Electric motor with cryogenic cooled armature windings

Abstract

A cryogenic cooled electric motor (500), comprising: a stator (510), the stator (510) comprising a magnetic core (510, 510a); a rotor (520); an armature arrangement (550); and a refrigerant source arranged for providing a freezing fluid (544) to the armature arrangement (550) to cool the armature arrangement (550) to a temperature below 77 K, where the armature arrangement (550) comprises a plurality of Litz wires (552), and where the armature arrangement (550) is capable of providing a current density in excess of 25 A / mm during operation of the motor.

Description

Technical Field

[0001] The present invention relates to aircraft propulsion systems and, in particular, to aircraft propulsion arrangements and motors capable of providing extremely high efficiency. In particular, the use of cryogenic sources and electrical energy enables the high-efficiency systems disclosed herein to provide thrust to an aircraft in a manner that avoids the use of typical combustible fuels that can result in the release of harmful greenhouse gases. Background Art

[0002] Although hydrogen fuel and hydrogen synfuels are occasionally used in aircraft, they are not commonly used in large aircraft and are not used at all in passenger aircraft. This is due to the specific power that a gas turbine can provide compared to a hydrogen system. A gas turbine can reach approximately 5 to 8 kW / kg for a typical system, while a hydrogen system can reach approximately 1 kW / kg. Thus, hydrogen is a reasonable and environmentally friendly option for small aircraft but is almost completely excluded from use in commercial large-scale systems.

[0003] Fuel cells using hydrogen are being studied, and recent work has shown that, optimistically, the specific power values of such systems may reach 2 kW / kg in the next 5 to 10 years. Some other work has shown that there may be an absolute maximum of approximately 1.8 kW / kg. Thus, it appears that these systems are not viable for use in commercial passenger aircraft without significant economic drawbacks.

[0004] Therefore, there is a need to provide more power than existing systems to achieve a more environmentally friendly flight solution. The present invention seeks to provide improvements in this area.

[0005] There are advancements that can be made in this field and advantages that can be obtained from these advancements. However, the inventors of the invention described herein have created a superior motor arrangement that has a wide range of previously unattainable advantages as described herein. Summary of the Invention

[0006] Aspects of the present invention are set forth in the appended claims.

[0007] In a first aspect, there is provided a motor, the motor comprising: a stator comprising a magnetic core; a rotor; an armature arrangement; and a cryogenic source arranged to provide cryogenic temperature to the armature arrangement, wherein the armature arrangement comprises a plurality of litz wires, and wherein, during operation, the armature arrangement provides a current density of more than 25 A / mm².

[0008] The current density mentioned above can be the RMS current density exceeding 25 A / mm². During the operation of the motor, the armature arrangement can provide an RMS current density exceeding 25 A / mm²; an RMS current density exceeding 30 A / mm²; an RMS current density exceeding 35 A / mm²; an RMS current density exceeding 40 A / mm²; or an RMS current density exceeding 50 A / mm².

[0009] The motor disclosed herein provides a current density much greater than that currently provided by standard motors. The use of a magnetic core stator and a refrigerant source that supplies refrigerant to the armature arrangement provides a very effective and highly efficient electromagnetic arrangement, which allows the armature to handle a significantly higher current density than previously used arrangements.

[0010] This higher current density enables the armature to carry a high electrical load while maintaining extremely low electrical losses. Furthermore, this means that the motor has a more efficient power output and can provide greater thrust to a vehicle. When combined, each advancement herein results in a motor that is suitable for use as a main propulsion system for an aircraft while reducing dependence on fossil fuels.

[0011] Therefore, such a motor is an attractive option for use in environmentally friendly vehicles where previous motors did not provide sufficient thrust. In a specific example, the motor disclosed herein is particularly effective for use in an aircraft with low impact emissions.

[0012] In one example, the low-temperature source is a refrigerant source arranged to supply refrigerant to the armature arrangement. The refrigerant is suitable for providing a low temperature; however, the refrigerant is not essential for obtaining the advantages outlined herein. A cooler or cryocooler can also be used to provide a low temperature to the armature and other components in the motor.

[0013] In one example, the refrigerant source is a supply source of at least one of hydrogen, neon, helium, or nitrogen. These refrigerants are advantageous because they have thermal properties that enable the refrigerant to achieve a temperature below 60 K. In practice, the refrigerant can be used to provide a wide temperature range. These refrigerants can be used to provide a low temperature (60 K and below) to the armature arrangement. This cooling provides electrical efficiency, which helps in the delivery of an extremely high current density by the armature.

[0014] In one example, the refrigerant is at a temperature below 77 Kelvin and is arranged to maintain the armature arrangement at a temperature below 77 Kelvin. It has been found that such a temperature is very effective for the arrangement disclosed herein. Specifically, such a temperature can utilize the high conductive physical properties of various materials that can be used in the arrangement to assist in the delivery of an extremely high current density by the armature.

[0015] In one example, each of the plurality of Litz wires includes a plurality of Litz wire strands, and the number of Litz wire strands of each of the plurality of Litz wires is between 50 and 5000. The Litz wire provides a number of bundled filaments that have high resistance to the generation of eddy currents, thus reducing losses in these arrangements such as those disclosed herein. For the arrangements disclosed herein, it has been found that 50 to 5000 is effective for providing a high current density; further, it has been found that 750 to 1250 Litz wire strands are particularly effective.

[0016] In one example, the diameter of the Litz wire strands is in the diameter range of 0.05 mm to 1 mm. In one example, the resistivity of the plurality of Litz wires is 1x10 -9 Ωm or less. Such a diameter range and resistivity correspond to an operating frequency of about 150 Hz (resistivity about 1x10 -9 Ωm) to an operating frequency of about 10 kHz (resistivity about 2x10 -10 Ωm). Thus, this is relevant to the reasonable application range of the motor and is particularly effective for use in aircraft propulsion machines, as operating frequencies below 150 Hz may be insufficient for aircraft propulsion. In addition, it has been found that the listed resistivity ranges are very effective in the ultra-high efficiency conduction region. The above operating frequency range can be obtained using a temperature of about 40 K to about 60 K.

