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techdirections March 2017 : Page 16

Image courtesy learnengineering.org Figs. 3 and 4—induction motor have rotors, both have stator cores, and both have distributed windings. The magnets within the rotor of the DC brushless motor are replaced with stacked laminations of steel or a squirrel cage rotor in the induction motor. Currents within the stator wind-ings produce a rotating magnetic field and the rotor reacts accordingly by applying a rotational force. Of course there is a lot of engineering that goes into monitoring and ap-plication of current, voltage peak-to-peak, and frequency in these motors to maintain the optimal torque and power at any given speed. This brain is also called an inverter. They actually seem more alike than different, and they are, but the differences are there and they mean a lot depending on what you want the motor to do. In the DC brushless drive the magnetic field produced by the permanent magnets is constant. This puts the motor at a disadvan-tage where peak performance at all times is required. In the induction motor, this mag-netic field is adjustable by changing voltage, frequency, and current to maintain optimal torque and per-formance at all speeds. That being said, the programming in the inverter brain of the induction motor is expo-nentially more complicated. Rare Earth Metals are another dif-ference. The Rare Earth Metals are, in all actuality, not that rare. Some of these metals, like scandium and lanthanum, are just as abundant as nickel, copper, and zinc, but because they are usually accompanied with thorium and uranium, the extraction and refining processes is expensive, lengthy, and toxic. The last of these mining facilities in the United States was closed almost 20 years ago. Since then, China has taken con-trol of the production of rare earth metals, now producing 97% of the world’s supply. The DC brushless motor abso-lutely depends on these and the induction motor uses absolutely none. Opting for copper and steel, the induction motor is controlled by a computer. Tesla Motors was the first to inno-vate with the introduction of the AC good for cost and availability). Now, with all of this information, you would think that the DC brush-less motor would be falling behind, but currently there is no real advan-tage leader between the two. In the DC brushless motor it comes down to efficiency—it is the efficiency king. When this motor is running in its happy place, it can top 96% efficiency turning that applied electricity into electromotive force. When coupled with a multi-speed transmission to keep it in that happy place, it is the efficiency champ. Meanwhile, the induction motor’s big advantage—apart from its sim-Fig. 5—A three-phase power supply provides a rotation magnetic field in an induction motor. induction motor in automobiles and others have followed suit. Recently both BMW and Toyota have started experimentation, and utilization, of the induction motor so they could remove something from their cars that has a market that is both vola-tile and single sourced (probably not plicity and ruggedness—has always been its ability to tolerate a wider range of temperatures and speeds. Providing adequate cooling for the Toyota Prius’ permanent-magnet mo-tor adds significantly to the vehicle’s weight. An induction motor, by contrast, can be cooled passively— 16 tech directions ◆ march 2017

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