Patent Publication Number: US-2022239199-A1

Title: Systems and methods for electric propulsion systems for electric engines

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a U.S. patent application claiming priority to, and the benefit of, U.S. Provisional Patent Application No. 63/141,078, titled “SYSTEMS AND METHODS FOR ELECTRIC PROPULSION SYSTEMS FOR ELECTRIC ENGINES” filed on Jan. 25, 2021, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Electric and hybrid aircraft (EHA) are rapidly becoming a reality. At the same time, there are many problems that need to be resolved to progress successfully and affordably. The electric machines (EM), power electronics, and thermal management systems (TMS) for advanced electric propulsion systems (AEPS) play a significant role in the modern aerospace/military industry. This is particularly true in electric aircraft, including electric and hybrid propulsion. A substantial demand has arisen for improved electric drive performance including increases in high power density, improved robustness, and reduced operating costs and safety, as compared to the existing hardware. For example, one metric used to gauge an electric propulsion system is the power density. An electric propulsion system may produce a power density of 3-5 killowatts/kilogram (kW/kg). However, EHA and other electric propulsion system under development are expected to have power density specifications of 12 kW/kg or greater. Moreover, those electric propulsion systems developed so far that can achieve 12 kW/kg or greater do not adequately address thermal management sufficiently to permit prolonged operation as would be needed for real-world vehicle operations. These trends have created a significant increase in AEPS needs including increased operating voltages and reduced system losses, weight, and volume. 
     For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for electric propulsion systems for electric engines. 
     SUMMARY 
     The Embodiments of the present disclosure provide methods and systems for electric propulsion systems for electric engines and will be understood by reading and studying the following specification. 
     In one embodiment, an advanced electric propulsion system comprises: An advanced electric propulsion system, the system comprising: a housing; an electric motor within the housing; a motor drive coupled to the electric motor; a thermal management system that comprises: a manifold-mini-channel heat sink (MMHS) integrated into the housing, wherein the manifold-mini-channel heat sink comprises: an inlet manifold having a plurality of air inlets formed in a front of the housing; a set of plurality of circumferentially grooved micro-channels formed in the housing and coupled to the air inlets and conductively thermally coupled to stator windings of the electric motor; an outlet manifold having a plurality of air outlets formed at a back of the housing and coupled to the set of plurality of circumferentially grooved micro-channels; wherein the electric motor comprises Pseudo-Edge Wound (PEW) stator windings configured to provide a low thermal resistance path from the stator of the electric motor to the housing; wherein the PEW stator windings comprise a high temperature tolerant thermally conductive electrical insulator. 
    
    
     
       DRAWINGS 
       Embodiments of the present disclosure can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which: 
         FIGS. 1, 1A, 1B and 1C  illustrate an example Advanced Electric Propulsion System (AEPS) embodiment. 
         FIG. 1D  illustrates an optional fan impeller that either enhances or replaces the airflow from the propulsion system propeller. 
         FIGS. 2A and 2B  are front-view and rear-view sectionalized diagrams of the AEPS of  FIG. 1  illustrating a manifold-mini-channel heat sink integrated into the housing of the AEPS  100 . 
         FIG. 3  is a graph illustrating a preliminary comparison of a conventional mini-channel heat sink and a manifold-mini-channel heat sink. 
         FIG. 4  is a diagram that illustrates a section of PEW stator windings with a high thermal conductivity pad between the windings the AEPS housing. 
         FIG. 5  is a diagraming that shows a small total temperature gradient due to benefits of PEW. 
         FIG. 6  illustrates a thermal model that simulates a ⅓ circumferential section of an example Advanced Electric Propulsion System embodiment. 
         FIG. 7  illustrates predicted temperatures in an example Advanced Electric Propulsion System embodiment throughout a 20-minute takeoff transient simulation. 
         FIG. 8  illustrates predicted temperatures at relevant locations of an example Advanced Electric Propulsion System embodiment at a stabilized, steady operation condition at an assumed 3.0 km operating altitude. 
         FIG. 9  illustrates example alternate electric motor topologies an example Advanced Electric Propulsion System embodiment. 
         FIG. 10  is a chart of Electromagnetic (EM) weight comparisons. 
         FIG. 11  an example arrangement of PEW windings. 
         FIG. 12  shows an example embodiment of an electric motor topology. 
         FIG. 13  is a diagram illustrating a motor drive comprising power electronics for an example Advanced Electric Propulsion System embodiment. 
     
    
    