[0017] The diameter of the Litz wire strands is selected such that the skin effect is substantially avoided because the diameter is less than the skin depth. In a particular example, a Litz wire strand with a diameter of 1 mm has a resistivity of about 1x10 -9 Ωm at about 60 Kelvin, corresponding to an operating frequency of about 150 Hz; a Litz wire strand with a diameter of 0.05 mm has a resistivity of about 2x10 -10 Ωm at about 35 to 40 Kelvin, corresponding to an operating frequency of about 10 kHz.

[0018] As described above, operating frequencies below 150 Hz are unlikely to be sufficient for aircraft propulsion, and thus, 1 mm is a particularly effective diameter because it has been found that higher diameters introduce skin effect losses or require the operating frequency to be reduced below 150 Hz. Thus, the present invention can use effective diameter and temperature ranges to provide an efficient operating frequency for flight.

[0019] A diameter of about 0.05 mm can be selected because the production of such wire is routine at present; if smaller diameters can be manufactured routinely, then smaller diameters (and the corresponding higher operating frequencies) would be suitable. Thus, temperatures below 35 to 40 K and the corresponding lower resistivity would be suitable without introducing undesirable skin effect losses. Factors to be offset include: as the temperature for the thinner wire is further reduced, the cryogen budget becomes increasingly expensive; and the manufacture of the thinner wire. Thus, these diameters are relevant to the reasonable application range of the motor and are particularly effective for use in aircraft propulsion machines.

[0020] The above temperature values are suitable because they can be obtained by cryogens. For higher purity aluminum and copper, a resistivity of about 1x10 -9 Ωm can be obtained at a temperature of about 60 K. For higher purity aluminum, a resistivity of about 2x10 -10 Ωm can be obtained at a temperature of about 40 K. The temperature region around these values can be broadly referred to as the "ultra-high efficiency conduction region". It has been found that this temperature region (and the corresponding resistivity) is very effective for electrical efficiency, especially when used in the arrangements disclosed herein.

[0021] While industrially standard aluminum typically has a purity of about 99.5%, the present invention preferably uses higher purity aluminum of at least 99.99%. In the ultra-high efficiency conduction region, high purity aluminum has a superior resistivity compared to its industrially standard counterpart. Thus, combined with the diameter of the Litz wire strands described above, this motor provides a much superior current density compared to previously disclosed machines. Similarly, while industrially standard copper has a purity of about 99.9%, the present invention preferably uses higher purity copper of at least 99.99%. Similarly, the resistivity of this higher purity copper is superior to its industrially standard counterpart.

[0022] The arrangements herein can utilize a particularly effective temperature region known as the ultra-high efficiency conduction region. In the ultra-high efficiency conduction temperature region, the Litz wire has superior conductivity compared to its conventional counterpart. Compared to conventional temperatures above the ultra-high efficiency conduction temperature region, the Litz wire has a significantly lower resistivity within the ultra-high efficiency conduction temperature range. Thus, compared to both a conventional armature arrangement and an armature arrangement containing Litz wire (where the armature arrangement is maintained at a temperature above 77 Kelvin), the ultra-high efficiency conduction armature arrangement including Litz wire is much higher in electrical efficiency. This arrangement synergistically integrates these two factors. This arrangement has high electrical efficiency and can provide a current density that was previously impossible in motors for propulsion.

[0023] In one example, the total current loss experienced by the armature arrangement is 0.6% or less of the total input power of the motor. In the arrangements herein, the power losses (associated with current losses) are associated with eddy currents and conduction. Accordingly, the present arrangements tightly control and greatly reduce losses, resulting in a very high electrical efficiency.

[0024] "Current loss" can be understood to refer to the power losses associated with the various currents in a conductor (i.e., a litz wire). Specifically, current loss is a combination of eddy current loss and power loss associated with conduction. In the present arrangements, an armature arrangement including a plurality of litz wires is maintained at a super-efficient conduction temperature, with significantly reduced eddy current loss, resulting in a resistivity reduction of approximately 100-fold. Accordingly, the current density of the armature of the present invention is approximately 10 times greater (due to the inverse square relationship between current density and resistivity), which is a significant increase over modern systems. This significant improvement is provided by the present arrangements by taking advantage of the resistivity characteristics of litz wires in the super-efficient conduction temperature region.

[0025] The arrangements disclosed herein have a high electrical efficiency and, accordingly, the losses experienced in the present arrangements are much lower than those experienced by current systems. By achieving a higher current density and also having low current losses, the present system is far more effective in generating motive power for use in transportation. In turn, this means that the present system can provide an environmentally friendly solution to problems that were previously not feasible, such as aircraft flight.

[0026] In one example, the temperature of the magnetic core is maintained in at least one of the following temperature ranges: 223 K or higher; 77 K or higher; or between 77 K and 223 K. Between 77 K and 223 K, it has been found that the electrical efficiency can be balanced with the cooling losses. In such an example, the core losses of the magnetic core may be higher, but the slots can have a slightly more compact shape. At approximately 77 K, superconducting phenomena can be used to provide a high electrical efficiency in the arrangements disclosed herein. The cryogenic source can be controlled at a temperature to provide a magnetic core temperature within any of the above ranges.

[0027] Using a magnetic core has advantages over air-core machines and has specific advantages for the present invention. The magnetic core, which can be referred to as an "iron-core" machine, provides a higher magnetic field level but also introduces iron losses, which reduce the gain obtainable from such machines. In the present arrangements, the advantageous aspects of the magnetic core are maintained and utilized while the disadvantages are intelligently mitigated.

