EP1433241A1 - Machine electrique pouvant produire des forces laterales - Google Patents

Machine electrique pouvant produire des forces laterales

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Publication number
EP1433241A1
EP1433241A1 EP02800654A EP02800654A EP1433241A1 EP 1433241 A1 EP1433241 A1 EP 1433241A1 EP 02800654 A EP02800654 A EP 02800654A EP 02800654 A EP02800654 A EP 02800654A EP 1433241 A1 EP1433241 A1 EP 1433241A1
Authority
EP
European Patent Office
Prior art keywords
windings
electrical
component
conductors
machine according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP02800654A
Other languages
German (de)
English (en)
Inventor
Seamus Dominic Garvey
Wee Keong Khoo
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB0123927.6A external-priority patent/GB0123927D0/en
Application filed by Individual filed Critical Individual
Publication of EP1433241A1 publication Critical patent/EP1433241A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C32/00—Bearings not otherwise provided for
    • F16C32/04—Bearings not otherwise provided for using magnetic or electric supporting means
    • F16C32/0406—Magnetic bearings
    • F16C32/044—Active magnetic bearings
    • F16C32/0474—Active magnetic bearings for rotary movement
    • F16C32/0493—Active magnetic bearings for rotary movement integrated in an electrodynamic machine, e.g. self-bearing motor
    • F16C32/0497—Active magnetic bearings for rotary movement integrated in an electrodynamic machine, e.g. self-bearing motor generating torque and radial force
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C32/00—Bearings not otherwise provided for
    • F16C32/04—Bearings not otherwise provided for using magnetic or electric supporting means
    • F16C32/0406—Magnetic bearings
    • F16C32/044—Active magnetic bearings
    • F16C32/0444—Details of devices to control the actuation of the electromagnets
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
    • H02K7/08—Structural association with bearings
    • H02K7/09—Structural association with bearings with magnetic bearings

Definitions

  • the present invention relates to rotating electrical machines with integrated magnetic bearings serving a dual capacity function, namely to generate torque and magnetically levitate the rotor.
  • Magnetic bearings are a non-contacting technology employed to perform the same task as conventional bearings but with advantages due to their active nature.
  • the active nature of magnetic bearings offers a higher level of control of rotor vibration, diagnostics and load measurement capabilities (Knopse & Collins, 1996). Among the advantages are: elimination of friction, wear and lubrication; high speed capability; ability to operate in higher temperatures; potential for vibration control; and longer life.
  • the magnetic forces In order to levitate and position a rotor, the magnetic forces must be exerted along five axes, usually two perpendicular axes at each rotor end and a fifth axis along the rotor's rotational axis.
  • Radial bearings are responsible for the levitation of the shaft in the plane of the two perpendicular axes.
  • the axial or thrust bearing is used to counteract axial forces in both directions. The way they usually operate is by injecting currents into the coils such that a net attractive force is created to minimise the displacement of the rotor.
  • Feedback control is indispensable for active magnetic bearings because they are inherently unstable. Sensors measure the position of the rotor and this signal passes through an anti-aliasing filter to eliminate high frequency noise. The controller then processes the filtered signal and sends request currents to the power amplifiers which in turn drive the coils.
  • bearingless machines are an advance which possess the capabilities of both magnetic bearing and motor to levitate the rotor and generate torque simultaneously.
  • a bearingless motor can have a shorter shaft than a motor and bearing configuration, thus higher speed operations are possible.
  • the bearingless motor has fewer components and therefore a reduction of cost is possible.
  • one set of windings is the conventional motor windings for torque generation and the other set is known as position control windings.
  • the flux densities in the air gap are created solely by the motor windings.
  • the motor magnetic field in the air gap is deliberately unbalanced by the currents of the position control windings. This causes the flux density at a certain position to decrease while the flux density at the diametrically opposite position increases. As a result, a net lateral force is exerted on the rotor towards the position with a higher flux density.
  • a net lateral force at any arbitrary direction can be produced.
  • B Torq (U) the magnetic flux causing torque production
  • D angular position
  • Npp ⁇ is the number of pole pairs of the torque-producing component of flux and D is a frequency.
