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Electric Machine Performance Criteria:


With over a century of mature manufacturing practices, design templates, and overarching study, all forms of magnetic electric motors or generators (i.e., electric machines or EM) are well known and simultaneously follow three electromagnetic relationships of physics, which are Ampere Circuital Law, Faraday's Law, and Lorentz Force Relation with the Synchronous Speed of any EM in revolutions per minute (RPM) equal to the product of 60 and the frequency of excitation divided by the number of Magnetic Pole-Pairs.  Following Electric Machine 101, the cost, size, and efficiency of all of today's EM(s) are also bounded by the same laws of physics, by the same principles of speed-frequency-based excitation control, and by the same packaging techniques, such as materials, construction techniques, winding arrangements, cooling methods, etc., regardless of electric machine footprint (e.g., axial flux, radial flux, or transverse flux) or electric machine type (e.g., asynchronous, synchronous, reluctance, or permanent magnet (PM)).[1]


NOTE: A multiphase AC winding set with an independent electrical power port (or armature) is an essential and virtually similar assembly of any EM. Generally located on the stator assembly, all armatures comprise slot channels (or saliency for concentrated windings) for holding the current carrying winding-turns (i.e., magneto-motive-force or MMF) of the multiphase winding set in an orientation that cuts the flux density of the air-gap. With slots increasing the total air-gap area beyond the effective air-gap area (less slots), with air-gap flux density predominantly determined by the same "saturation limit" of the electrical steel core material that is available to all, and using the same packaging techniques also available to all, the stator armature (as designed) predominantly determines the constant-torque rating, the constant-torque speed range, the power rating, the total air-gap area, and more importantly, the physical volume (or size) of all EM(s). Contrary to popular belief, the high coercivity of the rare-earth PM or the potential flux density of the rare-earth PM (or even the higher flux density potential of an electric winding set) is less relevant to the size, cost, and efficiency of the electric machine than the limited saturation properties of the electrical steel core material, which is available to all.


NOTE: As a wound-rotor  doubly-fed synchronous electric machine system (EMS) as only provided by the patented rotor excitation generator (REG) under brushless real time control (BRTC), SYNCHRO-SYM is the only EMS with a truly independent electrical port that brushlessly provides bi-directional power excitation to the rotor multiphase winding set. As a result of not relying on the asynchronous speed between the rotor and stator winding set (i.e., slip) for current induction (i.e., slip-induction), the saliency (i.e., reluctance) of the rotor, or a rotor assembly of permanent magnets (PM), SYNCHRO-SYM is the only EMS with the rotor actively participating in the electromechanical energy conversion process simultaneously with the stator. By assuming the rotor and stator assemblies occupy the same physical volume with a similarly power rating, which is particularly true in an axial-flux (or disk shape) footprint, SYNCHRO-SYM is the only EMS providing double the power density before introducing the same volume reducing packaging techniques that are available to all. For all other electric machine systems that rely on slip-induction, saliency, or PMs, including the Brushless doubly fed induction EMS (BDFM), the wound-rotor doubly-fed induction EMS, the PM EMS, and so on, at least a half portion of the stator volume (for slip-induction) or at least the full portion of the rotor volume (for saliency or PM) does not actively participate in the energy conversion process and as a result, these EMS occupy at least twice the volume as SYNCHRO-SYM for a given power rating and before introducing the same volume reducing packaging techniques that are available to all.


With similar reasoning, other attractive attributes follow:

  • Since half or less of the current flows through the rotor and stator electrical ports for a given power rating, SYNCHRO-SYM shows half the total I2R loss as the other EMS.

  • Since  half the current enters the rotor and stator electrical ports for a given power rating, the electronic controller of SYNCHRO-SYM (BRTC) shows half the total loss as the other EMS.

  • Since the air-gap flux density remains relatively constant with increasing torque current (i.e., symmetrical transformer circuit topology), SYNCHRO-SYM shows significantly higher peak torque density as the other EMS before flux saturation.

  • Since the air-gap flux density remains relatively constant with increasing torque current (i.e., symmetrical transformer circuit topology), the air-gap flux density of SYNCHRO-SYM can be safely designed closer to the saturation flux density of the magnetic core materials as the other EMS.



NOTE: The rotor assembly real-estate of all electric machine systems serves three purposes:


1) Completes the magnetic circuit through the rotor magnetic core;

2) Sets-up the air-gap flux density by focusing the magnetic path to the air-gap;

3) Provides the moveable frame connection to the magnetic repulsion or attraction between the synchronized moving magnet fields of the stator armature and the moving magnetic field of the rotor as a result of rotor reluctance saliency, rotor permanent magnets, or rotor electromagnets;


NOTE: But only the rotor assembly real-estate of SYNCHRO-SYM (i.e., the patented brushless wound-rotor synchronous doubly-fed electric machine) serves a fourth purpose:


4) Actively participates in the energy conversion process by providing an independent rotor armature rotating magnetic field in conjunction with the rotor movement and the stator armature rotating magnetic field.



With all electric machines constrained by the same three laws of electric machine physics, only four enhancements uniquely affect the cost, loss, and size of an electric machine system and determine the electric machine type, such as the singly-fed or doubly-fed asynchronous (i.e., induction) EMS(s), the singly-fed reluctance or synchronous field-wound or PM EMS(s), or the Synchro-Sym EMS (SS-EMS). Using the prevalently applied Induction (or Asynchronous) Electric Machine System (I-EMS) as the comparison baseline, the four unique enhancements are:


Rare-Earth Permanent Magnets (RE-PM)


Electric Machine (EM) Core Material


Superconductor Electromagnets For EMs


Patented Brushless Real Time Control (BRTC)


Considering the electric machine type in accordance to the four unique enhancements, the following analysis shows the cost-performance trade-space is limited to packaging techniques, which are available to all, and as a result, the SS-EMS will always outperform any other EMS using the same packaging techniques:


Transformer Type Electric Machines


Electric Machine Performance Comparison


Electric Machine Cost & Power Density Analysis


Peak Constant Torque Potential of EMS Types


Simple Real Life Comparison




[1] All analysis of this website considers major losses between electric machine contestants to be electrical loss (e.g., I2R) and core loss (e.g., Eddy, Hysteresis). The analysis does not consider stray losses or mechanical losses, which are not associated with any specific electric machine type. Difficult to calculate, stray losses are associated with harmonic content with non-overlapping windings (or non-sinusoidally distributed concentrated windings) showing higher harmonic content but shorter end-turns between slot channels, which shows lower winding resistance and electrical loss. Mechanical loss between electric machines of similar rating and application, which are associated with windage (or friction) losses for instance, can be equalized with similar mechanical considerations. 

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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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