     In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize features relevant to the present disclosure. Reference characters denote like elements throughout figures and text. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of specific illustrative embodiments in which the embodiments may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense. 
     Embodiments of the present disclosure provide for embodiments of advanced electric propulsion systems (AEPS) that combine the features of a manifolded mini-channel heat sink (MMHS), pseudo-edge wound windings (such as pseudo-edge wound copper windings, PEWCW, for example) and a high temperature tolerant thermally conductive electrical insulator (such as High Temperature Insulation, HTI, for example). In some embodiments, this combination provides an AEPS having a direct drive to the propulsive device without using a torque amplifier for low weight, cost and volume, and high reliability. As disclosed below, the electric rotating machine (i.e., an electric motor) and the motor drive (i.e., power and control electronics) of the AEPS can be heavily integrated for better performance sharing a common chassis and cooling system. In other embodiments, however, an optional torque amplifier/gearbox may be included with the disclosed AEPS for applications where propeller speed is very low in order to facilitate utilization of the relatively high speed lightweight AEPS discussed herein. 
     The embodiments disclosed herein improve the power density of the electric propulsion systems (in some embodiments by about 4 times existing electric propulsion systems) facilitating new electric propulsion vehicles such as, but not limited to, narrow body electric hybrid propulsion aircraft, Urban Air Mobility (UAM) vehicles, and recreational, training, and general aviation aircraft. The embodiments described herein also disclose several innovative and transformative technologies that address the technical challenges of designing, developing and fabricating a high-power density propulsion system for electric and hybrid vehicles. 
       FIG. 1  is diagram illustrating a 3-Dimensional model of an example AEPS  100  embodiment for use in a vehicle. As shown in  FIGS. 1 and 1A , the AEPS  100  disclosed herein includes components of a thermal management system TMS  140 , an electric motor  142  and a motor drive  144 , for a vehicle  10 , which are described and characterized in the following sections. 
     Thermal Management System (TMS) 
     The TMS  140  of AEPS  100  utilizes a high-speed air flow  103  from the aircraft propeller/fan over the AEPS  100  exterior as a heat sink. TMS  140  comprises four elements, which combined provide significant improved temperature management and therefore increased life for high power-density machines. These elements of the TMS  140  include: Air Cooling, a Manifold Mini-Channel Heat Sink (MMHS), Pseudo Edge Wound windings (PEW) with optional high thermal conductivity padding between the stator windings and the AEPS  100  housing  110 , and high temperature winding insulation provided by a high temperature tolerant thermally conductive electrical insulator. 
       FIG. 1B  is a cross-section diagram illustrating an example AEPS  100  and the various elements discussed in this disclosure. The electric motor  142  includes a rotor  170  that comprises a plurality of permanent rotor magnets  171  (which may be NeFeB magnets or other permanent magnets). The rotating shaft  113  of the electric motor  142  penetrates through the end bell  172  which seals the rotary  170  within the housing  110 . The shaft  113  is supported by bearings  173 . The stator  174  of the electric motor  142  comprises PEW stator windings  175  wound around a stator iron  176 . As further discussed below, the housing  110  comprises circumferentially grooved micro-channels  214  of the TMS  140  for dissipating heat generated within the electric motor  142  section of the AEPS  100 . The high temperature tolerant thermally conductive electrical insulator coating the stator windings  175  is thermally conducting to facilitate transfer of heat generated in the stator  174  to the housing  110 . The motor drive  144  comprises power modules  240  that are operated by a DSP controller  1314  via a gate driver  1316 . DC power may be fed to the motor drive  144  via a DC power connector  180  while control signals are input via a signal connector  180 . Further shown in  FIG. 1C  are the stator windings  175  and stator laminations  176  of the stator  174 , and shaft  113  and rotor magnets  171  of the rotor  170 . In some embodiments, the structural elements of the rotor  170  and/or shaft  113  may comprise light-weight composite materials such as, but not limited to, a polyether ether ketone (PEEK) based composite material, Polyetherimide (Ultem), Polyamide-imide (Torlon), Polyimide (Vespel), Polyphenylene Sulfide (Ryton), Polyoxymethylene (Delrin), a plastic infused mesh or other fiber or plastic composite material. 
     Manifold Mini-Channel Heat Sink (MMHS): The MMHS integrates a novel air-cooled heat sink into the outer surface of the housing  110  of the AEPS  100 . Air cooling reduces system complexity, improves system reliability, and reduces system mass by eliminating the need for auxiliary pumps and heat exchangers. An external air flow across and through the housing  110  provides an adequate heat sink for the AEPS  100 . As shown in  FIG. 1 , an external air flow  103  (which flows both around the housing  110  and through the MMHS) is provided by a propeller  102  mounted to shaft  113  of the rotor  170  at the front  112  of the AEPS  100 . That airflow  103  is further motivated by the velocity of the vehicle when it is in motion. 
