Nd-Fe-B permanent magnet with cerium, rotor assembly, electromechanical transducer, wind turbine

Abstract

The invention describes an Nd-Fe-B permanent magnet (354) comprising 28% to 35% by weight of a rare earth element, where the total content of Nd (neodymium) and Pr (praseodymium) is between 20% to 25% by weight, where the content of Ce (cerium) is between 5% to 10% by weight, where the spatial extension is between 18 mm and 26 mm, and where the total content of Nd (neodymium) and Pr (praseodymium) is between 20% and 25% by weight. That is, the height (h) of the magnet (354) in the main magnetization direction of the Nd-Fe-B permanent magnet (354) is between 18 mm and 26 mm. A rotor assembly (350) for an electromechanical transducer (340) is also described herein.

Description

Technical Field

[0001] This invention relates to the technical field of Nd-Fe-B type rare-earth permanent magnets. It also relates to rotor assemblies for electromechanical transducers, the rotor assembly comprising at least one such Nd-Fe-B permanent magnet. Furthermore, this invention relates to electromechanical transducers comprising such rotor assemblies, and to wind turbines comprising such electromechanical transducers. Background Technology

[0002] The electromechanical transducer is a machine that converts electrical energy into mechanical energy or vice versa. An electric motor is such an electromechanical transducer, using a magnetic field chain to convert electrical energy into mechanical energy. A generator is such an electromechanical transducer, also using a magnetic field chain to convert mechanical energy into electrical energy.

[0003] The electromechanical transducer includes a stator and a rotor. The stator is a component representing the stationary part of the electromechanical transducer. The rotor is a component representing the moving part of the electromechanical transducer. The aforementioned magnetic field chain connects the stator and the rotor.

[0004] In recent years, particularly since the introduction of rare-earth magnetic materials, permanent magnet (PM) electromechanical transducers have become popular because they eliminate the need for commutators and brushes, which are typically used with conventional DC electromechanical transducers. The absence of external electric rotor excitation eliminates losses on the rotor side and makes PM electromechanical transducers more efficient. Furthermore, the brushless design of PM electromechanical transducers allows the conductor coils to be exclusively positioned in the stationary stator. It is worth mentioning in this respect that non-PM electromechanical transducers equipped with commutators and brushes are susceptible to significantly higher maintenance costs.

[0005] The PM electromechanical transducer is also known for its durability, controllability, and spark-free operation. Thanks to these advantages, the PM electromechanical transducer is widely used in many applications, such as electric vehicles (i.e., the transducer is an electric motor) or power generation systems (i.e., the transducer is a generator), such as, for example, in wind turbines. The PM electromechanical transducer is used particularly in so-called direct-drive (DD) wind turbines, where the generator is directly connected to the rotor (hub) of the corresponding DD wind turbine via a main shaft.

[0006] Currently, high-efficiency PM electromechanical transducers are typically equipped with Nd-Fe-B type rare-earth PM, which generates a strong magnetic field and thus ensures a strong magnetic field chain between the rotor and stator. This is also applicable to generators in modern wind turbines, and particularly to generators in DD wind turbines. Therefore, to realize (direct drive) wind turbine generators, using PM material Nd-Fe-B, the wind turbine generator has a permanent magnet excitation synchronous generator.

[0007] To increase the resistance of Nd-Fe-B PM to demagnetization, it is known to add the elements dysprosium (Dy) and / or terbium (Tb) to the magnet designation. In other words, by adding Dy and / or Tb, the so-called intrinsic coercivity HcJ of Nd-Fe-B PM is increased.

[0008] Due to high demand and scarce availability, the elements Dy and Tb have recently become quite expensive. Currently, the cost level of Dy is particularly challenging for wind turbine manufacturers. Furthermore, not all new mines developed globally can supply Dy and / or Tb. They can only supply the rare earth element neodymium (Nd) and the corresponding rare earth element praseodymium (Pr). Praseodymium is often used in Nd-Fe-B magnets because it has similar chemical and magnetic properties to neodymium. Therefore, experts predict that the price of Dy and / or Tb will further increase in the coming years as demand for Nd-Fe-B PM increases.

