Let's clarify the electric motor. How it's made and how works the most common electric motor: the synchronous motor IPM.
How is an EV electric motor made? How an electric motor works? These are questions that often go round in the head of those interested in understanding more of how the propulsion of a battery-powered vehicle works. How are things really about transmission? Let's try to understand how the propulsion of an electric vehicle occurs where traction is usually provided by an electric motor.
To make it work, which technology is used between “asynchronous”, “synchronous”, direct or alternating current, “single-phase”, “three-phase” and step-by-step? Let's say that the electric motor has a much simpler structure than an internal combustion, petrol or diesel. An electric motor is essentially composed of two parts: the stator and the rotor which generate two magnetic fields whose interaction produces the driving torque. To generate the magnetic fields, the rotor and stator are both powered by current, except in brushless motors where only the stator is powered by the current. It's curious that the stator of the AC three-phase motor and that of the brushless DC synchronous motor are practically identical. Both have three sets of distributed windings that are inserted inside the stator core.
The main difference between the two electric motors is the rotor. Both of these motors use the inverter necessary for the generation of three-phase current to work: they differ in the rotor and obviously in the operating logic of the inverter itself which must drive the current in a different way.
In the synchronous motor, the rotation speed of the axis is rigidly bound to the frequency of the supply voltage while in the asynchronous motor the rotation speed of the axis is always less than the rotation speed of the rotating field linked to the frequency of the supply voltage. Most EV use permanent magnet synchronous motors because they have to work with varying loads at different speeds and consume less current. The motor used on EVs is usually a synchronous motor powered by direct current from lithium batteries called "brushless" because it is brushless: it has a permanent magnet rotor (magnet type) and a current-powered stator that generates a rotating magnetic field.
The efficiency of the brushless permanent magnet synchronous motor is higher than that of asynchronous direct current motors and even reaches 98%. These motors made with a rotor of laminated ferromagnetic material have a very low rotor inertia which allows for extremely precise control and rapid acceleration.
On the efficiency issue this motor is better because it can operate with a unit power factor, while a current fed rotor motor reaches 85 percent: the peak point energy efficiency for a brushless DC unit will typically be some percentage points higher than an induction motor.
The operation of the synchronous motor is managed through the inverter. While the motor rotates, dedicated electronics are used to generate the rotation of the magnetic field in the stator, namely the inverter, with some power transistors on board driven by a microcontroller. The inverter receives, in addition to the direct DC current from the battery, the signal from the accelerator pedal and the position of the rotor with respect to the stator on the basis of which it determines the orientation to be given to the magnetic field. With these parameters, the inverter adjusts the frequency and intensity of the current to be sent to the stator.
The advantages of the brusheless synchronous motor are greater mechanical resistance, absence of sparks and zero periodic maintenance. This is essentially due to the absence of brushes, the weak point of an electric motor because they generate sparks, wear out and produce "magnetic noise" which can also cause interference in radio communications These motors are indestructible, can run for decades and travel millions of miles without the slightest wear. Among the pros to add also the compactness with a limited footprint and an optimal efficiency as no electricity is consumed to generate the magnetic field on the rotor.
The main disadvantage of the brushless brushless motor compared to other electric motors is the cost. There are essentially two reasons that make it rise: the presence of an advanced electronic device such as the inverter, which is essential to manage its operation, and the cost of manufacturing the rotor with its permanent magnets. On brush motors, power (and speed) management is entrusted to a simple, inefficient and equally economical potentiometer.
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