developed by analyzing the WRIM as an Open-End Winding Induction Machine (OEWIM). To demonstrate the performance of the proposed DDTC technique, the experimental results obtained from 3 kW WRIM are presented, under various transients and steady state conditions. The reduction in the torque ripple is demonstrated by estimated torque ripple waveforms, at different speeds.

Two-Degree-of-Freedom (2-DOF) electrical machines require position sensors for their motion control. In comparison with using two independent sensors, using a 2-DOF sensor enhances closed-loop control system’s performance. However, due to 3-D structure of the 2-DOF sensor, its performance evaluation needs 3-D analysis. Also, due to helical motion the accuracy deterioration of the sensor, under mechanical faults needs more attention. Although Finite Element Method (FEM) is the best way to simulate such sensors, most of the commercial packages for transient finite element simulations are not able to consider two separate motions simultaneously. Furthermore, FEM has high computational burden that limits its usage in iterative design and optimization process or under mechanical faults. Therefore, developing a fast, and comprehensive analytical model to be used for performance evaluation of helical motion resolvers under mechanical faults is appreciate. Consequently, in this paper an analytical model based on winding function method is developed for a helical motion resolver. The model can predict the performance of the sensor in health condition, as well as that under eccentricity fault. The success of the model is verified using 3-D FEM and the experimental measurements on the prototype sensor.

Multi-speed resolvers are used in the applications that need higher accuracy. However, they suffer from losing absolute position information. To overcome this challenge and improve the reliability of detecting position, using multi-turn resolvers is recommended. The conventional configuration of multi-turn resolver is using two individual resolvers on one shaft and into a common frame. Using such configuration needs special care on setting the distance between two resolvers. In this paper a new structure based on dual side configuration is proposed. The performance of the double sided resolver is analyzed and optimized using an analytical model based on magnetic equivalent circuit (MEC). Then, time stepping finite element method (FEM) is employed to verify the success of the new configuration and the applied optimization. Finally, the optimal resolver is built and tested. Experimental measurements confirm the success of the proposed sensor.

One of the major challenges of diagnosing rotor symmetry faults in induction machines is severe modulation of fault and supply frequency components. In particular, existing techniques are not able to identify fault components in the case of low slips. In this paper, this problem is tackled by proposing a novel approach. First, a new use of singular spectrum analysis (SSA), as a powerful spectrum analyser, is introduced for fault detection. Our idea is to treat the stator current signature of the wound rotor induction machine as a time series. In this approach, the current signature is decomposed into several eigenvalue spectra (rather than frequency spectra) to find a subspace where the fault component is recognisable. Subsequently, the fault component is detected using some data-driven filters constructed with the knowledge about characteristics of supply and fault components. Then, an inexpensive peak localisation procedure is applied to the power spectrum of the fault component to identify the exact frequency of the fault. The fault detection and localisation methods are then combined in a recursive regime to further improve the diagnosis’ performance particularly at high rotor speeds and small rotor faults. The proposed approach is data-driven and is directly applied to the raw signal with no suppression or filtration of the frequency harmonics with a low computational complexity. The numerical results obtained with real data at several rotation speeds and fault severities, unveil the effectiveness and real-time feature of the proposed approach.

Winding configuration is a crucial factor that highly affects the accuracy of resolvers. A nonoptimal winding could also make the manufacturing process complicated and costly inefficient. In this article, an approach to determine the optimal winding configuration for the resolvers is proposed. This method is applicable for both wound rotor (WR) and variable reluctance (VR) resolvers, and significantly simplifies the winding configuration of resolvers with different pole pairs and teeth numbers. Based on the proposed approach, the winding configuration of multiturn resolvers, which are generally more complicated than single-turn resolvers, is simplified for WR and VR type resolver with different number of stator teeth. In this approach, the reliability of the sensor is also considered. The proposed winding facilitates the manufacturing process and decreases the production costs for the multiturn resolver. The three-dimensional time-stepping finite-element method is used to confirm the correctness of the analysis. Finally, a prototype of the sensor is built and tested to verify the validity of the proposed winding approach. The measured value of the average of absolute position error for 1X/5X resolver is 0.197°/0.081°, and the maximum position error is 0.716°/0.212°.

Fault detection of a rotating rectifier for a wound-rotor synchronous starter/generator (WRSSG) without a rotor position sensor in the stationary state is necessary for a successful engine start. Based on high-frequency (HF) voltage injection, a novel fault detection method of the rotating rectifier for the WRSSG in the stationary state is proposed. The rotating HF voltage is imposed on the stator windings of the main machine, and the HF feature current signal extracted on the stator windings of the main exciter is used for fault detection. In this article, the HF current signal in the main exciter with the rotating rectifier under different working conditions is analyzed first. To obtain the HF response current on the stator windings of the main exciter, the HF model of the WRSSG is analyzed. Through the Fourier series, the HF feature current signal together with fault detection is achieved. Compared with the existing fault detection methods, the proposed method shows no dependency on the rotor position information. Experimental results verify the feasibility and effectiveness of this method.

