In AC, as the name states the electrons flow direction is alternated/changed periodically reversing the polarity of the circuit. By connecting an oscilloscope to an AC circuit, we can see its waveform. As shown in this graphic, this would be one of the waveforms we expect on an AC circuit and we can see in fact that the voltage is reversed throughout time hitting its maximum and minimum in every completed period.
The first ever AC motor was created by Nikola Tesla. After dropping out of university and gambling his fortune away, Thomas Edison hired Nikola Tesla to work for him. Tesla caught Edison´s attention with his incredible work and offered him 50.000$ if he could improve Edison´s DC dynamos design. At the time, Alternate Current was believed to be extremely dangerous to handle, and therefore he turned down his offer. Tesla moved on and not long after this happened, he took his design to the American Institute of Electrical Engineers and George Westinghouse was intrigued and approached Tesla offering him 65.000$ for his patent, 15.000$ more than what he had asked for. With this, Westinghouse was one of the first pioneers of alternating current systems.
This experiment showed that there is a connection between electricity and magnetism. He proved this by showing that whenever a current was switched on through a wire, it made a compass needle turn so that it would be positioned perpendicularly to the wire. This would prove that the current had produced a magnetic field strong enough to cause the compass needle to turn.
Faraday´s First Law on electromagnetic induction states that any changes in the magnetic field of a coil of wire will cause an electromotive force to be induced in the coil. This force is called induced EMF and if the conductor circuit is closed, the current will also circulate through the circuit and this current is called induced current.
Faraday´s Second Law on electromagnetic induction states that the magnitude of emf induced in the coil is equal to the rate of flux change that links with the coil. The flux linkage of the coil is the product of the number of turns in the coil and the flux associated with the coil.
Lenz's law states that the direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field that produced it.
The stator is the stationary part of the motor is kept inside the frame. It is made of ferromagnetic sheets which have gaps on them. These gaps would be where a set of 3 coils stays. All the sets are then connected to each other by an AC current. Each set is called a phase which makes the induction motor of a Tesla a 3-phase induction motor. Every phase has a 120º rotation angle from each other, each one creating a magnetic field. Since the motor is powered by alternating current, the magnetic field created inside each phase will periodically change its polarity. Furthermore, as each phase won't change polarity at the same time, it will create a rotating magnetic field (RMF), which will continue to rotate provided that we have an alternating current flowing through the three phases.
The rotor is the physical rotating part of the motor being connected to the motor axis. It is kept inside the stator and it is made of good conductors.
The rotor is inside the stator which means that the rotor will be affected by the rotating magnetic field created by the stator, and with this an electric current flowing through the conductive bars is created. Since we have an alternating current flowing through the rotor, it will create a rotating magnetic field on the rotor that has a reverse polarity to the RMF of the stator. Since the magnetic fields will have opposite polarities the RMF of the rotor will try to catch up with the rotating magnetic field of the stator, however this will be virtually impossible making this an asynchronous motor.On an asynchronous motor the rotor speed will always lag behind the RMF: this difference is called slip. Since the rotor speed is directly proportional to the RMF speed if the frequency of the AC current increases the overall speed of the motor would increase as well.
The motor gets its energy by the lithium ion batteries, but like all batteries it stores DC power and the motor uses AC. So, in order for the battery to supply the motor it is used an inverter. Normally an inverter just transforms DC to AC but on an electric car the inverter is also connected to the motor controller. Together they act as the brain of the car since it is with the motor controller that we can control the frequency of the alternating current that reaches the stator, which leads to the increase or decrease of the speed of the motor. In an electric car, Induction motors are overall very efficient but no machine can be 100% efficient.So, engineers had to think in a way to make the motor even more reliable. The solution for this is when the car is not accelerating the kinetic energy that would be lost is converted to energy by transforming the induction motor on an induction generator. On an induction generator the rules are basically the same but now the RMF speed would actually be lower than the rotor speed. The energy is then converted to DC and stored on the battery this all process is called regenerative breaking
Being simple, reliable and cost-efficient, induction motors are used on various applications being even found on households’ appliances. Induction motors have a big impact on industries too, with about 70% to 80% of all industries energy being transformed into movement by induction motors. Apart from this, induction motors as a whole, are maintenance free and very durable, which lead to their wide use, since their invention to the modern times
