Stator Winding Configuration Research Articles

A Universal High-Frequency Induction Machine Model and Characterization Method for Arbitrary Stator Winding Connections

High-frequency modeling of induction machines plays an important role in investigating motor drive electromagnetic interference issues such as stator winding reflected-wave overvoltage and bearing discharging current. Characterization of high-frequency machine models requires measurements of machine's differential-mode (DM) and common-mode (CM) impedances up to tens of MHz. The machine's stator winding connections, e.g., single-, and series-, parallel-winding Y/Δ configurations, influence the measured DM and CM impedances and model parameters. In this paper, a universal high-frequency equivalent circuit model capable of representing induction machines with arbitrary stator winding connections is proposed. The new model features a simple structure with a straightforward characterization method. Specifically, only one stator winding configuration is required for impedance measurements to fully characterize the machine model for arbitrary stator winding connections. The proposed methodology is demonstrated using a 7.5 hp dual-voltage nine-terminal/lead induction machine and a drive system. The simulated DM and CM impedances as well as the motor overvoltages show excellent agreement with the experimental results. The proposed model and characterization method represent significant improvement in terms of accuracy, applicability/generality, and convenience compared to prior conventional models.

Design and implementation of brushless doubly fed induction machine with new stator winding configuration

Brushless doubly fed induction machine has acquired relevance as a wind electric generator because of its relative merits over doubly fed induction generator. However, the main drawback of brushless doubly fed induction machine is the presence of torque ripples due to spatial and time harmonics caused by two stator windings and complex rotor structure. In this article, a special design of brushless doubly fed induction machine using delta-star connection in one of the two stator windings is proposed to reduce the torque ripples. Simulation of the new brushless doubly fed induction machine design is performed in ANSYS Maxwell software, and the results when compared with the conventional winding design validated the effectiveness of the new design in minimizing the torque ripples. Prototype of the new brushless doubly fed induction machine has been fabricated and tested in laboratory. Tests have been conducted in both synchronous and asynchronous modes of brushless doubly fed induction machine. Simple induction and cascade connections have been tested in asynchronous motoring mode. Motoring as well as generating conditions have been tested in synchronous mode. Test results show that the new brushless doubly fed induction machine has not only the desired characteristics for wind turbine generator but also capabilities suited for variable torque–variable speed motor applications as well as constant speed applications.

A Novel Synthetic Loading Method for Multiple Three-Phase Winding Electric Machines

This paper develops a version of the synthetic loading method, suitable for the testing of multiphase machines with multiple three-phase distributed windings. The method is at first discussed in general terms for a structure with k three-phase stator windings (i.e., total number of phases is n = 3 k ). Subsequent detailed development is described for a dual three-phase (six-phase) stator winding configuration. With a control architecture that allows the use of half of the three-phase windings as a motor and the other half as a generator, the machine (and/or the converter) can be tested under full rated power without the need for any mechanical load. Moreover, the power consumed from the grid is in essence equal only to the total losses of the system. Modeling, based on the double d-q approach, and the control layout that includes full cross-coupling decoupling are described for a permanent magnet (PM) synchronous machine. An experimental test rig with a double three-phase PM machine of 150 kW rating is detailed and the samples of experimental results are provided to verity the theoretical considerations.

Reduction of Inverter Carrier Harmonic Losses in Interior Permanent Magnet Synchronous Motors by Optimizing Rotor and Stator Shapes

In this paper, we investigate rotor and stator designs of interior permanent synchronous motors for variable speed/load applications to reduce the carrier harmonic losses caused by pulsewidth modulated inverters. The rotor core and magnet shapes are determined by automatic optimization methods with electromagnetic field analysis, which considers the inverter carrier. Appropriate stator-winding configurations are also investigated by this analysis. It is clarified that the total carrier harmonic loss can be reduced by more than 20% by optimizing both the stator and rotor shapes, whereas the other important characteristics are not deteriorated. The mechanism of carrier loss reduction is also clarified.

