WO2009056879A1 - Machines à réluctance à aimant permanent - Google Patents

Machines à réluctance à aimant permanent Download PDF

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Publication number
WO2009056879A1
WO2009056879A1 PCT/GB2008/051009 GB2008051009W WO2009056879A1 WO 2009056879 A1 WO2009056879 A1 WO 2009056879A1 GB 2008051009 W GB2008051009 W GB 2008051009W WO 2009056879 A1 WO2009056879 A1 WO 2009056879A1
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WO
WIPO (PCT)
Prior art keywords
armature
field
machine
stator
machine according
Prior art date
Application number
PCT/GB2008/051009
Other languages
English (en)
Inventor
Charles Pollock
Helen Pollock
Original Assignee
Technelec Ltd
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
Application filed by Technelec Ltd filed Critical Technelec Ltd
Publication of WO2009056879A1 publication Critical patent/WO2009056879A1/fr

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K19/00—Synchronous motors or generators
    • H02K19/02—Synchronous motors
    • H02K19/10—Synchronous motors for multi-phase current
    • H02K19/103—Motors having windings on the stator and a variable reluctance soft-iron rotor without windings
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/22—Rotating parts of the magnetic circuit
    • H02K1/24—Rotor cores with salient poles ; Variable reluctance rotors
    • H02K1/246—Variable reluctance rotors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K19/00—Synchronous motors or generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K19/00—Synchronous motors or generators
    • H02K19/02—Synchronous motors
    • H02K19/04—Synchronous motors for single-phase current
    • H02K19/06—Motors having windings on the stator and a variable-reluctance soft-iron rotor without windings, e.g. inductor motors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K19/00—Synchronous motors or generators
    • H02K19/16—Synchronous generators
    • H02K19/26—Synchronous generators characterised by the arrangement of exciting windings
    • H02K19/32—Synchronous generators characterised by the arrangement of exciting windings for pole-changing
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K21/00—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets
    • H02K21/38—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with rotating flux distributors, and armatures and magnets both stationary
    • H02K21/44—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with rotating flux distributors, and armatures and magnets both stationary with armature windings wound upon the magnets
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
    • H02P25/08—Reluctance motors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
    • H02P25/08—Reluctance motors
    • H02P25/092—Converters specially adapted for controlling reluctance motors

Definitions

  • Permanent magnet synchronous machines (sometimes referred to as brushless ac or brushless dc) have a stator containing armature windings and a rotor carrying permanent magnets.
  • the magnetic field produced by the stator currents interacts with the magnetic field of the rotor magnets to produce torque.
  • the rotor magnets may be mounted near to the surface of the rotor and magnetised in a radial direction. In such a motor the air-gap flux density is limited by the magnet flux density which is usually less than the saturation flux density of steel.
  • the magnets are buried within the rotor structure with paths of high and low reluctance to guide and focus the magnet flux and create magnetic poles at the surface of the rotor with a flux density higher than that of the magnet itself.
  • Reluctance machines such as switched reluctance machines or flux switching machines having laminated steel rotors with a salient pole structure (at least one radially aligned regions of high magnetic reluctance alternating with at least one radially aligned region of low magnetic reluctance.
  • the rotor of a reluctance machine carries no magnets or windings and can therefore be very robust.
  • the stator assembly carrying coils is energised to create a magnetic field which causes the rotor to rotate into a position where the axis of low magnetic reluctance is aligned with the magnetic field of the stator.
  • the rotor poles can be shaped to provide a sinusoidal or trapezoidal flux so that appropriate control of the current in the stator delivers very smooth torque at all rotor angles whereas the reluctance machine torque varies strongly with position producing significant torque ripple;
  • the reluctance rotor is very robust and can spin to high rotational speeds without any risk of magnets becoming detached or needing the complication of a carbon fibre sleeve to retain the magnets;
  • armature voltage is proportional to speed. If the machine is to be used as a battery charger then at low speeds the machine may not generate enough voltage to charge the battery and at higher speeds the armature voltage may be too high and excessive current would flow into the battery causing damage to either the battery or the generator.
  • a reluctance machine can operate as a generator over a much wider speed range since the field current is supplied through the stator windings and can be varied inversely with the speed to produce a constant voltage generator.
  • Figure 1 shows a flux switching machine with a stator 1 and rotor 2 according to the prior art.
  • the stator 1 is made from laminated steel and in this example has 12 stator teeth 3.
  • Alternate slots 4 in the stator carry armature field windings and alternate slots 5 carry field windings.
  • the rotor 2 has six teeth 6 which, as the rotor rotates within the stator varies the mutual coupling between the armature winding and the field winding.
  • the operation of the flux switching machine has been described in published papers. In a paper "Low cost high power density, flux switching machines and drives for power tools", in IEEE IAS Annual Meeting 2003 by H. Pollock, C. Pollock, R. Walter and B.
  • Figure 2 shows a flux plot of the prior art machine in Figure 1 when only the field windings are energised such that the field slots 5 carry current.
  • the field winding comprises 3 or 6 coils connected in series or parallel or may be one long coil wound as a consequent pole winding.
  • the conductors in the field slot are arranged such that the current in three of the field slots 11 are opposite in direction to the currents in the three other field slots 12.
  • a six pole magnetic field is produced which passes through the stator teeth to the rotor.
  • the six pole pattern also links the armature winding, the conductors of which are located in slots 4 of the stator.
  • the flux switching machine shown in Figure 1 and Figure 2 and as described in the prior art has the advantage that it is simple to manufacture. It also has a rotor structure which carries no windings or magnets and is very robust.
  • the flux switching machine, with field winding allows control of the field flux over the operating conditions of the machine. However, the efficiency of the machine is reduced by the losses in the field winding.
  • FIG. 3 shows a further flux switching motor from the prior art in which the field coils are replaced by permanent magnets.
  • This motor was described in a paper "A permanent magnet flux switching motor for low energy axial fans", by Y. Cheng, C. Pollock and H. Pollock published in IEEE IAS Annual meeting, 2005, Vol. 3, pp 2168-2175.