[0009] Further increases in Dy / Tb prices will increase PM costs for direct-drive generators and lead to high overall costs for wind turbines.

[0010] In price-sensitive applications, neodymium and praseodymium can be replaced by cheaper rare-earth materials such as cerium (Ce), lanthanum (La), and / or yttrium (Y), leading to a reduction in magnet prices. Unfortunately, these materials negatively affect the magnetic properties of the magnets, which may be acceptable in many applications.

[0011] There may be a need for cheaper Nd-Fe-B permanent magnets with low or even absent content of expensive Dy and / or Tb, and containing cheaper rare earth materials such as Ce, Y and / or La, while still having sufficiently high coercivity Hc and remanence Br, so that the magnets can be used under temperature conditions that allow them to be used in generators of wind turbines. Summary of the Invention

[0012] The aforementioned needs can be met by applying the subject matter of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0013] Indicators used to measure the performance of neodymium magnets include remanence Br, coercivity HcB (i.e., the coercivity HcB in a given composite magnetic field, which is the sum of the magnet's remanence Br and the magnetic field H of the "attempting demagnetization" magnet), intrinsic coercivity HcJ, and maximum energy product (BH)max. Additionally, the knee point Hknee at a given remanence B is another indicator.

[0014] Hysteresis occurs when an external magnetic field is applied to a ferromagnetic material such as iron or Nd-Fe-B magnets and the atomic dipoles align themselves with it. Even after the magnetic field is removed, partial alignment is retained: the material is magnetized with remanence B. Once magnetized, the magnet will remain magnetized indefinitely. Demagnetization requires heat or a magnetic field H in the opposite direction. The relationship between the magnetic field strength H and the magnetization B is not linear in such materials. If the BH relationship is plotted for all strengths of the applied magnetic field H, the result is a hysteresis loop with four quadrants. This can be seen in documents such as this one. Figure 4 and Figure 5 The demagnetization behavior of the magnet is seen in the second quadrant of the hysteresis loop shown.

[0015] In the context of this document, remanence Br is a measurement of the magnetic flux density or magnetic induction retained in a permanent magnet after successful magnetization. In short: the higher the remanence Br, the "stronger" the magnetic force that the permanent magnet can produce. Once magnetized, the magnet will remain magnetized. T (Tesla) is used as the unit for measuring magnetic induction and the corresponding magnetic flux density. To demagnetize a magnet, heat or a magnetic field H acting in the opposite direction is required.

[0016] In the context of this document, coercivity, also known as magnetic coercivity, coercive field, or coercivity, is a measure of the ability of a permanent magnet (ferromagnetic material) to resist demagnetization by an external magnetic field H. Coercivity is typically measured in Oersted or amperes per meter and is expressed as Hc or HcB. In ferromagnetic materials, coercivity refers to the magnetic field strength (H-field) required to demagnetize the material after its magnetization has been driven to saturation by a strong magnetic field. The demagnetizing field is applied in the opposite direction to the original saturation magnetic field.

[0017] The inherent curve or BH demagnetization curve in Figure 4 and Figure 5 The image is shown in the second quadrant of the hysteresis loop (not shown) of the magnet. The inherent magnetic flux density generated after a permanent magnetic material is magnetized under the influence of an external magnetic field is called the inherent magnetic flux density (remanence) Br, also known as the magnetic polarization intensity J. The curve of the magnetic polarization intensity J of the magnet versus the external magnetic field intensity H reflects the change in the inherent magnetic properties of the permanent magnet material. This curve is called the inherent demagnetization curve (or, simply the inherent curve), also known as the JH demagnetization curve or the BH demagnetization curve.

