Modelling and analysis of asynchronous and synchronous torques in split-phase induction machines

In this thesis, the nature of asynchronous and synchronous torques in a split-phase induction machine is investigated and quantified. The equivalent circuit for this type of machine is derived using the rotating field theory. It is extended to include harmonic effects. Using this model, winding harmonics and permeance harmonics may be calculated independently of each other so that the model can be used to analyse asynchronous torques from winding harmonics as well as synchronous torques from permeance harmonics. These are calculated separately. The asynchronous torques appear as perturbations in the steady-state torque-speed curve while the synchronous torques only appear at specific speeds. The synchronous torques are superimposed onto the torque-speed curves to model both effects together. The model predictions are compared against test results using purpose-built experimental machines together with production machines. These have varying rotor bar number and skew. Different methods are used to assess the synchronous torques. It is found that measuring synchronous locking torque is not a straightforward matter; however, reasonable agreement is found between calculation and measurement. The work highlights the need for the correct choice of stator and rotor slot numbers together with the effect skew has on reducing the synchronous and asynchronous locking torques

Analytical prediction of the electromagnetic torques in single-phase and two-phase AC motors

The single-phase and two-phase versions of AC motors can be modelled by means of the two-axis (d-q) theory with sufficient accuracy when the equivalent circuit parameters are correctly estimated. This work attempts to present a unified approach to the analytical prediction of the electromagnetic torque of these machines. Classical d-q axes formulation requires that the reference frame should be fixed on the frame where the asymmetries arise, i.e. the stator and rotor. The asynchronous torques that characterize the induction motors are modelled in a stationary reference frame, where the d-q axes coincide with the physical magnetic axes of the stator windings. For the permanent magnet motors, that may exhibit asymmetries on both stator and rotor, the proposed solution includes: a series of frame transformations, followed by symmetrical components decomposition. As in single-phase and two-phase systems the homopolar component is zero; each symmetrical component – negative and positive – is further analysed using d-q axes theory. The superposition principle is employed to consider the magnets and rotor cage effects. The developed models account for the most important asymmetries of the motor configuration. These are, from the stator point of view, different distribution, conductors' dimensions and number of effective turns, non-orthogonal magnetic axes windings and from the rotor point of view, asymmetrical rotor cage, variable reluctance, and permanent magnets effect. The time and space harmonics effect is ignored. Test data are compared with the computed data in order to observe how the simplifying assumptions affect the level of accuracy. The analytical prediction methods make possible torque computation according to the nature of the torque being computed, namely, induction, reluctance and excitation (permanent magnet). The results are available for quasi steady-state, steady-state (rated or synchronous speed) and dynamic analyses. All the developed mathematical models can be used in preliminary design for further optimisation and accurate estimation in complex numerical models. Another important feature of the analytical models for single-phase and two-phase AC motors, is that they can be directly implemented in any suitable electrical drives control strategy.reviewe

Single-Phase Motors for Household Applications

Single-phase motors are widely used in household applications. Shaded-pole and split-phase capacitor-start single-phase induction motors are very popular for their ruggedness and their comparatively low cost. Recently, line-start single-phase motors are gaining market shares. However, their superior efficiency and torque density are counterbalanced by the higher cost of the rotor construction due to the magnets. This chapter compares the main structures of single-phase line-start motors, presenting their lumped parameter models and the finite element analysis. The equivalent circuits of the single-phase induction motor and of the line-start permanent magnet are derived. Different rotor structures for single-phase line-start permanent magnet (PM) motors are compared. The finite element method (FEM) is used to compare the characteristics of the motors. Motors with the same stator have been tested. No-load and load tests have been performed and compared to the FEM simulations and to the analytical model. Finally, the performances of line-start PM motors are compared to the shaded-pole induction motors in terms of torque density and efficiency

Preliminary Studies and Test Results of a Superconducting Hysteresis Motor with Multiphase Windings and Variable Number of Magnetic Poles

Part 15: Energy TransformationInternational audienceIn this paper a procedure for determining the number of different synchronous speeds that can be obtained from the stator of a drum motor as a function of the number of slots is presented. This preliminary study is foreseen for a hysteresis high-temperature superconducting motor, but the approach is directly applied in conventional motors. The targeted device has multiphase windings, in order to achieve full flexibility in torque-speed space through electronic variation of magnetic poles. Simulations are performed in order to achieve a qualitative understanding of the behaviour of the motor, namely in what concerns to torque and settling times from initial to synchronous speed. A prototype with eighteen slots in the stator and a bulk YBCO rotor is described and built, and experimental values of torque are obtained