  • the stator 20 carries four permanent magnet sections where the field windings would have been located and four slots 22 carry the armature winding.
  • the stator has eight teeth 23.
  • the permanent magnets are magnetised with their magnetic axis parallel to the air gap. Alternate magnets have opposing magnetic poles so that magnets 21 and 24 will have like poles facing each other. This creates a 4 pole magnetic field.
  • the armature coils are also arranged so that the armature current flows in opposite directions in alternate armature slots.
  • the resultant field created from the combination of armature mmf and field magnets passes from four of the stator teeth to the four rotor teeth. By reversing the direction of the current in the armature winding the flux will switch into the other four stator teeth.
  • the machine of Figure 3 has no field winding and no field losses and therefore provides a machine of high efficiency.
  • the field flux produced by the magnets is relatively constant and cannot be adjusted with load or speed. This means that the operating speed range of such a motor is limited because the emf will increase with speed and at high speed the armature current will be reduced and resulting torque output will be very small.
  • total flux in the machine is the combination of two magnetic circuits which interact to allow the armature flux linkage to be the combination of the field flux produced by the magnet and the flux controlled by the field current to give a machine of high efficiency while retaining as much as possible of the very simple and robust stator structure of a reluctance machine without magnets.
  • an electrical machine comprising a rotor without windings, a stator having stator teeth and slots between each stator tooth, the stator carrying armature windings wound with a pitch corresponding to a plurality of stator teeth and arranged in a first set of slots around the stator to make one or more electrical phases, the stator also including a field means to establish field flux to link the armature windings, the field means comprising at least one field winding and at least one permanent magnet arranged in a second set of slots around the stator between the slots of the first set, each slot in the second set comprising either a field winding or a permanent magnet, and a control means for supply of current to or from the at least one field winding such that the magnitude of the flux linking the armature windings is controllable.
  • An electrical machine according to the invention will commonly have an even number of permanent magnets in the field means and the permanent magnets are magnetised in a direction parallel to the air-gap.
  • the permanent magnets of the field means extend radially through substantially all of the stator.
  • a machine according to the invention may have two of the permanent magnets in the field means separated by two, six or ten stator teeth.
  • the magnets in the stator structure will usually be magnetised in a direction parallel to the air-gap of the machine and in machines with more than one magnet, the magnets will be arranged around the stator so that alternate magnets have opposite magnetic polarity, such that the permanent magnet flux acts primarily on a first set of stator teeth and links at least one first armature coil and passes through the rotor of the machine.
  • the field winding in a machine according to this invention will be used to produce an additional magnetic field which acts primarily on a second set of stator teeth, linking at least one second armature coil, such that as the value of the direct current in the field winding changes, the magnetic field of the field winding works in combination with the magnetic field of the magnet to change the number of magnetic poles in the machine.
  • the at least one first armature coil is connected in series with the at least one second armature coil to create an armature winding, such that the armature winding emf is the combination of the emf induced in each armature coil, this armature winding then connected to an electronic control means to operate the machine as a motor or a generator, carrying current, varying in magnitude and direction in synchronism with rotation of the rotor.
  • the at least one first armature coil is connected to a first electronic control means and the at least one second armature coil is connected to a second electronic control means such that the current in the at least one first armature coil can be controlled independently of the current in the at least one second armature coil when the machine is operating as a motor or a generator.
  • a double salient reluctance generator with a simple and robust stator structure in which permanent magnet sections are inserted in the stator to provide an initial emf to self excite some of the armature windings of the generator thus avoiding the need for a separate dc power supply or battery.
  • a machine in which the at least one first armature coil is connected to a first electronic control means and the at least one second armature coil is connected to a second electronic control means such that the current in the at least one first armature coil can be controlled independently of the current in the at least one second armature coil when the machine is operating as a motor or a generator, wherein the first electronic control means is connected to a first power system and the second electronic control means is connected to a second power system.
  • the first power system may be a battery and the second power system may be a rectified ac supply.
  • a machine constructed according to this aspect of the invention could operate using the first electronic control means when only a battery supply is available and would therefore have high efficiency. When an ac power system was also available the machine could operate using the second electronic control means.
  • the armature windings of the machine are arranged into two electrical phases with two pairs of permanent magnets and two field coils.
  • the armature windings of the machine are arranged into three electrical phases with three pairs of permanent magnets and three field coils.
  • Figure 1 shows a prior Art Flux Switching Machine with 12 stator teeth and 6 rotor teeth
  • Figure 2 shows a flux plot in the prior art flux switching motor when the field winding is excited with a total MMF of 2400 At.
  • Figure 3 shows a further prior art flux switching motor with 8 stator teeth and 4 rotor teeth and four permanent magnet sections in the stator.
  • Figure 4 shows a machine according to the invention with 12 stator teeth and 6 rotor teeth and two permanent magnet sections embedded within the stator and the location of field and armature coils.
  • Figure 5 shows a flux plot of the machine in Figure 4 with no current in any windings at a rotor position where the rotor is aligned with a first set of stator teeth
  • Figure 6 shows a flux plot of the machine in Figure 4 with no current in any windings at a rotor position where the rotor is aligned with a second set of stator teeth
  • Figure 7 shows a flux plot in the machine of Figure 4 with no current in any windings, at a rotor position, midway between aligned positions with stator teeth.
  • Figure 8 shows a flux plot of the machine in Figure 4 with 2400 At in the field winding at a rotor position where the rotor is aligned with a first set of stator teeth.
  • Figure 9 shows a flux plot of the machine in Figure 4 with 2400 At in the field winding at a rotor position where the rotor is aligned with a second set of stator teeth.
  • Figure 10 shows the total Armature flux linkage at different rotor angles and at different values of Field MMF in the prior art flux switching motor shown in Figure 1 and 2.
  • Figure 11 shows the Flux linking each of the six armature coils in the machine shown in Figure 4 over one rotor pitch when there is no current in the field windings.