[0018] When the magnetic polarization J on the demagnetization curve is 0, the corresponding magnetic field strength is called the intrinsic coercivity HcJ. The value of the intrinsic coercivity reflects the magnitude of the permanent magnetic material's resistance to demagnetization.

[0019] The knee point is at Hknee.

[0020] When the external magnetic field increases continuously, the magnetic flux density / magnetic polarization of the magnet decreases very slowly. However, when the external magnetic field exceeds a certain value Hknee, the magnetic flux density of the magnet decreases rapidly, leading to at least partial demagnetization. The bending point or knee point at Hknee on the demagnetization curve has special significance. The magnetic field corresponding to this point is Hknee, also known as the knee coercivity Hknee. When the external magnetic field H is greater than Hknee, irreversible loss of magnet performance will occur, making the Hknee value an important characteristic (alongside HcB, Br, and HcJ).

[0021] According to a first aspect of the invention, an Nd-Fe-B permanent magnet is provided, the permanent magnet comprising 28% to 35% by weight rare earth elements; wherein the total content of Nd (neodymium) and Pr (praseodymium) is between 20% and 25% by weight; wherein the content of Ce (cerium) is between 5% and 10% by weight; wherein the operating temperature of the magnet is between -30°C and 80°C; wherein the magnet has the following characteristics at a temperature of 20°C:

[0022] -Inherent coercivity, wherein the inherent coercivity is between -990kA / m and -1210kA / m;

[0023] -Magnetic remanence Br, wherein the magnetic remanence is between 1.296T (Tesla) and 1.584T;

[0024] The magnet has the following properties at a temperature of 60°C:

[0025] - At the remanence B of 0.282T, the coercivity at the minimum knee point is greater than the absolute value of 738kA / m (or less than -738kA / m);

[0026] - At a remanence r(B) of 0.176T, the coercivity at the maximum knee point is less than the absolute value of 1032kA / m (or greater than -1032kA / m);

[0027] - Remanence (Br), wherein the remanence is between 1.246T (Tesla) and 1.523T.

[0028] The Nd-Fe-B permanent magnet extends between 18 mm and 26 mm along the main magnetization direction, i.e., the height (h) of the magnet (354) is between 18 mm and 26 mm; the total content of Dy (dysprosium) and Tb (terbium) is less than 0.5% by weight, preferably less than 0.1% by weight, and more preferably 0% by weight.

[0029] The described Nd-Fe-B permanent magnet (PM) is based on the concept that, by combining the geometry of the PM with a shape having sufficient thickness oriented parallel to the magnetization direction of the magnet, and the indicated content of Ce, Dy, and Tb, the content of expensive elements Nd, Pr, Dy, and / or Tb and / or Pr can be significantly reduced while maintaining acceptable values, which indicate good demagnetization behavior of the magnet. Therefore, the magnet exhibits sufficient resistance to demagnetization fields.

[0030] It is mentioned that the described Nd-Fe-B magnet can even be realized with zero Dy and Tb content, where unintentional impurities are not considered. Such impurities are possible because different rare earth elements cannot typically be separated with 100% reliability due to their similar chemical behavior.

[0031] According to another embodiment of the invention, the Nd-Fe-B permanent magnet has a magnet length between 40 mm and 75 mm along the axial direction of the generator, and / or a magnet width between 90 mm and 125 mm along the circumferential direction of the generator. These dimensions are important for applications in large permanent magnet synchronous generators in order to maintain good magnetic properties.

[0032] According to another aspect of the invention, there exists a rotor assembly for an electromechanical transducer, particularly for a generator, especially for a permanent magnet synchronous generator for a wind turbine, said rotor assembly comprising a support structure and at least one Nd-Fe-B permanent magnet, wherein the Nd-Fe-B permanent magnet is mounted to the support structure. The implementation of the magnet in the rotor assembly ensures the reliability of the transducer over a lifespan exceeding 20 years.