Four quadrant control of induction motors

Induction motors are the nation's workhorse, being the motor of choice in most applications due to their simple rugged construction. It has been estimated that 14 to 27 percent of the country's total electricity use could be saved with adjustable speed drives. Until now, induction motors have not been suited well for variable speed or servo-drives, due to the inherent complexity, size, and inefficiency of their variable speed controls. Work at NASA Lewis Research Center on field oriented control of induction motors using pulse population modulation method holds the promise for the desired drive electronics. The system allows for a variable voltage to frequency ratio which enables the user to operate the motor at maximum efficiency, while having independent control of both the speed and torque of an induction motor in all four quadrants of the speed torque map. Multiple horsepower machine drives were demonstrated, and work is on-going to develop a 20 hp average, 40 hp peak class of machine. The pulse population technique, results to date, and projections for implementation of this existing new motor control technology are discussed

Multiphase induction motor drives - a technology status review

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operatio

Transient harmonic torques in induction machines: measurement and impact on motor performance

This paper focuses on the measurement of transient torques produced by the field harmonics in three phase squirrel cage motors and on the assessment of the operating conditions under which these torques might become significant. The paper presents first a model of the induction machine with any stator and rotor phase number and configuration, fed by arbitrary voltage waveforms and taking into account the space harmonics. Then, very much attention is paid to a reliable model validation against actual transient torques measurements. In this sense, the actual and great difficulties of measuring pulsating electromagnetic torques of several hundreds of Hertz are brought into light, the possible measurement techniques are critically reviewed and the solution chosen is discussed. Once the model accuracy has been experimentally confirmed, it is used to carry out a systematic plan of more than 250 simulations under clearly distinct operating conditions on five different motors. The analysis of these simulations yields a main practical conclusion: field harmonics may have (depending on the motor structure) a significant impact on electromagnetic torque, but only during transients characterized by high instantaneous frequencies of the rotor currents. For low slip transients, their impact is negligible. This conclusion is also theoretically justified in the paper.Echeverria Villar, JA.; Martínez-Román, J.; Serrano Iribarnegaray, L. (2012). Transient harmonic torques in induction machines: measurement and impact on motor performance. Electrical Engineering. 94(2):67-80. doi:10.1007/s00202-011-0216-4S6780942White D, Woodson H (1959) Electromechanical energy conversion. Wiley, LondonTaegen F, Hommes E (1972) Das allgemeine Gleichungssystem des Käfigläufermotors unter Berücksichtigung der Oberfelder. Teil I and II. Archiv für Elektrotechnik 55:21–31 and 98–105Van der Merwe FS (1976) The analysis of an electric machine with a smooth air-gap allowing for all winding MMF harmonics. Parts I and II. Archiv für Elektrotechnik 58:283–292 and 293–303Fudeh HR, Ong CM (1983) Modeling and analysis of induction machines containing space harmonics. Parts I, II and III. IEEE Trans Power Apparatus Syst PAS-102(8):2608–2615; 2616–2620; 2621–2628Hommes E, Paap GC (1984) The analysis of the 3-phase squirrel cage induction motor with space harmonics. Part 1 and 2. Archiv für Elektrotechnik 67:217–226 and 227–236Heller B, Hamata V (1977) Harmonic field effects in induction machines. Elsevier Scientific Publishing Co, AmsterdamSeinsch HO (1992) Oberfelderscheinungen in Drehfeldmaschinen. B.G. Teubner, SuttgartOberretl K (2007) Losses, torques and magnetic noise in induction motors with static converter supply, taking multiple armature reaction and slot opening into account. IET Electr Power Appl 1(4): 517–531Levi E, Bojoi R, Profumo F, Tolyat HA, Williamson S (2007) Multiphase induction motor drives. A technology status review. IET Electr Power Appl 1(4): 489–516Park RH (1933) Two-Reaction theory of synchronous machines. A.I.E.E. Trans 48:716–730, 1929 and 52:352–355Wallin C, Ling H, Rasool A (2001) Evaluation of torque pulses in industrial applications using the torque sensor TorductorR-s presented at Sensor for Industry conference. Illinois, USANCTE (2011) High dynamic, non contact, rotary torque sensor—Series 2000. http://www.ncte.de/ncte/cms/front_content.php?idcat=27Hübner Berlin (2002) Acc. sensor ACC93, Preliminary leafletDenne A, Rausch H, Freise W (1981) Aufnehmer zur Messung schnell veränderlicher Drehbeschleunigungen und Drehmomente. Technisches-Messen-tm 48: 339–342Hillner L (2002) Hübner Berlin. Notes about ACC93 installation in motor ABB M2AA112 M-4 from Universidad Politecnica de ValenciaSerrano-Iribarnegaray L, Martínez-Román J (2005) Critical review of the analytical approaches accounting for interbar currents and experimental study of ageing in two-speed asynchr. motors for elevator drives. IEE Proc Electr Power Appl 152: 72–80Echeverría-Villar JA (2004) Aplicación de la teoría de los fasores espaciales al estudio de los campos armónicos en los regímenes transitorios de las máquinas asíncronas y sus repercusiones en los pares pulsantes. PhD Th.; Universidad Politécnica de ValenciaOberretl K (1994) Parasitäre synchrone Dreh- und Pendelmomente in Asynchronmotoren. Einfluss von Ausgleichsvorgängen und Eisensättigung. Parts I and II. Archiv für Elektrotechnik 77:179–190 and 277–288Oberretl K (1965) Ueber den Einfluss von parallelen Wicklungs- zweigen, Dreieckschaltung, Spulensehnung. Nutzschlitzbreite und Nutenschrägung auf das Drehmoment von Käfigläufermotoren in ETZ-A Bd 86: 619–627Brüderlin R (1921) Ueber eine graphische Zerlegung der Feld-Erregerkurve einer unregelmässigen Mehrphasenwicklung in ihre Einzelwellen. ETZ-Archiv für Elektrotechnik 42: 1093–1096Köhler G, Walther A (1931) Fouriersche Analyse von Funktionen mit Sprüngen, Ëcken und änlichen Besonderheiten. Archiv für Elektrotechnik 25: 747–755Lax F, Jordan H (1940) Über die Fourier-Entwicklung der Felderregerkurve von schrittverkürzen Drehstromwicklungen beliebiger Phasenzhal. Archiv für Elektrotechnik 34: 591–597Stepina J (1979) Einführung in die allgemeine Raumzeiger Theorie der elektrischen Maschinen. Press of University of Kaiserslauter

