Classifications

• • 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
  • H02K1/27—Rotor cores with permanent magnets
  • H02K1/2786—Outer rotors
  • H02K1/2787—Outer rotors the magnetisation axis of the magnets being perpendicular to the rotor axis
  • H02K1/2789—Outer rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets
  • H02K1/2791—Surface mounted magnets; Inset magnets
  • H02K1/27915—Magnets shaped to vary the mechanical air gap between the magnets and the stator
• • A—HUMAN NECESSITIES
  • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
  • A23B—PRESERVATION OF FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES; CHEMICAL RIPENING OF FRUIT OR VEGETABLES
  • A23B11/00—Preservation of milk or dairy products
  • A23B11/10—Preservation of milk or milk preparations
  • A23B11/18—Preservation of milk or milk preparations by addition of preservatives
• • A—HUMAN NECESSITIES
  • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
  • A23B—PRESERVATION OF FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES; CHEMICAL RIPENING OF FRUIT OR VEGETABLES
  • A23B11/00—Preservation of milk or dairy products
  • A23B11/30—Preservation of cream or cream preparations
  • A23B11/35—Preservation of cream or cream preparations by addition of preservatives
• • A—HUMAN NECESSITIES
  • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
  • A23B—PRESERVATION OF FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES; CHEMICAL RIPENING OF FRUIT OR VEGETABLES
  • A23B11/00—Preservation of milk or dairy products
  • A23B11/40—Preservation of butter or butter preparations
  • A23B11/45—Preservation of butter or butter preparations by addition of preservatives
• • A—HUMAN NECESSITIES
  • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
  • A23C—DAIRY PRODUCTS, e.g. MILK, BUTTER OR CHEESE; MILK OR CHEESE SUBSTITUTES; PREPARATION THEREOF
  • A23C21/00—Whey; Whey preparations
  • A23C21/08—Whey; Whey preparations containing other organic additives, e.g. vegetable or animal products
• • A—HUMAN NECESSITIES
  • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
  • A23V—INDEXING SCHEME RELATING TO FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES AND LACTIC OR PROPIONIC ACID BACTERIA USED IN FOODSTUFFS OR FOOD PREPARATION
  • A23V2002/00—Food compositions, function of food ingredients or processes for food or foodstuffs
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K2201/00—Specific aspects not provided for in the other groups of this subclass relating to the magnetic circuits
  • H02K2201/06—Magnetic cores, or permanent magnets characterised by their skew
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K29/00—Motors or generators having non-mechanical commutating devices, e.g. discharge tubes or semiconductor devices
  • H02K29/03—Motors or generators having non-mechanical commutating devices, e.g. discharge tubes or semiconductor devices with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems
• • 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
  • H02K7/18—Structural association of electric generators with mechanical driving motors, e.g. with turbines
  • H02K7/1807—Rotary generators
  • H02K7/1823—Rotary generators structurally associated with turbines or similar engines
  • H02K7/183—Rotary generators structurally associated with turbines or similar engines wherein the turbine is a wind turbine
• • 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
  • H02K7/18—Structural association of electric generators with mechanical driving motors, e.g. with turbines
  • H02K7/1807—Rotary generators
  • H02K7/1823—Rotary generators structurally associated with turbines or similar engines
  • H02K7/183—Rotary generators structurally associated with turbines or similar engines wherein the turbine is a wind turbine
  • H02K7/1838—Generators mounted in a nacelle or similar structure of a horizontal axis wind turbine
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/72—Wind turbines with rotation axis in wind direction

Definitions

• the invention concerns a permanent magnet generator with reduced cogging effect comprising a stator with a plurality of stacks of tooth-shaped magnetic laminations having electric windings located radially around the rotation axis of the generator which alternate with a plurality of slots having a correspondent opening and a rotor having a plurality of permanent magnets arranged radially spaced from the rotation axis of the generator, in which said permanent magnets have skew edges.
• the invention also relates to corresponding magnets.
• the cogging torque (stick-slip phenomenon) is the typical braking torque which opposes the rotation of the rotors of electric permanent magnet motors (PMM) even with no load.