[0028] During operation, the magnetic field generated by the permanent magnets or electromagnets of the rotor rotates. At the same time, the armature current generates a strong variable magnetic field. These combined variable magnetic fields cause additional eddy current losses to be generated in the armature coils. In turn, this can lead to reduced efficiency, a higher cooling burden, and thus limit the achievable current density. However, the magnetic core guides the magnetic flux around and away from the armature coils, thereby reducing the resulting induced eddy currents and thus reducing losses. In essence, the magnetic stator core is advantageously used herein to shield the armature coils. This is due to the difference in magnetic permeability between the magnetic core used herein and air (on the order of 10 3 ). Thus, although some electrical inefficiencies are also provided, the magnetic core directly contributes to the motor disclosed herein providing an extremely high current density.

[0029] As described above, the temperature of the magnetic core can be maintained within at least one of the following temperature ranges: 223 K or higher; 77 K or higher; or between 77 K and 223 K. Between 77 K and 223 K, it has been found that the electrical efficiency can be balanced with the cooling losses. In such an example, the core losses of the magnetic core can be higher, but the slots can have a more compact shape. As will be explained, it is very beneficial for the present invention to ensure that the magnetic core is maintained at a relatively high temperature relative to the armature arrangement to ensure that it does not experience excessive losses. This is because ferromagnetic materials have a significantly reduced resistivity at the ultra-high efficient conduction temperature of the armature arrangement, which in turn leads to an increase in eddy currents and related losses. The additional cooling required to maintain the ultra-high efficient conduction temperature of the magnetic core would be too large and would quickly deplete the refrigerant budget of the system. Therefore, it would be beneficial to maintain the magnetic core at a relatively high temperature, both to prevent a significant increase in core losses and to shield the armature coils.

[0030] To provide a current density of more than 25 A / mm² in the Litz wire, each of these aspects is balanced and controlled. In the present invention, such a current density is provided in a motor for the first time. The magnetic stator core is included herein for providing the current density disclosed by the present invention. There is a synergistic effect, that is, combining the shielding effect of the magnetic stator core with maintaining it at a relatively high temperature relative to the armature arrangement.

[0031] The magnetic core can include any ferromagnetic material; for example, the magnetic core includes at least one of iron, cobalt, nickel, or any combination thereof.

[0032] In one example, the stator can be maintained at a temperature between 120 K and 150 K. This range has been found to be a favorable balance between thermal management costs and loss reduction.

[0033] In one example, the stator is arranged in a vacuum. Such a vacuum isolates the stator from the cryogenic cooling of the armature. This allows the armature to be at a preferentially cooler temperature while also permitting the stator to be at a preferentially very different warmer temperature. It is assumed that the stator is arranged in a vacuum to ensure a thermal barrier between it and the armature, and the vacuum barrier can be provided in the air gap between the stator and the rotor. In this case, the air gap length may need to be slightly increased relative to a conventional air gap to accommodate the vacuum.

[0034] In another example, each individual armature coil can be enclosed within a separate vacuum tube passing through a slot in the stator core, and wherein the stator core itself is not enclosed within the vacuum. Such separate vacuum tubes isolate the stator from the cryogenic cooling of the armature. Alternatively, the stator can be isolated from the cryogenic cooling of the armature in any suitable manner.

[0035] Although it is desirable to maintain the magnetic core at a warmer temperature, it is still necessary to provide thermal management means to prevent overheating of the magnetic core (which in turn leads to increased losses). Conventional methods for cooling the magnetic core can be considered. In the case of a vacuum, alternative or additional cooling methods for the stator are considered. In one example, circulating air passes through the outer end of the magnetic core that is not within the vacuum and cools that outer end. In another example, the motor includes a fluid arranged in thermal communication with the magnetic core, and the fluid is arranged to remove thermal energy from the magnetic core. In this way, the magnetic core can be maintained at a warmer temperature without experiencing runaway heating.

[0036] In one example, the motor includes a fluid jacket arranged to keep a fluid in thermal communication with the magnetic core. This ensures strong thermal communication between the fluid and the magnetic core, thereby enhancing the performance of the fluid in maintaining the warmer environment of the magnetic core against the influence of the coolant.

[0037] In one example, the fluid is water. Water has a high heat capacity and is thus very effective in performing this thermal management function. Alternatively, the fluid can be any liquid or gas suitable for the purpose of cooling the stator.

[0038] In one example, the rated power of the motor exceeds 1 MW.

[0039] In one example, the armature includes aluminum. Aluminum has been found to be an effective conductor for the arrangements disclosed herein. High-purity aluminum has been found to be particularly effective. High-purity aluminum can have a purity of 99.99% or higher. In one example, the armature includes copper. High-purity copper has been found to be particularly effective. High-purity copper can have a purity of 99.99% or higher. In one example, the armature includes silver. High-purity silver can have a purity of 99.99% or higher.

[0040] From another aspect, there is provided an aircraft, the aircraft including an electric machine as described in any of the above aspects or examples.

[0041] In one example, a refrigerant source is disposed in a tail portion of the fuselage of the aircraft. Due to the shape and temperature of the fuselage during flight, the tail portion is a favorable location for such storage. In addition, such areas are not typically used in an aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] One or more embodiments of the present invention will now be described only by way of example and with reference to the following drawings, in which:

[0043] Figure 1 A schematic diagram of an electric machine according to an example of the present invention is shown;

[0044] Figure 2 A schematic cross-sectional view of an electric machine according to an example of the present disclosure is shown;

[0045] Figure 3 A schematic cross-sectional view of a thermal insulation arrangement for a cryogenic system is shown;

[0046] Figure 4 A schematic perspective view of a coil within a containment vessel is shown;

[0047] Figure 5 A schematic cross-sectional view of a cryogenic-cooled electric machine arrangement according to an example of the present disclosure is shown;

[0048] Figure 6 A schematic cross-sectional view of a cryogenic-cooled electric machine arrangement according to an example of the present disclosure is shown; and,

[0049] Figure 7 A schematic cross-sectional view of a cryogenic-cooled electric machine arrangement according to an example of the present disclosure is shown.