Stator- and rotor-side voltage source inverters (VSIs) (VSI-S and VSI-R) of a double-inverter-fed wound rotor induction machine (DI-WRIM) drive individually feed 1-p.u. power each, to extract 2-p.u. power at a 2-p.u. speed. This feature of the DI-WRIM drive is explored, in this article, to model this drive as two virtual cage rotor induction machines (CRIMs). The VSI-S connected to the stator is emulated as one VSI-fed CRIM with the rotor short circuited, while the VSI-R connected to the rotor is emulated as another VSI-fed CRIM with the stator short circuited. The mathematical modeling of the DI-WRIM drive as two virtual CRIMs, in the synchronous reference frame, is presented by considering the angle between the stator and rotor currents ( $\gamma$ ) as a medium of coupling between the two virtual CRIMs. The proposed mathematical model of the DI-WRIM is used to demonstrate the performance of the drive in a current-oriented control (COC) technique. In the COC technique, the VSI-S is controlled in the stator current-oriented frame and the VSI-R is controlled in the rotor current-oriented frame. The proposed model and technique is tested on a 4-hp WRIM drive and the experimental results are also presented to demonstrate the satisfactory performance of the drive.

[EN] Wound rotor induction motors are used in a certain number of industrial applications due to their interesting advantages, such as the possibility of inserting external rheostats in series with the rotor winding to enhance the torque characteristics under starting and to decrease the high inrush currents. However, the more complex structure of the rotor winding, compared to cage induction motors, is a source for potential maintenance problems. In this regard, several anomalies can lead to the occurrence of asymmetries in the rotor winding that may yield terrible repercussions for the machine¿s integrity. Therefore, monitoring the levels of asymmetry in the rotor winding is of paramount importance to ensure the correct operation of the motor. This work proposes the use of Bicoherence of the stray flux signal, as an indicator to obtain an automatic classification of the rotor winding condition. For this, the Fuzzy C-Means machine learning algorithm is used, which starts with the Bicoherence calculation and generates the different clusters for grouping and classification, according to the level of winding asymmetry. In addition, an analysis regarding the influence of the flux sensor position on the automatic classification and the failure detection is carried out. The results are highly satisfactory and prove the potential of the method for its future incorporation in autonomous condition monitoring systems that can be satisfactorily applied to determine the health of these machines., This work was supported in part by Generalitat Valenciana, Conselleria de Innovacion, Universidades, Ciencia y Sociedad Digital, (project AICO/019/224) and in part by MEC under Project MTM2016-75963-P.

Expansion of Two Degrees of Freedom (2-DOF) electrical machines, for simultaneous linear-rotational motions, leads to employment of more than one sensor in closed-loop control systems. Such control systems can use two separate sensors for linear and rotational motions or employ a 2DOF sensor. The last, will result in lower volume and mass and also less complexity of the control system. Therefore, development and design optimization of 2DOF sensors can be an interesting research topic. However, 3-D geometry of such sensors needs 3-D finite element analysis. Due to high computational burden of 3-D time stepping finite element method (3-D TSFEM), it can hardly applicable in iterative design and optimization methods or performance evaluation of the sensor under fault conditions. Therefore, it is preferred to predict the accuracy of such linear-rotational sensors using an accurate, computationally fast method. Hence, in this paper, a comprehensive analytical model based on Magnetic Equivalent Circuit (MEC) is proposed for a helical motion resolver. The developed model can predict the performance of the sensor in health condition, as well as that under short circuit fault. Finally, the obtained results are verified using experimental measurements on the prototype helical motion resolver.

A mathematical description of an asynchronous machine with unreduced parameters in the space of real phase coordinates is given. When studying an asynchronous motor in a dual power supply system with controlled converters in rotor and stator circuits, there is a need for an AM model without parameters, in which the processes in the stator and rotor circuits will correspond to reality in magnitude. In addition, such a model is necessary when analyzing the energy parameters of the whole electric drive controlled by the rotor. To observe real processes in the stator and rotor, the model should be designed in separate spatial coordinate systems. In reference books for AM with a wound rotor (WR), as a rule, the real parameters (resistances, currents and voltages) of the stator and rotor and the voltage reduction coefficient ( ke ) are given. Bringing currents and resistances (inductances) is carried out by coefficients ki=ke and kr=ke2 respectively. Let's consider the description of the machine without reduction of parameters. For the convenience of further consideration, let's introduce the general value of the mutual inductance. We obtain an equation for the electromagnetic moment in real coordinates. Let's design a model in the MATLAB dynamic modeling environment using vector-matrix representation. Matrix algebraic operations with vector variables are implemented by Matlab Fn blocks, which are the calls to userdefined functions described in the form of M-files. The content of Matlab Fn functions is considered. On the model, the processes of starting of an AM with a phase rotor of AK-52-6 type were. Shows the graphs of start-up transients. The processes in the obtained model coincided with the results of modeling of this engine in the model with the coordinates reduced to the rotor. Thus, the energy processes described by this model correspond to the processes to the model with the given parameters, and the processes of currents and flux linkages changing of the stator and rotor are real. The model designed in the MATLAB/Simulink dynamic modeling environment can be used to study double-powered asynchronous electric drives.

