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NOTE: The symmetrical relationships of the multiphase wound-rotor synchronous doubly-fed electric machine (as only provided by SYNCHRO-SYM) is the classic classroom textbook study for all electric machines, such as permanent magnet (PM) electric machines, induction electric machines, reluctance electric machines, etc.,  by de-optimizing the symmetrical relationships (and the performance) with the asymmetry of PM, induction, or reluctance.  


NOTE: Packaging, winding, and thermo management techniques consume significant size and cost of any electric machine because of the large dynamic and magnetic forces exerted on the frame and bearings and the thermo dissipation of the active multiphase winding set(s) and harmonics found in all electric machines, including PM electric machines.


NOTE: Only a multiphase winding set excited with multiphase alternating current (AC) develops a moving (or rotating) magnetic field relative to its frame and accordingly, only an AC multiphase winding set "actively" contributes to the electromechanical power conversion (i.e., electrical to mechanical power or vice versa).  All electric machines must comprise at least one "directly" excited multiphase (or active) winding set (i.e., singly-fed), which is generally located on the stator for connection convenience, or at most two active winding sets (i.e., doubly-fed) without duplicating electric machine circuit topology.


NOTE: The power rating of any electric machine is determined by the sum of the power ratings of all active winding sets. A multiphase winding set that is "indirectly" excited via slip-induction, such as the rotor squirrel cage winding set of an induction machine, is actually powered by another active winding set (such as the stator active winding set of a "singly fed" induction electric machine) and as a result, the squirrel cage winding set is effectively an extension of the powering active winding set, which must be power rated for both.


NOTE: With superconducting electric machines as the exception, a reasonable design goal of any electric machine is to design to the flux density saturation limit of the core material, such as at the slots for holding the windings or PMs where concentration of flux is highest, regardless of the flux density potential of PM coercivity or the higher flux density potential of winding MMF. Since flux density is proportional to the vector sum of all flux producing components, such as by PM coercivity or winding MMF, asymmetric electric machines, such as singly fed synchronous (e.g., PM and field wound)  and singly fed and doubly fed induction electric machines, must lower the rated steady state flux density design to compensate for the combined peak flux with torque MMF.  As provided by SYNCHRO-SYM, only symmetric wound rotor "synchronous" doubly fed electric machines with a truly dual ported transformer circuit topology provided by the rotor and stator winding sets, which in accordance with physics, air-gap flux density remains constant with increasing active current (or torque current for electric machines) beyond magnetizing MMF, can be designed closer to the flux density saturation limit of the core material for another level of power density. 


NOTE: Electric machines with a dual ported primary and secondary winding transformer circuit topology (asymmetric or symmetric), such as single and doubly fed "induction" electric machines, show higher peak torque potential (e.g., 2-3 times rated torque) than electric machines that are wholly asymmetric (e.g., no rotor or secondary multiphase winding set), such as electric machines with PMs or saliencies (reluctance) replacing the secondary winding set. Universal electric machines, such as the electromechanically commutated DC electric machine, show peak torque up to 5 times rated torque. Only SYNCHRO-SYM with a symmetric (or dual ported) transformer circuit topology shows factors of higher peak torque potential (e.g., 8 times rated torque). See electric machine torque 101 whitepaper for details.


NOTE: Generally located on the rotor, permanent magnets (PM) do not "actively" contribute to electromechanical power conversion and as a result, PMs are "passive" devices (e.g., PMs have no electrical power port to contribute active power to the electromechanical power conversion). In reality, the "active" multiphase winding set required by all electric machines (that is generally located on the stator for electrical connection convenience) determines the torque and power rating of any optimally designed electric machine, including PM electric machines, with the high energy product of the very expensive rare earth (RE) PMs only determining the ease of setting up the air-gap flux density (without considering the addition of field weakening).  When optimally designed, the effective air-gap area and the following size of the active multiphase winding set (per unit power rating) are determined by the air-gap flux density, which is design constrained by the flux saturation limit of the magnetic core and core material, such as laminated electrical steel, instead of the high energy product of RE-PMs or the even higher peak magneto-motive-force (MMF) potential of a winding compensated for heat dissipation (after all it takes winding MMF to actually magnetize or demagnetize a PM). (Note: Superconductor electric machines are excluded from this discussion, although SYNCHRO-SYM Technologies can bring superconductor electric machines closer to practicality).  The high energy product of RE-PMs does show smaller size and support a deeper air gap (for instance, 1 mm vs 2 mm) but electromagnetic windings conveniently provide field weakening for preferred extended speed range. In consideration, the size of the stator assembly (with the active multiphase winding set) determines the size of the rotor body and together, the rotor and stator bodies with robust structural frames overwhelmingly determine the size of the electric machine.  It follows that all optimally designed electric machines with similar air-gap flux density will show similar "rated" torque, similar effective air-gap area, and similar size of active winding sets. As supporting evidence, today’s specialty induction electric machines (with optimized copper rotor and materials) are achieving similar size and efficiency for a given rated torque as optimally designed RE-PM electric machines (but without the extravagant cost and manufacturing issues of RE-PMs).


