Electric mobility promises to become one of the most successful, emission-free solutions for urban areas, ensuring low pollution, low power consumption, simple use, and fast movement. This is confirmed by the growing interest by manufacturers in projects such as KTM.
Harald Plöckinger, a KTM executive board member for production and business development, recently told motorcyclenews.com: “We believe in electro-mobility on two wheels… We are convinced that electric mobility can succeed in urban areas.”
The new generation of electric scooters offers an interesting solution to the issue of recharging the lithium battery. These e-scooters use the energy of the braking system (regenerative braking), which increases their autonomy. USB connectors allow users to connect their mobile devices. There is also flexible support for iPhones, thanks to an app that allows you to turn your iPhone into a mobile information center.
I'm working on a project for the qualification of high-reliability power MOSFETs. The idea is to use FETs as part of a three-phase H-bridge that serves as the core of the motor drive circuitry. Here is a quick overview of some of the important parts.
The bridge is made of three switch branches (A, B, and C). Each branch has two switches (upper and lower). The output (center point) of each branch drives one phase of the electric motor. The two switches of one branch are never turned on simultaneously; this would open a direct path between the DC voltage source (36V) and the ground. Obviously, this would create a very high disruptive current flow (shoot-through). To give an idea of the magnitude of this current, the mean value of the RDS-ON of the MOSFETS is 10mΩ. The current that would flow into the branch, in case of simultaneous turn on, would be:
This is certainly dangerous current value, even if it is a pulsed current.
The path between the DC voltage source and the ground is closed by two switches belonging to two different branches or phases. Current flows from an upper FET to one phase of the motor. The current flows out of a separate phase to the corresponding lower FET to ground. Within the motor, it flows to the corresponding motor brush, through the commutator, and into one rotor winding. The rotor windings can be thought of as rectangular windings that are free to rotate in a fixed magnetic field provided by permanent magnets.
Note that the construction can be reversed — the windings can be fixed as part of the motor stator, and the permanent magnets can be part of the rotor.
A Hall effect sensor senses the position of the rotor. This sensor is part of the control circuitry that determines when the transistors in the three-phase H-bridge turn on and off.
The Hall effect sensor converts the position of the rotor into a voltage signal that is the input of a microcontroller unit that drives the H-bridge. Here is a view of the motor control subsystem.
The e-scooter is an interesting example of electric mobility. This fast-growing technology is very promising for big companies that produce electric vehicles. Have you ever tried an e-scooter? What do you think of electric mobility? Do you think it is a way to reduce pollution in urban areas?
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