       FIG. 1C  illustrates an embodiment where an optional fan impeller  160  is attached to the shaft  113  of the electric motor  142  that will force/motivate an airflow  164  through the airflow channels  162  of the MMHS to either enhance or replace the airflow  103  from the propeller  102 . 
     The MMHS concept disclosed herein has been shown to simultaneously reduce pressure drop and pumping power, thereby enabling use of smaller hydraulic diameter channels which can reduce thermal resistance.  FIGS. 2A and 2B  are front-view and rear-view sectionalized diagrams of the motor drive  144  section of the AEPS  100  of  FIG. 1 , illustrating an all air-cooled system which utilizes a manifold-mini-channel heat sink  200  integrated into the housing  110  of the AEPS  100 . The manifold-mini-channel heat sink  200  includes an inlet manifold  210  that comprises a plurality of air inlets  212  (also shown in  FIG. 1 ) formed in the housing  110  at the front  112  of the AEPS  100 . Each of the air inlets  212  define an entry to an internal airflow passageways  162  within the housing  110  leading to a set of a plurality of circumferentially grooved micro-channels  214 . The circumferentially grooved micro-channels  214  are formed in the housing  110  adjacent to, and conductively thermally coupled to, the stator windings  175  of the electric motor  142  and the power modules  240  of the motor drive  144 . The manifold-mini-channel heat sink  200  further comprises an outlet manifold  220  that comprises a plurality of air outlets  222  formed in the housing  110  at the back  118  of the AEPS  100 . Each of the plurality of air outlets  222  are coupled by an internal airflow passageway within the housing  110  to the respective set of the plurality of circumferentially grooved micro-channels  214 . As such, in operation, airflow  103  entering an air inlet  212  flows through the circumferentially grooved micro-channels  214  in both the electric motor  142  and motor drive  144  sections, and exhausts from the housing  110  at an air outlet  222 . In some embodiments, power modules  240  (discussed below) are thermally coupled to an internal mounting surface  230  of the motor drive  144  to dissipate heat via the manifold-mini-channel heat sink  200 . 
     The micro-channels  214  reduce thermal resistance due to their very high surface area to volume ratio. By including in the MMHS  200  a plurality of parallel shorter airflow channels (i.e., from an inlet  212  air passage, through the micro-channels  214  and to an immediately adjacent outlet  222  air passage), the effects of pressure drop and pumping power are mitigated. In some embodiments, heat sink grooves cut circumferentially (rather than axially) within the material of the housing  110  form the circumferentially grooved micro-channels  214 . The MMHS  200  improves performance as an air cooled heat sink. Because of the simultaneous reduction in both flow rate and flow distance, the pressure drop and pumping power reduces by the square of the number of divisions. Thus, manifolding channels in this way facilitates use of smaller hydraulic diameter channels  214  and the associated increase in heat transfer surface area, without the associated increase in pressure drop and pumping power. Alternatively, for the same channel dimensions, the pressure drop, pumping power, and thermal resistance can be reduced, and the heat transfer coefficient and coefficient of performance (COP) can be increased. Obtaining lower thermal resistances at higher COPs is particularly advantageous for high specific power electric motors, where the weight and pumping power of the heat sink solution are minimized. 
     A preliminary comparison of a conventional mini-channel heat sink and a MMHS  200  with the same mini-channel dimensions is given in  FIG. 3 . The results indicate that the manifold mini-channel has significantly lower thermal resistance for the same COP. The results indicate that the MMHS has significantly lower thermal resistance for the same COP. In addition, a 3-D Finite Element Analysis (FEA) model of a MMHS  200  was created. Due to the periodic nature of the flow, only 1/12 of the total domain was simulated. Based on preliminary and full 3-D FEA models, the predicted performance of the MMHS  200  is given in Table 1 for typical take-off and cruise conditions. Total thermal resistance includes the 
                     TABLE 1                  Predicted performance metrics for the                                 Metric   Take-Off   Cruise                                             Mass Flow Rate [kg/s]   0.5   0.235           Pressure Drop [Pa]   840   260           Heat Transfer Coefficient [W/m 2 -K]   800   700           Caloric Thermal Resistance [K/W]   0.0017   0.0042           Convective Thermal Resistance   0.0057   0.0065           COP [—]   40   100                        
internal conductive resistance between the heat sources and the heat transfer surfaces, the convective resistance between heat transfer surfaces and fluid, and caloric resistance of the fluid.
 