  • a main priority in the design of bearingless machines will be that at least one of the above integrals will be substantial in magnitude for a given magnitude of Bi ev f ⁇ ).
  • a variable-speed dynarnotor having magnetic capability for suppressing vibrations and controlling the damping of the rotor was disclosed by Fukao et al. US Pat. No. 5,880,550.
  • This invention does not require the stator to be structurally modified, but only needs an additional winding to be wound around the stator.
  • the levitation field also differs from the main motor field by a pole-pair.
  • Fukao et al. US Pat. No. 5,936,370 disclosed another rotating machine with position control windings. It includes a circuit for sensing the rotor displacement based on the induced voltage or current and the magnitude and speed of the rotating magnetic field.
  • Chiba et al. US Pat. No. 5,955,811 disclosed a high speed rotary induction machine with position control windings fitted in the stator.
  • the stator core has a four-pole stator winding and a two-pole position control windings and they are independently wound.
  • the cage conductors of the rotor are designed such that the mutual inductance between the conductors and position control windings is zero in order to avoid excessive heating.
  • the whole induction machine assembly comprises two stator and two rotor segments and an axial bearing to accomplish stable levitation.
  • the two rotor segments are offset with respect to stators to eliminate the use of an axial magnetic bearing.
  • Such an arrangement is capable of generating axial forces to counter axial movement of the rotor when the coils are excited.
  • a single rotor segment extending from one stator segment to another may be used since there is no current flow in the rotor.
  • stator assembly has permanent magnets to levitate and passively centre a magnetic stainless steel rotor along the vertical axis.
  • stator position control coils By energizing the stator position control coils, the interaction of fluxes generated by the control coils and DC flux produced by permanent magnets give rise to an active position control. Torque is developed when the polyphase drive coils are excited.
  • Satoh et al. US Pat. No. 6,078,119 disclosed a bearingless induction machine with a second set of windings to levitate the squirrel-cage rotor.
  • the magnetic flux distribution in the air gap is detected by integrating the counter-electromotive voltage induced in the stator winding.
  • the inventors addressed the difficulty of controlling the levitated rotor when a low frequency component is detected at an attenuated level.
  • the stator winding is supplied with a corrective current.
  • Mishkevich et al. US Pat. No. 5,949,162 disclosed a method of damping and counteracting mechanical vibrations of an induction motor by means of inducing unbalanced forces on the motor shaft.
  • the stator coils are divided into a 4 groups of star-connected coils in which each group is separately excited by a drive unit. By providing currents to all four groups of coils, the required four-pole rotating field is generated. Two sets of levitation fields (two-pole) that rotate at different frequencies and opposing each other are generated by selectively exciting the group of three-phase coils with appropriate frequency and phase relationships.
  • Maurio et al. US Pat. No. 6,020,665 disclosed a permanent magnet synchronous machine with integrated magnetic bearings.
  • the four-pole stator windings are split in half to form a 2-pole magnetic bearing winding and a four-pole motor winding.
  • the windings are injected with currents having polarity relationship with the permanent magnets in the rotor so as to produce torque and levitation.
  • Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.
  • preferred embodiments of the invention seek to provide a bearingless rotating electrical machine that is capable of generating torque and lateral forces, utilising only a single set of windings.
  • the same conductors within the set of windings may carry currents from the torque and lateral force-producing components simultaneously. This represents a more efficient use of the stator iron.
  • Preferred embodiments of the invention also seek to provide a bearingless rotating electrical machine that uses the physical connection of the coils within the phases of the machine such that separate inverters or supplies can be used for the torque and lateral force producing components of field.
  • This machine benefits from being able to use only one standard supply for the normal torque-producing function of the machine and therefore, the usual way of motor control is preserved unlike the presently available bearingless motors with a single set of windings.
  • Other drives employed are relatively low-rated power electronic devices for the achievement of lateral forces. In the presence of other suitable rotor support means, these low- rated power supplies can be switched off and the motor is driven by the conventional motor supply.
  • Preferred embodiments of the invention also seek to provide a connection scheme that is applicable to various types of motor or topologies.
  • Preferred embodiments of the invention also seek to provide a solution that can be extended to any polyphase machines such as two-phase, three-phase or higher phase machines.
  • motor inverter and “bearing inverter” will be used to mean the power supplies for producing torque and lateral forces respectively.
