Stator Field Research Articles

Investigating the impact of magnetic air gap variations on short circuit characteristics of partially high temperature superconducting generator

Partially high-temperature superconducting generators (PHTSGs) feature large magnetic air gaps imposed by using cryostats for HTS field windings. This increased air gap significantly affects end winding inductance and can lead to elevated fault torque levels. This study investigates the influence of magnetic air gap variation on generator design and end winding inductance and its implications for short-circuit faults in PHTSGs. Through a combination of numerical simulations and analytical analysis, the study explores how changes in the magnetic air gap affect end winding inductance and subsequently influence short-circuit fault behavior. The results reveal a direct correlation between magnetic air gap length, end winding inductance, and key short-circuit parameters such as stator current, field currents, and electromagnetic torque. Notably, an increase in the magnetic air gap is observed to elevate stator and field currents and electromagnetic torque during short-circuit events. These insights underscore the importance of considering magnetic air gap variation and its impact on end winding inductance and its relationship with short circuit characteristics in the design and operation of PHTSGs, providing valuable insights for enhancing the resilience and performance of high-temperature superconductor-based generator systems.

Design and improvement of torque characteristics of half‐wave rectified variable field flux motor with axial gap structure

AbstractThe axial gap structure of a half‐wave rectified variable field flux motor (AG‐HVFM) has been proposed, which has a double stator structure and field winding short‐circuited by a diode. Although the AG‐HVFM can achieve a high‐efficiency drive in wide speed and torque range via variable field flux control, its structure deteriorates the average torque and torque ripple. In this paper, we sequentially design the core shape, aspect ratio, and current control method for an AG‐HVFM to improve its torque characteristics.

Torque Ripple Reduction in Brushless Wound Rotor Vernier Machine Using Third-Harmonic Multi-Layer Winding

This article aims to realize the brushless operation of a wound rotor vernier machine (WRVM) by a third-harmonic field produced through stator auxiliary winding (X). In the conventional model, a third-harmonic current is generated by connecting a 4-pole armature and 12-pole excitation windings serially with a three-phase diode rectifier to develop a pulsating field in the airgap of a machine. However, in the proposed model, the ABC winding is supplied by a three-phase current source inverter, whereas the auxiliary winding (X) carries no current due to an open circuit. The fundamental MMF component developed in the machine airgap creates a four-pole stator field, while the third-harmonic MMF induces the harmonic current in the specialized rotor harmonic winding. The rotor on the other side contains the harmonic and the field windings connected through a full-bridge rectifier. The electromagnetic interaction of the stator and rotor fields generates torque. Due to the open-circuited winding pattern, the proposed machine results in a low torque ripple. A 2D model is designed using JMAG-Designer, and 2D field element analysis (FEA) is carried out to determine the output torque and machine’s efficiency. A comparative performance analysis of both the conventional and proposed topologies is discussed graphically. The quantitative analysis of the proposed topology shows better performance as compared to the recently developed third-harmonic-based brushless WRVM topology in terms of output torque and torque ripples.

Питание сверхпроводящих систем динамическим вращением трехфазного поля

In this work a device for powering superconducting systems by pumping magnetic flux is presented. The pumping is carried out by dynamic rotation of the 3-phase magnetic field in the motor stator, which has three pairs of coils.

Experimental investigation on the heat transfer performance of Galinstan liquid metal driven by electromagnetism

Liquid metals have excellent heat transfer performance and unique electromagnetic characteristics, providing new visions for cooling the high speed motorized spindle shaft. Liquid metal can be driven by the magnetic field of the motor stator to induce current with no dynamic seal problem. In the present study, a shaft cooling structure of a motorized spindle with Galinstan liquid metal as the working fluid was designed and the heat transfer performance of the designed structure was investigated experimentally. The obtained results at the rated speed and rated current show that the induced voltage in the wire installed on the shaft reaches 1.2 V, which can circulate the liquid metal in an 8 mm diameter copper pipe. In this case, its equivalent thermal conductivity reaches 8.1?104 W/m ?C, which can effectively reduce the temperature of the motorized spindle rotor and make the temperature distribution of the motorized spindle more uniform.