     Pseudo-Edge Wound (PEW) Windings: In some embodiments, the electric motor  142  of the AEPS  100  comprises Pseudo-Edge Wound (PEW) Windings  175  on the stator  174  for reducing the thermal resistance in the AEPS  100  electric motor from the stator winding  175  copper of the electric motor  142  to the structure of the housing  110  cooled by the MMHS  200 . In some embodiments, the windings  175  are PEW copper windings. See, for example, U.S. Pat. No. 10,062,497 “PSEUDO EDGE-WOUND WINDING USING SINGLE PATTERN TURN”; U.S. patent application Ser. No. 16/997,720 “ELECTRIC MACHINE STATOR WINDING”; and U.S. patent application Ser. No. 16/442,144 “INTEGRATED TRACTION DRIVE SYSTEM”, each of which are incorporated herein by reference in their entirety. Electric motor windings typically comprise round wires formed into bundles that make it very difficult to get the heat out from the stator windings even at the winding end turns where heat is able to dissipate from the windings. For embodiments for the present disclosure, the PEW winding configuration of the stator windings  175  comprises segments of bar-type windings where the ends are flat, and a thermal pad (such as an electrically insulating silicone thermal interface material “Sil Pad”, for example) can optionally be placed against the winding end turns and housing walls to facilitate a thermal conductive heat path (i.e., a low thermal resistance path) from the windings  175  to the housing  110 . The PEW winding configuration also comprises a segmented winding arranged such that at each turn of the stator windings  175  has access to a conductive thermal path to the housing  110 . The resulting structure is very efficient for moving heat from the electric motor  142  to the housing  110  where it can be efficiently discharged to the environment by the airflow through the MMHS  200 . The PEW windings  175  of stator  174  provide a much higher percentage of winding material (for example, copper) by volume, and vastly improves the thermal conductivity through the stator windings  175 , as compared to conventional wound wire bundles with their relatively low copper content by volume. A stator  174  with PEW copper windings also increases the effective thermal conductivity and uniformity of the stator windings  175 , resulting in at least an order of magnitude reduction in winding thermal resistance compared with typical wire-bundle approaches. It should be understood that although the use of copper is mentioned as the material for the stator windings  175  throughout this disclosure, any of these embodiments may instead use windings made of other electrically conductive metals or alloys. 
     In some embodiments, a thermal management feature optionally used in combination with the PEW copper windings is the use of high thermal conductivity padding, for example “SIL PADS”, at the ends of each copper winding bundle to facilitate heat rejection from the heat-generating copper of the stator windings  175  to the AEPS  100  actively cooled (via the MMHS  200 ) housing  110 .  FIG. 4  illustrates a section of PEW copper stator windings  175  where a high thermal conductivity pad  420  is pressed in to contact both the windings  175  and the AEPS housing  110 . This arrangement greatly reduces overall thermal resistance as compared to conventional round copper windings.  FIG. 11 , discussed below, similarly illustrates a partial PEW stator configuration where for each of the illustrated lamination stack, high thermal conductivity padding  420  establishes a thermally conductive path between the windings  175  and the end bell  172  to reduce thermal resistance. 
     High Temperature Tolerant Thermally Conductive Electrical Insulation: In some applications, an AEPS  100  can be subject to a wide power requirement. For example, for an aircraft application an AEPS  100  may consume 166 kW at cruise but have peak demands on the order of 500 kW. In order to avoid the need for a bigger and heavier electric motor  142  to handle the peak conditions, the thermal management system needs to be able to handle the excess heat dissipation at peak demand conditions. Accordingly, in some embodiments, high temperature insulating layers are used for the PEW stator winding  175  arrangement, with nearly twice the temperature capability of typical varnishes. Instead of the electrically insulation layers (varnish) found in typical wire-bundle approaches, the electric motor  142  comprises electrically insulation layers comprising a much higher temperature-tolerant thermally conductive electrical insulation, which in some embodiments may be applied to the stator windings  175  as a coating. For some embodiments, the high temperature tolerant thermally conductive electrical insulator may comprise an insulated wire technology such as the Honeywell Inc. Hight-Temperature Wire Insulator (HTI). 
     The high temperature tolerant thermally conductive electrical insulation provides a high thermal conductivity heat path from the PEW stator winding  175  to the stator iron  175  and housing  176  so that heat generated in the stator windings  175  can be directed to the MMHS  200  and dissipated into the environment. Moreover, this insulation is referred to a “high temperature tolerant” because the insulation material itself can tolerate very high temperatures without degradation. In some embodiments, the insulation is tolerant to temperatures of 220° C. or greater and in some embodiments from 280° C. up to 600° C. which is much greater than what expected temperature would in the material of the PEW stator winding  175 . In some embodiments, the insulator may be tolerant to temperatures exceeding the melting temperature of the material of the PEW stator winding  175  (e.g., up to the 1084° C. melting point of copper for copper windings). 
     In some embodiments, the high temperature tolerant thermally conductive electrical insulator is produced from a formulated wire liquid coating comprised of glass solids suspended into a solution. Such an insulator can be tolerant to temperatures of 1200-2000° C. That solution may include surfactants, solvents, and polymers. The resulting liquid coating can be used to coat single strand magnetic wire, using typical industrial methods, to form the stator windings  175 . In some embodiments during the application of the high temperature tolerant thermally conductive electrical insulator to the stator windings  175 , the liquid coating is cured at low temperature to enable the coated wire to be applied to EM assemblies and machines in the same manner as polyimide coated wire. The resulting coating of the cured solution of suspended glass solids, is durable and can be manipulated without damage during assembly. In some embodiments, once the assembly is completed, a final heat curing “firing” is performed to set the final chemistry to remove all carbon chemistry making it capable of operating at 540° C. with long term exposure with suitable durability and electrical insulation performance. This coating can handle temperatures of 400° C. for prolonged operating periods. The conventional wire bundle approach can handle temperatures only of about 220° C. for prolonged periods. Considering that the approximation for predicting life of copper/insulation systems assumes a doubling or halving of system life for every 10° C., this is a significant improvement in capability. 
     High temperature capability is achieved by using the high temperature tolerant thermally conductive electrical insulator to coat single strand magnetic electrical wire due to the oxidation protection for the winding conductors. The wire coating is capable of 540° C. and is superior to polyimide for dielectric protection for temperature exposure beyond 10K hours. In some embodiments, the dielectric performance is equivalent to polyimide up to 220° C. and maintains the protection up to 540° C. This is 320° C. beyond the capability of polyimide. Electrical conductivity is identical to typical magnetic copper wire that are coated with polyimide. Thus, no additional windings or larger wire gage application is necessary for EM components. The coating is resistant to high frequency exposure of pulse width modulation controllers. Degradation of polyimide dielectric performance in the stator windings  175  can thus be avoided. 
     Notable characteristics of high-power electric machines such as motors and generators are the highly orthogonal thermal conductivity of the wire bundles and the temperature dependence of the I 2 R losses generated by the current in the wires. Failure to properly account for these characteristics can lead to significant temperature prediction error. In the TMS  140  disclosed herein, the orthogonality of the thermal conductivity in the copper is nearly eliminated using the PEW stator windings  175 .  FIG. 5  is a diagram at  500  that shows a small total temperature gradient with copper stator windings  175  is only about 12° C., which is due to benefits of PEW. The volume occupied by the copper windings is so much more efficiently utilized that the thermal resistance within the windings is greatly reduced. Temperature gradients and internal peak temperatures are accordingly reduced. 
     The temperature dependence of the losses in copper stator windings  175  is modeled by adjusting the local heat generation in the copper as a function of the local temperature. As noted in Table 2, the reference temperature for the copper losses in a machine evaluation was set at 220° C., and the losses are reset within the model as part of the solution. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Operating Conditions for Thermal Evaluation of the AEPS 
               