  • Currents produced by the former and latter are known as “motor current” and “bearing current” respectively.
  • levitation will be used frequently to mean producing a lateral force.
  • a rotating electrical machine including:- a first component; a second component adapted to be received by said first component and to rotate relative thereto; and at least one set of windings provided on at least one of said first component and said second component, wherein at least one said set of windings includes a first electrical conductor and a second electrical conductor connected in series with said first electrical conductor, a third electrical conductor and a fourth electrical conductor connected in series with said third electrical conductor, and wherein the group consisting of said first electrical conductor and said second electrical conductor is connected in parallel to the group consisting of said third electrical conductor and said fourth electrical conductor, such that said conductors are adapted to conduct first electrical currents to generate a magnetomotive force tending to rotate the second component relative to the first component, and to conduct second electrical currents, applied through different terminals of the machine from those through which said first electrical currents are applied, to generate a magnetomotive force to produce a net translational force between the first component and the second component.
  • the conductors of the machine can be provided in a symmetrical arrangement such that there is a substantial absence of coupling between the first and second currents.
  • the levitation producing currents can be arranged to have negligible effect on the torque producing magnetomotive force (MMF), and the torque producing currents can similarly be arranged to have negligible effect on the MMF producing translational forces.
  • MMF torque producing magnetomotive force
  • Said first and second electrical conductors and/or said third and fourth electrical conductors of at least one said set of windings may be adapted to receive said second electrical currents at a junction, of said first and second electrical conductors and/or at a junction of said third and fourth electrical conductors, and to receive said first electrical currents at a junction of said first and third conductors and/or at a junction of said second and fourth conductors respectively.
  • At least one said first winding may comprise at least one respective coil arranged substantially diametrically opposite to the corresponding second winding comprising at least one coil and/or said third electrical conductor may be arranged substantially diametrically opposite to the corresponding said fourth electrical conductor.
  • diametrically opposite in the present context means located on opposite sides of the axis of rotation of the first component relative to the second component.
  • Said first and fourth and/or said second and third windings of at least one said set of windings may be substantially co-axial to each other.
  • This provides the advantage of enabling the first and third and/or the second and fourth windings of at least one set of windings to be wound on a single tooth, which in turn enables the number of teeth of the machine to be reduced. As a result, the number of coil turns on each tooth can be increased, which increases magnetomotive force for generating torque for a given size of machine, which in turn increases the efficiency of the machine.
  • said first component includes a plurality of teeth, and said first, second, third and fourth windings of at least one said set of windings each provide effective MMF for a respective plurality of said teeth.
  • the machine may comprise a plurality of said sets of windings, wherein a plurality of said sets of windings are adapted to generate respective said net translational forces in directions not parallel to each other.
  • a plurality of said sets of .windings correspond to respective phases, and at least one said set of windings is connected in series or in parallel with a respective further set of windings of the same phase.
  • This provides the advantage of enabling more than one set of windings for each phase to be supplied with torque-producing electrical current by the same power supply, thus further reducing the number of power supplies required.
  • Said first and second and/or third and fourth windings of at least one set of windings may be connected in series to each other by means of respective connectors located externally of said first and/or second component.
  • Said first and second and/or said third and fourth windings of at least one said set of windings may be connected in series with each other by means of further windings of the same phase.
  • the return path connecting the first and second windings of one phase may be provided by a further winding of the same phase, so that the magnetic field generated by all of the windings appears across the gap between the first and second components.
  • the machine may further comprise control means for supplying said first and second electrical currents.
  • the machine may further comprise at least one position detector for providing an output signal to said control means representing the position of said second component relative to said first component.
  • the machine may further comprise at least one rotor speed detector for outputting an input signal to said control means representing the speed of rotation of said second component relative to said first component.
  • the bearingless machine described here comprises two major components - usually termed the rotor and the stator. It has windings on at least one of the major components. Most electrical machines are conventionally connected such that lateral forces are balanced even if an unbalanced supply is applied. This is achieved by using parallel connection of coils on diametrically opposite sides of the machine so that if one of these sees an unusually high or low current, its partner also sees this and the increase in net lateral force is zero.
  • phase is an independent circuit which can carry current even if the other phases are open circuit.