Performance Optimisation of Single-Phase Variable Reluctance Shaded-Pole Motor

Shaded pole induction motors’ theoretical analysis is quite difficult because of the presence of strong harmonic components and the elliptical rotating field. The change of air gap reluctance is affecting the air gap flux distribution and thus the performance of the motor. In the study, the effect of the change in the SPIM’s stator, rotor and squirrel cage on the performance of the motor is analysed by the Finite Element Method. The flux distributions and torque values of the closed-interpoles type and the stator with different interpoles clearances are obtained. The effects of single and double cage structures in the rotor part and the effects of copper and aluminium cage materials in the squirrel cage were analysed. According to the analyses, it was determined that the single cage motor with aluminium cage material exhibited the best torque performance with a torque value of 132.78 mNm

Investigation on contribution of inductance harmonics to torque production in multiphase doubly salient synchronous reluctance machines

This paper investigates the contribution of each order inductance harmonic to the torque (both average torque and torque ripple) of multiphase doubly salient synchronous reluctance machines (DS-SRMs). Such machines are similar to switched reluctance machines but supplied with sinewave currents. The investigations in this paper are as follows: first, a general analytical torque model based on Fourier Series analysis of inductances has been built for machines with different phase numbers, slot/pole number combinations and also winding configurations. The instantaneous torque for DS-SRMs with any given phase number can then be accurately predicted. Using such model, contribution of each order inductance harmonic to torque can be investigated separately. It is found that the torque ripple frequency of the DS-SRM only depends on phase number. For example, for a m-phase machine, there will be m×kth order torque ripple if mod(mk,2)=0, where m is phase number and k is a natural number. This study also explains why certain phase numbers inherently produce lower torque ripple than others. The findings in this paper provide a future direction for potential torque ripple reduction methods either from machine design or advanced control. The simulations have been validated by experiments using a 6-phase DS-SRMs