Two Degrees of Freedom (2DOF) electrical machines are widely used in robotics. They need position sensors for their electronic commutation and high performance control loop. 2DOF resolvers are the best choice for such applications. Therefore, in this paper a new configuration is proposed for rotational-linear position estimation. Then, an optimization is done to reduce the sensor’s volume by 25.99%. The optimal design also has more accuracy in both rotational (about 75%) and linear (about 56%) motions. The performance of the initial design and the optimal one is analyzed using three-dimensional (3-D) transient finite element method (FEM). Afterwards, the optimal configuration is built and experimentally tested. Measured results confirms the success of the proposed design.

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.

In this article, an online method is proposed to find the magnetic model of a wound rotor synchronous machine (WRSM). To identify the magnetic model, the stator flux is first estimated by considering two auxiliary variables and using a partially known model of the WRSM. Using this model, the stator flux is estimated at the $dq$ reference frame. Then, to identify the magnetic model or in other words to find the relationship between the machine flux linkage and the machine currents, the stator flux is mapped in terms of stator and rotor excitation currents. To validate the proposed method, simulations and experimental tests are carried out on a WRSM.

The brushless doubly fed machine (BDFM), which eliminates slip rings and brushes, shows great potential in application fields where reliability is a prime concern. This paper presents the generalized design methodology of the novel three-phase Y-connected wound rotor for both additive modulation BDFM and differential modulation BDFM with specific schemes. First, the above two types of BDFMs are explicated by magnetic field modulations of two main magnetic fields. Then, design principles are illustrated to further improve the conductor utilization ratio of the rotor winding (RW) and reduce harmonic contents of the magnetomotive force (MMF) with a three-phase AC winding. Design examples and specific procedures of the proposed novel three-phase Y-connected wound rotor are also presented for both additive and differential modulation BDFMs, respectively. Finally, finite element models of two types of the BDFM are established and a differential modulation prototype is manufactured. Proposed design schemes are verified by comparative simulation and experimental results at different speeds and load conditions.

The wound rotor type Doubly Fed Induction Generator (DFIG) based adjustable velocity wind generator system is the most promising wind turbine system in the wind industry. A fractional-order proport...

This article deals with the determination of the rotor time-constant of an induction machine by performing a flux-decay test in generic load conditions. The flux-decay transient occurs when the supply stator voltage is turned off suddenly. In this way, from the decay envelope of stator back-electromotive forces and, in the case of the wound rotor machine, from that of the rotor currents, the rotor time-constant can be extrapolated with a high level of accuracy. In this article, an in-depth analysis of this methodology is reported, whose validation has been carried out on both the squirrel cage and wound rotor motors. The estimated value of rotor time-constant can be used for the machine torque regulation, using the well-known control schemes presented in the literature and whose performance in the low-speed operation is affected by the detuning of this parameter. Since the inverter-fed motors nowadays characterize most of the share in the market of adjustable speed drives, experimental results concerning the flux decay test performed under the pulsewidth modulation supply are also presented.

Brushless structure is beneficial for air-core compensated pulsed alternator (ACPA) because its field current and rotation speed are too large for the slip rings and carbon brushes. To achieve the brushless structure, a cascaded brushless self-excited ACPA (CBSACPA), which consists of an exciter and a generator in cascade, is proposed, in this article. The exciter and generator have a common rotor. A novel squirrel-cage rotor winding (SCRW), which can eliminate the end winding compared with conventional wound rotor winding (WRW), is proposed to simplify the rotor structure and improve the performance. First, the structure of the CBSACPA with the SCRW is introduced. Second, the operation principles of the machine are elaborated. Third, the dynamic mathematical model is presented. Fourth, the operation principles are demonstrated by the finite-element method. In addition, the performance of the SCRW is compared with the WRW as well. Finally, a prototype of CBSACPA is developed and tested to validate the analyses and simulations. In conclusion, this study gives detailed introduction, analyses, and validation about the CBSACPA, which provides a new solution to achieve a brushless structure for the ACPA.