  • phase has two terminals. Sometimes, the ends of phases are connected together inside a machine but most commonly, all phase ends are brought out to the terminal box.
  • Each phase may comprise two or more parallel groups.
  • each phase comprises an even ' number of parallel groups. For simplicity of description, we assume that this number is two but the extension to higher numbers is straightforward.
  • each group comprises a series connection of coils.
  • each group comprises an even number of series coils.
  • this number is two but the extension to higher numbers is straightforward. Cases where there are, say, 4 coils in a group are easily dealt with by considering certain pairs of coils to comprise a single "coil" in the following description.
  • currents are injected into the phase windings such that an unbalanced flux distribution occurs in the air gap, so as to produce a net lateral force in any desired arbitrary direction.
  • the role of the bearing inverter is to inject differential currents into the windings in order to produce the requisite unbalancing of the flux distribution.
  • the principle of operation involves supplying currents from two separate sources to the fundamental connection so that the required magnetic polarities or flux distributions can be generated in the air gap.
  • a permanent magnet synchronous machine is given as an example in the second embodiment.
  • the fundamental connection is extended to form a concentrated winding scheme producing a 4-pole motor field and a 2-pole levitation field in a 24-tooth stator.
  • the rotor has surface mounted pennanent magnets at an equiangular spacing around its periphery, forming the same number of magnetic pole pairs as the stator.
  • External sensors are employed to give information on the rotor radial displacement and speed of rotation, which will then be processed by the controllers before sending out appropriate signals for switching the inverters.
  • Separate inverters are used, namely a standard motor inverter and a number of small voltage and current ratings bearing inverters for producing the necessary currents to generate torque and lateral forces respectively.
  • the third embodiment describes how the groups of parallel coils can be arranged to form the same MMF distribution in the air gap as in the second embodiment, but with an added advantage of reducing the required number of stator teeth by half. This is also a concentrated winding arrangement.
  • the possibility of extending to a double layer distributed winding arrangement is described in the fourth, fifth and sixth embodiments.
  • These embodiments describe a means of generating a sinusoidal flux distribution in the air gap with a minimum number of bearing inverters.
  • the fourth embodiment deals with a toroidal winding scheme which is best used in stators with a short axial length and large diameter to reduce the end winding effect.
  • the fifth embodiment describes how the windings connection can be manipulated such that all conductors can be arranged within the stator slots, and thus removing the need for toroidally wound coils at the stator back core.
  • a further manipulation of the connection is described in the sixth embodiment where it is possible to reduce the number of bearing inverters by at least half.
  • Fig. 1 is a circuit diagram of one phase of a bearingless electric motor of a first embodiment of the present invention
  • Fig. 2 is a schematic representation of magnetic polarities produced by motor and levitation currents flowing in the loop connection of Fig. 1;
  • Fig. 3 is a schematic representation of a loop of Fig. 1 in which the same magnetic polarity is produced at diametrically opposite stator teeth when the motor current is excited;
  • Fig. 4 is a schematic representation of a loop of Fig. 1 in which opposing magnetic polarities are produced at diametrically opposite stator teeth when the levitation current is excited
  • Fig. 5 is a schematic representation, corresponding to Fig.2, but in which the polarity of a pair of coils is reversed;
  • Fig. 6 is a schematic representation of a three-phase permanent magnet synchronous motor of a second embodiment of the present invention.
  • Fig. 7 is a schematic representation of a three-phase star connection of the embodiment of Fig. 6 showing instantaneous motor current and levitation current excitations;
  • Fig. 8 is a schematic cross sectional view showing a four-pole motor field generated in a 24- slot stator in the arrangement of Fig. 7;
  • Fig. 9 is a schematic cross sectional view, corresponding to Fig. 8, showing a two-pole levitation field generated in a 24-slot stator in the arrangement of Fig. 7;
  • Fig. 10 is a schematic representation of a three-phase delta connection as an alternative to the star connection of Fig. 7;
  • Fig. 11 is a schematic representation of a control system for use with the present invention.
  • Fig. 12 is a schematic representation of a coil arrangement of a third embodiment of the invention.