[0033] According to another aspect of the invention, an electromechanical transducer is provided, particularly a generator for a wind turbine, especially a permanent magnet synchronous generator for a wind turbine, said electromechanical transducer comprising a stator assembly and a rotor assembly. The implementation of magnets in the electromechanical assembly ensures the reliability of the transducer over a lifespan exceeding 20 years.

[0034] According to another aspect of the invention, a wind turbine for generating electrical energy is provided, the wind turbine comprising a tower, a rotor, and an electromechanical transducer, the rotor being disposed at the top portion of the tower and including at least one blade, wherein the electromechanical transducer is mechanically coupled to the rotor. The implementation of magnets in the wind turbine ensures the reliability of the transducer over a lifespan exceeding 20 years.

[0035] It is mentioned that the provided electromechanical transducer can be implemented in different designs. One common design option is characterized by the fact that the rotor assembly is located within the stator assembly. Another design option is characterized by the fact that the rotor assembly is located outside the stator assembly. In the latter option, during operation of the PM electromechanical transducer, the magnetic flux interacting between the stator coils and the Nd-Fe-B magnet components can be directed radially outward from the stator.

[0036] It should be noted that embodiments of the present invention have been described with reference to different subjects. However, those skilled in the art will understand from the above and the following description that, unless otherwise stated, any combination of features relating to different subjects, except for any combination of features belonging to one type of subject matter, is also considered to be disclosed in this document.

[0037] The foregoing limitations and other aspects of the invention will become apparent from the examples of the embodiments described below, and will be explained with reference to these examples. The invention will be described in more detail below with reference to examples of embodiments, but the invention is not limited to these examples. Attached Figure Description

[0038] Figure 1 A wind turbine according to an embodiment of the present invention is shown.

[0039] Figure 2 and Figure 3 This illustration shows a comparison between a known electromechanical transducer and an electromechanical transducer according to an embodiment of the present invention. The known electromechanical transducer includes a rotor assembly equipped with an Nd-Fe-B magnet having a specific Dy / Tb content, while the electromechanical transducer according to the embodiment of the present invention uses an Nd-Fe-B magnet that includes Ce and has a significantly reduced Dy / Tb content or contains no Dy / Tb.

[0040] Figure 4 Showing has Figure 3 The illustrated BH diagram of the tolerance curves of the magnet disclosed herein is defined at a temperature of 20°C. Figure 3 The tolerance of the magnetic properties of the magnet.

[0041] Figure 5 Showing has Figure 3The illustrated BH diagram of the tolerance curves of the magnet disclosed herein is defined at a temperature of 60°C. Figure 3 The tolerance of the magnetic properties of the magnet. Detailed Implementation

[0042] The illustrations in the accompanying drawings are illustrative. It should be noted that similar or identical elements or features may be labeled with the same reference numerals in different drawings, or with reference numerals that differ from the corresponding reference numerals only in the first digit. To avoid unnecessary repetition, elements or features already explained in conjunction with the previously described embodiments will not be repeated later in the specification.

[0043] Figure 1 A wind turbine 100 according to an embodiment of the present invention is shown. The wind turbine includes a tower 120 mounted on a foundation (not shown). A nacelle 122 is arranged on top of the tower 120. A yaw angle adjustment device 121 is provided between the tower 120 and the nacelle 122, the yaw angle adjustment device enabling the nacelle 122 to rotate about a vertical axis (not shown), the vertical axis being aligned with the longitudinal extension of the tower 120. By controlling the yaw angle adjustment device 121 in a suitable manner, it can be ensured that the nacelle 122 is always correctly aligned with the current wind direction during normal operation of the wind turbine 100. However, the yaw angle adjustment device 121 can also be used to adjust the yaw angle to a position in which the nacelle 122 is intentionally not perfectly aligned with the current wind direction.

[0044] The wind turbine 100 also includes a rotor 110 having three blades 114. Figure 1 Only two blades 114 are visible in the perspective view. The rotor 110 is rotatable about a rotation axis 110a. The blades 114 are mounted at the hub 112 and extend radially relative to the rotation axis 110a.