            
           
           
               
               
            
               
                   
                 Key Parameters for Transient and Continuous Conditions 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Peak 1 min 
                 Peak 5 min 
                 Peak 10 min 
                 Peak 15 min 
                 Peak 20 min 
                 Continuous 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 copper losses, W (@220 C.) 
                 18243 
                 8169 
                 4232 
                 2716 
                 1878 
                 3763 
               
               
                 iron losses, W 
                 4093 
                 3504 
                 3150 
                 3012 
                 2935 
                 1955 
               
               
                 module losses, W 
                 3452 
                 1789 
                 1067 
                 767.5 
                 595 
                 960 
               
               
                 windage and bearings estimate, W 
                 125 
                 125 
                 125 
                 125 
                 125 
                 125 
               
               
                 total, W 
                 25913 
                 13587 
                 8574 
                 6620.5 
                 5533 
                 6803 
               
               
                 air flow thru MC heat sink, kg/sec 
                 0.50 
                 0.43 
                 0.37 
                 0.30 
                 0.24 
                 0.24 
               
               
                 air Taverage in MC heat sink, ° C. 
                 39 
                 50 
                 41 
                 36 
                 32 
                 34 
               
               
                   
               
            
           
         
       
     
     This model was used for predicting temperatures throughout the AEPS  100 , both at the continuous flight condition and through a transient simulation of a 20-minute takeoff condition. 
     This thermal model used for evaluation simulates a ⅓ circumferential section of an AEPS  100  (as shown in  FIG. 6 ) by taking advantage of the symmetry around the axis of the AEPS shaft  113 . All significant internal heat sources are modeled including heat generated in the stator  174  copper layers, the stator laminations  176 , the inverter modules, windage generation between the rotor and stator, and estimated bearing losses. The model provides credible verification that the advantages expected to be obtained from the TMS  140  do indeed combine to produce a viable, survivable device to handle the desired great increase in overall power density.  FIG. 6  shows several of the AEPS  100  components included in the thermal model, which includes ⅓ of the total circumference of the actual AEPS  100  device. In addition to the housing  110 , other modeled AEPS  100  components include the bearings  173  for the shaft  113  and the rotor  170  of the electric motor  142 , stator laminations  614 , stator windings  616  and the inverter  618  of the motor drive  114 . 
     The thermal analysis simulation assumes that the outside air heat sink is at a standard hot day condition of 39.4° C. at sea level when the transient takeoff simulation begins. The completion of the 20 minutes transient takeoff simulation is assumed, for thermal analysis purposes, to be 3.0 km altitude at which the standard hot day temperature is 20° C. Higher altitudes will benefit from lower ambient air temperatures and will be increasingly benign for AEPS inner temperatures. Using these ambient air temperatures and the air flow rate through the microchannel heat sink, the average temperature of air through the heat sink was calculated based on the total heat rejection from the AEPS  100 . This average air temperature was used for the ambient heat sink effective temperature. For the initial one-minute peak transient, however, the ambient temperature of 39.4° C. was used for the heat sink since the great majority of heat generation during that short period is accounted for by the heat capacity of the AEPS  100  mass. 
     Table 2 also shows the operating conditions and associated losses through the various timed phases of a takeoff transient, and the continuous operating condition. The estimated air mass flow rates and the air heat sink temperatures used for analysis are also shown.  FIG. 7  shows the predicted temperatures in the AEPS throughout the 20-minute takeoff transient simulation. The copper temperature briefly reaches a maximum temperature of 392° C. at about 3.5 minutes, remaining below the maximum allowable temperature of 400° C. The rotor with its PM magnets briefly reaches about 170° C. at 12 minutes, remaining below its maximum allowable temperature of 180° C. The inverter case reaches maximum allowable temperature of about 140° C. at 3.5 minutes.  FIG. 8  shows the predicted temperatures at relevant locations at a stabilized, steady operation condition at the assumed 3.0 km operating altitude. For this long-term operating condition, all relevant temperatures are well below maximum desired values. This will provide long operating life and high reliability. Table 3 shows the resultant thermal resistances achieved by the proposed TMS  140  at takeoff and at continuous cruise. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Thermal Resistances at Takeoff 
               
            
           
           
               
               
               
               
            
               
                   
                 Thermal Resistances, K/W 
                 Take-Off 
                 Cruise 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Caloric Resistance 
                 0.0017 
                 0.0042 
               
               
                   
                 Convective Resistance 
                 0.0057 
                 0.0065 
               
               
                   
                 Conductive Resistance 
                 0.036 
                 0.036 
               
               
                   
                 Overall Thermal Resistance 
                 0.0434 
                 0.047 
               
               
                   
                   
               
            
           
         
       
