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Detailed SYNCHRO-SYM  Concept Of Operation





                                          FIGURE 1                      FIGURE 2


The “Overview of Research and Development Status of Brushless Doubly-Fed Machine System”) illustrates the evolution of functional control of doubly-fed electric machines, which started with the so-called cascaded electric machine with their rotor shafts connected and running together (as shown in  FIGURE 1). Since both electric machines are position dependent flux rotating transformers, all phase windings are mutually coupled with each other and across the air-gap by slip-induction in accordance to the synchronous speed relation (, where Wr is the electrical angular frequency of the rotor winding excitation, Ws is the electrical angular frequency of the stator winding excitation, and Wm is the mechanical angular frequency of the rotor). With the speed synchronized frequency from the rotor multiphase winding of one multiphase slip ring-brush electric machine exciting the multiphase windings of the second multiphase slipring-brush electric machine through their multiphase slipring-brush assemblies, each electric machine would automatically and sensorlessly remain speed-frequency synchronized, regardless of speed. Because slip induction ceases to exist (or becomes irrelevant) about synchronous speed (Wr = 0), the cascaded electric machine configuration cannot controllably ride through synchronous speed to super-synchronous speed (without extraordinary means, such as brushless real time emulation control (BRTEC), prime mover, etc.) and as a result, the cascaded electric machine cannot legitimately satisfy the criteria of a “practical” doubly-fed electric machine without contiguously and stably operating to twice synchronous speed with constant torque. Furthermore, with equally sized electric machines but without special excitation or phase connections, the torque from each electric machine will equally fight (or oppose) each other. The cascaded electric machine of Figure 1 comprises the complex and sizable real estate of two rotors, two stators, and two multiphase slipring assemblies but may only provide the power of one electric machine under certain operating circumstances.


After years of study, it was learned that dual cascaded electric machines with unlike pole pairs would mitigate torque fighting (and would offset their common synchronous speed to guarantee slip-induction across the speed range) and as a result, the so-called brushless doubly fed induction or reluctance electric machine (BDIM) was born, although torque fighting and mutual cross coupling between the dual armatures of unlike pole pairs could never be completely addressed while operating at their common low frequency. With continued research and development, the BDIM became a dual stator armature of unlike pole-pairs configuration with a magnetic focusing rotor that reduces stator armature cross couple. Although the length is nearly halved, the diameter is nearly doubled.  Still, BDIMs are rising in popularity due to the unique attributes of robustness, reliable operation, ease of maintenance, adjustable power factor, small converter capacity and low cost (compared to singly-fed electric machines).


In accordance with a simple Concept of Operation (CONOPS) of a patented architecture comprising an electric machine circuit (i.e., multiphase wound rotor doubly fed) and brushless, sensor-less and automatic control (i.e., BRTEC as only provided by SYNCHRO-SYM), SYNCHRO-SYM configures one of the dual cascaded electric machines as a “high frequency” position dependent flux transformer with individual MODEMs (or simple high frequency choppers) on each side of the air-gap that modulate and demodulate the individual phase signals with the high frequency carrier. Based on the ratio between the low and high operating frequencies of the cascaded electric machines, physics dictates that the high frequency electric machine entity is extremely more compact with extremely lower mutual inductance (and associated fighting (opposing) torque) compared to the low frequency electric machine entity. For example, in accordance to Faraday’s Law, the product of the core winding turns, the core flux density, the core size/weight and the mutual inductance are inversely proportional to operating frequency and as a result, with 24 kHz excitation (or chopping) frequency for the high frequency electric machine entity and 60Hz excitation frequency for the low frequency electric machine frequency (i.e., ratio of 400 to 1), the mutual inductance (and torque) of the high frequency machine would be reduced by 400 times compared to the low frequency machine and the high frequency core size/weight, winding turns, and flux density would each be typically reduced by nearly 8 times (i.e., one-eighth the size/weight, one-eighth the winding turns, and one-eighth the flux density) but more importantly, the large electric machine pumps out the power of two active winding sets of equal power on the rotor and stator, respectively, or twice the power. With BRTEC (which includes a PDF-HFRT in place of the low power cascaded electric machine and the multiphase slip-ring assembly), the cascaded electric machine of  FIGURE 1 (with the power of one electric machine) becomes  FIGURE 2 with double the power (i.e., dual armature) and virtually half the size. Also, there would never be loss of induction about synchronous speed because of the difference between the low and high operating frequencies; but more importantly, the individual rotor phase winding excitation (or even the level of DC at synchronous speed) would be sensorlessly and automatically (i.e., real time emulation) phase position dependent (as programmed) for precise torque angle control, regardless of position or speed of the rotor shaft, including at synchronous speed. As only provided by BRTEC, SYNCHRO-SYM becomes the only symmetrically stable multiphase wound-rotor “synchronous” doubly-fed electric machine. Already mentioned, the high frequency axial-flux electric machine entity (or BRTEC of SYNCHRO-SYM) is located in the otherwise wasted annulus space of the low frequency axial-flux electric machine for another level of power density.



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Shown As Our Icon: The Radial Flux Prototype of the Advanced Brushless Wound-Rotor Synchronous Doubly-Fed Electric Motor Or Generator System, which predates the axial-flux SS-EMS Technology.