[0045] Blade adjustment devices 116 are respectively provided between the hub 112 and the blades 114 to adjust the blade pitch angle of each blade 114 by rotating the respective blade 114 about an axis (not shown), which is substantially parallel to the longitudinal extension of the respective blade 114. By controlling the blade adjustment devices 116, the blade pitch angle of the respective blade 114 can be adjusted in such a way that maximum wind energy can be extracted from the available wind energy, at least when the wind force is not too strong. However, the blade pitch angle can also be intentionally adjusted to a position in which only reduced wind energy can be captured.

[0046] like Figure 1As shown, a gearbox 124 is provided within the engine compartment 122. The gearbox 124 is used to convert the rotational speed of the rotor 110 to a higher rotational speed of the shaft 125, which is connected to an electromechanical transducer 140 in a known manner. The electromechanical transducer is a generator 140.

[0047] It should be noted that the gearbox 124 is optional, and the generator 140 can also be directly coupled to the rotor 110 via the shaft 125 without changing or converting the rotational speed of the rotor 110. In this case, the wind turbine 100 is a so-called direct-drive (DD) wind turbine. In another alternative to the DD wind turbine (not shown), the hub 112 is connected to the outer rotor 252 of the generator (…). Figure 2 and 3 The outer rotor 252 is supported by the inner stator 245 via a single main bearing (not shown).

[0048] Furthermore, a brake 126 is provided to stop the operation of the wind turbine 100 or to reduce the rotational speed of the rotor 110, for example: (a) in an emergency, (b) in excessively strong winds that may damage the wind turbine 100, and / or (c) in cases where fatigue life and / or fatigue life consumption rate of at least one structural component of the wind turbine 100 is intentionally reduced.

[0049] The wind turbine 100 also includes a control system 153 for operating the wind turbine 100 in an efficient manner. In addition to controlling, for example, the yaw angle adjustment device 121, the illustrated control system 153 is also used to adjust the blade pitch angle of the rotor blades 114 in an optimized manner.

[0050] Based on basic principles of electrical engineering, the generator 140 includes a stator assembly 145 and a rotor assembly 150. The stator assembly 145 includes a plurality of coils (not shown) for generating current in response to time-varying magnetic flux. The rotor assembly 150 includes a plurality of Nd-Fe-B permanent magnet elements arranged in an array around a curved surface region of the rotor assembly 150.

[0051] It is mentioned that the rotor assembly 150 does not necessarily need to be arranged within the stator assembly 145. Instead, it is also possible that the rotor assembly surrounds the stator assembly.

[0052] Figure 2 and Figure 3A cross-sectional view is shown comparing (a) a known electromechanical transducer 240 with (b) an electromechanical transducer 340 according to an embodiment of the invention. The known electromechanical transducer includes a rotor assembly 250 equipped with an Nd-Fe-B magnet element 254 having a specific content of Dy and / or Tb. In the electromechanical transducer 340 according to the embodiment of the invention, an Nd-Fe-B magnet element 354 is used, having a composition including Ce, which partially replaces the Nd and / or Pr content of the magnet element 354 because Ce is much cheaper than Nd or Pr. Furthermore, the total content of (extremely expensive) Dy and Tb is significantly reduced to further reduce the magnet price.

[0053] According to embodiments of the present invention, the Nd-Fe-B permanent magnet component comprises a Ce content of 5% to 10% by weight. To ensure that the Nd-Fe-B permanent magnet component still possesses sufficiently high intrinsic coercivity, these Nd-Fe-B permanent magnet components (abbreviated PM) have a specific physical spatial extension along a direction parallel to the magnetization direction. Specifically, the physical extension (also referred to in this document as the height h of the PM component) is between 18 mm and 26 mm.