• the blades begin to move with a rather high wind speed: about 4 m/s, while with a cogging torque of 1% a wind speed of 2 m/s is sufficient (the usable power varies with the cube of the wind speed).
• Figure 1 schematically illustrates how the cogging effect works.
• the cogging torque is caused by the interaction between the magnets mounted on the rotor R and the anisotropy of the stator due to the opening of the slots A (change in the magnetic reluctance). In fact, the highest value is found during the rotation when the magnet edge B and the slot A are facing each other, while when the magnet edge B is in the middle of the tooth D or in the middle of the slot A the cogging torque is equal to zero, as can be seen in the representation of the cogging torque C in the diagram below.
• the arrow M shows the movement direction of the rotor R.
• cogging torque value depends on the application.
• the cogging torque is not particularly important for electric generator units equipped with PMG (permanent magnet generators), therefore values close to 20% of the rated torque are acceptable.
• the cogging torque is an important parameter of PMGs when used in wind generation technology: the typical reference values may range from 3% to 5% of the rated value, a value of 1% is considered extremely low for mass production wind generators.
• the object of the present invention is to construct a permanent magnet generator with a low cogging effect, and in particular a low power wind generator (microwind generator) with a lower cogging effect compared to generators of the known art.
• a further object of the invention is to propose a generator in which the lower cogging effect does not result in a high power loss.
• Another object of the invention is to construct a permanent magnet that helps to reduce the cogging effect with a limited loss of power.
• variable air gap magnets means magnets that due to their specific design (size, thickness, arc configuration, ...) are suited to create a variable air gap, that is, an air gap that is not uniform during the rotation of the rotor.
• the skew of the edges means, as is known in the state of the art, an inclination with respect to the vertical axis of the magnet that is parallel to the rotation axis of the generator.
• the optimization of one or more parameters is added to the variable air gap and the skew magnets, including: the ratio between the number of slots and pairs of poles, the pole expansion of the magnets with respect to the pole pitch in relation to the slots/poles ratio, the value of the air gap as a function of the slot opening, as well as the stack length to reduce the cogging effect.
• the adjustment must be a good compromise between the construction needs and the performance (power) of the generator.
• the slots/poles (c/2p) ratio is an important parameter that enables the value of the fundamental cogging frequency to be raised as much as possible. This value corresponds to the lowest common multiple between slots and poles.
• the value of the air gap is a parameter that can be varied depending on the opening of the slot in order to obtain a smaller variation of the magnetic reluctance when the magnet passes underneath the slot opening.
• the choice of the opening of the slot and the width of the tooth is preferably a compromise between the cogging torque, magnetic saturation, the Carter factor, leakage inductance and an acceptable geometric dimension suited to allow the automatic winding of the stator.
• the variability of the air gap is achieved thanks to the fact that the top and bottom sides of the magnets define a curved internal surface and a curved external surface having the same curvature direction and defining, in cross section, non concentric circle arcs with different radiuses, such that the distance between the two surfaces, representing the magnet thickness, is variable in said cross section, and thanks to the fact that the arc of a circle determined by the radius of the curved internal surface in cross section, located in front of the stacks of tooth-shaped magnetic laminations, is not concentric with the arc of a circle determined by the radius corresponding to the cylindrical surface described by the stacks of tooth-shaped magnetic laminations themselves. In this way, a variable air gap that is effective from the stand point of the reduction of the cogging effect can be easily obtained.
• the thickness of the magnet is variable in the radial direction.
• magnets that in cross section are midway between a “bread loaf shape that is, "D-shaped”, and a radial shape, that is, "C-shaped”.
• the magnet thickness is constant in the middle direction of the magnet, so that the cross section follows a helicoidal path where the middle direction is defined, in a top view of the magnets, as a bisecting line parallel to the skew sides of the magnets.
• the magnet in top view, has substantially the shape of a parallelogram.
• the middle direction of the magnet can be defined as a segment joining the midpoints of two opposite sides and parallel to the skew sides.
• the external curved surface is a part of a cylindrical surface and is concentric with the radius of the cylindrical surface described by the stacks of magnetic laminations, while the internal curved surface of the magnet is not cylindrical.
• a constant thickness in the middle direction ZZ ensures a smaller cogging effect and a reduced loss of power compared to a magnet with variable thickness in its middle direction Z.