  • Figure 12 shows the Flux linking each of the six armature coils in the machine shown in Figure 4 over one rotor pitch when there is an MMF of 800 At in the field windings in addition to the MMF created by the two permanent magnets.
  • Figure 13 shows the variation in flux linking a first armature winding in a machine according to the invention over one rotor pitch at various values of field winding MMF.
  • Figure 14 shows the variation in flux linking a second armature winding in a machine according to the invention over one rotor pitch at various values of field winding MMF.
  • Figure 15 shows the variation in flux linking a first and second armature winding, and the total armature flux linkage in a machine according to the invention at the maximum flux linkage position over a range of field winding MMF.
  • Figure 16 shows the variation in total armature flux linkage with field winding MMF at the maximum flux linkage position for a design according to the invention compared to a prior art machine of the same dimensions.
  • Figure 17 shows three possible coil connections for the armature coils in a machine according to the invention.
  • Figure 18 shows a possible electronic switching circuit for a machine according to the invention.
  • Figure 19 shows a further electronic switching circuit for a machine according to the invention.
  • Figure 20 shows a further electronic switching circuit for a machine according to the invention.
  • Figures 21, 22 and 23 show electronic switching circuits for the armature and field windings in a machine according to the invention.
  • Figure 24 shows an electronic switching circuit for the connection of the machine according to the invention from separate power systems.
  • Figure 25, 26 and 27 shows a three phase machine according to the invention.
  • Figure 28 shows a flux plot of the machine in Figure 25 with no current in the field winding.
  • Figure 29 shows a flux plot of the machine in Figure 25 with current in the field winding.
  • Figure 30 shows a plot of the flux linking the three armature phase windings as the rotor turns through 36°.
  • FIG 4a shows an example of a machine according to the invention.
  • the stator 101 compromises two laminated stator sections 102, 103 which may be linked by a thin section of steel to maintain rigidity.
  • the two laminated sections are separated by two permanent magnet blocks 104, 105.
  • the permanent magnet blocks are magnetised with their magnetic axis parallel to the air gap i.e. in a vertical direction in Figure 4a.
  • the pole faces of 104 and 105 touching stator section 102 will have the same magnetic polarity e.g. both north and the pole faces of the magnets 104, in contact with stator section 103 will also have the same magnetic polarity, though opposite to the poles on the other stator section e.g. both south poles.
  • Each laminated stator section carries 5 slots.
  • Slots 106, 107, 108, 109, 110 and 111 contain armature windings and slots 121, 122, 123, and 124 carry field windings.
  • a field winding would usually be made up of two field coils, connected in series or in parallel.
  • One field coil 191 would span slots 121 and 122, the second field coil 192 would span slots 123 and 124 as shown in Figure 4b.
  • the armature winding in slots 106, 107, 108, 109, 110, and 111 will usually comprise six coils each spanning adjacent armature slots, as illustrated further in Figure 4c.
  • a first coil 151 would span slots 106 and slot 111, each coil side occupying half of the available slot area in slots 106 and 111 such that the next armature coil 152 spans slots 107 to 106 continuing around the machine with coils 153, 154 and 155 with a sixth armature coil 156 spanning slots 111 to 110.
  • Methods of connection of the six armature coils will be discussed later.
  • the rotor of the machine according to the invention illustrated by the example in Figure 4 has six salient teeth and is usually made of laminated steel. There are no magnets or windings on the rotor.
  • FIG. 5 and Figure 6 show flux plots of the two pole magnetic field set up by the magnets at two rotor positions where the six rotor teeth are aligned with alternate sets of stator teeth.
  • Figure 7 shows the flux plot in the example of the machine according to the invention when the rotor is at a position mid- way between two sets of stator teeth. There is no current in the field winding or the armature winding. The flux pattern is still a two pole pattern with all the teeth in section 102 acting as north poles and all the teeth in section 103 acting as south poles.
  • Figure 8 and Figure 9 shows flux plots of the machine according to the invention when current is now flowing in the field coils 191 and 192, spanning slots 121 & 122 and 123 & 124.
  • the current direction in slot 121 is into the paper creating a magnetic field in the steel behind the field slot 121 which opposes the north pole of magnet 104.
  • the current direction in slot 122 is then opposite of that in slot 121 since the two slots are filled with conductors of a single coil.
  • the magnetic field pattern shown in Figures 8 and 9 are completely different from the magnetic field pattern in Figures 5, 6 and 7.
  • the addition of the field current has changed the two pole magnetic field into a six pole magnetic field.
  • the six pole magnetic field in Figures 8 and 9 is similar to the six pole pattern in a machine of the prior art.
  • the machine according to this invention therefore has a field magnet means comprising permanent magnets and field coils which interact in a way so that the addition of field current changes a two pole field system into a six pole field system.
  • Figure 10 shows the armature flux linkage in a machine according to the prior art and illustrated in Figures 1 and 2.
  • the graph shows the armature flux linkage as the rotor turns through one electrical cycle which with six rotor teeth represents a rotor angle of 60 mechanical degrees.
  • Four graphs are shown in Figure 10, lines 141 and 142, each calculated with increasing values of field current.
  • Line 141 shows the armature flux linkage with an MMF of 1200At in the field winding. This corresponds to six field coils spanning the six field slots 5 in Figure 1, each field coil carrying 200At of MMF. It can be observed that there is a large increase in armature flux linkage as the field MMF increases from 1200At to 2400At.
  • stator steel then saturates and there is limited further increase in armature flux linkage.
  • the variation in armature flux linkage with rotor rotation induces an emf in the armature winding allowing the machine to be used as a motor or generator by connection of an appropriate switching circuit to the armature windings.
  • Figure 4c showed the six armature coils 151, 152, 153, 154, 155 and 156 in the machine according to the invention, each armature coil spanning two stator teeth. As the rotor rotates there is a variation in the flux linking each of the armature coils.
  • the unusual feature of the machine according to the invention is that the variation in armature flux linkage in each of the armature coils is not all identical. Unlike the prior art machine the flux linking each armature coils is different as the magnetic field pattern changes from 2 pole to 6 pole due to increasing field current.