[0054] Figure 2 The known electromechanical transducer 240 shown in the figure and Figure 3 The electromechanical transducer 340 shown in the figure, according to an embodiment of the present invention, has the same stator assembly 245. As can be seen from the figure, the stator assembly 245 has a stator support structure 247 and a plurality of stator windings 249. The stator support structure comprises a stack of multiple laminates, and the stator windings are housed within the stator support structure 247. The windings 249 are interconnected in a known manner via electrical connections not shown.

[0055] The rotor assembly 250 of the known electromechanical transducer 240 is separated from the stator assembly 245 by an air gap ag. The rotor assembly includes a rotor support structure 252, which provides a mechanical base for mounting the Nd-Fe-B PM element 254. The support structure 252 includes a magnetic material, such as a steel alloy laminate with soft ferromagnetic properties, to optimize the magnetic field generated by the Nd-Fe-B PM element 254. Figure 2 The magnetic field generated by other Nd-Fe-B PM components (not shown) is thus optimized, based on known principles in the design of the electromechanical transducer, to maximize the magnetic field chain between the stator assembly 245 and the rotor assembly 250.

[0056] The rotor assembly 350 of the electromechanical transducer 340 includes a rotor support structure 352 that provides a mechanical base for mounting the Nd-Fe-B PM component 354. Furthermore, the support structure 352 incorporates a magnetic material to optimize the magnetic field linkage between the stator assembly 245 and the rotor assembly 350.

[0057] According to the embodiment described herein, the air gap ag between the rotor assembly 350 and the stator assembly 245 can be used to guide cooling fluid, such as cooling air, through the electromechanical transducer 340 to remove waste heat generated during operation, particularly by the stator coils 249 of the stator assembly 245.

[0058] It is mentioned that the plurality of PM components can be mounted to the support structure 352. The PM components are preferably arranged in a matrix-like structure surrounding a curved surface region of the support structure 352, the support structure having a generally cylindrical geometry. Figure 3 For clarity, only one PM file, 254, is shown in the image.

[0059] like Figure 3 As shown, the height h of the Nd-Fe-B PM part 354 (or magnet 354) is between 18 mm and 26 mm in order to align with the corresponding content of Ce by weight of 5% to 10% and the corresponding magnetic properties.

[0060] In other words, by changing the composition of Nd-Fe-B PM and limiting its size, the magnetic properties can be maintained within the required range for the generator.

[0061] Given the high price of element Dy and the low price of element Ce, the total cost of PM can be reduced by decreasing the total amount of Dy and increasing the total amount of Ce (compared to the total amount of Nd and / or Pr), thereby adapting the height h of Nd-Fe-B PM within a specific range. The operating temperature of magnet 354 is between -30°C and 80°C.

[0062] Figure 4 and Figure 5 An illustration of the corresponding second quadrant of the hysteresis loop is shown, where the BH tolerance curve defines the... Figure 3 The exemplary magnet 354 shown in the figure exhibits demagnetization behavior at different temperatures of 20°C and 60°C.

[0063] The y-axis represents the magnetic flux density B of magnet 354 (in Tesla [T]). The x-axis represents the strength H of the magnetic field acting on magnet 354 along the demagnetizing direction (in kA / m). Therefore, the value of H is negative. The coercivity Hc of the magnet is usually expressed as its absolute value.

[0064] The demagnetizing field H may be generated in a permanent magnet generator by the magnetic field produced by the current in the stator coil.

[0065] The curves C1 and C2 are positioned between the dashed lines "maximum" and "minimum", which represent the maximum and minimum ranges in which the values ​​of curves C1 and C2 are located.

[0066] In the xy-curve or BH-curve, the actual magnetic flux density B of magnet 354 depends on the magnetic field strength H. The exemplary curves C1 and C2 of magnet 354 represent its magnetic properties and its ability to resist the demagnetizing field H. This ability is referred to as the coercivity of the magnet, as mentioned above. Two parallel dashed lines indicate minimum and maximum boundaries, within which the BH coercivity curves C1 and C2 of magnet 354 are correspondingly located.