A Novel Asymmetric and Unconventional Stator Winding Configuration and Placement for a Dual Three-Phase Surface PM Motor

Multi-phase permanent magnet (PM) motors are becoming more popular because of their higher torque densities, enhanced efficiency, and fault-tolerant capabilities. In this paper, a novel six-phase PM synchronous motor with a new asymmetric stator ac winding scheme and placement is proposed. Two identical dual three-phase asymmetrical winding sets are placed in two separate half of the stator in 180 mechanical degrees. This approach reduces the phase resistance and thus copper losses. Torque quality of the proposed motor is also analyzed using 2-D finite element method in detail. It can be concluded that the proposed novel asymmetric stator has more advantages to offer than conventional six-phase PM motors.

Static coupling effect of a two‐degree‐of‐freedom direct drive induction motor

Two-degree-of-freedom motors are capable of producing linear, rotary, and helical motion, and thus have widespread applications in special industries. In this study, a new concept- static coupling effect is studied in the two-degree-of-freedom direct-drive induction motor (2DoFDDIM). The proposed approach is based on the image method and the three-dimensional (3D) finite-element method. The image method model is established to analyse its reasons and predict the main effects, which are then verified by the proposed 3D finite-element static coupling model and experiments. The induced voltages and currents are produced in the static part and induced torque or force is obtained, even though the static part is not energised. It is concluded that the static coupling effect increases with the supply frequency and is influenced by the stator winding configuration. Thus, the existence of the static coupling effect is confirmed, which must be taken into account in future optimisation and precise control of the 2DoFDDIM.

An Investigation of Motor Topology Impacts on Magnet Defect Fault Signatures

This paper presents a study on the topology-dependent magnet defect fault signatures in permanent-magnet motors. A new analytical approach is introduced to characterize the fault signatures in stator back electromotive force (EMF) and current waveforms using magnetic equivalent circuit. Stator winding configuration, winding connection type and location of damaged rotor magnets are some of the physical properties affecting the fault signature characteristics. Several cases with different number of pole and slot are investigated through the proposed method. In addition, different winding connections (including star and delta connection), different winding configurations (including single and double layer, fractional and full coil pitch), and different magnet defect number and location are scrutinized. It is shown that there are some cases exhibiting different fault patterns than the ones obtained through well-known fault models defined in the literature. It is essential to take these discrepancies into account in order to avoid false alarms. In addition, it is observed that some of the fault signatures show up in the stator back EMF spectrum but not in the current spectrum due to location and severity of magnet defect, and design specs. Comparative 2-D finite-element simulations and experimental results justify the theoretical magnet defect fault analysis and show the efficacy of the proposed approach.

Theoretical Analysis and Calculation Model of the Electromagnetic Torque of Nonsalient-Pole Synchronous Machines With Interturn Short Circuit in Field Windings

This paper studies the electromagnetic torque (EMT) of a nonsalient-pole synchronous generator with the interturn short circuit of field windings (ISCFW). First, the virtual displacement method serves as a basis for analyzing the postfault steady-state harmonic characteristic of EMT. The interactions among various space magnetic fields with different orders, speeds, and rotation directions generated by the stator and rotor are considered. A general conclusion on the EMT characteristics under the fault is then derived. Second, based on the connection conditions of the rotor and stator windings under the fault, the voltage and flux relationships among each circuit are analyzed and the calculation model of the EMT under the fault is built. Through comparisons among the simulations, experiments, and theoretical analyses, the correctness of the calculation model is verified. In addition, a three-pole-pair nonsalient-pole synchronous generator after transformation is used for the case study. The calculation and analysis results indicate that ISCFW generates ac pulsation components with their harmonics closely linked to the stator winding configuration. This paper deepens the fault mechanism of ISCFW and lays a foundation for fault monitoring based on mechanical characteristics.