  • Figure 11 shows the graphs of the flux linking each of the six armature coils in Figure 4c when there is no current in the field winding.
  • the magnetic field pattern is a two pole pattern under these conditions.
  • Line 161 is the magnetic flux linkage in coil 151 and lines 162, 163, 164, 165, 166 are the armature flux linkages in coils 152, 153, 154, 155, and 156 respectively, all calculated when there is no current in the field winding.
  • the flux linking coils 151, line 161, and the flux linking coil 154, line 164 has a significant variation with rotor rotation whereas the flux linking coils 152, 153, 155 and 156 (Lines 162,163,165 and 166 respectively) shows minimal variation with rotor angle.
  • the flux linking 152, Line 162, and the flux linking 153, Line 163, is a constant negative value at all rotor positions. This is because both stator teeth spanned by each coil 152 and 153 are north poles at all rotor positions.
  • the flux linking coils 155, Line 165 and the flux linking 156, Line 166, are both positive, and also show little variation with rotor position as the stator teeth spanned by coils 155 and 156 are south poles at all rotor positions when there is no current in the field winding.
  • Figure 12 shows the flux linking each of the armature coils when the field winding MMF is increased to 800At. This is an equivalent of 400At in each of the two field coils 191 and 192 spanning 121 to 122 and 123 to 124 respectively. This is therefore the same slot current (400 A/slot) which occurs in a prior art flux switching machine with six coils of 200At (400A/slot) and a total MMF of 1200At.
  • Lines 171, 172, 173, 174, 175 and 176 correspond to the armature flux linkage in armature coils 151, 152, 153, 154, 155 and 156 respectively.
  • Lines 171 and 174 have larger variations in flux linkages compared to lines 161 and 164 in Figure 11.
  • the increase in field current has therefore increased the magnetic flux linking the two armature coils spanning the two permanent magnet sections.
  • the addition of field current excitation has caused a change from two pole magnetic field towards a six pole magnetic pattern and has reduced the dc flux in coils 152, 153, 155 and 156 but significantly increased the alternating component of the flux linkage in these armature coils.
  • an armature emf will be induced in coils 152, 153, 155 and 156.
  • the armature emf in coils 152, 153, 155 and 156 is calculated by the rate of change of the armature flux linkage graphs 172, 173, 175 and 176.
  • Each of these coils will therefore have an equal emf and can be connected in series or parallel providing care is taken to orientate the armature connections so that the positive emf is towards the same end of the winding.
  • Figure 13 shows the total armature flux linkage variation in coils 151 , 154 at four different field current MMF values illustrated by lines 200, 201, 202, 203.
  • Figure 14 shows the summation of the armature flux linkages in coils 152, 153, 155 and 156, illustrated by lines 210, 211, 212 and 213 at field winding MMFs of OAt, 800At, 1600At and 2400At respectively. It can be seen that correct addition of the armature flux linkages cancels the dc flux components of the 2 pole magnetic field. Since armature emf is the rate of change of flux linkage, the emf associated with the armature coils 152, 153, 155 and 156 is zero with no field current and then increases as field current increases.
  • Figure 15 shows the variation in peak value of the combined armature flux linkage in coils 151 and
  • Line 221 starts above zero indicating that there is a variation in armature flux linkage with no field winding MMF.
  • Line 222 is zero at a field MMF of zero.
  • Line 221 increases slowly with field current indicating that the peak to peak flux linkage in coils 151 and 154 increases slightly with field current.
  • Line 222 increases steeply with field current to a value which is just under twice the value of line 221 at the equivalent field MMF. Since line 222 is the combined flux linkage of four armature coils, rather than two, as in line 221, this is an expected result.
  • Line 223 in Figure 15 shows the total flux linkage if all six armature coils are combined.
  • Figure 16 shows a comparison between a machine according to the invention and an identical size of flux switching machine according to the prior art. Both machines have 12 stator teeth and six rotor teeth. Line 230 corresponds to the prior art machine and line 231 corresponds to the machine according to the invention. Both machines have outside diameters of 65mm and the total armature flux linkage is quoted per metre of stack length. It is clear from Figure 16 that the armature flux linkage in a machine according to the invention is significantly higher than in the prior art machine for the same field winding MMF. Some key comparisons are shown in Table 1.
  • a machine according to the present invention offers the feature of a simple and robust machine with a field winding system combining a simple permanent magnet field and a variable excitation field winding resulting in a field controlled flux switching machine which is simple to construct and produces significantly more armature flux linkage than a prior art machine for a given field winding MMF.
  • Figure 17 shows some possible methods for the connections between the armature coils 151-156.
  • Figure 17a shows the arrangement where all the armature coils 151-156 are connected in series. It is important to ensure that the induced voltages of all the series connected coils are in phase so that the voltage across the series combination increases with each additional coil. This is represented by the dot notation on each coil.
  • the complete armature winding has two end connections 300 and 301. When all the armature coils are series connected the current through them will be equal.
  • the electromechanical energy conversion in coils 151 and 154 may however be different from the electromechanical energy conversion in 152, 153, 155 and 156. This is because the emf induced in 151, 154 follows a different relationship with field current than 152, 153, 155 and 156 as was illustrated by Figure 15. This does not prevent the machine configured in this way from operating very successfully as a motor or generator.
  • the emf across the complete armature winding will be higher for a given field current than a similar machine constructed according to the prior art.
  • Figure 17b shows a further connection method for the armature coils in a machine according to the invention.
  • Coils 151 and 154 are connected together in series to make a first armature winding 401 with connections 310 and 311.
  • Armature coils 152, 153, 155 and 156 are connected together in series to make a second armature winding 402 with end connections 312 and 313.
  • the induced emf across 310 to 311 will follow a characteristic like line 221 in Figure 15. As field current increases the induced emf between 310 and 311 will increase slowly.
  • the induced emf across 312 to 313 will start at zero with zero field current but will increase faster with field current, as illustrated by line 222 in Figure 15.