[0050] Figure 8 A schematic cross-sectional view of a cryogenic-cooled electric machine arrangement according to an example of the present disclosure is shown.

[0051] Any reference in this specification to prior art documents should not be taken as an admission that such prior art is well known or forms part of the common general knowledge in the field. The terms "comprising", "including" and similar terms used in this specification should not be construed as having an exclusive or exhaustive meaning. In other words, they are intended to mean "including, but not limited to". The present invention is further described by the following examples. It should be understood that the claimed invention is not intended to be limited in any way by these examples. It should also be recognized that the present invention covers not only individual embodiments, but also combinations of the embodiments described herein.

[0052] The various embodiments described herein are only for helping to understand and teach the claimed features. These embodiments are provided only as representative samples of the embodiments and are not exhaustive and / or exclusive. It should be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein should not be considered as limitations on the scope of the present invention defined by the claims or as limitations on the equivalents of the claims, and other embodiments can be utilized and modified without departing from the spirit and scope of the claimed present invention. Each embodiment of the present invention may suitably include, consist of, or consist essentially of a suitable combination of the disclosed elements, components, features, parts, steps, devices, etc., other than those specifically described herein. In addition, the present disclosure may include other inventions that are not currently claimed but may be claimed in the future. Detailed Description

[0053] The invention described herein relates to generating propulsive force for a vehicle by an electric motor. The specific electric motor disclosed herein has a very high current density to provide greater propulsive force from the electric motor. The generation of the propulsive force is related to the current density and current loss. The system disclosed herein is very efficient, combining the stable use of a high current density with minimizing current loss. The electric motor of the present disclosure provides a current density of about greater than 25 A / mm² in the armature arrangement. In some examples, the present disclosure provides a current density of about greater than 40 A / mm² in the armature arrangement.

[0054] The present invention provides many creative strategies that provide an electric motor capable of providing much higher electrical efficiency than previous systems. It has been found that using specific materials, dimensions, refrigerants, and thermal control can further improve the efficiency of the main arrangement disclosed herein.

[0055] Now referring to Figure 1 , there is shown an electric motor 100 including a stator 110 that includes a magnetic core. The electric motor 100 further includes a rotor 120. The electric motor 100 further includes an armature arrangement 130 and a low temperature source 140 arranged to provide a low temperature to the armature arrangement 130. During operation of the electric motor 100, the armature arrangement 130 provides a current density of more than 25 A / mm². In one embodiment, this arrangement has been shown to provide a current density greater than 40 A / mm². In an example, this arrangement has been shown to provide a current density ranging from about 50 A / mm² to 100 A / mm². Such a current density has not been provided by an electric motor with this configuration before. Therefore, this represents a significant step forward compared to previously provided electric motors.

[0056] The stator 110 includes a magnetic core, which can be mainly formed of iron or similar materials. The stator 110 can have a series of slots in the stator located between the stator teeth. The stator 110 can have a series of phase A, B, and / or C coils in these slots. Additionally or alternatively, the magnetic core can also be formed of cobalt or nickel or similar materials. The core can be laminated or can not be laminated.

[0057] The rotor 120 can be formed by a set of elements that provide a change in reluctance or magnetic flux or both. The rotor 120 can include a permanent magnet having its own magnetic flux, which provides a torque force to the rotor in response to the time-varying magnetic field generated by the armature arrangement, thereby generating motive power thereon. Alternatively, the rotor 120 can include an electromagnet. The rotor can include any ferromagnetic material, such as iron.

[0058] The armature arrangement 130 includes a plurality of Litz wires. These Litz wires can have a plurality of filaments wound together along an axis. These filaments can be twisted along the axis. A Litz wire can be a wire harness in which the strands are insulated from each other. Each of these wires is a conductive member. Therefore, due to the isolation of each conductive element within the Litz wire, the use of Litz wires significantly reduces the generation of eddy current losses.

[0059] The low temperature source 140 can be a refrigerant source 140 arranged to supply refrigerant to the armature arrangement 130. The refrigerant source 140 can be a container containing refrigerant. Alternatively, the refrigerant source 140 can contain a material that provides refrigerant. In one example, the refrigerant source 140 is a supply source of at least one of hydrogen, neon, helium, or nitrogen. The terms "refrigerant source" and "low temperature source" can be used interchangeably below. The machine does not require cryogenic temperatures but rather low temperatures. The low temperature source 140 can have one or more stages. One stage of these stages can be a cryogenic stage (e.g., at a temperature of 20K), while another stage can not be a cryogenic stage (e.g., at a higher temperature).

[0060] In one example, the low temperature source can also be a conduction cooling source using conduction and a cryogenic radiator for mechanical cooling. Such an arrangement can also provide cryogenic cooling for the armature arrangement. In one example, the refrigerant source arranged to supply refrigerant can be a cryogenic cooling source arranged to provide cryogenic cooling.

[0061] Examples of such refrigerants are advantageous in that they are able to maintain the temperature of the armature arrangement 130. Hydrogen can be liquid at about 20 K at atmospheric pressure. Neon can be gaseous at about 30 K. Thus, gaseous neon and liquid hydrogen can provide a similar cooling effect at reasonably low temperatures. Helium can be gaseous below 5 K. Thus, for neon, gaseous helium may be sufficient to cool the armature 130 as described herein. Thus, using gaseous neon and helium allows the machine to operate at about 30 K to about 40 K or at about 30 K to about 45 K. Thus, the refrigerant can be a gas or a liquid. Preferably, the armature is maintained at a temperature below 77 K.

[0062] In one example, the temperature of the refrigerant is below 77 Kelvin and is arranged to maintain the armature arrangement 130 at a temperature below 77 Kelvin. Other advantageous temperature ranges include maintaining the refrigerant at a temperature below 60 K. High temperature superconductors can operate at temperatures up to about 80 K (currently, with an upper limit of 120 K).