Accurate and timely fault diagnosis of the rotating rectifier in wound-rotor synchronous starter–generator (WRSSG) plays an important role in improving the reliability of the WRSSG system. By analyzing the geometric features of the rotor current trajectory of the main exciter (ME) under health and different fault conditions of the rotating rectifier, in this article, a fault diagnosis method for the rotating rectifier based on the geometric features of ME rotor current trajectory is proposed. In this method, ME rotor currents are estimated first, and then the center distance, center angle, and length–width ratio of the ME rotor current trajectory are calculated and used to detect fault occurrence, locate the faulty diode, and identify the fault type for the rotating rectifier, respectively. The experimental results verified the feasibility and effectiveness of the proposed fault diagnosis method.

In this article, a novel structure is proposed for a wound rotor synchronous machine with a small ferrite magnet in each rotor pole. The key is to achieve a higher reluctance torque term and also acquire torque-angle approaching that would allow the field torque and reluctance torque to reach maximum values at the closed current phase angle for efficient production of the average total torque. The assisting ferrite magnet in the proposed model helps compensate the q- axis flux while keeping the d- axis flux unchanged as much as possible, for enhancing reluctance torque and power factor. Meanwhile, the assisting ferrite magnet makes an asymmetrical magnetic flux distribution to close the current phase angles between the maximum of the field torque and the reluctance torque. Moreover, the related parameters of the assisting ferrite magnet in the proposed structure were determined by optimal techniques using the Kriging method and genetic algorithm. In addition, the potential for demagnetization of the assisting magnet was analyzed and the results verified that this would not affect the motor output performance. Finally, prototypes are manufactured for the experiments to verify the principle analysis and finite element analysis results.

This paper compares the performance of a wound rotor induction motor drive (WRIM) with two rotor impedance profiles. The first system involves a diode rectifier followed by variable impedance in the rotor circuit. The second system involves a three-phase variable impedance in the rotor circuit. The comparison concerns the magnitude of starting transients of stator and rotor voltages and currents, the transients settling time of the stator and rotor voltages and currents, the stator and rotor consumed active and reactive power, the electrical torque, and the stable range of operation at sub-and super-synchronous speeds. This comparison is helpful for deciding the more efficient drive to be utilized, the drive with lower harmonics in currents and voltages, and the drive allowing wider speed stable operation range. Better results are obtained for the drive with the three-phase variable impedance connected to the rotor circuit.

The paper details modern saturation modeling and performance calculation to the analysis of grid-connected cylindrical wound-rotor synchronous motors. The developed models give reliable results with limited computation effort. The finite element based method uses iterative procedures to calculate the motor performance during which the motor parameters are evaluated in detail. Experimental results prove that the method has a high degree of accuracy and is computationally efficient.

The performance of the resolver as a position sensor is significantly influenced by electrical and mechanical faults. Among different faults, short circuit in the stator windings has more destructive effect than others on accuracy of resolver. Furthermore, due to thin wires of the stator it is highly likely to occur. Therefore, in this paper a robust design is proposed for wound-rotor resolvers to not only suppress the influence of short circuit fault in the stator/rotor winding, but also improve the accuracy of the sensor under mechanical faults. The effectiveness of the proposed robust design is demonstrated by an analytical model based on winding function method and then approved by time stepping finite element analysis (TSFEA) and experimental measurements on a prototype sensor.

In the supersynchronous mode of double-inverter-fed wound rotor induction machine (DI-WRIM) drive, torque ripple is dependent on the sum of the quadrature ( $q$ ) axis stator and rotor flux ripples (termed as overall flux ripple). Therefore, in the existing method, the torque ripple is reduced by merely changing the slope of one of the flux ripples such that their sum is reduced. However, the torque ripple can be further reduced, as the overall flux ripple in DI-WRIM resembles the $q$ -axis stator flux ripple of a double-inverter-fed open-end winding induction machine which is generally analyzed as a three-level neutral-point-clamped inverter fed squirrel cage induction machine (SQIM) (3L-SQIM) drive. Thus, in this article, the stator and rotor voltage source inverters are switched together and the resemblance is explored to develop stator–rotor pulsewidth modulation (PWM) combinations, such that the overall flux ripple is equivalent to the $q$ -axis flux ripple of 3L-SQIM. The effect of phase shift between the stator and rotor voltage vectors on torque ripple is analyzed and a hybrid PWM combination is also proposed to minimize the same. The reduction in torque ripple, with the proposed combinations, is validated in terms of the estimated instantaneous and RMS torque ripples. The simulation and experimental results further validate this reduction.