Detection of interturn faults in PMSMs with different winding configurations

Interturn faults in permanent magnet synchronous motors (PMSMs) may develop fast into more severe faults such as coil-to-coil, phase-to-phase and phase-to-ground short circuits. These faults are very destructive and may irreversibly damage the PMSM. Therefore, it is highly desirable to develop suitable methods for the early detection of such faults. The effects of interturn faults are visible in both the stator currents and the zero-sequence voltage component (ZSVC) spectra. By designing appropriate fault diagnosis schemes based on the analysis of the harmonic content of such electric variables it is possible to detect short circuit faults in its early stage. However, the stator winding configuration of the PMSM deeply impacts the harmonic content of both spectra. This paper studies the effects of different stator winding configurations in both the stator currents and the ZSVC spectra of healthy and faulty machines. Results presented may help to develop fault diagnosis schemes based on the acquisition and further analysis of the stator currents and/or the ZSVC harmonic components.

Effect of Stator Winding Connection on Performance of Five-Phase Induction Machines

This paper studies the effect of stator winding configuration on the performance of five-phase induction machines under healthy as well as faulty conditions. The study compares two connections, namely, star and pentagon connections. The comparison is conducted using both simulation and experimental results. The steady-state model based on symmetrical components theory is introduced for both connections with one-line open due to a converter fault, and the corresponding machine characteristic curves are estimated. During faults, two alternatives for machine operation are possible, namely, open-loop control and optimal current control. While the first alternative corresponds to higher torque ripple and unbalanced winding currents, the second option necessitates unbalanced phase voltages and typically an increased dc-link voltage to source the required optimal currents. Consequently, an increase in the employed semiconductor device rating is required, which is a critical design factor particularly in medium-voltage applications. A new V/f control technique is proposed to ensure disturbance-free operation with one-line open for both winding connections. Based on the unbalanced machine model and experimental verification, the derating factors that ensure safe machine operation for both winding connection alternatives are calculated. The comparison between the two connections shows the superiority of the pentagon connection under fault conditions in terms of efficiency, average torque, torque ripples, and derating factor.

Winding distribution effects on induction motor rotor fault diagnosis

The sidebands around stator currents harmonics as a potential tool for supporting the diagnosis of rotor faults in induction motors are analyzed in this paper. The presence of broken bars introduces high frequency components in the machine currents spectrum in addition to the characteristic sidebands around the fundamental component. These additional components are due to the interaction between, rotor asymmetry and either the voltage harmonics, or winding distribution, or rotor slots. In particular, the components at frequencies near to fifth and seventh harmonics, produced by the interaction between the rotor faults and the harmonics of the spatial distribution of stator windings, are analyzed in this work. A multiple coupled circuit model of the induction motor is used to evaluate the sensitivity of these components for different stator winding configurations, load level, supply voltage conditions, and different number of broken bars. Simulation results showed that a particular analyzed component near to fifth harmonic depends mainly on fifth harmonic of winding distribution, which remains almost constant for most common distributions. Therefore, it is expected that this component should be found in most motors with broken bars. Finally, experimental laboratory results and two industrial cases that validate the analysis are presented.

Rotor demagnetization effects on permanent magnet synchronous machines

The effects of asymmetrical magnet faults on the rotor of Permanent Magnet Synchronous Machines (PMSM) are analyzed in the present work. Two different stator winding configurations, series and parallel connected windings, are considered in the analysis. From PMSM with parallel windings, a fault detection strategy based on the information contained in the branch-current spectrum is proposed. A fault severity factor is defined to quantify demagnetization on a single magnet. This factor is practically independent from the motor load conditions. Simulation results using a finite element model are obtained to evaluate the feasibility of the proposal. Additionally, voltage reduction and current derating due to rotor demagnetization are also evaluated. Experimental results are presented to validate the proposal.