[0063] In one example, the temperature of the magnetic core is maintained in at least one of the following temperature ranges: 223 K or higher; 77 K or higher; or 77 K to 223 K. These regions can be described as near ambient and higher temperatures, ultra - efficient conduction temperature to higher temperatures, and between ultra - efficient conduction temperature and near ambient temperature. In a preferred example, the magnetic core is not ultra - efficiently conducting, but the armature is ultra - efficiently conducting. As described herein, significantly cooling the magnetic core (e.g., cooling to ultra - efficient conduction temperature) results in losses. Cooling the armature has been found to be advantageous for electrical efficiency gains.

[0064] The armature arrangement 130 can include a large number of Litz wires. In one example, each Litz wire of the plurality of Litz wires includes a plurality of Litz wire strands. The number of Litz wire strands in each Litz wire of the plurality of Litz wires can be between 50 and 5000. The strands are the filaments within each Litz wire that are electrically insulated from each other and bundled together to form the Litz wire. Increasing the number of strands increases the total current that can be transmitted in the Litz wire, yet increases the structural complexity. It has been found that the ranges herein provide a favorable balance between these factors.

[0065] In one example, the diameter of the Litz wire strands is in the diameter range of 0.05 mm to 1 mm. This diameter range of the Litz wire strands provides a further balance. The larger the diameter, the easier the construction and the greater the amount of current that any one strand can carry. In contrast, thinner strands improve the reduction of eddy currents in the system and thus increase the electrical efficiency by reducing losses. It has been found that the ranges herein provide a favorable balance between these factors.

[0066] The ranges disclosed above correspond to particularly effective operating frequencies of from about 150 Hz to about 10 kHz. Thus, the ranges disclosed above correspond to a resistivity of from about 1 x 10 -9 Ωm to about 2 x 10 -10 Ωm. While other ranges are possible, it has been found that such ranges are very effective in providing extremely high current densities in this arrangement.

[0067] Thus, this is relevant to the reasonable operating range of the motor and is particularly effective for use in aircraft propulsion machines. In addition, the resistivity ranges described above have been found to be very effective in the ultra-high efficiency conduction region.

[0068] In one example, the current loss experienced by the armature arrangement 130 is 0.6% or less of the total input power of the motor. In one example, the total Litz wire current loss in the motor is about 0.6%. The upper limit of the loss is related to the thermal budget, which ultimately depends on the hydrogen flow rate (in one example arrangement, this is related to the potential fuel cell and motor power) and the fuel cell and motor efficiency.

[0069] For an example of a fuel cell stack, the limitation of a standard design is to overcome the cooling of the motor without introducing expensive and bulky additional equipment. In one example solution, the coupling between the fuel cell stack and the motor demonstrates a beneficial and symbiotic relationship. For an example of a hydrogen fuel cell, the fuel cell stack provides power to the motor, and the hydrogen cools the motor before being used in the fuel cell stack itself.

[0070] The rate at which the hydrogen used to cool the motor is evaporated can be no higher than the hydrogen flow rate used to generate sufficient power for the motor to consume. Thus, the current loss in the stator windings cooled by ultra-high efficiency conduction can be less than 0.6% to meet this requirement. When used in the arrangement of the present invention, a minimum motor efficiency of greater than 99% is provided. This can be understood by considering the following equation for motor efficiency:

[0071]

[0072] where represents the motor efficiency, is the heat of vaporization of hydrogen, is the enthalpy of combustion of hydrogen, and is the combustion efficiency (in this case, referring to the efficiency of converting the chemical energy of hydrogen into electrical energy).

[0073] Considering that the heat of vaporization of hydrogen is very low relative to the enthalpy of combustion of hydrogen (and considering that the combustion efficiency of fuel cells is higher than that of traditional gas turbines), it can be seen that in order to ensure that the vaporization cooling of the motor does not exceed power generation, the motor efficiency has to be maintained at higher than 99%.

[0074] Specifically, the arrangements disclosed herein are particularly characterized by a particularly high current density handling capacity and a particularly low total current loss. This results in the arrangements having a much greater output overall than previous electrical arrangements. For medium speeds, the cryogenic machines described herein are particularly advantageous at an input power of approximately 750 kW. The arrangements are equally advantageous for powers of approximately 1 MW and higher. In this context, medium speed corresponds to the motor operating at approximately 5,000 to 10,000 rpm. At such medium speeds, the preferred torque is a balance between the output torque and the associated losses, such that the motor is particularly power dense and efficient. The motor can operate at speeds higher than 10,000 rpm.

[0075] The litz strands can be made of aluminum or copper. The litz strands can be made of high purity aluminum or copper. Although these materials are advantageous due to their electrical properties at low temperatures, the litz strands can comprise any suitable material.

[0076] In one example, the stator 110 is disposed in a vacuum. The entire stator 110 can be maintained in a vacuum to isolate the stator 110 from the cryogenic cooling applied to the armature arrangement 130. This vacuum also encompasses the magnetic core of the motor 100. Preferably, the vacuum is contained by non-magnetic tubes placed in the air gap.

[0077] In one example, the arrangement includes a fluid arranged to be in thermal communication with the magnetic core. The fluid is arranged to supply thermal energy to the magnetic core. In use, the heat capacity of the fluid is arranged to maintain the temperature of the magnetic core, notwithstanding the indirect cooling by the cryogen acting primarily on the armature arrangement 130. Thus, the fluid is arranged to "pump out" the iron losses from the vacuum, as described above, which is to increase the resistivity of the iron by raising its temperature, thereby reducing the iron losses in the iron core machine. This is counterintuitive for using low temperatures to improve the electrical efficiency (i.e., of the armature arrangement).