Purpose This paper aims to present an analytical electromagnetic model for wound rotor synchronous machines with a salient-pole rotor structure based on the two-dimensional subdomain technique. Design/methodology/approach The machine is divided into five active sub-regions: stator slots, stator slot openings, air gap, rotor slots and rotor slot openings. For each sub-region, the governing partial differential equations are derived and solved analytically. Findings The magnetic flux density distributions in all active sub-regions are analytically computed and other quantities such as back-emf, inductances, electromagnetic torque and unbalanced magnetic forces are also analytically calculated. The results of the analytical model are compared to those obtained from the finite element analysis to show the accuracy of the proposed model. Originality/value The two-dimensional analytical model of a wound rotor salient-pole synchronous machine using the sub-domain technique is the main contribution of the research.

In this article, a new low-cost small-scale three-phase brushless motor topology is proposed. This is a new topology for self-excitation of brushless wound rotor synchronous motor investigated initially for rated speed. For brushless excitation, the stator is designed to contain two windings, namely, three-phase armature winding and exciter winding. The rotor consists of two windings, that is, harmonic winding and field winding, and a diode rectifier. An inverter feeds the three-phase armature winding which is connected in series through an uncontrolled three-phase rectifier to a single exciter winding. When the current is supplied from the inverter, both the armature and exciter windings are energized eventually producing a flux in the air gap. Since the flux produced by the exciter winding is not synchronized with the field winding, it produces a harmonic to be intercepted by the harmonic winding on the rotor. Eventually, the voltage produced in the harmonic winding is used to feed dc current to the field winding for brushless operation. The results obtained by 2-D finite-element analysis (FEA) validate the brushless operation of the motor. The proposed motor is analyzed basically for topology verification with the FEA results. Since the topology can be verified, further effort can be put to investigate such low-cost topologies for brushless wound rotor synchronous motor. It can be an alternative to a costly permanent magnet synchronous motor for specific applications.

In this paper static eccentricity (SE) fault diagnosis in wound rotor (WR) resolver is considered and a new noninvasive index is proposed. Using the proposed index not only leads to SE detection but also, helps to precisely determine the eccentricity level. Furthermore, the location of the fault is determined using two search coils. In this regard, a mathematical model based on the winding function method is proposed. In the proposed model the influence of non-uniform air-gap length on calculating the inductances is considered. Then, time-stepping finite element method (TSFEM) is used for approving the success of the proposed index. Finally, experimental tests are done to validate the simulation results.

Resolver is an electromagnetic position sensor typically used in the closed-loop control of permanent magnet synchronous motors (PMSMs). In terms of structure and principle of operation, resolvers are very similar to electrical machines. In this regard, different numerical and analytical models have been developed for the performance prediction of a resolver, with a compromise between computational burden and accuracy. Therefore, a fast and accurate hybrid model of the resolver is presented in this article, which can be used for resolvers with different structures. Additionally, this model can easily be implemented in software such as MATLAB/SIMULINK. The performance of different variable reluctance (VR) and wound rotor (WR) resolvers calculated from the model and finite element analysis (FEA) is compared to show the value of the proposed model. The model is also used to improve the position determination accuracy of a VR resolver. Finally, a prototype of the optimized resolver is used for experimental tests to confirm the validity of the analysis.

Employing Multi-Turn Wound-Rotor (WR) resolvers are suggested for applications that high accuracy and absolute measurement are required, simultaneously. Conventional multi-turn resolvers are consisted of two individual resolvers in a common frame and suffer from high cost and big size that has a loading effect on the driven machine. Those challenges are over-come in proposed structures of recent researches in the price of a complicated winding process in manufacturing where the aim of this paper is laying. To find the best solution, an index is proposed and calculated. All the simulations are done using time-stepping finite element analysis (TSFEA). Then, the prototype of the optimal configuration is built and its appropriate performance is approved by the experimental test.

This paper presents a detailed analysis of short circuit fault (SCF) in wound rotor (WR) resolvers. For this purpose, an analytical model based on winding function (WF) method is developed considering the stator and rotor windings’ fault, the severity of the fault, the phase of the stator faulty winding, and the tooth of shorted turns. The proposed model leads to a comprehensive understanding of the SCF behavior of WR resolvers and also leads to define proper fault detecting signatures. All the predictions are verified by time stepping finite element analysis as well as the experimental tests on two prototyped resolvers.

An efficient online flux-based diagnostic approach is proposed to detect turn-to-turn faults in the stator and rotor windings of wound rotor induction machines, at an early stage of development, which can be applied in the online mode. Some flux sensors are installed in the stator slots to detect the rotational magnetic field at various positions along the air-gap circumference. These sensors measure the flux linked to all winding coil groups, in the three phases. Any fault occurring either in the stator or rotor windings will disturb the air-gap flux and create an asymmetry in the rotational magnetic field, which is detectable through the difference of the induced voltages in the corresponding flux sensors. The proposed diagnostic technique is evaluated by finite element analysis as well as by multiple experimental tests. The obtained results show that such invasive technique is able to detect and discriminate various faults in the stator and rotor windings with high accuracy, low calculation burden, proper sensitivity and appropriate robustness in the face of machine load level variations.

