Tesla Model 3 Motor Best Engineering
Tesla motors engineers made a stunning design choice when they developed the tesla model 3they abandoned the conventionally used and well-proven induction motors and replaced them with a new kind of motor the IPMsynRM
these motors have a totally different design making use of both magnetic and reluctance action the big news is that tesla motors have started replacing the induction motors in their model S with these new motors as well how do these motors work what’s so special about the IPMsynRM let’s explore to get a clear answer we first need to understand the model s’s electric motor which is an induction motor clearly as you can see the rotating part here is an arrangement of conducting bars.
Alternating currents from the battery packs flow into the motor’s outer windings this will create a rotating magnetic field the fluctuating field interacts with the rotor bars and generates electromotive forces on them which in turn generates currents in the rotor bars the interaction between these induced currents and the RMF imposes a force on the rotor bars and the rotor starts to spin these motors are efficient but not up to the mark, for instance, long drives at cruise speed lose 3% to 4% of energy to generate currents in the rotor bars which is definitely not efficient moreover for an automobile the most crucial performance parameter is its starting torque even though the induction motors have a better starting torque than ic engines there is a motor technology that provides even better starting torque from the same motor volume of motor technology based on permanent magnets.
The pm motors work on the basis of the attraction between two magnetic fields they produce a good starting torque when you operate them using a controller and they do not experience energy loss in the rotor an efficient permanent magnet rotor can be made by placing permanent magnets around a solid iron cylinder so why not replace the squirrel cage type rotor with a permanent magnet one these four permanent magnets produce a combined magnetic field the shape of this combined field is quite important for further analysis with a little intuition the combined magnetic field of these four magnets can be plotted as shown.
now we need to analyze the interaction between the RMF and the combined magnetic field analyzing force interaction between two magnetic fields is simple just observe how the south and north poles interact with each other for simplification let’s hide the magnetic field produced by the permanent magnets and keep only the north and south poles the force interactions between the different poles are shown here.
at this angle, the RMF definitely produces a torque on the rotor now let’s rotate the RMF to 45 degrees interestingly at this angle the rotor experiences maximum torque because the attractive and repulsive forces are passing almost tangential to the rotor and they are producing the torques in the same direction ( which is good for support ) using this simple ball analogy the reason behind why tangential forces produce maximum torque is clear thus this is the perfect angle to start your electric car maintaining this angle or further angle regulation is the smart controller’s job in this design the rotor has no induced current which reduces the input energy required and leads to higher efficiencies than those of induction motors along with higher starting torque the pm motor also runs at synchronous speeds but the search for the perfect electric motor is not over yet a permanent magnet motor produces good torque when you start the car or ride up a hill.
however, when the car cruises down the road at high speeds permanent magnet motors have terrible performance the villain here is the back emf the magnetic field lines produced with the aid of the permanent magnets hyperlink with the stator windings and generate an emf there this emf is known as lower back emf which is, in reality, a reverse voltage to the stator’s furnish voltage the greater the rotor velocity the extra it produces lower back emf this phenomenon is why the permanent motors perform terribly in high-speed applications moreover these high strength magnets also result in magnetic eddy current losses which increases the heat in the machine.
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