[0078] Specifically, while the armature arrangement 130 is cooled by the refrigerant source 140, this fluid (rather than the refrigerant) prevents the magnetic core from being significantly cooled by the refrigerant source 140. In this way, the heat capacity of the fluid can inhibit the cooling of the magnetic core. The fluid can be a liquid or a gas. In particular, an air flow from the engine nacelle is advantageous for use in such an arrangement because this is already a reasonably high thermal energy fluid that can be used for additional electrical efficiency in this arrangement. In one example, the fluid can be held in a fluid jacket to increase the heat conductivity between the fluid and the magnetic core. In a specific example, the fluid can be a liquid with a high heat capacity such as water. Alternatively, the liquid can be a high heat capacity liquid with a freezing point below 0 °C so that the liquid is less likely to freeze during use. Such a liquid provides stronger protection for the colder locations of this arrangement, such as locations in close thermal communication with the refrigerant of the refrigerant source 140. When the magnetic core (which can be made of iron) is maintained at a higher temperature to avoid excessive heat generation due to AC induction and hysteresis effects, the electrical efficiency of cooling the armature can be provided. The stator can be cooled using the air flow along the engine nacelle.

[0079] In one example, the rated power of the motor exceeds 1 MW. In one arrangement, some gaps can advantageously be present in the slots and ends of the stator to facilitate the cooling system, and thus this arrangement is particularly suitable for medium speed machines with a rated power exceeding 750 kW (which can be about 5,000 to 10,000 rpm).

[0080] In one example, the armature arrangement includes aluminum. It has been found that high purity aluminum is particularly effective for the arrangements disclosed herein.

[0081] The armature arrangement, also known as the motor coil, can be made of other materials with similar properties, such as niobium titanium oxide, high temperature superconductors, or magnesium boride. These options allow the use of superconducting properties, where extremely high electrical efficiency can be provided with effectively zero resistance. However, the thermal conductivity of these materials is relatively low. In addition, while superconductors exhibit extremely low DC losses, the AC losses associated with their use are significant.

[0082] Reference Figure 2 , shows a schematic cross-sectional view of the motor 200. The machine 200 has a stator 210. The machine 200 also has a rotor 220. The rotor 220 is centrally located within the stator 210. As Figure 2 shown in the example of Figure 2The three-phase arrangement shown; alternatively, the stator may include any number of phases. Similarly, the rotor may contain any suitable number of magnetic poles.

[0083] The rotor 220 may be formed by a set of elements that provide a change in reluctance or magnetic flux or both. As an example, the rotor 220 may include surface-mounted permanent magnets 270 having their own magnetic flux, which respond to a time-varying magnetic field generated by the armature arrangement (e.g., Figure 1 ) to provide a torque force to the rotor 220 and thereby generate motive power thereon. Alternatively, the rotor 220 may include electromagnets. Other rotors may be used in the arrangements disclosed herein.

[0084] Referring Figure 3 , an insulation arrangement 300 for a cryogenic machine is shown. The insulation arrangement 300 has a cryogenic region 310 around which components of the insulation arrangement may be arranged. The arrangement 300 includes two containers between which a high-quality vacuum is maintained. The inner container 320 is located inside the outer container 330. Inside the arrangement 300 is the cryogenic region 310 maintained at a low temperature. Outside the outer container 330 is a temperature region that may be ambient temperature or some other non-low temperature. Between the inner container 320 and the outer container 330 is a vacuum and multi-layer insulation, which may be referred to as a radiation shield. By arranging several layers of parallel thin reflective materials (multi-layer insulation, MLI), radiative heat transfer in this region can be reduced. In such an arrangement, the armature can be cooled to cryogenic temperatures without being thermally coupled to the stator core.

[0085] Referring Figure 4 , a perspective view of a coil within a containment vessel 400 is shown. The vessel 400 may include ports for providing refrigerant inlets and outlets. The coil may be arranged in a "racetrack" form. The "racetrack" form may be generally in the form of a discorectangle.

[0086] Figure 5 A schematic cross-sectional view of a cryogenically cooled motor arrangement 500 is shown, where the stator iron 510 is maintained at ambient temperature and where the coil 550 is cryogenically cooled. An outer container 560a surrounds the entire stator 510, which is located in a vacuum 580. This arrangement provides high electrical efficiency. Figure 5 The arrangement shown has at least one refrigerant dispenser 540 for refrigerant circulation 544 within at least one inner container 560b. This results in a refrigerant collector 542. The arrangement has a stator iron 510 and a wedge 510a, where stator slots are located in the wedge. The coil 550 is shown as including Litz wire 552. In Figure 5Air is shown by arrows. The air is circulating. The air cools the rotor. The air also cools the stator. The temperature of the stator can be maintained between about 200 K and about 320 K, or between about 223 K and about 313 K. A multi-layer insulation (MLI) 570 of several layers is arranged close to the inner container 560b and within the vacuum.

[0087] Figure 6 is a schematic cross-sectional view of a cryogenically cooled motor arrangement 600, similar to Figure 5 the motor arrangement shown in Figure 6 In the example of

[0088] Figure 7 is a schematic cross-sectional view of a cryogenically cooled motor arrangement 700, similar to Figure 6 the motor arrangement in Figure 7 In the example of

[0089] Figure 8 shows a cryogenically cooled motor arrangement 800 in which the stator iron 810 is maintained at an "intermediate" temperature, i.e., a temperature between the ambient temperature and the temperature of the coils (cooled). In one example, such as Figure 8 the example shown in

[0090] Figure 8 In the example of Figure 5 the motor arrangement shown in Figure 8The example shown has a refrigerant dispenser 840 at 25 K. Depending on the selected refrigerant, this can be a liquid or a gas. The refrigerant dispenser can be around 20 K to 30 K. When the refrigerant is a liquid at the dispenser 840, as the refrigerant travels, it can turn into a gas (or remain a liquid) at a temperature of about 25 K to about 30 K. Then, the cryogenic fluid can interact with power electronics at about 80 K. The power electronics can be about 70 K to 90 K. Then, the refrigerant travels through a portion of the stator 810 while maintaining the stator at about 120 to about 150 K. Figure 8 The example also has a refrigerant collector 842 for collecting gas that can be at a temperature of about 150 K. The temperature of the refrigerant collector can be about 140 K to about 170 K. Lower temperatures can be used to obtain additional electrical efficiency.