An improved and more robust flux vector orientated control scheme for an emerging doubly-fed reluctance generator without a shaft angular position or velocity sensor has been proposed, computer-simulated, and experimentally verified. Whilst retaining the cost and other advantages of using a fractional power electronics converter rating, this promising medium-speed brushless machine technology has been viewed by research and industrial communities as an appealing economical solution for the compromised reliability and high maintenance requirements associated with the presence of slip rings, brushes, and the failures prone three-stage gearbox of conventional wound rotor doubly-fed induction generators, traditionally deployed for commercial wind turbines. The comprehensive comparative simulation and test results obtained have been shown to agree very well undoubtedly demonstrating the good overall performance of the sensorless controller. A precise speed reference tracking with smooth, intrinsically decoupled real and reactive power responses of the grid-connected winding has been achieved for the typical variable loading profiles and narrow speed ranges (e.g. around 2 : 1 or so) of a laboratory emulated wind turbine.

International audience; The lack of precise mathematical model of nonlinear systems, such as electric machines, brings certain limits to design a powerful controller for such systems. This article presents a model-free-adaptive-control (MFAC) scheme as a good alternative to the commonly used model-based-control (MBC) methods in order to improve the controller design limitations due to the need for system model information. In this regard, an MFAC is developed in this article for current control of a wound rotor synchronous machine (WRSM) drive system and compared with a proportional-integral (PI) controller as a well-known model-based controller. Since the controller performance can be affected by unexpected phenomena, such as model errors, parameter variations, and changes in operating point, beforehand, the robustness of developed MFAC is first tested under the mentioned conditions in the simulation area. Then, through experimental validation on a specifically designed test bench, a satisfactory performance was obtained for the MFAC scheme.

The static excitation part of a brushless wound rotor hybrid excitation generator without an exciter (brushless WRHEG) is analyzed in this paper. The DC stator excitation windings and rotor harmonic coils are placed in the iron core as the excitation part, so that the brushless excitation for a wound rotor hybrid excitation generator (WRHEG) can be realized. In this study, the selection of stator excitation windings and rotor harmonic coils, which are essential for achieving of the brushless excitation, is providing. The effect of the static magnetic field on the air-gap magnetic field is studied theoretically. The harmonic content of the air-gap magnetic field is analyzed by Fourier series form and the effect of harmonics on the output voltage is also investigated. The influence of the static excitation field on the iron loss is also considered. A 1.5 kVA prototype is fabricated to verify the validity of the theoretical and Finite Element (FE) analysis. The output voltage under the no-load and the rated load conditions are measured. The field regulation capacity and the efficiency of the brushless WRHEG are tested. It shows that the brushless excitation is achieved by remaining the operating performance of WRHEG unchanged.

In this paper, a new design configuration has been proposed in which a prototype of resonant inductive power transfer-based contactless power transfer to wound rotor has been developed which provides field power to brushless alternating current (BLAC) or brushless direct current (BLDC) motors without the use of permanent magnets in the rotor. Further, wound field in the rotor of DC motor can be powered without carbon brushes. The proposed design facilitates motor performance improvement by adding an extra dimension of field flux control, while the armature circuit is conventionally fed from position detection and commutation schemes. It contains a primary multilayer concentrated coil fed with high-frequency resonating AC supply or switched mode supply. A single layer helical secondary coil coaxially fixed on the shaft receives high frequency wireless AC power transmitted from primary coil. Fast rectifier inside the hollow shaft and DC filter provides the transferred DC power to field terminals in the rotor. It has been verified that rotor power can be varied linearly with linear variation in input DC power with the highest efficiency at the resonant frequency. Available power to the rotor remains invariable with rotational speed and angle, which is a necessary requirement for rotor field. DC voltage on the rotor terminals can be effectively controlled during standstill as well as during rotation at any speed.