[0067] Multiple magnets 354 are positioned on the rotor support structure 350. Figure 3 On the ), each magnet 354 has tolerances and therefore different magnetic properties, which are located within the boundaries, i.e., between the “minimum” and “maximum” dashed lines.

[0068] Br_min is the minimum magnetic (saturation) remanence of magnet 354 (intersection with the y-axis). Br_max is the maximum magnetic (saturation) remanence of magnet 354 (intersection with the y-axis).

[0069] If the demagnetizing field H has an absolute value higher than the inherent coercivity HcB of the magnet, the magnet will be at least partially demagnetized. This will occur in situations such as... Figure 3 The generator shown in this application, "Generator", can lead to reduced generator performance or complete generator failure.

[0070] Figure 4 The BH diagram, showing the upper tolerance curve "maximum" and the lower tolerance curve "minimum", is shown in... Figure 3 The coercivity curve C1 of magnet 354 is located between the tolerance curves when the magnet temperature T is 20℃.

[0071] Graph C1 shows the magnetic remanence B, which depends on the demagnetizing field H acting on magnet 354. Graph C1 extends primarily linearly, intersecting the x-axis and y-axis at its ends. The intersection of graph C1 with the B-axis (y-axis) shows the magnetic (saturation) remanence Br of magnet 354 at demagnetizing field H = 0. The intersection of graph C1 with the H-axis (x-axis) shows the magnetic (intrinsic) coercivity HcB of magnet 354 (at the maximum permissible demagnetizing field H).

[0072] There are three points Br_min, B300_min and HcB_min located on the dashed line called “minimum”, which define the lower boundary of the minimum value of the magnetic flux density B, which depends on the demagnetizing field strength H of magnet 354.

[0073] There are three points Br_max, B300_max and HcB_max located on a dashed line called “maximum”, which defines the upper boundary of the maximum value of the magnetic flux density B, which depends on the demagnetizing field strength H of magnet 354.

[0074] Br is the magnetic (saturation) remanence of magnet 354, with a value of approximately 1.45 T under curve C2. Br_min is the minimum magnetic (saturation) remanence of magnet 354 (intercept of the y-axis), and equals 1.296 T. Br_max is the maximum magnetic (saturation) remanence of magnet 354 (intercept of the y-axis), and equals 1.584 T. B300_min is the minimum magnetic flux density of magnet 354 at the demagnetization field, where the demagnetization field has a magnetic field strength H = -300 kA / m. B300_min equals 0.903 T. B300_max is the maximum magnetic flux density of magnet 354 at the demagnetization field, where the demagnetization field has a magnetic field strength H = -300 kA / m. B300_max equals 1.191 T. HcB_min is the minimum intrinsic coercivity of magnet 354, and equals -990 kA / m, at which the magnetic flux density B is 0. HcB_max is the maximum intrinsic coercivity of magnet 354, and is equal to -1210 kA / m, at which the magnet flux density is 0.

[0075] Figure 5 The BH diagram, showing the upper tolerance curve "maximum" and the lower tolerance curve "minimum", is shown in... Figure 3 The curve C2 of magnet 354 is positioned between the tolerance curves when the magnet temperature T is 60℃.

[0076] At the temperature of 60°C, the coercivity of the magnet 354 is weaker, as indicated by the knee point Hknee of curve C2 and the corresponding boundary lines "min" and "max". If the demagnetizing field H has a higher absolute value than the coercivity values ​​Hknee_min, Hknee, and Hknee_max of the magnet 354 at the corresponding knee point, the magnet will be at least partially demagnetized.

[0077] There are three points Br_min, B300_min, and HcB_min located on the dashed line called "minimum". These points define the lower boundary of the minimum value of the magnetic flux density B, which depends on the demagnetizing field strength H of magnet 354.

[0078] There are three points Br_max, B300_max and HcB_max located on a dashed line called "maximum". These points define the line, which defines the upper boundary of the maximum value of the magnetic flux density B, which depends on the demagnetizing field strength H of magnet 354.