  • the armature emfs can be further adjusted by different numbers of turns in coils 151 and 154 compared to coils 152, 153, 155 and 156.
  • Figure 17c shows another possible connection method for the armature coils. Assuming coil 151 and coil 154 have the same number of turns then, at any given speed and field current, their induced emfs will be equal and the two coils can be connected in parallel to create a first armature winding 401 with end connections 310 and 311. Similarly if coils 152, 153, 155 and 156 each have the same number of turns then these four coils will have the same emf at any given speed and field current and they can be connected in parallel to create the second armature winding 402 with end connections 312 and 313.
  • connection patterns not shown in Figure 17 are possible. These include the coils of the first armature winding connected in series while the coils of the second armature winding are connected in parallel. Alternatively the second armature winding could comprise two of the coils in series and then connected in parallel with the other two coils in series. In another arrangement coils 151 and 154 could be connected in parallel and then connected in series with a series or parallel combination of coils 152, 153, 155 and 156 to create a single armature winding.
  • each armature coil may be made up of two closely coupled coils (sometimes referred to as bifilar strands). This bifilar arrangement is known for flux switching motors as it provides an electronic control circuit of low cost.
  • Figure 18 shows an electronic control circuit for one aspect of the invention.
  • the circuit of Figure 18 can be used in conjunction with the armature connection scheme of Figure 17a. All the armature coils are connected together to make a single armature winding with terminations 300 and 301.
  • the circuit of Figure 18 is a single phase inverter with four power transistors or IGBTs 321, 322, 323 and 324 which can control the flow of alternating current through the armature winding by appropriate switching of the four IGBTs.
  • End connection 300 of the armature winding is connected to the node between the two IGBTs 321 and 322 and end connection 301 is connected to the node between IGBTs 323 and 324.
  • the field winding 325 comprising the parallel or series combination of the two field coils 191 and 192 in a machine according to the invention is connected between the positive dc supply and the positive supply rail of the inverter. In this position, the current flowing in the inverter switches is drawn in series through the field winding. In this series configuration the field current varies as the armature current varies giving a characteristic like a series connected brushed motor.
  • a diode 326 or a capacitor 327 is also usually present to provide a path for the field current during switching transitions of the armature switched. The operation of this circuit is identical to circuits to control the prior art flux switching machine.
  • a machine according to this invention which changes the number of magnetic poles as the field current is increased can therefore be configured to have a single field winding and a single armature winding and can be controlled using the same inverter circuits as used on prior art flux switching motors.
  • the inverter circuit can be one of low cost but the unique magnetic geometry of the machine according to the invention leads to a machine of high efficiency, combined with low manufacturing costs.
  • Figure 19 is an alternative electronic control circuit which can be used to control the first aspect of the machine according to the invention.
  • This circuit is also from the prior art and gives independent control of the armature and field currents with the windings forming parallel (or shunt) paths within the converter.
  • the armature circuit employs four IGBTs (or mosfets or other transistor switch) 321, 322, 323 and 324 connected to the first end 300 and second end 301 of the armature winding.
  • a further IGBT 328 controls the current through the shunt field winding 330.
  • a diode 329 carries the field current when the IGBT 328 is turned off.
  • the whole circuit is connected to a dc power source 331.
  • the dc power source may be a battery or may be the output from a rectifier to convert ac to dc. Some smoothing capacitance may also be present though it does not have to be large.
  • the shunt field winding 330 in Figure 19 will typically have higher numbers of turns and use thinner wire compared to a field winding 325 designed for series connection as in Figure 18. In either case the field winding will be made up of the series or parallel combination of field coils 191 and 192.
  • the field winding could be excited by a separate excitation circuit.
  • Figure 19 has an advantage over Figure 18 in that it is suitable for motoring or generating operation of the machine according to the invention.
  • the inverter switches 321, 322, 333 and 334 can be controlled so that current flows out of terminal 300 when the emf in the armature winding at terminal 300 with respect to 301 is positive.
  • the field winding is not in series with the generated current.
  • the shunt field winding in Figure 19 can easily be controlled independently of the generated armature current to control the magnetic configuration of the machine.
  • Figure 20 is a circuit suitable for use with the second aspect of the invention.
  • the machine according to the second aspect of the invention uses the fact that the armature coils can be connected into two armature windings as shown in Figure 17b and 17c.
  • the first armature winding comprises coils 151 and 154 and has an emf with no field current.
  • This first winding has terminals 310 and 311 and is connected to a first inverter circuit with electronic switches 351, 352, 353 and 354.
  • the second armature winding comprising series and or parallel combinations of armature coils 152, 153, 155 and 156 with terminals 312 and 313 is connected to a second inverter circuit comprising electronic switches 355, 356, 357 and 358.
  • a further IGBT 328 controls the current through the shunt field winding 330.
  • a diode 329 carries the field current when the IGBT 328 is turned off.
  • Figure 19 allows the current in the first and second armature windings to be independently controlled. Furthermore the magnitude of the field winding is controlled by pulse width modulation of switch 328. This allows maximum benefit to be obtained from the second aspect of the invention.
  • the second inverter circuit of Figure 20 can be used to increase the armature current in the second armature winding.
  • the configuration of the machine changes from predominately two pole to predominately six pole and operation at maximum efficiency is obtained for all loads.
  • the circuit in Figure 20 is also suitable for operation of the machine according to the second aspect of the invention as a generator with high efficiency, particularly over a wide range of load conditions.
  • the induced emf present in the first armature winding even with no field current is particularly valuable to induce voltage in the generator when no external excitation is present.
  • Figure 21 shows a further variation to the circuit of Figure 20 in which the field winding, 325, is in series with the current flowing into the inverter circuit controlling the second armature winding of a machine according to a second aspect of the invention.
  • This circuit is more suited to a motor rather than a generator.
  • the first armature circuit and first armature winding can be used for torque production.
  • the emf in this winding is induced from the permanent magnet flux and does not require field current.