[0091] In one example, the power electronics can include any device suitable for modulating DC electricity into AC current, such as an inverter. This is particularly applicable for converting DC power from a fuel cell stack into AC power suitable for powering the electric motor of the present invention. Such power electronics must be maintained at a higher temperature than the armature arrangement, but the temperature should be close enough to prevent large thermal gradients in the connecting wires. In one example, it has been found that the power electronics are particularly effective at temperatures between 80 K and 110 K. One way to maintain a reasonable temperature gradient is to use relatively short connecting wires. Such an arrangement can reduce or prevent overvoltage in the coils during the switching process. The electric motor of the present invention can include an integrated motor-inverter, thereby using relatively short connecting wires.

[0092] By reducing the stator core to an intermediate temperature, the radiant heat transferred by the stator core is significantly reduced. In one example, reducing the stator core temperature from 300 K to 150 K is equivalent to a 16-fold reduction in the heat transferred by radiation, because radiant energy is proportional to the fourth power of the absolute temperature (Stefan-Boltzmann law). Thus, in Figure 8 the embodiment, by reducing the temperature of the stator core to an intermediate temperature, less MLI is required to protect the armature arrangement from radiant energy passing through the vacuum. In this embodiment, the stator core can be covered with some thin MLI to improve the stability of its temperature.

[0093] In this embodiment, the cryogenic cooling circuit may be pressurized. For an example where hydrogen is the refrigerant, the boiling temperature of hydrogen at ambient pressure is 21 K. It can be advantageous to maintain the refrigerant source in a pressurized environment such that the boiling temperature is elevated relative to its boiling temperature at ambient pressure. The armature arrangement may be maintained at a temperature slightly higher than the refrigerant source at the refrigerant dispenser. In one example, the temperature of the armature arrangement is about 30 K to 40 K, thus providing a sufficient thermal gradient for heat to flow out of the coil and into the refrigerant. In one example, about 35 K is considered a suitable temperature to maintain the armature arrangement, and those skilled in the art will understand that for any refrigerant source that can be maintained at a temperature sufficiently below 21 K, any temperature for maintaining the armature arrangement below 35 K is suitable.

[0094] In one example, by this technique, an aircraft propulsion motor with a power exceeding 1 MW, a specific power of at least 15 kW / kg, and an efficiency exceeding 99% can be achieved.

[0095] The systems disclosed herein have significant advantages in providing propulsion. These systems can ultimately provide much greater thrust than the currently existing systems used in propulsion arrangements. In particular, the systems disclosed herein provide higher current densities than previously possible in electric machines. Thus, the systems of the present disclosure make the use of electric machines in modern propulsion systems more reasonable and thus encourage the use of such machines. Another advantage of these machines over modern propulsion combustion systems is that they use more environmentally friendly fuels.

[0096] Although most of the electric machines disclosed are described in the context of aircraft, other vehicles such as spacecraft, marine vessels / ships, and submarines, etc., can also use the electric machines described herein. The vehicle may or may not carry a refrigerant or a low-temperature source for other purposes such as power generation, etc., but still benefits from the arrangements disclosed herein. Although the refrigerant may be carried for other reasons, integrating the refrigerant into the currently disclosed system will not be mechanically complex. Thus, the disclosed systems will advantageously be provided in such vehicles. Vehicles that may be propelled by electric machines such as those described herein will all benefit from the use of the systems disclosed herein. Vehicles can include cars, amphibious boats, aircraft, and the like.

[0097] Similarly, cooling can in principle be provided by electromagnetic means. Superconducting vehicles have shown that it is feasible to use mechanical coolers. Thus, any vehicle can benefit from the use of the electric machines disclosed herein.

[0098] The iron core rotor in the above description can be a conventional permanent magnet iron core rotor.

[0099] The systems disclosed herein can be advantageously used to provide propulsion in vehicles or systems that can benefit from a system capable of providing high output power from an electric machine using a more environmentally friendly fuel. The systems proposed herein are also compact and lightweight, thus providing additional advantages in terms of weight and space savings. In the specific examples used herein, the AC and DC loss contributions of the armature have been carefully balanced to achieve minimum total losses. In one example, for a strand diameter of 0.1 mm, very low losses of 0.4 to 0.45 A / strand have been found, and in this arrangement, such components can be used in an electric machine to provide a current density of approximately 55 A / mm².

[0100] Providing thrust through an electric machine rather than through a typical combustion engine offers many advantages. Producing water (etc.) instead of harmful gas emissions (NO, CO, etc.) has obvious associated advantages. In addition, the operation of the vehicle can have a significantly reduced noise level. In a specific example, the landing phase of an aircraft can be carried out at a significantly reduced noise level.

[0101] Therefore, the applications of the system can include automotive, aerospace, household, or commercial, etc.

[0102] Further examples of combinations of features taught by this disclosure are listed in the following numbered clauses:

[0103] 1. An electric machine, comprising:

[0104] A stator, the stator including a magnetic core;

[0105] A rotor;

[0106] An armature arrangement; and,

[0107] A low temperature source, the low temperature source being arranged to provide a low temperature to the armature arrangement,

[0108] wherein the armature arrangement includes a plurality of litz wires,

[0109] wherein during operation, the armature arrangement provides a current density of more than 25 A / mm².

[0110] 2. The electric machine according to clause 1, wherein the low temperature source is a refrigerant source arranged to provide a refrigerant to the armature arrangement.