     
     Electric Motor Design 
     The electric motor  142  of AEPS  100  includes an air-cooled permanent magnet (PM) motor that utilizes the TMS  140  for thermal cooling as discussed above. In some embodiments, to limit the amount of stator iron  176  in the stator  174 , the electric motor  142  comprises a multi pole/multi-slot Halbach array electric rotating machine. The rotor  170  of the electric motor  142  may include multiple high mega-gauss oersteds (MGO) magnets  171  contained within a composite sleeve resulting in reduced rotor  170  losses and smaller airgap. In some embodiments, the rotor  170  structure comprises a composite material, offering improved mechanical stress capabilities and drastic weight reduction of the entire rotor assembly. The stator  174  of the electric motor includes concentric windings  175  and use the PEW winding arrangement discussed above, which can improve the fill factor of the slot by as much as 100%. 
     In alternate embodiments, various other types of PM motors may be utilized to implement a low speed, high pole count, direct drive electric motor  142  for the AEPS  100 . Example alternate motor  142  topologies (illustrated in  FIG. 9 ) may include (a) surface PM rotor with distributed winding (DW SPM, 48 poles 144 slots), (b) surface PM rotor with concentrated winding (CW SPM, 48 poles, 72 slots), a surface PM rotor with fractional slot winding (FW SPM, 48 poles, 54 slots), (e) interior PM rotor with concentrated winding (CW IPM, 48 poles, 72 slots), (d) Halbach array with concentrated winding (CW Halbach, 48 poles, 72 slots), and Halbach array with fractional slot winding (FW Halbach, 48 poles, 54 slots). It should be understood that these are non-limiting examples and in other embodiments, other motor topologies may be utilized for the AEPS  100 .  FIG. 10  provides a comparison of Electromagnetic (EM) weight (weight of active magnetic materials including electrical steel, copper winding, and magnets). Weight of the FW Halbach topology machine is lower than that of other PM topology motors. The result shows that the torque density of the Interior Permanent Magnet (IPM) motor is not better than FW Halbach topology for very high pole count applications. A motor with fractional slot winding produces more torque than motor with concentrated winding because of its higher back-emf constant. 
     In some embodiments, the stator windings  175  of the electric motor  142  use the PEW winding arrangement, which improves the copper fill factor of the slots by 100% compared to that of round magnet wires. An example arrangement of the PEW windings for one embodiment is shown in  FIG. 11 . To achieve the utilization of higher voltages above 5 kVdc, the high temperature tolerant thermally conductive electrical insulator is applied to the wire elements of the stator to operate continuously up to 400° C. The insulator is used in some embodiments to precision bond laminations together for the electric motor stator core. The formulation may be applied to the stator windings  175  wire using a conventional factory setting and is configured to allow normal handing and winding machine operation to accomplish motor assemblies. The coated finished wire size is equivalent to standard polyimide coated wire to allow conventional machine sizing. 
     EM Design of Direct Drive Motor.  FIG. 12  shows an example embodiment of an electric motor  142  topology  1200  that comprises a 3-phase PM motor with Halbach array. The stator  174  lamination uses cobalt-iron electrical steel for high value of magnetic saturation. The stator winding  175  in each phase includes 16 turns of PEW single tooth coil. The rotor  170  comprises of 38 MGOe NdFeB segmented magnets contained within a Carbon Fiber Reinforced Polymer (CFRP) sleeve resulting in reduced rotor losses and smaller airgap. 
     Motor Drive (Power &amp; Signal Electronics) 
     The function of the motor drive  144  is to convert DC input power (e.g. from the vehicle&#39;s battery) to variable AC voltage and variable AC frequency to drive the electric motor  142 . The motor drive  144  is integrated with the electric motor  142  and TMS  140 . In some embodiments, AEPS  100  includes a motor drive  144  comprising power electronics that includes a three-phase multi-level inverter  1310  as shown in  FIG. 13 . That is, while  FIG. 13  illustrates a two-level inverter, in other embodiments the inverter  1310  may comprise more than two inverters. In some embodiments, a high voltage bus (for example, of 3-5 kV or more) is utilized to reduce electrical current demand of the motor drive  144  inverter  1310  for very high-power vehicle applications (such as the all-electric propulsion system for narrow-body aircraft, for example.) Electric propulsion vehicles can draw 10 MWatts to several hundred MWatts of electric power that will result in significant weight and efficiency penalties if low bus voltage is used. In some embodiments, the three-phase multi-level inverter comprises SiC MOSFET power devices  1312  (which may be for example, SiC MOSFET (Silicon Carbide metal-oxide-semiconductor field-effect transistor), IGBT (Insulated Gate Bipolar Transistor) or GaN (Gallium Nitride) power devices) to achieve substantial improvements in high voltage, high power levels and cost reduction. In some embodiments, the power devices  1312  act as electronic switches (controlled by the gate driver and DSP controller) that chop the incoming DC voltage converting it to a variable frequency and voltage AC signal. In some embodiments, the power devices  1312  are positioned in the power modules  240  (as shown in  FIGS. 1B, 2A, and 2B ). In some embodiments, each power module  240  is associated with a single AC power phase. In other embodiments, the six power devices  1312  that supply 3-phase AC power are comprised within a single power module  240 . As such, the power module(s)  240  operate to provide 3-phase AC power to each stator winding. Additional modules may be used for applications where the stator winding draws more AC power that can be supplied by a set of six power devices  1312 . In some embodiments (as shown in  FIG. 1 , for example) the power modules  240  for power stator windings may be mounted to one or more of the stator winding stacks (shown in  FIGS. 2A and 2B ) to provide a conductive heat path for heat dissipated by the power devices  1312  to be conducted to the housing  110  that is cooled by the MMHS  200  as discussed above. In other embodiments, power modules  240  may be elsewhere positioned within the AEPS  100  where a conductive heat path is present for heat dissipated by the power devices  1312  to be conducted to the housing  110 . 