ANALYSIS OF VOLTAGE FORMING METHODS FOR MULTIPHASE INVERTERS / DAUGIAFAZIŲ DAŽNIO KEITIKLIŲ ĮTAMPOS FORMAVIMO METODŲ ANALIZĖ

The article discusses advantages of the multiphase AC induction motor over three or less phase motors. It presents possible stator winding configurations for a multiphase induction motor. Various fault control strategies were reviewed for phases feeding the motor. The authors propose a method for quality evaluation of voltage forming algorithm in the inverter. Simulation of a six-phase voltage source inverter, voltage in which is formed using a simple SPWM control algorithm, was performed in Matlab Simulink. Simulation results were evaluated using the proposed method. Inverter’s power stage was powered by 400 V DC source. The spectrum of output currents was analysed and the magnitude of the main frequency component was at least 12 times greater than the next biggest-magnitude component. The value of rectified inverter voltage was 373 V. Article in Lithuanian. Santrauka Straipsnyje pristatomi daugiafazių variklių pranašumai, palyginus su trifaziais ir vienfaziais. Apžvelgiama variklių sandara ir pristatomi daugiafazių variklių apvijų tipai. Pristatomos variklių valdymo strategijos sugedus apvijos ar inverterio galios pakopos raktui. Pasiūloma daugiafazių dažnio keitiklių įtampos formavimo algoritmų vertinimo metodika. Matlab Simulink terpėje modeliuojamas šešiafazis dažnio keitiklis, kuriame veikia sinusinio impulso skvarbos moduliavimo įtampos formavimo algoritmas. Pagal sukurtą vertinimo metodiką įvertinami dažnio keitiklio modeliavimo rezultatai, pateikiamos išvados.

Simplified mathematical model of inter-turn short circuit of field windings in hydro-generators and its application

Inter-turn short circuit of field windings is a common electrical fault of generators. Simulation is an important method of investigating the fault and providing data support for fault monitoring. However, huge numbers of pole pairs and damper loops in large hydro-generators would lead to lengthy calculation time, hindering scientific research and engineering application. To deal with this problem, we analyze a theoretical basis for a damper winding simplified model and then propose an equivalent treatment method. Through the analysis of steady-state current harmonic characteristics of generators with different stator winding configurations during the fault, the simplified models suitable for steady-state calculation are derived from two aspects, namely, additional rotor harmonic current frequency characteristics and the relationship of the amplitude as well as the phase of each branch current of the stator. The calculation and experimental results of the two simplified models are then compared to verify the models’ correctness. A calculation example of the Three Gorges left bank VGS generator shows few deviations between the calculation results of the simplified model and the original model. Moreover, the calculation time using the simplified model is 1/1500 that using the original model, which provides a more effective tool for on-line fault monitoring. Finally, the sensitivity-verification application of the fault-monitoring scheme based on the stator steady-state unbalanced current RMS is depicted. The result shows that the scheme can monitor two-turn short circuits of field windings in the Three Gorges generator and provide high sensitivity.

Wide Operational Speed Range of Five-Phase Permanent Magnet Machines by Using Different Stator Winding Configurations

The winding changeover technique is an effective method for extending the operational speed range of permanent magnet synchronous machines (PMSMs). Unlike three-phase machines which could be wound in wye or delta connections, there are three possible connections, i.e., star, pentagon, and pentacle for five-phase electric machines. In this work, the effects of these three winding connections on a five-phase PMSM performance are studied. First, based on the mathematical model and finite-element analysis, the effects of different stator winding connections on torque-speed and efficiency characteristics are investigated. Then, the complete electric machine drive system including the winding changeover mechanism is simulated to present its dynamic performance. Finally, experimental results are provided to show the transient and steady-state operation of a five-phase PMSM with star, pentagon, and pentacle winding connections.

Geometry Optimization of PMSMs Comparing Full and Fractional Pitch Winding Configurations for Aerospace Actuation Applications

Optimization of electromechanical aerospace actuators requires a multi-objective and comparative analysis in order to account for performance and manufacturing cost terms. This paper introduces a particular optimization methodology presenting stable convergence characteristics which has been applied to optimize the geometry of both Fractional Slot Concentrated Winding (FSCW) and Full Pitch Concentrated Winding (FPCW) permanent magnet motor configurations. The proposed algorithm combines technical and physical advantages of the FSCWs and FPCWs into an optimally shaped stator-winding configuration. The resultant motor design has been validated through a prototype and experimental results illustrated its suitability for aerospace actuation applications.