Simulation of PMSM Vector Control Using Multisim and LabVIEW

This paper represents the simulation of field-oriented control of a permanent magnet synchronous motor. Using Clark-Park transform and three PI controllers for controlling speed, direct-axis current, and quadrant axis current. As maximum torque occurs when the rotor field and stator fields are 90 degrees from each other. The goal is to bring the stator field always orthogonal to the rotor field. The simulation is performed using Multisim and LabVIEW software

Sub-harmonic-based Cost-effective Brushless Wound Rotor Synchronous Machine Topology

This paper proposes a sub-harmonic-based brushless wound rotor synchronous machine (WRSM) topology. The proposed topology involves two three-phase stator windings with a different number of turns. Both windings are linked in parallel and are provided with current from a single inverter. One of these windings is a four-pole winding while the second winding is a two-pole winding. This arrangement generates a magneto-motive force (MMF) in the air-gap of the machine comprising of two components: a regular fundamental MMF and a sub-harmonic MMF. The fundamental component produces the main stator field whereas the sub-harmonic component generates a sub-harmonic field that is utilized to produce a harmonic current in a two-pole rotor harmonic winding. The induced harmonic current is rectified to inject direct current (DC) to the field winding and produce a four-pole rotor magnetic field. The four-pole rotor magnetic field when magnetically interacts with the same number of the main stator field poles producing torque. Finite element analysis (FEA) is carried out to confirm the operation and achieve the electromagnetic behavior of theproposed topology.

Rotor Field-Oriented Control of Doubly Fed Induction Generator in Wind Energy Conversion System

In this study, robust and high-performance vector control of a rotor side converter (RSC) was performed for stability and efficient operation doubly fed induction generator (DFIG) based on the variable speed wind turbine (VSWT). The mathematical model of the DFIG is simulated in the computer. Amplitude and frequency of the voltage in the DFIG were controlled for different values of load and variable speeds. In the experimental study, a DFIG-based wind turbine system was set up in the laboratory. The field position of the stator was detected from stator voltages by a phase-locked loop (PLL) circuit. The rotor position was measured with an incremental encoder connected to the rotor shaft of the DFIG. The angular position of the slip was calculated by the difference between the rotor and the stator field positions. The frequency and amplitude of rotor currents were determined with the angular position of slip. To generate output voltages of converter feeding rotor windings, the space vector pulse width modulation (SVPWM) technique was used. In the experimental study, the RSC was controlled with the DS1103 board. The prepared experiment set was tested at different operating speeds.

Rotating Rectifier Fault Diagnosis of Nuclear Multiphase Brushless Excitation System Based on DTW Metric and kNN Classifier

Multi-phase annular brushless excitation system is widely used in large-capacity nuclear power units. Accurate fault diagnosis of the rotating rectifier is of great significance to improve the reliability of the excitation system. However, the traditional diagnosis method based on harmonic analysis of stator field current has some deficiencies. In this paper, a novel diagnosis method using field current waveforms and artificial intelligence is presented. Firstly, the various shape features in field current waveforms of the different rotating rectifier faults are analyzed. Then, the field current waveforms are used as the input of a hybrid algorithm based on the dynamic time warping (DTW) metric and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -Nearest Neighbors ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> NN) classifier (DTW- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> NN). That is, a DTW metric is used to calculate the distance among the shape features in field current waveforms and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> NN classifier is used to diagnose the specific rotating rectifier fault. Finally, experiments on an 11-phase prototype prove the effectiveness of the hybrid method DTW- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> NN. It is worth mentioning that an improved training set including all trends of field current waveforms should be selected to avoid the asymmetry between each pair of field poles. The learning method provides a new idea for fault diagnosis of the rotating rectifier.

Design and Analysis of a Stator Field Control Permanent Magnet Synchronous Starter–Generator System

In recent years, the permanent magnet synchronous motor (PMSM) has garnered significant attention due to its high power density and efficiency in applications such as electric vehicles, aviation, and other domains. This paper proposes a stator field control permanent magnet synchronous starter–generator (SFC-PMSSG) system. The starter–generator system comprises the SFC-PMSSG and a field controller (FC). A mathematical model of the SFC-PMSSG is established. Finite element analysis (FEA) is employed to obtain the electromagnetic parameters of the SFC-PMSSG, and the characteristics of the SFC-PMSSG are analyzed. A circuit simulation model of the FC is established to assess the control effect and the loss of the FC. A co-analysis of the system is conducted, and the results demonstrate that the SFC-PMSSG system can maintain output voltage stability as load and speed conditions vary.