     The signal electronics of the motor drive  144  comprises a digital signal processing (DSP) controller  1314  that executes sensor-less control and protection algorithms that control firing of the power devices  1312  via gate driver  1316 . The DSP controller  1314  may send and receive control instructions, messages, and other I/O data (such as vie an RS-422 interface) with other components and systems of the vehicle  10  and in some embodiments control operation of the motor drive  144  (and thus control the AEPS  100 ) in response. In some embodiments, the DSP controller  1314  further executes prognostics, diagnostics, and health monitoring. In some embodiments, the processing power of the DSP controller  1314  can be used for heavy implementation of aircraft connectivity with opportunity for implementation of artificial intelligence. As shown in  FIG. 13 , the motor drive  144  may comprise a DC-link/EMI filter  1318 , switching power devices  1312 , voltage and current sensors  1320  and signal control electronics. The components for this high voltage application are discussed in more detail below. 
     Inverter Topology. In some embodiments, wide band gap power devices (such as but not limited to, SiC or Gan MOSFETs or IGBT power devices), may be used to implement the inverter function  1310  of motor drive  144 . The SiC MOSFET has been shown to be much more efficient than Si IGBT due to the significant lower switching losses of the SiC MOSFET. A three-level inverter uses more switches and is more complex, resulting in lower power density of the inverter compared to the two-level inverter. The volume of the three-level inverter is bigger than the volume of the two-level inverter due to space for connecting the additional switch per motor phase. As an example, high voltage devices for 6.5 kV and 10 kV allows use of a two-level inverter in the proposed 5 kV DC link voltage. 
     DC-link Capacitor. In some embodiments, the motor drive  144  includes a DC-link EMI filter  1318 , to filter the heavy high frequency DC-link current harmonics and protecting the high voltage battery  1330 . The capacitors of the filter  1318  are affecting the switching losses of the inverter  1310  helping at the same time the thermal behavior and the efficiency of the system. Two different filter technologies are explored for this application: ceramic and film capacitors. Ceramics are more sensitive to a single point failure, more sensitive to mechanical stress, and more expensive, but offer higher capacitance density due to higher dielectric constant. Going to high DC-link voltage approach helps to reduce thermal stress on capacitor due to lower RMS current that needs to be handled for the same power level and to use lower capacitance value due to higher switching frequency of the SiC MOSFET  1312  components. 
     Gate Driver Design Considerations. The DC/AC converter part (i.e., inverter  1310 ) that is a direct link between the high voltage (high power level) and the low voltage (signal level) electronics is the gate driver  1316 . Additional insulation features between DSP signal level PBA, PWM outputs, and Gate driver BA outputs could be achieved using optical coupling isolation or SiO 2  capacitive isolation technology implemented on a single chip gate driver circuit. The current sensing of motor phase currents may be implemented by using current sensing resistive shunts (such as 200 μohm/12 W as an example) that are equipped with galvanically isolated voltage sensing. 
     Integrated Powertrain (Mechanical &amp; Electrical) In some embodiments, the AEPS  100  comprises a single highly integrated powertrain. The powertrain system includes the three subsystems detailed in the previous sections, the TMS  140 , the electric motor  142 , and the motor drive  144 . The AEPS  100  packaging design has an overall objective to minimize physical size while maximizing thermal efficiency. 
     In some embodiments, an aluminum motor and controller housing  110  direct the incoming air from an axial direction to a radial direction increasing heat rejection. Referring to  FIG. 11 , the heat conduction for the motor stator  174  has two paths. Heat generated in the steel laminations  1120  mainly conducts directly into the back iron  1110  of housing  110  beneath the circumferentially grooved micro-channels  214  of the MMHS  200 . The heat generated in the stator windings  175  mainly conducts axially to the magnesium end bell  172  and to housing  110 . By controlling the manufacturing dimensions of the components and using a thermally conductive pad  1150  between the windings  175  and the end bell  172 , the thermal resistance is minimized. Once the heat from the stator windings  175  is transferred into the end bell  172  and housing  110  it then conducts to the heat exchanger MMHS  200  and dissipated into the environment. Additive manufacturing can be employed to construct the housing to maximize heat transfer, provide structural support and minimize weight. The housing  110 , with the end bell  172 , secure the bearings  173  for the rotor  170  providing structural support. Composite materials may be used in some embodiments for non-conducting elements of motor  142  (such as the rotor  170 ), motor driver  144  or other elements of the AEPS  100  to further minimize weight. 
     Full integration of the motor drive  144  with the electric motor  142  minimizes the overall size and weight. For example, in some embodiments, the power modules  240  of the motor drive  144  are affixed to the AEPS  100  housing beneath circumferentially grooved micro-channels  214  of the MMHS  200 , thus minimizing thermal resistance. Gate driver circuitry, bus bars and capacitors are closely packaged to minimize volume. 
     Example Embodiments 
     Example 1 includes an advanced electric propulsion system, the system comprising: a housing; an electric motor within the housing; a motor drive coupled to the electric motor; a thermal management system that comprises: a manifold-mini-channel heat sink (MMHS) integrated into the housing, wherein the manifold-mini-channel heat sink comprises: an inlet manifold having a plurality of air inlets formed in a front of the housing; a set of plurality of circumferentially grooved micro-channels formed in the housing and coupled to the air inlets and conductively thermally coupled to stator windings of the electric motor; an outlet manifold having a plurality of air outlets formed at a back of the housing and coupled to the set of plurality of circumferentially grooved micro-channels; wherein the electric motor comprises Pseudo-Edge Wound (PEW) stator windings configured to provide a low thermal resistance path from the stator of the electric motor to the housing; wherein the PEW stator windings comprise a high temperature tolerant thermally conductive electrical insulator. 
     Example 2 includes the propulsion system of Example 1, further comprising high thermal conductivity padding positioned between the PEW stator windings and the housing to establish a thermal conductive heat path from the PEW stator windings to the housing. 
     Example 3 includes the propulsion system of any of Examples 1-2, wherein the electric motor comprises an air-cooled permanent magnet (PM) motor coupled to the thermal management system for thermal cooling. 