• the magnets are defined by the fact that the maximum thickness is constant along the midline ZZ which follows a helicoidal path and decreases symmetrically towards the edges of the magnet.
• the fact that the cross section follows a helicoidal path also means that the individual cross sectional areas which follow one another at different heights of the magnet in the helicoidal path are essentially congruent.
• the internal curved surface and the external curved surface are parts of cylindrical surfaces and the magnet thickness varies in the middle direction of the magnet (Z), where the middle direction is defined as above.
• This closure system is more feasible and more effective with regard to the reduction of the cogging torque than the known method in which ferrite plates are placed directly on the windings inside the slots.
• the shaped clefts in the stacks of magnetic laminations are not tied to generators with variable air gap and/or skew magnets. Obviously, they can also be applied to generators with straight magnets and constant air gap or generators with variable air gap and straight magnets or even generators with skew magnets and constant air gap etc.
• the keys are made from a composite of insulating resin and iron powder.
• the iron content is above 50%.
• the length of the stack of magnetic laminations is variable.
• the cogging torque like the power, varies as a function of the stack length and thus as regards the desired power there is a certain amount of cogging torque which increases as the power increases.
• a stack length of 42 mm gives an output of 700 W in continuous service at 415 rpm with a rated torque of 16.1 Nm, and a maximum output power of about 1000W (415 rpm) with a torque of 23 Nm.
• the cogging torque is 0.20 Nm.
• the generator according to the invention is a wind generator, preferably with an output power between 400 W and 5 kW and a torque between 9 and 120 Nm.
• Given powers and torques are characteristics of the generator that can be easily attained by selecting suitable construction parameters and sizes that are well known to the experts.
• NdFeB neodymium iron boron
• Br 1.2 + 1 :35 T
• He KA/m
• BH max KJ/m 3
• a low-power (1000 W), permanent magnet mini-wind turbine is obtained: at 415 rpm (with a corresponding torque of 23 Nm), with dimensions of the active parts not exceeding 170 mm in diameter and 42 mm in length, the cogging torque does not exceed 0.20 Nm (about 1% of the rated torque).
• Another aspect of the invention also relates to a permanent magnet suited to create a variable air gap in a permanent magnet generator in which the top and the bottom sides of said magnet define a curved internal surface and a curved external surface having the same curvature direction and defining in cross section, with respect to the longitudinal height of the magnet, non-concentric circle arcs with different radiuses, so that the distance between the two surfaces that represents the thickness of the magnet varies in said cross section where said magnet has skew edges, wherein the distance between the two curved surfaces is constant along the middle direction of the magnet, so that the cross section follows a helicoidal path, or wherein the internal curved surface and the external curved surface are parts of cylindrical surfaces, and wherein the thickness of the magnet varies in the middle direction of the magnet, where the middle direction is defined, from time to time, in a top view of the magnet, as a bisecting line parallel to the skew sides of the magnet.
• FIG. 1 shows a schematic representation of the cogging effect according to the state of the art
• FIG. 2 shows a cross section of a detail of the stator and the rotor of a wind generator according to the invention
• FIG. 3 shows an enlarged view of a detail of Figure 2;
• Figures 4a-4f show various views of a skew magnet with variable air gap and variable thickness along the midline according to the invention, and in particular: Figure 4a is an axonometric view of the magnet, Figure 4b is a top view of the magnet, Figures 4c and 4d are side views of the magnet, Figure 4e shows a cross section of the magnet along line A1-A1 of Figure 4c, while Figure 4f shows a cross section of the magnet along line B1-B1 of Figure 4b;
• Figures 5a and 5b illustrate the cutting of an essentially rectangular magnet to produce the skew magnet with variable air gap according to Figures 4a- 4f ( Figure 5a in a top view and Figure 5b in a side view), while Figures 5c and 5d show cross sections of the magnet along the lines C1-C1 ( Figure 5c) and D1-D1 ( Figure 5d) of Figure 5a;
• - Figures 6a-6g show various views of a skew magnet with variable air gap and constant thickness along the midline according to the invention, and in particular: Figure 6a is a top view of the magnet, Figures 6b and 6e are side views of the magnet, Figure 6c shows a cross section of the magnet along line A2-A2 of Figure 6b, and Figures 6d, 6f and 6g show cross sections of the magnet along the lines C2-C2 ( Figure 6d), D2-D2 ( Figure 6f) and B2-B2 ( Figure 6g) of Figure 6a;
• Figure 7a shows the helicoidal cut made to obtain the magnet according to Figures 6a-6g, while Figure 7b shows an enlarged view of the detail circled in Figure 7a;
• Figure 9a shows a cross section of a detail of a rotor according to the invention, in which the stacks of magnetic laminations have shaped clefts suited to house correspondingly shaped magnetic keys, and Figure 9b shows an enlarged view of a detail of Figure 9a with a magnetic key inserted in a cleft;
• FIG. 10a and 10b show the inclination of a magnet according to the invention.