The use of rotary assembly platforms is common in several automation applications, such as in bottle filling and capping systems. One of the problems that designers has to address is how to supply the electric actuators, sensors and process controllers located on the rotating disk of the machine. The traditional solution is to use slip-ring contacts. However, they suffer from aging and thus a scheduled maintenance program is required. In this paper, the motion of the platform and the contact-less energy transfer to the auxiliary loads located on the rotating disk is obtained through a direct drive wound-rotor five-phase induction motor. The experimental tests on a scaled prototype demonstrate the practical potential of the machine

Numerical and analytical methods are two methods to evaluate the performance of electrical machines. This article provides a comparison between numerical and analytical methods. Electrical machine software typically uses numerical methods to solve the electromagnetic equations. On the other hand, analytical methods are faster and more intuitive. A general analytical modeling technique to evaluate the performance of axial flux machines including but not limited to wound rotor resolvers is presented here. The proposed model is based on the actual three-dimensional (3-D) magnetic equivalent circuit (MEC). The accuracy of the proposed model depends on the number of radial layers in the reluctance network of the machine and the time step of simulation. Flux fringing effect, skewed slots, static and dynamic eccentricity, and core magnetization curve are included in the model. Excitation method of the resolver determines the input(s) and output(s) of the algorithm. Both current and voltage excitations are discussed in the article. Finally, the results of the proposed 3-D MEC model under healthy and eccentric (static and dynamic) rotor conditions are compared with the finite-element analysis in terms of computation time and accuracy. The results confirm high-accuracy high-speed performance of the 3-D MEC model.

The dc grid is emerging as a new electric power distribution concept for several types of vessels due to its higher fuel efficiency compared with the conventional ac grid. Until today, wound rotor generators (WRGs) and diode rectifiers have been applied to the generation part of the onboard dc grid although the efficiency, weight, reliability, and footprint of the WRGs are inferior to those of permanent magnet generators (PMGs). In this article, the possibility of adopting the PMG in the onboard dc grid instead of the WRG is studied. According to the analysis, even though the PMG is inherently incapable of adjusting rotor flux, the rectified dc voltage can be controlled in a certain range under all load conditions. Simultaneously, the diesel engine can be controlled near its optimal operating line (OOL) to minimize fuel consumption. The controllability of the rectified dc voltage of the PMG is verified by computer simulation and small-scaled experimental tests. When comparing the operating trace of the proposed system to the specific fuel oil consumption (SFOC) map of a 350-kW diesel engine, i.e., AD158TI, the fuel-saving by applying the PMG is expected to be more than 10% at light load condition and around 3% average in overall operating conditions.

With less fragile power electronics integrated, the overall shipboard power system (SPS) safety level is prone to increase. In this article, the motion equation concept of a less power electronics-based more-electric ship is proposed to study the SPS dynamics. A wound rotor induction machine (WRIM) acts as the propulsion load, whose stator and power converter are regarded as a synthetic internal voltage vector (SIVV). The small-signal model of a WRIM-based electric drivetrain (WRIM-ED) is established in the electromechanical control timescale. Besides, the external dynamic behaviors of the propulsion load are investigated in detail according to the phase and amplitude of SIVV. The control effects of phase-locked loop (PLL), rotor speed control (RSC), and reactive power control (RPC) are taken into account. In addition, the control schemes by applying the traditional PLL-based vector control (PLL-VC) and an emulated stator voltage-oriented VC (ESVO-VC) for WRIM-ED are described. Moreover, with ESVO-VC, the expression of equivalent inertia for WRIM-ED is much simplified, and there is no need to tune the PLL controller gains. MATLAB/Simulink is applied to carry out simulations to investigate the control effects of both PLL-VC and ESVO-VC on the system dynamic performance.

Multi-turn resolvers are proposed to be used in high accuracy, high-reliability applications that need to have the benefits of absolute measurement and high accuracy, simultaneously. In this paper, the influence of different arrangements of rotary transformer (RT) and resolvers’ core on the accuracy of a multi-turn wound rotor (WR) resolver is discussed. Then, an optimal configuration with the aim of reducing the total cost, and the total volume of the sensor is proposed. All the analysis is done using 3-D time-variant finite element method (3-D TVFEM) and the optimal structure is built for experimental tests. Finally, experimental measurements are employed to verify the simulation results.

Cost, durability and reliability are three critical issues in electrical/hybrid electrical vehicles (EV/HEV). In this regard, resolvers are often used as position and speed sensors in such applications. In this paper design and analysis of a novel multi-turn resolver is discussed to address all the mentioned issues. The proposed resolver has got one stator core and one rotor core. Double sets of signal windings on the stator and a special excitation winding on the rotor are designed to achieve both absolute and multi-speed operations. Mathematical model of the proposed resolver is verified using time stepping finite element analysis and experimental measurements.