Modular Motor/Converter System Topology With Redundancy for High-Speed, High-Power Motor Applications

A novel motor/converter system topology is presented, which is ideal for high-power, high-speed motor applications, especially in the case of utilizing permanent-magnet synchronous AC motors. The proposed system utilizes space-shifted, split-phase, motor stator configuration, with a modular converter topology. The stator winding configuration allows current harmonics from the different phases to cancel out each other, while maximizing the fundamental space vector. Hence, the proposed topology does not require the high-frequency pulsewidth modulation normally needed to reduce the time-domain harmonics found in the phase currents. The switching frequency of the power converters can actually be as low as the fundamental frequency, which significantly reduces the switching losses, associated electromagnetic interference mitigation, and cooling requirements. The modularity of the proposed topology also simplifies overall system design and manufacturability, and provides redundancy and inherent fault tolerance. In this paper, the system topology and control strategy are discussed. Simulation and finite-element analysis results are presented to illustrate the harmonic cancellation and other advantages of the proposed topology. Experimental results also confirm the validity of the proposed system topology.

Design Considerations for Tubular Flux-Switching Permanent Magnet Machines

This paper describes a tubular, three-phase, flux-switching permanent magnet (PM) brushless machine that combines salient features from switched reluctance (SR) and conventional PM brushless machines. Feasible slot-pole number combinations, which are also applicable to rotary flux-switching machines, are derived. This paper also examines an alternative stator winding configuration, which is unique to the tubular machine topology. It is shown that this yields ~10%-15% higher thrust force capability as compared to a flux-switching machine equipped with a conventional winding.

Eddy-current loss in the rotor magnets of permanent-magnet brushless machines having a fractional number of slots per pole

We develop an analytical model for predicting the eddy-current loss in the rotor magnets of permanent-magnet brushless machines that have a fractional number of slots per pole, when either all the teeth or only alternate teeth are wound, and in which the unwound teeth may be narrower than the wound teeth. The model enables the magnetic field distribution in the air gap and magnet regions to be determined, by neglecting the eddy-current redistribution effect and assuming that the eddy currents are resistance limited. It can account for space-harmonic magnetomotive forces (MMFs) resulting from the winding distribution and time-harmonic MMFs due to nonsinusoidal phase currents, as well as for the effect of curvature and circumferential segmentation of the magnets. We have validated the model by finite-element analysis, and used it to investigate the eddy-current loss in the magnets of three surface-mounted magnet brushless motors that have similar slot and pole numbers, and employ identical rotors but different stators, when they are operated in brushless ac (BLAC) and dc (BLDC) modes. We show that the stator winding configuration, as well as the operational mode, significantly influence the resultant eddy-current loss.

An improved high-resolution hybrid stepper motor for solar-array drive of Indian remote-sensing satellite

This paper presents the computer-aided design and development of an improved 720-steps hybrid stepper motor used as the drive motor for the solar array of the Indian remote-sensing (IRS) satellite in the polar Sun-synchronous orbit. The motor is of pancake type with coil redundancy, and the step angle is 0.5/spl deg/. It is designed to deliver a constant holding torque of 1 Nm against a varying DC supply voltage of 28-42 V and in an operating temperature range from -10/spl deg/C to +60/spl deg/C. The authors introduce a phenomenon named as "torque saturation", achievable in a hybrid stepper motor by properly choosing the operating point of the rotor permanent magnet and the stator winding configuration. Apart from the computer-aided design procedure, relevant details regarding fabrication and testing are also provided. The test results of the developed motor match fairly well with the computed values and confirm the high performance of the developed hybrid stepper motor.