ELECTRIC MOTORS

The first electric-powered vehicles date back to the first half of the 19th century. However, these vehicles were characterised by much lower speeds than vehicles with internal combustion engines could offer. Furthermore, due to the still underdeveloped technology of rechargeable batteries, recharging times were much longer than those of a common refuelling.
Electric motors are essentially composed of two elements, called the 'rotor' and 'stator', each of which is capable of generating a magnetic field. The 'driving torque', which makes the rotary motion of the drive shaft possible, is in fact produced by the interaction of the two generated magnetic fields.
These magnetic fields can be generated by the electric current that powers the rotor and stator. In the case of 'brushless' motors, however, it is only the stator that is powered by the electric current, while the rotor generates its magnetic field by means of two or more permanent magnets.
Electric motors can operate in direct current (DC) or alternating current (AC). Furthermore, these motors can be of the 'synchronous' or 'asynchronous' type.
In synchronous motors, the speed of rotation of the shaft is closely linked to the frequency of the supply voltage, whereas in asynchronous motors, the speed of rotation of the shaft is always lower than the speed of rotation of the magnetic field generated in the stator, where the speed of rotation of the magnetic field is linked to the frequency of the supply voltage.
Most electric vehicles adopt a synchronous, brushless type of motor because it offers the possibility of working at different speeds and with varying loads. In addition, this type of motor usually consumes less energy, which is very often supplied by lithium-ion batteries.
An 'inverter' is used to regulate the speed of the vehicle, which responds to accelerator pedal commands by varying the frequency of the electric current supplying the motor.
In addition to the direct current from the battery, the inverter also receives the accelerator signal and the position of the rotor relative to the stator. From this information, a controller in the inverter determines the orientation to be given to the magnetic field, thus regulating the frequency and intensity of the current to be sent to the stator.
In other words, the inverter manages the power delivery to the vehicle's electric motor.
When, on the other hand, the vehicle is decelerating, energy recovery is made possible thanks to the presence of a 'rectifier' which, working in reverse to the inverter, converts the alternating current produced by the motor into direct current, which goes to recharge the battery.
Thanks to the use of inverters and power electronics, it was also possible to solve a major problem of the synchronous motor: the problem of starting from standstill. In fact, due to inertia, the motor shaft would not be able to follow the rotating magnetic field, remaining stationary.
When starting, therefore, the motor is supplied with direct current, i.e. zero frequency, capable of generating a starting torque capable of starting the motor shaft. Then, by varying the frequency, the desired speed of rotation can be set by working on the frequency of the electric current and the angular speed of the motor shaft in perfect 'synchronism'.
The efficiency of a brushless synchronous motor is higher than that of asynchronous DC motors and can be as high as 98%. These motors are in fact made with a rotor of laminated ferromagnetic material and have a very low rotor inertia, allowing for extremely precise control and good acceleration speed.
The advantages of the brushless synchronous motor include a small footprint, greater mechanical strength and the absence of periodic maintenance. This is essentially due to the absence of brushes. The sparks generated by an electric motor, in fact, wear out the motor itself and produce 'magnetic noise' that can also interfere with radio communications.