In the topology of double-inverter fed wound rotor induction machine (DI-WRIM) two voltage source inverters (VSIs) are connected one each on stator and rotor terminals. This leads to ripple in both stator and rotor currents. In this paper, these current ripples are analyzed in terms of the stator- and rotor-flux ripples, which are estimated from their respective terminals. To reduce the current ripples, the VSIs of the stator and rotor terminals are modulated with different pulsewidth modulation (PWM) sequences. The switching loss in the DI-WRIM is also analyzed for the proposed stator–rotor PWM sequence combinations, based on the flexibility of changing the power factor, by changing the flux component of the current fed from either side of a DI-WRIM drive. The proposed PWM combinations with the proposed flux component in currents are found to reduce the stator and rotor current ripples and, the switching losses. The analytically estimated root mean square current ripples for the proposed PWM combinations are validated using the simulation and the experimental results obtained from a 3-kW DI-WRIM drive. The analysis on switching losses is validated by measuring the temperature rise of heat sinks present in the individual stator and rotor side VSIs of the DI-WRIM drive.

Aim of this study is to investigate a sensor-less speed-observer with the principles of vector control for the industrial applications of Wound-Rotor Induction Motors (WRIM). The proposed estimatio...

Due to manufacturing tolerances and bearing ageing, rotor eccentricity is inevitable in electrical machines. The existence of rotor eccentricity in electrical machines will cause unbalanced magnetic pull (UMP), which would increase bearing friction losses. In addition, the additional magnetic flux harmonics caused by rotor eccentricity may incur additional copper and iron losses. Here, induction machines are analysed as they are more sensitive to rotor misalignment due to smaller air gap compared to other types of machines. The magnetic flux distribution and UMP for both squirrel cage and wound rotor induction machines are discussed, as they have a dissimilar rotor configuration. The existence of rotor eccentricity would increase rotor copper loss in squirrel cage induction machines and would increase iron losses in wound rotor induction machines, where the additional power losses are a function of the degree of eccentricity. Analytical models are used to estimate the additional power losses, and they were validated using finite element analysis. Finally, we investigated the impact of power losses when implementing the slip control method which is proposed in our previous literature, in order to reduce UMP.

Doubly fed induction generators (DFIGs) are negatively affected by inter-turn short-circuit faults (ITSCFs) of rotor windings, and considering the safety and continuous operation of the wind turbine surveillance of DFIGs is of immense importance. For this purpose, an experimental platform was designed to detect ITSCFs in rotor windings. An experimental set-up with a 100 kW three-phase wound rotor induction machine and a condition monitoring system was constructed to obtain real-time experimental data. Different tapping points were set up to induce different ITSCFs. The rotor current was used for the analysis of the ITSCFs. First, spectral analysis was performed, and the ensuing results suggest that some harmonic frequency components were generated during the ITSCFs in addition to the fundamental frequency component. Additionally, the RMS value of the rotor current was measured during the process. In the next step, a wavelet coefficient of detail level 9 was found to be effective in analysing such harmonic frequency components in the rotor current. In the end, a new method based on the RMS value of the wavelet coefficient and the RMS value of the rotor current was proposed that can calculate the fault severity. It is concluded that such signal processing techniques are appropriate to detect ITSCFs and determine the fault severity in rotor windings in DFIGs.

The use of brushes electric motors for propulsion of electric vehicles have come to stay not because of its impressive innovation but mainly due to economic and environmental imperatives. Internal Permanent Magnet Synchronous Motors (IPMSMs) and Flux Switching Machines are being employed in electric vehicles to improve vehicles torque and speed and their performances have proved excellent for gas emission reduction or no fuel usage at all. This paper presents a new outer rotor permanent magnet flux switching machine enveloped by eternal non-ferromagnetic segmental rotor to secure the structure while rotating at very high speed. The segmental rotor is simple and easy to manufacture at low cost employing less material. The geometric topology of this outer rotor is introduced using Eclimo electric scooter parameters. Two dimensional finite element analysis (2D-FEA) models is used to investigate four machine performances namely flux distribution, cogging torque, induced back-EMF, torque and speed versus power characteristics. Results proved high torque and high power sustainability for long distance travel.

Flywheel Energy Storage Systems (FESSs) are commonly integrated with wind farms to help them to provide many grid services, including frequency control, voltage control, and power smoothing. Although such systems are not concerned by the severe grid code requirements, their ability to ride-through voltage dips is important to ensure better stability of the power grid. In this paper, the authors propose a robust H∞ current controller for a Wound Rotor Induction Machine (WRIM) based FESS during grid voltage dips. The proposed H∞ controller decreases the negative effects of voltage dips in the WRIM system, such as the rotor over-currents and the active power oscillations. On the other hand, it also guarantees the robustness in the presence of parameter perturbation. The proposed controller is designed using a modified mixed-sensitivity H∞ technique to take into consideration grid disturbances and parameter perturbation. Finally, simulations are made in MATLAB/Simulink using SimPowerSystems to verify the effectiveness of the H∞ controller under grid voltage dips with WRIM parameter perturbation. The simulation results show that the proposed H∞ controller can improve the stability of the WRIM based FESS subject to grid voltage dips and guarantee the robustness with parameter perturbation.