     Example 4 includes the propulsion system of Example 3, wherein a rotor of the electric motor comprises multiple high mega-gauss oersteds (MGO) magnets contained within a composite sleeve. 
     Example 5 includes the propulsion system of any of Examples 1-4, wherein a rotor of the electric motor comprises a surface permanent magnet rotor with one of: a distributed winding, a concentrated winding, or a fractional slot winding. 
     Example 6 includes the propulsion system of any of Examples 1-5, wherein a rotor of the electric motor comprises an interior permanent magnet rotor with a concentrated winding. 
     Example 7 includes the propulsion system of any of Examples 1-6, wherein the electric motor comprises a multi pole/multi-slot Halbach array electric rotating machine. 
     Example 8 includes the propulsion system of any of Examples 1-7, wherein the motor drive comprises a three-phase multi-level inverter. 
     Example 9 includes the propulsion system of any of Examples 1-8, wherein the motor drive comprises: a plurality of power devices mounted to one or more stator winding stacks of the electric motor, wherein the one or more stator winding stacks provide a conductive heat path for heat dissipated by the plurality of power devices to be conducted to the MMHS integrated into the housing. 
     Example 10 includes the propulsion system of Example 9, wherein the plurality of power devices comprise one of: wide bandgap metal-oxide-semiconductor field-effect transistor (MOSFET) power devices; Silicon Carbide (SiC) MOSFET power devices; Gallium Nitride (GaN) power devices, or Insulated Gate Bipolar Transistor (IGBT) power devices. 
     Example 11 includes the propulsion system of any of Examples 9-10, the motor drive comprising: a digital signal processing (DSP) controller; and a gate driver coupled to the power devices; wherein the DSP controller executes control and protection algorithms that control firing of the power devices via the gate driver. 
     Example 12 includes a vehicle comprising: an electric propulsion system; and a battery; wherein the electric propulsion system comprises: a motor drive coupled to the battery; an electric motor coupled to the motor drive, wherein the motor drive and the electric motor are housed within a housing; a manifold-mini-channel heat sink (MMHS) integrated into the housing; the electric motor comprising Pseudo-Edge Wound (PEW) stator windings configured to provide a low thermal resistance path from a stator of the electric motor to the housing; a high temperature tolerant thermally conductive electrical insulator coating the PEW stator windings 
     Example 13 includes the vehicle of Example 12, the manifold-mini-channel heat sink comprising: an inlet manifold having a plurality of air inlets formed in a front of the housing; a set of plurality of circumferentially grooved micro-channels formed in the housing and coupled to the air inlets and conductively thermally coupled to stator windings of the electric motor; an outlet manifold having a plurality of air outlets formed at a back of the housing and coupled to the set of plurality of circumferentially grooved micro-channels. 
     Example 14 includes the vehicle of Example 13, the electric propulsion system further comprising a fan impeller coupled to a shaft of the electric motor and configured to force an airflow through the plurality of circumferentially grooved micro-channels of the manifold-mini-channel heat sink. 
     Example 15 includes the vehicle of any of Examples 13-14, wherein the motor drive comprises: a plurality of power devices mounted to a surface of the motor drive adjacent to the set of the plurality of circumferentially grooved micro-channels. 
     Example 16 includes the vehicle of any of Examples 12-15, further comprising high thermal conductivity padding positioned between the PEW stator windings and the housing to establish a thermal conductive heat path from the PEW stator windings to the housing. 
     Example 17 includes the vehicle of any of Examples 12-16, wherein the motor drive comprises a three-phase multi-level inverter. 
     Example 18 includes the vehicle of Example 17, wherein the plurality of power devices comprise one of: wide bandgap metal-oxide-semiconductor field-effect transistor (MOSFET) power devices; Silicon Carbide (SiC) MOSFET power devices; Gallium Nitride (GaN) power devices, or Insulated Gate Bipolar Transistor (IGBT) power devices. 
     Example 19 includes the vehicle of any of Examples 17-18, the motor drive comprising: a digital signal processing (DSP) controller; and a gate driver coupled to the plurality of power devices; wherein the DSP controller executes sensor-less control and protection algorithms that control firing of the plurality of power devices via the gate driver. 
     Example 20 includes the vehicle of any of Examples 12-19, further comprising a propeller mounted to a shaft of a rotor of the electric motor at a front of the electric propulsion system. 
     In various alternative embodiments, system and/or device elements, method steps, or example implementations described throughout this disclosure (such the motor drive, DSP controller, gate drive, or any controllers, processors, circuits, or sub-parts thereof, for example) may be implemented at least in part using one or more computer systems, field programmable gate arrays (FPGAs), or similar devices comprising a processor coupled to a memory and executing code to realize those elements, processes, or examples, said code stored on a non-transient hardware data storage device. Therefore, other embodiments of the present disclosure may include elements comprising program instructions resident on computer readable media which when implemented by such computer systems, enable them to implement the embodiments described herein. As used herein, the term “computer readable media” refers to tangible memory storage devices having non-transient physical forms. Such non-transient physical forms may include computer memory devices, such as but not limited to punch cards, magnetic disk or tape, any optical data storage system, flash read only memory (ROM), non-volatile ROM, programmable ROM (PROM), erasable-programmable ROM (E-PROM), random access memory (RAM), or any other form of permanent, semi-permanent, or temporary memory storage system or device having a physical, tangible form. Program instructions include, but are not limited to computer-executable instructions executed by computer system processors and hardware description languages such as Very High Speed Integrated Circuit (VHSIC) Hardware Description Language (VHDL). 
     As used herein, terms such as “power module”, “inverter module”, “sensor”, “controller”, “processor” refer to the names of elements that would be understood by those of skill in the art of avionics and transportation industries and are not used herein as nonce words or nonce terms for the purpose of invoking 35 USC 112(f). 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the presented embodiments. Therefore, it is manifestly intended that embodiments be limited only by the claims and the equivalents thereof.