  • Fig. 13 shows a four-pole motor field generated in a 12-slot stator in the embodiment of Fig. 12;
  • Fig. 14 shows a two-pole levitation field generated in a 12-slot stator in the embodiment of Fig. 12;
  • Fig. 15 shows a prior art distributed winding scheme producing a four-pole motor field
  • Fig. 16 shows a prior art distributed winding scheme producing a two-pole levitation field
  • Fig. 17 is a schematic representation of a three-phase connection of a fourth embodiment of the invention showing instantaneous motor current and levitation current excitations;
  • Fig. 18 shows a four-pole motor field generated by means of a toroidal winding arrangement in the embodiment of Fig. 17;
  • Fig. 19 shows a two-pole levitation field generated by means of a toroidal winding arrangement in the embodiment of Fig. 17;
  • Fig. 20 is a perspective view of the toroidally wound stator of Figs. 18 and 19;
  • Fig. 21 is a schematic representation of a three-phase connection of a fifth embodiment of the invention showing instantaneous motor current and levitation current excitations;
  • Fig. 22 shows a four-pole motor field generated by means of a distributed winding arrangement in the embodiment of Fig. 21 ;
  • Fig. 23 shows a two-pole levitation field generated by means of a distributed winding arrangement in the embodiment of Fig. 21;
  • Fig. 24 is a schematic representation of a three-phase connection of a sixth embodiment of the invention showing instantaneous motor current and levitation current excitations.
  • the motor inverter 1 and bearing inverter 2 supply bi-directional cuixents for generating machine torque and lateral forces respectively.
  • the issue about impedance mismatch in the connection can be resolved by ensuring that the voltage rating of the bearing inverter 2 must be sufficient to withstand the voltage that will exist across it. With this implementation, unbalanced currents that arise from the mismatch coil impedance can be prevented from flowing into the bearing inverter 2 and the cunent that the bearing inverter 2 injects must be trimmed accordingly to take account of the imbalance.
  • FIG. 2 show how the motor and bearing currents flowing in the loop connection producing the magnetic polarities; the polarities as a result of motor and bearing cu ents excitation are labelled at the exterior and interior of the loop respectively. Accordingly, all coils 3 produce the same magnetic polarities N when a motor current is supplied, but when the bearing cunent is supplied, the polarities created at one pair of coils are of the opposite direction of the other pair. For the example given in FIG. 2 coils "al 1" and “al2” have an S polarity while both coils "al3" and "al4" have an N polarity as far as the bearing cunent flow is concerned.
  • FIGS. 3 and 4 respectively depict how the coils 3 in FIG. 2- may be wound and aixanged in a stator to produce N polarities at diametrically opposite stator teeth when the motor cu ent is excited, but when the bearing cunent is excited, the polarities at diametrically opposite teeth are of the opposite to each other.
  • Such cunent or polarity reversing properties are exploited to produce independent symmetrical torque and levitation-producing components of flux in the machine air gap.
  • An alternative connection is shown in FIG. 5 where parallel coils "al 1" and “al2” produce the same polarity but in the opposite to coils "al3" and "al4" when the motor cunent is supplied. Injection of bearing cunent will now result in the same polarity for all coils.
  • This configuration can be thought as having the connection scheme in FIG. 2 being reversed inside out.
  • the usefulness of such a connection scheme will be more apparent when it is extended to form a three-phase machine according to the second embodiment.
  • This particular embodiment is given as a crude example of how this invention can be realised.
  • the machine in question is a 4-pole permanent magnet synchronous machine having an air gap 4 separating the stator 5 and the rotor 6 as illustrated in FIG. 6.
  • the rotor has surface mounted pennanent magnets 7 producing a 4-pole magnetic field 8.
  • the tenninals of the phase coils are connected to form a star connection as shown in FIG. 7.
  • the instantaneous motor and levitation currents producing the conesponding 4-pole motor field 9 and 2-pole levitation field 10 are shown in FIG. 8 and 9 respectively.
  • connection scheme The significance of such a connection scheme can be perceived by considering the number of times the polarity changes per phase when a round trip along the periphery of the air gap 4 interface is undertaken. Since this is a 4-pole motor a round trip yields four times of polarity change per phase. The imposed 2-pole levitation field 10, however, yields only twice polarity change per phase, which implies that coil-pairs "all"-"al2" and "a21"-"a22" must be diametrically opposing coil-pairs "al3"-"a!4" and "a23"-”a24” respectively. In addition, the two groups of coils 3 in the top and bottom loops of phase "a" must be orthogonal to each other.
