One Hundred and Thirty-Six Years of Practical Electric Motor/Generator Evolution and Study:
DC Electric Motor/Generator (circa 1886):
The electromechanically commuted, direct current (DC) motor/generator (or more appropriately, the universal motor/generator), which still has venerable application today, was the first evolution of electric motor/generator technology due to the availability of DC electrical power sources at the time, such as batteries, and the ability to self-start from standstill. The traditional DC motor comprised at least two sliding contacts that would phase energize connected rotor winding sets in synchronism with the speed of the rotor and as a result, effectively produce the essential moving air-gap flux wave in accordance with Lorentz Force Law. Until the first so-called “practical” DC motor/generator was invented in 1886 by Frank Sprague, the DC electric motor/generator was only a scientific curiosity since perhaps 1740. Thomas Edison was a proponent of DC distribution and DC motor/generators (see War of the Currents).
AC Induction Motor (circa 1887):
The alternating current (AC) induction motor/generator was the next evolution of electric motor/generator technology with the advent of multiphase AC distribution and the ability to self-start from standstill. The AC induction motor/generator eliminated the archaic, unreliable, noisy, inefficient, and sparking sliding electromechanical contacts of the traditional DC motor by inducing speed-synchronized multiphase AC onto the rotor winding set by the asynchronous movement (i.e., slip) between the rotor winding set and the energized multiphase AC stator winding set (i.e., slip-induction). The AC induction motor/generator was invented by Tesla in 1887 and adapted to practical 3-phase operation in 1891. Westinghouse was a proponent of multiphase AC distribution and Tesla’s AC Induction Motor (see War of the Currents).
Motor/Generator Control (circa 1960):
Control of electric motors was electromechanical, which consisted of gearboxes, rheostats, gate-controlled mercury arc valve (in rare cases), etc., to match the single steady-state motor speed to the speed of the load, until practical electronic motor control was invented (circa 1960) to vary the speed of the motor to match the speed of the load.
Rare-Earth Permanent Magnet (RE-PM) electric motor/generator (circa 1980s):
The permanent magnet electric motor was an obvious improvement in the electromechanically commutated DC motor by simply replacing the DC field winding on the stator with permanent magnets. In fact, the novel electric motor by Faraday has been reported to have permanent magnets; however, it wasn’t until the advent of high energy product neodymium/dysprosium permanent magnets or RE-PM (circa 1980’s) and practical electronic control for self-start instead of an electromechanical commutator that made RE-PM motors viable in most applications (within a thermal tolerance) but recently, the geopolitical, cartel-controlled expensive, human suffering, and environmental consequences of producing RE-PMs by a global adversary seeking world dominance have recently become obvious. Even today, the RE-PM solution is to mate a gearbox to a high speed and therefore smaller RE-PM motor to only reduce the amount of expensive and delicate RE-PMs but ironically without considering the overall compounding complexity, size, loss, cost, noise, maintenance, and reliability consequences of the gearbox to the entire system of systems, instead of simply optimizing the induction electric motor system, which the RE-PM electric motor system is quickly replacing in at least electric vehicle (EV) applications. Also, the size, loss, and cost of magnetizing MMF, which was the basic reason for migrating to RE-PM motor systems, is ironically being re-introduced into high performance RE-PM motor systems to leverage the coveted attribute of field weakening, which is already inherently available in induction electric motor systems.
Reluctance Electric Motor/Generator (circa 2020):
Like the permanent magnet electric motor/generator, the reluctance electric motor/generator has been studied in the very early days of electric motor evolution. However, it was not until the advent of practical sophisticated electronic control that the reluctance electric machine system with a simple solid rotor of saliencies became a practical reality. Today, reluctance electric machine principles are being applied to at least enhance today’s RE-PM electric motor system in electric vehicles. Otherwise, a viable stand-alone RE-PM free reluctance electric motor alternative to the RE-PM electric machine system for at least propulsion applications is still a rarity because of seemingly unsolvable noise and pulsating torque issues.
The Symmetric Multiphase Wound-Rotor “Synchronous” Doubly-Fed Electric Motor/Generator (circa 2022):
The classic study of electric motors (circa 1889) begins with the symmetric multiphase wound-rotor “synchronous” doubly-fed electric motor/generator with the optimal symmetry of an “active” rotor and stator of directly excited multiphase winding sets but only by hypothesizing the invention of a brushless real-time emulation controller means (BRTEC) that provides stable synchronous operation from sub-synchronous to super-synchronous speeds, including at (or about) synchronous speed where slip-induction ceases to exist. The classic study becomes the follow-on study for all other electric motors/generators by deoptimizing the symmetry of an active rotor and stator, respectively, with the non-optimal asymmetry of a “passive” rotor with RE-PMs, slip-induction dependent windings, reluctance saliencies, or DC field windings, which cannot independently contribute additional active power to the electromechanical energy conversion process as does a directly-excited multiphase winding sets (or active winding sets). With continuously stable synchronous torque control from zero speed to twice synchronous speed or twice the constant-torque speed range (i.e., Maximum Load Speed) for a given continuous torque, air-gap flux density, port voltage, and frequency of excitation (as only provided by BRTEC), the classic study (from circa 1960) verified that the symmetric synchronous electric motor/generator provides twice the power density, half the cost, and half the loss (per unit of power rating) and octuple the peak torque within the same packaging of the asymmetric electric machine system. However, the invention of a practical BRTEC has been a formidable challenge until the patented invention of Frederick Klatt beginning in 1984, who is the sole keeper of the knowledge base with follow-on patents and trade secrets reaching today.
Just the idea of a practical brushless symmetric multiphase wound-rotor “synchronous” doubly-fed electric machine with an active rotor and stator, as only provided by SYNCHRO-SYM, which historically influenced the development of all (e.g., asymmetric) electric machine study, physics, and material, winding, and packaging techniques, has virtually been abandoned because: a) the essential invention of a practical brushless BRTEC from academia or industry has never materialized, 2) the optimal symmetric multiphase wound-rotor “synchronous” doubly-fed electric machine is subconsciously confused with the archaic and non-optimal “asymmetric” multiphase wound-rotor “slip-induction or asynchronous” doubly-fed electric machine system with an active stator, a passive rotor, and a multiphase slip-ring assembly, 3) the massive investment inertia in the asymmetric RE-PM electric motor/generator system industry has insidiously led to the cartel-control of RE-PM production and subsequently, all electric motor manufacture, academia research, and innovation acceptance by a global adversary seeking world dominance, and 4) the unconventional wisdom of a highly integral, synergetic electronic controlled (i.e., BRTEC) motor system, as only provided by SYNCHRO-SYM, challenges well established conventional wisdom of the remotely componentized electronic controller and motor/generator system, although recent advancements in EV propulsion is appropriately changing this wisdom.