  • the second armature inverter can be used with increasing armature current.
  • the field current also flows in the field winding 325 as this second inverter draws power from the supply, 331, automatically changing the machine from a two pole flux pattern to a six pole flux pattern and increasing the emf and electromechanical power conversion in the second armature winding.
  • Figure 22 shows a further circuit suitable for implementation of the second aspect of the invention.
  • US Patent 6, 140, ,729 describes a flux switching motor in which the armature windings comprise two closely coupled coils (bifilar strands). Bifilar strands can also be applied to the first or second aspect of the invention to control the first and second armature windings according to the invention.
  • the closely coupled coils are shown for use with the second aspect of the invention. Both coils 151 and 154 would be wound with bifilar strands to make closely coupled coils 371 and 372.
  • the two closely coupled coils, 371 and 372, making up the first armature winding are connected to two electronic switches, usually mosfets, 361 and 362 to create the first armature inverter. Operation of the first armature inverter can be performed in a manner similar to US 6,140,729. Using this first armature inverter alone, the machine according to the invention will have a dominant two pole magnetic field produced by the permanent magnets and will operate with high efficiency.
  • Closely coupled coils 373 and 374 are made from series or parallel connection of closely coupled coils within armature coils 152, 153, 155 and 156. These are connected in a manner similar to US 6,140,729 to two further mosfets 363 and 364. Operation of mosfets 363 or 364 in phase with mosfet 361 or 362 respectively with respective duty cycles chosen to optimise efficiency automatically draws the field current through the field winding 325. Diode 326 provides a path for the field current in 325 to free-wheel when mosfet 363 or mosfet 364 is turned off. Figure 22 therefore provides a circuit of low cost which provides independent control of the first and second armature windings of the machine according to the invention and therefore allows the currents in the first and second armature windings to be optimised for efficiency.
  • Figure 23 is a further example of a circuit which can be used to control the first and second armature windings of a machine according to the invention.
  • the first connection end 310 of the first armature winding 401 is connected to the node between inverter switches 411 and 412.
  • the first connection end 312 of the second armature winding 402 is connected to the node between armature switches 413 and 414.
  • the second connection ends 311 and 313 of the first and second armature windings are connected together to the node between inverter switches 415 and 416. Since the emf induced at the first ends of the first and second armature windings are substantially in phase the operation of inverter switches 415 and 416 can be shared between the two armature windings. However, the current in each of the two armature windings can be independently controlled using the inverter switches connected to the first end of each armature winding.
  • the machine according to both the first and second aspects of the invention can be manufactured easily because the magnets are simple rectangular blocks. Furthermore, the two magnets 104 and 105 have parallel magnetic axes and are both magnetised in the same direction. The machine can therefore be completely assembled with the magnets demagnetised. After assembly of all parts and windings are complete an external magnetic field can be used to simultaneously magnetise both magnets.
  • the method of magnetising the permanent magnets according to the first and second aspects of the invention is a third aspect of the invention.
  • stator teeth associated with the first and second armature windings are equally spaced.
  • stator teeth linked by the first and second armature windings have an offset angle relative to the rotor pole pitch.
  • the offset angle introduces a phase angle between the induced emf of the first and second armature winding and enables the torque output of the machine to be distributed more evenly over all angles of rotor rotation. This effectively reduces the torque minimum which is present in a symmetric flux switching machine if all the armature winding emfs pass through zero at the same time.
  • An offset of 5 mechanical degrees gives an offset in the electrical phase of first and second armature of 30 degrees which provides a significant reduction in torque ripple.
  • a circuit offering independent control of the first and second armature winding should be used.
  • a fifth aspect to the invention uses the fact that the first and second armature windings can be connected to completely different power switching circuits or electronic control means, each one connected in turn to different power systems.
  • a motor it is useful for a motor to be able to operate from either a battery supply or a mains ac supply source. Since the battery is usually a low voltage, such as 9, 12 or 24 V and the mains ac supply is usually a significantly higher voltage such as 120V or 230V, the design of a single motor to operate successfully from both power systems is difficult. Furthermore it is important to maintain electrical isolation between the ac supply and the battery terminals. Furthermore if the machine is operating as a motor from a battery supply it is vital that the machine has high efficiency so that the life of the battery is maximised.
  • a machine according to the invention can be configured to solve this problem.
  • the first armature winding 401 is connected to a first electronic control means 501 such as shown in Figure 24 and is in turn connected to a battery supply 510.
  • the machine can operate as a motor or generator taking power from the battery or returning energy to the battery. In both modes the machine will operate with high efficiency since there is no field losses. The machine will have reduced number of poles and may not be able to deliver maximum power but can be designed to be sufficient for the required task.
  • the second armature winding 402 can be connected to a second electronic control means 502 which is connected to a higher voltage ac supply 511 via a rectifier 512.
  • the field winding can be connected between output of the rectifier and the second electronic control means as shown in Figure 24.
  • a shunt field winding circuit as illustrated in Figure 19 could be used.
  • the higher voltage, mains ac supply is present the machine can operate as a motor drawing energy from the ac supply. If it is required to generate power back into the ac supply the rectifier would have to be replaced by an inverter as is well known in the art.
  • When operating from the ac supply it is beneficial to also excite the field winding to allow the machine to reach its full potential power capability. When the field winding is excited the machine will change from the lower number of poles to its full number of magnetic poles.
  • energy can be drawn from the ac supply into the second electronic control means to excite the field winding and/or the second armature winding.
  • the first electronic control means can operate independently such that energy is is delivered to the battery, charging the battery. By correct control of the switches in the electronic control means this battery charging can be obtained when the machine is turning or when the machine is stationary.
  • This aspect of the invention uses the fact that the first and second armature windings are mutually coupled and both are also coupled to the field winding. Energy can therefore be transferred from one winding to another to charge the battery.
  • Asymmetrical rotor teeth are common in the prior art and can be used very successfully with all aspects of the invention.
  • the machine according to this invention is particularly effective as a generator.