NOTE: Unlike winding magnetizing MMF, the passive, delicate, expensive, environmentally unfriendly, and cartel controlled permanent magnets, such as rare earth permanent magnets (RE-PMs), show degrading performance over normal operational life, such as demagnetization, which accelerates during peak torque stress, such as experienced in an electric vehicle application. More daunting, the globally minable supply of RE-PM materials may not meet the expected global demand (even with difficult recycling), if RE-PM electric machines become the electric machine of choice. In consideration, comparable alternatives are being aggressively researched. Fully Electromagnetic (i.e., no permanent magnets), only SYNCHRO-SYM provides a better alternative already.


NOTE: "Induction (or asynchronous)" electric machines (doubly fed or singly fed) solely operate on slip-induction, which is current induction into the rotor winding set due to the asynchronous speed (or slip) between the rotor and excited stator winding sets, and as a result, induction electric machines cannot operate at synchronous speed, where induction ceases to exist.  In contrast, traditional "synchronous" synchronous electric machines (or synchronous doubly-fed as only provided by SYNCHRO-SYM) do not rely on slip-induction for operation and as a result, synchronous electric machines can operate at synchronous speed. Also, synchronous electric machines allow a selectable but fixed magnetic field position (i.e., torque angle) between the synchronized rotor and stator rotating magnetic fields but in contrast, the torque angle of induction electric machine is stochastically the result of changing rotor time constant and rotor slip-induction due to shaft perturbations. Consequently for both induction and traditional synchronous singly-fed electric machines, delays in measurement and excitation synthesis by conventional state of art offline processing always contribute to instability issues, particularly at speeds or frequency with large time constants, such as at low speeds.   With the contrasting provisions of BRTEC, SYNCHRO-SYM is a synchronous doubly fed electric machine, which automatically phase locks the magnetic flux to a known and selectable phase position (without regard to speed), eliminates reliance on slip-induction for rotor magnetic field production, and does not have processing delays (real time) or shallow time constant signal measurement issues.


NOTE: "Synchronous doubly fed" electric machines (as only provided by SYNCHRO-SYM) uniquely show the performance and power of two active multiphase winding sets within the same package, which equates to twice the power density.


NOTE: Without considering the formidable issues of cryogenics, superconductor electric machines achieve tens of times more winding MMF (and resulting air gap flux density regardless of core saturation) than conventional copper windings or PM coercivity. Without providing details, SYNCHRO-SYM Technologies can bring superconductor electric machines closer to practical reality.


NOTE: Without actively contributing (or adding) to electromechanical conversion power, the core or permanent magnet material found in all conventional electric machines are “passive” materials, regardless of their performance improving qualities, such as directing the magnetic path to the air-gap by the high permeability of the core material. Note: Even the “coreless” or yokeless terms seem to suggest there is no core material but in fact, the magnetic path is routed through the PM core material, which exhibits the density of steel but the permeability of air, and the back-iron with the density and permeability of electrical steel.


The high peak torque density of SYNCHRO-SYM is essential for direct drive (transmission-less) drive-trains for electric vehicles, which are simpler, more reliable, less costly, lower maintenance, and most likely smaller than an electric motor and transmission combination. For instance, Rimac is selling a complete motor/transmission package for electric vehicles because of limited peak torque density of their RE-PM electric machine. For utility vehicles (without performance suspension), SYNCHRO-SYM is the best electric machine alternative for in-wheel motor applications, such as presently provided by Protean and Elaphe.


NOTE: Compared to the common radial flux form of electric machine, axial flux electric machines are known to use up to 10-20% less copper and steel than radial flux electric machines while providing higher efficiency and torque (see axial-flux whitepaper with MAGNAX marketing remarks).  As a fully electromagnetic electric machine (e.g., no permanent magnets), SYNCHRO-SYM most conveniently accommodates the axial flux form of electric machine.



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