[0111] 3. The electric machine according to clause 2, wherein the refrigerant source is a supply source of at least one of hydrogen, neon, helium, or nitrogen.

[0112] 4. The electric machine according to clause 2 or 3, wherein the temperature of the refrigerant is below 77 Kelvin and is arranged to maintain the armature arrangement at a temperature below 77 Kelvin.

[0113] 5. An electric machine according to any one of clauses 1 to 4, wherein each of the plurality of litz wires comprises a plurality of litz wire strands, and the number of litz wire strands of each of the plurality of litz wires is between 50 and 5000.

[0114] 6. An electric machine according to clause 5, wherein the diameter of the litz wire strands is in the range of 0.05 mm to 1 mm in diameter.

[0115] 7. An electric machine according to any one of clauses 1 to 6, wherein the resistivity of the plurality of litz wires is 1x10 -9 Ωm or less.

[0116] 8. An electric machine according to any one of clauses 1 to 7, wherein the current loss experienced by the armature arrangement is 0.6% or less of the total input power of the electric machine.

[0117] 9. An electric machine according to any one of clauses 1 to 8, wherein the temperature of the magnetic core is maintained within at least one of the following temperature ranges:

[0118] 223 K or higher;

[0119] 77 K or higher; or

[0120] 77 K to 223 K.

[0121] 10. An electric machine according to any one of clauses 1 to 9, wherein the stator is arranged in a vacuum.

[0122] 11. An electric machine according to any one of clauses 1 to 10, further comprising a fluid arranged in thermal communication with the magnetic core, the fluid being arranged to provide thermal energy to the magnetic core.

[0123] 12. An electric machine according to clause 11, further comprising a fluid jacket arranged to maintain the fluid in thermal communication with the magnetic core.

[0124] 13. An electric machine according to clause 12, wherein the fluid is water.

[0125] 14. An electric machine according to any one of clauses 1 to 13, wherein the rated power of the electric machine exceeds 1 MW.

[0126] 15. An electric machine according to any one of clauses 1 to 14, wherein the armature arrangement comprises aluminum.

[0127] 16. An aircraft comprising an electric machine according to any one of clauses 1 to 15.

[0128] 17. The aircraft according to clause 16, wherein the refrigerant source is arranged in the tail portion of the fuselage of the aircraft.

[0129] 18. A vehicle comprising an electric machine according to any one of clauses 1 to 15.

[0130] 19. An electric machine comprising:

[0131] A stator comprising a magnetic core;

[0132] A rotor;

[0133] An armature arrangement; and,

[0134] A low-temperature source arranged to provide a low temperature to the armature arrangement,

[0135] wherein the armature arrangement comprises a plurality of litz wires,

[0136] wherein during operation, the low-temperature source is arranged to maintain the armature arrangement at a super-efficient conduction temperature.

[0137] 20. The electric machine according to clause 19, wherein the super-efficient conduction temperature is a temperature below 77 Kelvin.

[0138] 21. The electric machine according to clause 19 or 20, wherein during operation, the armature arrangement provides a current density of more than 25 A / mm².

[0139] Thus, from one perspective, an electric machine has now been described, comprising: a stator comprising a magnetic core; a rotor; an armature arrangement; and a refrigerant source arranged to provide refrigerant to the armature arrangement, wherein the armature arrangement comprises a plurality of litz wires, and wherein during operation, the armature arrangement provides a current density of more than 25 A / mm².

Claims

1. A motor, comprising: a stator, the stator including a magnetic core; a rotor; an armature arrangement; and a low temperature source, the low temperature source being arranged to provide a low temperature to the armature arrangement, wherein the armature arrangement includes a plurality of Litz wires, wherein during operation, the armature arrangement provides a current density of more than 25 A / mm².

2. The motor according to claim 1, wherein the low temperature source is a refrigerant source, the refrigerant source being arranged to provide a refrigerant to the armature arrangement.

3. The motor according to claim 2, wherein the refrigerant source is a supply source of at least one of hydrogen, neon, helium or nitrogen.

4. The motor according to claim 2 or 3, wherein the temperature of the refrigerant is lower than 77 Kelvin and is arranged to maintain the armature arrangement at a temperature lower than 77 Kelvin.

5. The motor according to any one of claims 1 to 4, wherein each of the plurality of Litz wires includes a plurality of Litz wire strands, and the number of Litz wire strands of each of the plurality of Litz wires is between 50 and 5000.

6. The motor according to claim 5, wherein the diameter of the Litz wire strands is in the diameter range of 0.05 mm to 1 mm.

7. The electric machine according to any one of claims 1 to 6, wherein the resistivity of the plurality of litz wires is 1x10 -9 Ωm or less.

8. The motor according to any one of claims 1 to 7, wherein the current loss experienced by the armature arrangement is 0.6% or less of the total input power of the motor.

9. The motor according to any one of claims 1 to 8, wherein the temperature of the magnetic core is maintained in at least one of the following temperature ranges: 223 K or higher; 77 K or higher; or 77 K to 223 K.

10. The motor according to any one of claims 1 to 9, wherein the stator is arranged in a vacuum.

11. The motor according to any one of claims 1 to 10, further comprising a fluid arranged to be in thermal communication with the magnetic core, the fluid being arranged to provide thermal energy to the magnetic core.

12. The motor according to claim 11, further comprising a fluid jacket, the fluid jacket being arranged to keep the fluid in thermal communication with the magnetic core.

13. The motor according to claim 12, wherein the fluid is water.

14. The motor according to any one of claims 1 to 13, wherein the rated power of the motor exceeds 1 MW.

15. The motor according to any one of claims 1 to 14, wherein the armature arrangement includes aluminum.

16. An aircraft, comprising the motor according to any one of claims 1 to 15.

17. The aircraft according to claim 16, wherein the refrigerant source is arranged in a tail portion of the fuselage of the aircraft.

18. A vehicle, comprising the motor according to any one of claims 1 to 15.

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