  • lateral forces are predominantly caused by the interaction between the pennanent magnet field 8 and the excited levitation field 10.
  • the field created by the surface mounted permanent magnet 6 around the air gap periphery 4 is unbalanced by the levitation field 10 and thereby causing a net lateral force exerted on the rotor 6.
  • a minimum of two levitation MMF axes must be present at any operating instant such that the linear combination of these independent levitation MMFs will give rise to a resultant MMF in any arbitrary direction.
  • phase coils 3 can also be connected to fonn a three-phase delta connection in FIG. 10.
  • the method of loop connection in the present invention preserves the flexibility of having star- or delta-connections and concunently serving to offer locations for injecting cunents to exert lateral forces on the rotor 6.
  • each configuration requires 6 independent bearing inverters 2 for levitation. These bearing cunent sources have a phase difference relationship with each other so that the overall effect is to create the required number of pole field in the machine.
  • FIG. 11 shows a schematic block diagram of the control system employed to drive the motor and produce lateral forces ⁇ ich may be divided into two groups, namely motor control and magnetic bearing control.
  • the synchronous machine is provided with sensors 20 and 21 that detect the angular- positions and rotational speed of the rotor 6.
  • the signal ⁇ from the speed detector 21 is compared with the command signal ⁇ ); ?e in the comparator 23 and the resultant difference signal is input into the motor controller 24 which then calculates the required frequency and amount of cunent to be supplied to the motor.
  • the conesponding request signal is then sent to the motor inverter 1 to switch the magnitude and direction of the cunents.
  • Two discrete position sensors 25 and 26 located at orthogonal positions are employed to detect the displacement of the rotor 5 and signals are input into a filter 27 to eliminate high frequenc3' noise.
  • the desired horizontal (xp e f) and vertical (j>p e f) rotor positions are then compared with the signals (x and y) from sensors 25 and 26 in the comparators 28 and 29 and fed into a bearing controller 30.
  • the bearing controller 30 calculates the required resultant force and its conesponding direction based on the compared signals and information such as: the rotor speed; rotor orientation; and the torque-producing component of cunent or flux.
  • the magnitude and direction of the required force dictates how much cunent is needed for injection into each phase coil 3.
  • the controller 30 sends request signals to the bearing inverters 2 which in turn inject differential cunents into the phase coils 3.
  • FIG. 12 shows how coil-pairs "all"-"al2" and “al3"-"al4" of the top loop in FIG. 7 can be wound around 2 stator teeth instead of 4 as described in the previous embodiment.
  • Coils "all” and “al2” are stacked up and aligned at the same axis of symmetry, thereby producing the same magnetic effect as having a single coil with twice number of turns.
  • Another way of describing this is that each coil in a stator pole is split into two smaller coils with equal number of turns.
  • the conductors in the present machine carry both motor and bearing currents simultaneously.
  • FIGS. 14 and 15 show respectively the resultant motor field 9 and levitation field 10 generated according to the cunent excitations in FIG. 7.
  • the advantage of the present invention in this embodiment is that the number of stator teeth required has been reduced by half and this allows the coil turns to be increased in each stator tooth. It is intuitively obvious that for the same number of conductors accommodated in the slot, the present invention in the third embodiment will have a greater torque and lateral force producing capacity than conventional bearingless motors with dual set of windings.
  • the method of winding the stator for the present machine is most conveniently achieved by employing pre-wound coils where they can be placed or removed easily in the stator.
  • pre-wound coils depends primarily on the physical geometry or shape of an individual stator tooth.
  • the same control system described in the second embodiment also applies to present invention in the third embodiment.
  • a 24-tooth stator with concentrated coils connected according to the method described in the third embodiment would demand 12 independent bearing supplies to give a better sinusoidal waveform.
  • the fourth embodiment herein describes how coils can be arranged to form an equivalent double layer distributed winding.