  • the machine has a simple and robust stator structure making it suitable for easy manufacture. Furthermore the flux of the permanent magnet sections 104, 105, inserted in the stator induces an initial emf to self excite some of the armature windings of the generator. This provides an emf from the rotation of the rotor without requiring an excitation source thus avoiding the need for a separate dc power supply or battery.
  • the invention can be applied to other flux switching configurations as well as the example given here.
  • a flux switching machine with 12 stator teeth and 6 rotor teeth could have four permanent magnets and one field winding spanning the remaining two field slots.
  • the magnetic field pattern would be four pole while there was no field current in the remaining two field slots and would then become six poles when field current was applied during operation of the machine.
  • the invention can also be applied to a flux switching motor with eight stator teeth and four rotor teeth. Armature windings occupy every alternate slot, each spanning two stator teeth.
  • the field magnet means is interspersed between the armature slots and could comprise two permanent magnets and two field winding slots carrying a single field coil.
  • the two magnets would occupy field positions separated by 90 degrees and would be magnetised parallel to the air-gap but have like poles facing the 90 degree section of stator steel separating the two magnets.
  • the field pattern from the magnets alone would be a two pole pattern. However, this would become four pole when field current is supplied to the field winding.
  • the invention can therefore be applied to machines with eight teeth as well as twelve teeth on the stator providing that the magnets are inserted into the stator in positions where they can have opposite magnet faces in contact with the section of stator steel which separates the magnets.
  • the rotor of such machines will have 2*n rotor teeth, the spacing between rotor teeth (rotor pole pitch) therefore being 180/n degrees.
  • a machine according to the invention will have a two pole magnetic field when the magnets are magnetised increasing to 2*n magnetic poles when the field slots all carry field current.
  • the common feature in all the machines illustrated in Table 2 is that the number of magnetic poles in the machine under field only excitation is lower than the number of magnetic poles when the field coils are excited in addition to the permanent magnet fields.
  • the machines also have twice the number of stator teeth as rotor teeth and the armature emfs will all be substantially in phase and as such are known as single phase flux switching motors.
  • Flux switching machines with two or three electrical phase windings have also been described in the prior art. In such machines with two electrical phases the induced emf in each armature is separated by approximately 90 electrical degrees. In such machines with three electrical phases the induced emf in each armature is separated by approximately 120 electrical degrees.
  • a two phase machine would have eight stator teeth and either 3 or 5 rotor teeth or would have 16 stator teeth and 6 or 10 rotor teeth.
  • a three phase machine would have 12 stator teeth and five or seven rotor teeth or 24 stator teeth and 10 or 14 rotor teeth.
  • stators of these multiple phase flux switching machines have field excitation systems in alternate stator slots, they therefore have a similar structure to the machine according to this invention, and therefore the invention as disclosed can be applied directly to the stators of two phase and three phase flux switching motors.
  • the armature coils comprising each phase will have different induced voltage characteristics depending on whether they span a permanent magnet or a field slot.
  • a three phase flux switching motor is shown in Figure 25 with a stator 600 carrying twenty- four stator teeth and a rotor 610 with ten rotor teeth.
  • the stator contains six permanent magnets 601,602, 603, 604, 605 and 606.
  • Three permanent magnets 601, 603 and 605 are magnetised so that their North poles face in an anti-clockwise direction.
  • Three permanent magnets 602, 604 and 606 are magnetised so that their North poles face in a clockwise direction.
  • Figure 26 shows that six further slots between the stator teeth contain field windings ideally arranged as three coils 611, 612 and 613.
  • Figure 27 shows the arrangement of the armature coils 701 to 712.
  • Armature Coils 701, 704, 707 and 710 are associated with a first phase winding.
  • Armature Coils 702, 705, 708 and 711 are associated with a second phase winding.
  • Armature Coils 703, 706, 709 and 712 are associated with a third phase winding.
  • 701 and 710 are two coils associated with the first phase winding and they each span across a slot occupied by a permanent magnet while 704 and 707 are two coils associated with the first phase winding which span across a slot occupied by a field coil.
  • Figure 28 shows the field distribution when there is no field current in the field windings. Whilst the pole areas are quite different, the field pattern is substantially six pole, created by the six magnets.
  • Figure 29 shows the field distribution when field current is flowing in the field windings where the more conventional 12 pole pattern has been restored.
  • the increasing field current has increased the number of magnetic poles in the machine.
  • the permanent magnets can be thought of as being arranged in three pairs around the periphery of the machine, 602 and 603, 604 and 605, 606 and 601. Each pair have equal magnetic poles facing each other. The pairs are separated by two stator teeth. Between each pair are six stator teeth. Machines according to the invention will usually have spacings of two or six or ten stator teeth between the magnets.
  • the machine of Figure 25 illustrates an implementation of the invention where spacings of both six and two are present in the one machine. If the four coils associated with each phase winding are connected in series, the flux linking the three armature phase windings would have the form shown in Figure 30.
  • Plots 751, 752 and 753 show the flux linking the four armature coils of phase winding 1, phase winding 2 and phase winding 3 respectively when there is no current in the field windings.
  • the three plots are approximately sinusoidal.
  • Plots 761, 762 and 763 show the flux linking the four armature coils of phase winding 1, phase winding 2 and phase winding 3 respectively when there is current in the field windings in a direction required to create the higher pole number field.
  • the three plots are still approximately sinusoidal but have an increased magnitude.
  • the armature emfs in this machine are therefore as typically found in a three phase machine, with the major benefit that the magnitude of the induced emf in the armature winding is controllable with the field current independently of the speed. If the direction of the field current were reversed the armature emfs could be reduced below the level created by the permanent magnets alone.
  • Operation of the three phase machine according to the invention as a motor or generator can be done with a three phase inverter as is known in the industry.
  • the field winding can be separately excited with its own current controller or can be connected in series with the dc supply to or from the three phase inverter driving the armature.