Time–Frequency Characteristics Analysis and Diagnosis of Rotating Rectifier Faults in Multiphase Annular Brushless System

The excitation system with a multi-phase annular brushless exciter (MPABE) is widely used in large-capacity nuclear power plants. However, in field operation, the rotating rectifier of the excitation system often fails due to the damage of diodes, which can cause serious consequences in long-term operation. To better protect the rotating rectifier, accurate grasp of the characteristics after the rotary rectifier faults becomes essential. Since the rectifier rotates with the rotor at high speed, the rectifier fault cannot be monitored directly. However, it is feasible to monitor the fault according to the characteristics induced in the stator field winding of the MPABE. Hence, this paper makes a thorough theoretical analysis of the rectifier fault mechanism to obtain the time-domain and frequency-domain characteristics of the stator field current when the rectifier is under normal operation, one-tube open-circuit fault, one-phase open-circuit fault and two-phase open-circuit fault. Then a new rectifier open-circuit fault diagnosis method based on the time-frequency characteristics of the fault excitation current is proposed. The final prototype and field experiments show that this method is simple and reliable, which can be used to monitor and detect the rotary rectifier faults in MPABE system.

Analysis and weakening of radial electromagnetic forces in high‐speed permanent magnet motors with external rotors based on shape functions

AbstractIn this paper, a strategy of integrating direct‐drive turbine compressors with high‐speed permanent magnet external rotor motors is used to improve the problems of large footprint, low efficiency and high maintenance costs. The rotor of the motor will vibrate under the action of radial electromagnetic force when rotating, and under the action of high pressure and high speed gas, it may aggravate the rotor vibration. In the case of changing the original mechanical structure of the turbine, the vibration of the motor rotor needs to be analysed. In the paper, the radial electromagnetic force applied to the rotor is analysed. The influence of the order and size of the stator and rotor magnetic field harmonics on the size, frequency and order of the radial electromagnetic force wave is summarised. In order to weaken the radial electromagnetic force, this paper proposes a shape function about the magnetic pole size and designs a magnetic pole accordingly. The validity of the shape function was confirmed by comparing the radial electromagnetic force wave with a conventional, surface‐mounted, built‐in magnetic pole structure. Finally, based on the analysis of the rotor dynamics mode, the law of the effect of the change of the pole arc coefficient of the pole on the radial force was analysed using harmonic response, and reasonable conclusions were drawn.

Gradual Electronic Pole Changing Technique to Minimize the Circulating Currents During Pole/Mode Transition in Induction Motor Drive

This paper proposes a control strategy for the electronic pole changing (EPC) induction motor drive (IMD) for the transition between 3-ϕ,12-pole mode to 9-ϕ,4-pole mode. The proposed control strategy employs a gradual electronic pole changing (GEPC) technique which linearly demagnetizes the IMD winding from 3-ϕ,12-pole and magnetizes progressively to 9-ϕ,4-pole mode. The proposed GEPC technique is also compared with the instantaneous EPC technique for its performance. The proposed GEPC solution eliminates the issue of the circulating current, which exists in the instantaneous EPC technique and is responsible for negative torque generation during pole transition from 3-ϕ mode to 9-ϕ mode. Apart from eliminating the circulating current, the proposed GEPC strategy also sorts out various typical issues which exist in instantaneous EPC technique during pole/mode transition. The various issues in the instantaneous mode transition are (i) absence of interlocking between stator and rotor fields, (ii) oscillations in the flux between the 12-pole (3-ϕ) and 4-pole (9-ϕ), (iii) strengthening and weakening 4-pole formations in stator and rotor, (iv) distorted flux and pole formations, (v) dip in speed, and (vi) high oscillations/ripple content in torque and speed. Ansys simulation is done using Maxwell 2-D integrated with Twin-builder for EPC IMD for instantaneous and proposed GEPC techniques. Further, the paper presents the experimental results to validate the simulation studies.