  • Double layer distributed windings are very common in electrical machines where the windings are overlapped and continuous from one phase to another. These machines cannot be turned into bearingless motors by merely injecting the appropriate magnitude and phase combinations of motor and bearing cunents into the tenninals. It is also important to note that such conventional windings cannot be incorporated in conjunction with the present wiring scheme because the windings need to be broken to pennit bearing cunent injections. From a 2D-magnetostatic point of view, the windings described in the fourth embodiment herein will produce the same result as a conventional 4-pole motor with double layer distributed winding.
  • a 24-tooth stator is considered as a design example.
  • FIGS. 15 and 16 of the prior arts show the same set of double layer winding with distributed cunent densities in the stator slots producing 4- and 2-pole fields respectively. For the purpose of clarity only a minimum number of flux lines are drawn. As far as a 2D plane with neglected end effects is concerned, the same motor or levitation fields can be produced so long as the distributed cu ent densities are applied as in FIGS. 15 and 16. Consequently there are countless methods of winding the stator. Specifying that the same conductors must cany both motor and bearing cunents simultaneously has inevitably placed a restriction on how the stator can be wound. It is evident from FIGS.
  • FIG. 17 illustrates the motor and bearing cunents in all phases at one instant of time where the directions of motor and bearing cunents, whether flowing in "go" or “return” slots, are shown at the exterior and interior of the cunent loops respectively. Note that only coil sides that produce the fields in FIGS. 15 and 16 are shown in the connection diagram. All other associated go or return paths are omitted for clarity reasons, for example, coil "aal" of a go path is directly linked to coil "aa2" of the same path without undergoing a return path explicitly.
  • a total of six independent bearing inverters 2 are used in the present embodiment. It is also possible to reduce the number of bearing inverters 2 to four or two so long as ' they are properly controlled to produce two independent levitation MMF axes. Nevertheless, with more bearing inverters 2 used, the system has a degree of fault tolerance.
  • FIG. 20 depicts the toroidal winding scheme according to the fourth embodiment.
  • Toroidal windings are best used in stators with a short axial length and large diameter and thus, there is a reduction of end winding.
  • a toroidal winding scheme may be unattractive because the coils wound around the back of the stator core can prevent heat from dissipating.
  • the fifth embodiment describes how the connection can be manipulated so that the need for toroidally wound coils at the stator back core can be eliminated, and thus moving towards a more conventional distributed winding anangements. If the coils are coimected such that each ann of the loop connection consists of two coil sides at 90° apart in the stator slots (as opposed to 180° diametrically opposite), then all conductors can be arranged within the stator slots.
  • FIG. 21 illustrates the modified connection scheme according to the present embodiment producing a 4-pole motor field 9 and a 2-pole levitation field 10 in FIGS. 22 and 23 respectively. As before, the directions of the motor and levitation currents are shown at the exterior and interior of the loop respectively.
  • each phase is extended to 2 series connected loops. It can be seen that the circuit connection method and the number of power supplies are retained, i.e. one standard 3-phase motor supply 1 and six bi-directional levitation cunent supplies 2. As before the number of levitation supplies 2 may be reduced if required. Unlike the previous embodiment where each loop controls the cunent in diametrically opposite slots or teeth, the present variant connection controls the cu ent in all coil sides within a loop itself. Note that the resultant 4-pole motor field 9 is of the same distribution as the toroidal winding arrangement in the fourth embodiment would produce.
  • a net lateral force can be generated by appropriately exciting the phase levitation cunents in any combination so long as the resultant field around the air gap is of a 2-pole. It is important that at least two levitation MMF axes are generated so as to enable the control of force in any magnitude and arbitrary direction.
  • the present scheme may not .create a sinusoidal levitation field 10 as perfectly as its predecessor in the fourth embodiment because of the way it is connected. For example, when all phases are excited, the resulting levitation field 10 will have a slight notch at its maximum peaks. Despite this minor imperfection the overall levitation field 10 still resembles a sinusoidal waveform and a net lateral force can be accomplished.
  • the motor field for generating torque depends on the type of machines and it is directly related to the MMF crossing the air gap interface between the stator and rotor.
  • pennanent magnet machines the net MMF is contributed mostly by the pennanent magnets on the rotor, unless the stator is excited with a very high cunent.