  • the current flowing in the armature phases can be sinusoidal or trapezoidal or any other alternating current shape as is appropriate for the available voltage and speed range of the machine. Further improvements in efficiency can be achieved by operating the machine with two inverters; one inverter connected to armature coils spanning permanent magnets and a separate inverter driving the armature windings spanning slots containing field coils.
  • a three phase flux switching machine according to the invention can also be made with a similar stator structure to Figure 25 but could have a rotor with fourteen salient pole teeth.
  • stator Whilst for simplicity and clarity the drawings attached to this description show the stator as having two or more separate sections separated completely by the permanent magnets it is entirely possible to construct the machines from a single laminations which have a thin section of steel bridging the inner or outer or both surfaces of the magnet. Such a section may be useful in assembly of the stator, giving the machine increased structural strength. However the linking pieces of steel in such a lamination will act as magnetic short circuits around the magnet, reducing the amount of flux which usefully links the coils of the first armature winding. The magnet size can be adjusted to ensure that this does not compromise the performance of the machine.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Synchronous Machinery (AREA)
  • Permanent Magnet Type Synchronous Machine (AREA)

Abstract

L'invention concerne une machine électrique comprenant un rotor (11) à relief magnétique mais sans enroulements ; un stator (101) comprenant des dents de stator, le stator comportant des enroulements d'armature (106, 111) enroulés avec un pas correspondant à une pluralité de dents de stator et disposés autour du stator pour produire une ou plusieurs phases électriques, le stator comprenant également un moyen d'aimant à champ, intercalé toutes les deux dents de stator, le moyen d'aimant à champ comprenant au moins un enroulement de champ (191, 192) et au moins un aimant permanent (104, 105), et un moyen de régulation du courant de champ de telle sorte que la variation du courant continu dans les enroulements de champ modifie le nombre de pôles magnétiques dans la machine. Les bobines d'armature de la machine peuvent être configurées en un ou plusieurs enroulements d'armature et l'invention concerne également des circuits pour exciter les bobines d'armature de la façon la plus efficace possible, selon les besoins de charge ou d'application de la machine.
PCT/GB2008/051009 2007-10-29 2008-10-29 Machines à réluctance à aimant permanent WO2009056879A1 (fr)

Applications Claiming Priority (2)

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GB0721074.3 2007-10-29
GB0721074A GB2454170A (en) 2007-10-29 2007-10-29 Pole number changing in permanent magnet reluctance machines

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CN101789738A (zh) * 2010-03-05 2010-07-28 东南大学 双凸极永磁电机控制装置及控制方法
CN102510152A (zh) * 2011-11-24 2012-06-20 南京航空航天大学 双凸极电机的复合励磁结构
JP2013201869A (ja) * 2012-03-26 2013-10-03 Denso Corp 回転機
WO2013149088A1 (fr) * 2012-03-28 2013-10-03 Lee Randal Système et procédé pour un convertisseur électrique programmable
JP2015154675A (ja) * 2014-02-18 2015-08-24 株式会社小松製作所 回転電機
CN110572004A (zh) * 2019-09-26 2019-12-13 哈尔滨工业大学 永磁磁阻直线电机
CN110765649A (zh) * 2019-11-11 2020-02-07 南通大学 一种轴向磁场磁通切换永磁电机多目标优化方法
CN112491231A (zh) * 2020-12-31 2021-03-12 山东理工大学 一种混合励磁凸极分块转子开关磁通电机

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GB2455123A (en) 2007-11-29 2009-06-03 Technelec Ltd Control of electrical machines
GB2455122A (en) 2007-11-29 2009-06-03 Technelec Ltd Control of electrical machines
WO2011049980A1 (fr) * 2009-10-19 2011-04-28 Qm Power, Inc. Moteur à circuit magnétique parallèle
WO2012093951A2 (fr) * 2011-01-03 2012-07-12 Tudor-Frunza Florin-Eugen Générateur électrique polyphasé à reluctance commutée
GB2489423A (en) 2011-03-25 2012-10-03 Technelec Ltd Flux switching electrical machine with slotted rotor
DE102012104342A1 (de) 2012-05-21 2013-11-21 Linde Material Handling Gmbh Flurförderzeug mit elektrischem Antriebsmotor
DE102012104341A1 (de) * 2012-05-21 2013-11-21 Linde Material Handling Gmbh Einen elektrischen Pumpenmotor aufweisendes Flurförderzeug
BR112019019629A2 (pt) 2017-03-29 2020-04-14 Qm Power Inc motor de corrente alternada multivelocidade

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Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101789738A (zh) * 2010-03-05 2010-07-28 东南大学 双凸极永磁电机控制装置及控制方法
CN102510152A (zh) * 2011-11-24 2012-06-20 南京航空航天大学 双凸极电机的复合励磁结构
JP2013201869A (ja) * 2012-03-26 2013-10-03 Denso Corp 回転機
WO2013149088A1 (fr) * 2012-03-28 2013-10-03 Lee Randal Système et procédé pour un convertisseur électrique programmable
CN104396122A (zh) * 2012-03-28 2015-03-04 兰德尔·利 用于可编程电变换器的系统与方法
US9479014B2 (en) 2012-03-28 2016-10-25 Acme Product Development, Ltd. System and method for a programmable electric converter
WO2015125773A1 (fr) * 2014-02-18 2015-08-27 株式会社小松製作所 Machine tournante électrique
CN105917558A (zh) * 2014-02-18 2016-08-31 株式会社小松制作所 旋转电机
JP2015154675A (ja) * 2014-02-18 2015-08-24 株式会社小松製作所 回転電機
CN110572004A (zh) * 2019-09-26 2019-12-13 哈尔滨工业大学 永磁磁阻直线电机
CN110765649A (zh) * 2019-11-11 2020-02-07 南通大学 一种轴向磁场磁通切换永磁电机多目标优化方法
CN110765649B (zh) * 2019-11-11 2022-07-15 南通大学 一种轴向磁场磁通切换永磁电机多目标优化方法
CN112491231A (zh) * 2020-12-31 2021-03-12 山东理工大学 一种混合励磁凸极分块转子开关磁通电机

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