A study on the vibrations of the induction motors having squirrel cage rotor

In the present paper are examined the vibrations of the induction motors having squirrel cage rotor. The study is performed by means of spectrograms presenting the vibration speed depending on the frequency, drawn up for motors produced by S.C.Electroprecizia Electrical Motors Sacele and on the base of the study of the specialty literature. There have been studied the motors of 3000, 1500, 1000 RPM up to 7,5 kW and are proposed measures to reduce their vibration level. Among the possible solutions proposed are using of a waved spring washer between the end shield and the bearing's external ring, the inclination in V or zigzag of the cage's bars at a half of the rotor pitch and reducing the stator field harmonics.

A COMPREHENSIVE STUDY OF THE INFLUENCE OF DAMAGES OF THE STATOR WINDING OF ASYNCHRONOUS MOTORS DURING OPERATION OF VEHICLES

The efficiency of providing transportation is related to increasing the reliability of the transportation infrastructure. To ensure reliable and economical operation, it is necessary to develop systems of functional diagnostics of the main elements of vehicles, which provide continuous control of the technical condition of its main elements. Monitoring the state of asynchronous electric motors as part of electric drives of vehicles is an important modern issue, the solution of which depends on the reliability of the entire transport infrastructure. The most common type of damage in motors during operation is an inter-turn short circuit in the stator winding phase. Turn-to-turn closures are difficult to detect, but if they are present, the engine continues to operate with a change in its operating and electrodynamic indicators and characteristics. However, depending on the degree of turn-to-turn closures (the number of closed turns) in the winding phase, the probability and time of an emergency stop of the electric drive increase. In this paper, the influence of turn-to-turn closures of varying degrees on mechanical, electrical and energy parameters and engine characteristics under various operating modes has been studied. In the course of the research, a mathematical model of an induction motor was used with the established adequacy of the simulation results and the possibility of creating an asymmetric rotating stator field. The adopted simulation model of an induction motor with a squirrel-cage rotor is written in retarded coordinates. Also, studies were carried out on the effect of turn-to-turn closures on the ripple coefficient of the electromagnetic torque and the unbalance coefficient of the stator phase currents. Based on the data obtained, recommendations are given on choosing the most effective method of electric current for diagnosing interturn faults in assessing the technical condition and predicting the failure-free operation of an asynchronous electric motor for use as part of an electric motor under construction. - in diagnostic systems of cars.

Impact of Aspect Ratios of Solid Rotor, Large Air Gap Induction Motors on Run-Up Time and Energy Input

This article introduces a unique three-phase induction machine with a large air gap and a copper-coated iron cylinder. The motor is built in an X-ray tube for medical applications where key performance indicators are the start-up time, generated rotor, and total energy during the run-up. The common equivalent circuit for induction motors is utilized to systematically analyze the effect of the rotor protrusion length variation on these key performance indicators by means of three-dimensional (3D)-FEA. However, due to the large air gap and dominating winding head standard evaluation tools, such as the no-load and locked-rotor tests do not provide accurate circuit parameters. Thus, a combined no-load and locked-rotor test evaluation is introduced. Furthermore, to avoid the time and computational effort of time-stepping 3D-FEA, time harmonic and static 3D-FEA is introduced. To validate these simplified 3D-FEA simulations, results are compared with the selected time-stepping 3D-FEA results. Experimental results verify the 3D-FEA results. After establishing a routine to identify accurate equivalent circuit parameters by means of 3D-FEA, the parameters for three different stator lengths each combined with six different rotor lengths are identified. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V/f</i> -controlled run-up simulations are then conducted to generate the results. Results quantify the tradeoff between start-up time, generated rotor, and total energy depending on the rotor protrusion, e.g., the start-up time is indirectly proportional to the rotor protrusion and directly proportional to the rotor frequency (the relative frequency between stator field and rotor speed). The effect of the rotor temperature, which can reach up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim 390^\circ \,$</tex-math></inline-formula> C, on the results is included.