  • the net MMF is contributed by the induced rotor cunents and partly by the stator cunents. Both ⁇ 1 pole- pair fields from the excited stator and induced rotor cause a net lateral force to occur.
  • the otor of the switch reluctance machines is not excited by any means and so the stator alone contributes the net MMF.
  • the rotor of a bearingless motor must- be exerted by magnetic force along five axes, namely two orthogonal axes at each end and a fifth axis along the rotor's rotational axis. Therefore, two segments of bearingless motors and an axial magnetic bearing are required for full stabilisation.
  • the generation of unbalance lateral force is not only limited to providing necessary support to the rotor, but it also serves as a fault tolerant active magnetic bearing. Excessive vibrations can be counteracted by varying the loop cunents, which in turn confrol the stiffness and damping of the integrated magnetic bearing.
  • the present invention described in the prefe ed embodiments offers an optional secondary function, namely to generate unbalance forces, while serving the primary function of torque production.
  • This feature is of paramount importance because in the case where a suitable means of rotor support is available, the motor can be ran as a standard machine using only one standard power supply. Such a concept is applicable to various machines where a set of windings is present on at least one of the main components.
  • the prefened embodiments describe a generic 3-phase bearingless machine, it is relatively straightforward to extend the connections to other polyphase machines such as 2, 4, 5, 6, 12 or higher phases.

Abstract

L'invention concerne une machine électrique rotative qui comprend deux composants principaux pouvant tourner autour d'un axe commun et étant séparés par un entrefer dans lequel les champs magnétiques qui relient les deux principaux composants par l'intermédiaire de l'entrefer agissent de manière à exercer un couple et des forces latérales. Un ensemble d'enroulements se trouve sur au moins un desdits composants, et est utilisé pour la répartition du flux en deux parties: la première servant principalement à provoquer un couple et la seconde servant à provoquer une force latérale nette entre les deux composants principaux. Ladite machine utilise la connexion physique de bobines à l'intérieur des phases, de sorte que des sources séparées peuvent être utilisées pour alimenter des courants permettant de produire indépendamment un couple et des forces latérales. Les valeurs nominales des tensions et des courants de l'alimentation utilisée pour produire les forces latérales peuvent être sensiblement inférieures aux valeurs nominales correspondantes de l'alimentation utilisée pour produire le couple.
EP02800654A 2001-10-05 2002-10-07 Machine electrique pouvant produire des forces laterales Withdrawn EP1433241A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
GB0123927 2001-10-05
GBGB0123927.6A GB0123927D0 (en) 2001-10-05 2001-10-05 AC Bearingless rotating electrical machine
GB0213525 2002-06-13
GB0213525A GB2380618A (en) 2001-10-05 2002-06-13 Electric rotating machine with magnetic bearing
PCT/GB2002/004526 WO2003032470A1 (fr) 2001-10-05 2002-10-07 Machine electrique pouvant produire des forces laterales

Publications (1)

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EP1433241A1 true EP1433241A1 (fr) 2004-06-30

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EP (1) EP1433241A1 (fr)
CN (1) CN1565071A (fr)
WO (1) WO2003032470A1 (fr)

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Publication number Priority date Publication date Assignee Title
CN102510197A (zh) * 2011-11-14 2012-06-20 江苏大学 锥形无轴承异步电机
SE538502C2 (en) 2014-11-17 2016-08-16 Magström Ab C/O Urban Lundin Arrangement and method for force compensation in electrical machines
FI126506B (en) * 2015-06-26 2017-01-13 Lappeenrannan Teknillinen Yliopisto Control device and method for controlling magnetic support and torque development

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Publication number Priority date Publication date Assignee Title
US5084644A (en) * 1990-12-20 1992-01-28 Nova Corporation Of Alberta Control of magnetization of a machine with axial magnetic bearings
DE4111816A1 (de) * 1991-04-11 1992-10-15 Asea Brown Boveri Stromrichterschaltung
US6130494A (en) * 1995-08-18 2000-10-10 Sulzer Electroncis Ag Magnetic bearing apparatus and a method for operating the same
FR2742497B1 (fr) * 1995-12-18 1998-04-03 Aerospatiale Palier magnetique a actionneurs et capteurs alternes

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WO2003032470A1 (fr) 2003-04-17

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