[0079] Br is the magnetic (saturation) remanence of magnet 354, with a value of approximately 1.42 T under curve C2. Br_min is the minimum magnetic (saturation) remanence of magnet 354 (intercept of the y-axis), and is equal to 1.246 T. Br_max is the maximum magnetic (saturation) remanence of magnet 354 (intercept of the y-axis), and is equal to 1.523 T. B300_min is the minimum magnetic flux density of magnet 354 at the demagnetizing field, where the demagnetizing field has a magnetic field strength H = -300 kA / m. B300_min is equal to 0.855 T. B300_max is the maximum magnetic flux density of magnet 354 at the demagnetizing field, where the demagnetizing field has a magnetic field strength H = -300 kA / m. B300_max is equal to 1.131 T.

[0080] Hknee_min equals the coercivity of magnet 354 at its minimum knee point, which is -738 kA / m, with remanence B738 being 0.282 T. Hknee_max equals the coercivity of magnet 354 at its maximum knee point, which is -1032 kA / m, with remanence B1 being 0.176 T.

[0081] It should be noted that the term "comprising" does not exclude other elements or steps, and the use of the articles "a" or "an" does not exclude a plural. Elements described in association with different embodiments may also be combined. It should also be noted that reference numerals in the claims should not be construed as limiting the scope of the claims.

Claims

1. An Nd-Fe-B permanent magnet (354), said permanent magnet comprising 28% to 35% rare earth elements by weight. in, The total content of Nd (neodymium) and Pr (praseodymium) is between 20% and 25% by weight. The Ce content is between 5% and 10% by weight. The magnet (354) operates between -30°C and 80°C. The magnet (354) has the following characteristics at a temperature of 20°C: - Coercivity (HcB), wherein the coercivity is between -990 kA / m and -1210 kA / m. - Remanence (Br), wherein the remanence is between 1.296 T (Tesla) and 1.584 T. The magnet (354) has the following characteristics at a temperature of 60°C: - Coercivity, wherein the coercivity is between the following values: *The minimum knee point (Hknee_min) at a remanence B of 0.282T is -738 kA / m. *The maximum knee point (Hknee_max) is located at a remanence r(B) of 0.176T, which is -1032 kA / m. Among them, the remanence (Br) is between 1.246T (Tesla) and 1.523T. The Nd-Fe-B permanent magnet (354) extends spatially between 18 mm and 26 mm along the main magnetization direction, that is, the height (h) of the magnet (354) is between 18 mm and 26 mm. The total content of Dy (dysprosium) and Tb (terbium) is less than 0.5% by weight, preferably less than 0.1% by weight, and preferably 0% by weight.

2. The Nd-Fe-B permanent magnet as described in claim 1, wherein, The length (L) of the magnet (354) is between 90 mm and 125 mm, and / or the width (W) of the magnet (354) is between 40 mm and 75 mm.

3. A rotor assembly for an electromechanical transducer (140, 340), particularly for a generator (140, 340), especially for a permanent magnet synchronous generator (140, 340) of a wind turbine (100), said rotor assembly (350) comprising a support structure (352) and at least one Nd-Fe-B permanent magnet (354) as described in any of the preceding claims, wherein, The Nd-Fe-B permanent magnet (354) is mounted to the support structure (352).

4. An electromechanical transducer, particularly a generator (140, 340) for a wind turbine (100), particularly a permanent magnet synchronous generator (140, 340) for a wind turbine (100), the electromechanical transducer (140, 340) comprising a stator assembly (245) and a rotor assembly (350) as described in the preceding claims.

5. A wind turbine for generating electricity, said wind turbine (100) comprising: Tower (120), A rotor (110) is arranged at the top portion of the tower (120) and includes at least one blade (114) and an electromechanical transducer (140, 340) as claimed in the preceding claims, wherein the electromechanical transducer (140, 340) is mechanically connected to the rotor.

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