Research on Torque Performance of a Traction Motor by Using Fe-Co-V Soft Magnetic Alloys

As a device that realizes the “static-to-motion” transformation which influences the national economy and people’s livelihood, the electric machine (EM) has put forward higher requirements for the torque/power density with the development of industry. It is difficult to meet the new requirements by using traditional silicon steel. Therefore, the application of “new” materials has become a breakthrough point. This article studied the properties and the application of Fe-Co-V alloys (1J22) which has a high saturation magnetic polarization, then analyzed its performance in high torque density EMs. Since the stator field is a rotating magnetic field which changes with time, the variable-angle magnetic performance test was carried out on 1J22 to discuss the influence of the magnetic performance under different shear angles on the stator magnetic flux. The EM’s design and prototype production were carried out for the unique properties of the 1J22 material itself. Compared with the EM model using traditional non-grain-oriented (NGO) silicon steel 35ADG1900, the use of 1J22 material can solve the temperature rise problem under special working conditions. At the same time, the feasibility of 1J22 in high torque density traction motor has been verified.

A New Hybrid Magnet Dual Stator Field Modulation Machine With Different Split Ratios of Stators

A new type of hybrid magnet dual stator field modulation machine with different split ratios of stators (DSR-HMDSFMM) is proposed in this article, which has the merit of high torque density. The split teeth of stator sever as modulators to modulate air gap flux density based on the magnetic gearing effect for high torque production. The total split tooth number of inner stator is equal to that of outer stator because the pole pair numbers of armature reaction and permanent magnet (PM) excitation on rotor are equal. Furtherly, the inner and outer stators with different split ratios and same split tooth number are employed to increase torque production because armature windings with high winding factor and high turn number can be used. In addition, the employment of hybrid magnet excitation can increase space utilization and enhance the air gap flux density with low harmonic distortion. Therefore, the proposed DSR-HMDSFMM can achieve high torque production with the same volume and PM usage. In order to find the optimal split ratio match of stators, several DSR-HMDSFMMs with different combinations of split ratios are proposed and calculated. The configuration and operating principle are illustrated, together with electromagnetic performances of the proposed machines analyzed using finite element analysis (FEA). The FEA-predicted results show that the proposed HMDSFMM exhibits high air-gap flux density with low harmonic distortion and high torque density, which is promising for the direct-drive applications.

A New Partitioned Stator Field Modulation Machine With H-Shape Permanent Magnet Excitation

A new partitioned stator field modulation machine (PSFMM) with H-shape permanent magnet (HPM) excitation (HPM-PSFMM) is proposed, which is evolved from the conventional flux-switching machine (FSM) and flux-reversal machine (FRM). The proposed HPM-PSFMM combines the merits of high reliability and good heat dissipation characteristic. In addition, it exhibits high torque production with low torque ripple. Based on the theory of electrical machine operation, the FSM and FRM can be transformed into PSFMM with interior permanent magnet (IPM) and surface-mounted PM (SPM) excitation by changing the position of PM excitation, respectively. It benefits to improve space utilization and increase slot area for a large number of armature windings. For reducing the flux leakage and enhancing the flux density in air gaps, the IPM and SPM excitation are combined into HPM excitation. The iron-pole rotor between the inner and outer stators acts the role of modulator to modulate the magnetic field excited by HPM excitation to couple with the armature reaction for converting electromechanical energy. The evolution process, operating principle, and key design parameters of the proposed HPM-PSFMM are presented. Finally, using the finite element analysis (FEA), it can be proven that the proposed HPM-PSFMM has the merits of high torque production, low flux leakage, low total harmonic distortion (THD), and low torque ripple when compared to other stator-PM machines, which is a desirable choice for high stability applications.

Theoretical investigation of a novel three-phase alternating current liquid metal vortex magnetohydrodynamic generator

Magnetohydrodynamic (MHD) generators are a class of devices that directly convert mechanical energy of a flowing fluid into electrical energy. However, due to the production of low magnitude voltages at low fluid velocities, they are not very useful for harvesting energy from the everyday environment at a watt scale. This work theoretically investigates a novel three-phase alternating current liquid metal vortex MHD, capable of generating power on a scale of watts and voltages on a scale of volts from a wide range of environmental energy sources. A new theoretical approach is utilized, where the induced fields and the stator fields are calculated independently which makes it easy to analyze different operational modes of the system. Two limiting approximations namely duct flow and disk flow have been analyzed and the effect of the number of poles and of the electromagnetic slip on the generated power and current is studied. The obtained analytical and numerical results are in good agreement and provide a robust foundation for the generator design and experimental characterization. The formulated approach also shows that such MHD devices can be easily scaled for various applications requiring power in a range from mW to W.