• Figure 2 shows a cross section of a detail of a wind generator. It is possible to observe the external rotor 2 and the internal stator 4.
• the stator 4 is provided with a plurality of stacks of tooth-shaped magnetic laminations 6 arranged radially around the axis of rotation 8 of the rotor 2.
• the external radius of the stator corresponding to the external surface of the stacks of tooth-shaped magnetic laminations 6 is indicated by Rs.
• Each stack of tooth-shaped magnetic laminations 6 has an electrical winding 10.
• the stacks of tooth-shaped magnetic laminations 6 alternate with an equally large number of slots 12.
• the internal radius of the rotor casing which coincides with the external radius of the magnets is indicated by Rr.
• Each individual magnet 16 has an internal side that is opposite the stator and is curved following the shape of an arc of a circle whose centre 18 is not concentric with the centre 8 of the stator 4.
• the corresponding radius is indicated by Ri.
• the radius Rr is shorter than the radius Ri; furthermore Rr and Ri do not have the same centre. This eccentricity is responsible for ensuring that the air gap 20 is not constant, that is, that the air gap is variable, as shown best in Figure 3.
• the cross section geometry of the magnet 16 suggests a "D" which at the centre has a thickness b1 and on the sides a smaller thickness b2.
• Figure 4a shows an axonometric view of a skew magnet 116 with variable air gap in which the thickness of the magnet in the middle direction is not constant.
• the recesses 117c are useful to fasten the magnet in the rotor 116.
• the magnet seen from above is shown in Figure 4b.
• the width of the magnet is defined by the lengths 11. Compared to the length (height) I2 of the magnet, the magnet is inclined by an angle a1.
• Figures 4c and 4d show the magnet 116 in side views, seen respectively from one side 117a or 117b ( Figure 4a).
• Figure 6a shows, in a view from above, a skew magnet with variable air gap 216 in which the thickness is constant along the middle direction ZZ and along the skew edges.
• Figures 6b and 6e show side views of the magnet related to sides 217a and 217b.
• the width of the magnet 216 is indicated by 1201 ( Figures 6d-6g).
• FIG. 6c shows a cross section of the magnet along line A2-A2 of Figure 6b.
• the length of the magnet is indicated by I202.
• Figures 6d, 6f and 6g show different cross sections of the magnet 216, Figure 6d shows the section along line C2-C2 of Figure 6a, Figure 6f shows the section along line D2-D2 of Figure 6a and Figure 6g shows the section along line B2-B2 of Figure 6a.
• the thicknesses of the magnet edges are all equal and are indicated by s10, and the central thicknesses s11 are also all the same.
• the invention has achieved its object of creating a permanent magnet generator with low cogging effect ( ⁇ 1 %).

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• Engineering & Computer Science (AREA)
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• Food Science & Technology (AREA)
• Polymers & Plastics (AREA)
• Wood Science & Technology (AREA)
• Power Engineering (AREA)
• Permanent Field Magnets Of Synchronous Machinery (AREA)
• Permanent Magnet Type Synchronous Machine (AREA)

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• 2010
  • 2010-08-04 IT ITVI2010A000220A patent/IT1401625B1/it active
• 2011
  • 2011-08-04 EP EP11754917.0A patent/EP2601729A2/de not_active Withdrawn
  • 2011-08-04 WO PCT/IB2011/001814 patent/WO2012017303A2/en not_active Ceased

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