SYNCHRO-SYM Technologies


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                                          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 beginning with the rotor shafts  of two so-called multiphase slip-ring assembly (e.g., doubly fed) electric machines connected in cascade and running together (as shown in  FIGURE 1). Since both electric machines are low slip-frequency, position dependent flux rotating transformers, all phase windings of each electric machine 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 rotor multiphase windings of the second multiphase slip-ring-brush electric machine through their multiphase slip-ring-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 help, etc.), and as a result, the cascaded electric machine, which relies exclusively on slip-induction, cannot legitimately satisfy the criteria of a “practical” doubly-fed electric machine without contiguously and stably operating from sub-synchronous to super-synchronous speed, including synchronous speed, with constant controllable torque. Furthermore, with equally sized electric machines that are without special excitation or phase connections, the torque from each equally power and frequency (or MMF) rated electric machine would oppose each other. Furthermore, the cascaded electric machine of Figure 1 comprises the complexity and sizable real estate of two rotors, two stators, and two multiphase slip-ring 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 residing on the stator could never be completely addressed while operating at their common low excitation frequencies and speeds. With continued research and development, the BDIM became a dual stator armature of unlike pole-pairs configuration with a magnetic focusing rotor that reduces the cross coupling between the dual stator armatures. Although the length of the cascaded electric machine of Figure 1 is nearly halved, the diameter of two active winding sets is nearly doubled.  Still, the BDIM is rising in popularity due to the unique attributes of doubly fed electric machines (compared to singly-fed electric machines), such as robustness, reliable operation, ease of maintenance, adjustable power factor (e.g., leading, lagging, or unity), small converter capacity, and low cost.


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, bi-directional, sensor-less and automatic control (i.e., BRTEC), 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 bi-directional electronic choppers) on each side of the air-gap that modulate and demodulate the high frequency carrier of the individual phase signals in either direction. Conveniently, both the utility power and windings are bi-directionally driven with pure sinusoidal waveforms. 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 torque compared to the low frequency torque producing 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 the operating frequency and as a result, with 24 kHz excitation (or chopping) frequency (as an example) 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 equally rated active winding sets on the rotor and stator, respectively, or twice the power. With BRTEC (which includes a position dependent flux high frequency rotating transformer 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., power of dual armatures) and virtually half the size. Also, there would never be loss of (or reliance on) slip-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 the position or speed of the rotor shaft, including at synchronous speed. As only provided by BRTEC, SYNCHRO-SYM becomes the only practical symmetrically stable multiphase wound-rotor “synchronous” doubly-fed electric machine. In an axial-flux form, the high frequency axial-flux electric machine entity (or the 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.


Note: Reluctance saliencies, DC field windings, or permanent magnets occupy precious rotor real estate without incrementally contributing to electromechanical power production. Worst, squirrel cage induction windings are completely dependent on mutual slip-induction (or speed-based frequency induction) with the stator armature. Any active or passive power induced onto the rotor multiphase winding set (e.g., squirrel cage winding) of an induction electric machine is solely provided by the stator armature (e.g., no direct electrical port terminal to the rotor winding set) and as a result, the rotor winding set is simply a mutually coupled extension of the stator armature (as is any single coil in a winding of coils), which increases the power size and capacity of the stator armature, and should never be considered another armature; hence, an armature requires an independent bidirectional power port for incremental power excitation.


Detailed Concept Of Operation


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Why The Name: SYNCHRO-SYM?


SYNCHRO-SYM is the only wound-rotor doubly-fed electric machine system that never relies on speed-based induction (i.e., slip-induction) for operation at any speed and the synchronized rotating magnetic fields of the stator and rotor are phase fixed (as selected), regardless of speed and position of shaft.  As a result, SYNCHRO-SYM is a "synchronous" doubly-fed electric machine;


SYNCHRO-SYM is the only wound-rotor doubly-fed electric machine system that has brushless real time emulation control (BRTEC) and as a result, is "symmetrically stable" as a motor or generator;


SYNCHRO-SYM is the only wound-rotor doubly-fed electric machine system without discontinuity at synchronous speed and as a result, Synchro-Sym is a true "symmetrical" (or dual-ported) transformer topology.









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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.