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Following the same basic three laws of physics, all magnetic rotating or linear moving electric motors/generators (i.e., electric machines) are operationally simple to understand. As children, we were familiar with the phenomena of pulling and pushing a permanent magnet placed on top of a board by manually moving a magnet under the board by our hand with no physical contact between the magnets. Obviously, this “magnetic” motor gets its “active” power from the physical effort provided by our hand because after all, permanent magnets have no electrical or mechanical port for supplying or removing power (or for changing their persistent magnetic field) and as a result, permanent magnets only “passively” participate in the energy conversion process by simply providing a fixed persistent magnet field for attraction.


Since only a multiphase AC winding with an independent port for electrical power excitation, called an armature, causes a moving or rotating magnetic field that consumes or produces power by actively participating in the electromechanical energy conversion (just as a moving hand produced or consumed power in the magnetic motor example just described), all electromagnetic motors or generators need at least one armature on either the rotor or stator assembly with the other assembly having another magnetic assembly, such as : 1) a DC electromagnet, which is not an armature (i.e., multiphase AC electromagnet) and as a result, could be simply replaced with a passive permanent magnet; 2) a squirrel cage winding, which has no independent AC multiphase electrical port but instead compounds the armature power with electrical induction provided by the asynchronous speed slip between the rotor and stator windings; 3) an arrangement of salient of poles, which have no AC electrical port but instead, change the reluctance of the magnetic path with movement; or 4) another armature (i.e., dual armature or doubly-fed). With a single armature, the electric machine is singly-fed and with dual armatures, which is the most possible without duplicating the electric machine circuit topology, the electric machine is doubly-fed. In both cases, the active power rating of the electric machine is the sum of the power rating of all armatures (with two armatures being the most possible).  If the electric machine relies entirely on current induction for practical operation, the electric machine is a singly-fed (singly armature) or doubly-fed (dual armature) induction or asynchronous electric machine and if the electric machine does not rely on induction for practical operation (but may experience induction), the electric machine is a singly-fed or doubly-fed synchronous electric machine.  Reasonably assuming the armature is stationed on the stator assembly, which is generally the case to simplify electrical connection to the armature, and the permanent magnets, DC electromagnet, squirrel cage windings, saliency, or even another armature are stationed on the rotor assembly, the magnetic poles of the stator pulls or pushes along the magnetic poles of the rotor (or vice versa). Considering the simple magnetic motor example described earlier, an magnetic electric motor or generator (i.e., electric machine) must have moving magnetic fields on the rotor and stator, respectively, with their speed synchronized for at least average force (moving) or torque (rotating) production.


Although the operation of electric machines as just described is simple to understand, synchronizing the moving magnetic field of the armature assembly with the moving magnetic field of the “other assembly” for practical operation is complex.  Electronically controlling the multiphase AC excitation of the armature is the only practical means of synchronizing the moving magnetic fields because electronic measurement, such as magnetic speed and phase, and excitation response, such as frequency and phase, is quick enough to mitigate some instability but instantaneous (or real time) control is the Holy Grail. With a second armature (e.g., doubly-fed), excitation control has another level of complexity because synchronization must also consider the rotating magnetic field of the stator armature in conjunction with the rotating magnetic field of the other armature and of course, the speed of the rotor movement. In the case of the wound-rotor doubly-fed electric machine with an armature on the rotor and stator, respectively, doubly-fed control is further complicated by requiring a multiphase AC electrical connection (multiphase slip-ring assembly) to the rotating (rotor) armature.


Until the recent advent of the patented SYNCHRO-SYM technology with brushless real time control, the venerable electromechanically commutated (or so-called DC or single phase AC universal) electric machine was the first practical controllable electric machine and by incorporating brushes sliding across a bunch of electromechanical switches (i.e., electromechanical commutator) that energize specific windings in absolute synchronism with rotation, the so-called universal electric machine was the only electric machine system providing real time control.  Due to the poor efficiency, reliability, and high maintenance of the electromechanical commutator, the universal electric machine system with real time control is ironically being replaced with non-real time controlled electric machine systems utilizing derivatives of flux vector control (FOC), such as reluctance, PM, Induction, etc. electric machine systems, except in the most stringent precision controlled applications.


[Just The Facts For Comparisons]

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Note: The Radial Flux prototyping of the Advanced Brushless Wound-Rotor Synchronous Doubly-Fed Electric Motor Or Generator System is shown as our Icon, which predates the axial-flux SS-EMS Technology.


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