On some conventional electric vehicles (EV), there is still mechanical braking systems. In these types of braking systems, the kinetic energy of the vehicle is wasted as heat through the braking pads. Trying to achieve a higher battery efficiency the efforts are focused on reusing the braking energy wasted (Regenerative Braking). For this it’s necessary a DC motor, accompanied by an electric traction circuit, a battery system along with a converter to make an interface with the DC Bus and the respective charging topology from the electrical grid.

The search for articles in this area was based on DC motors and their most used topologies, battery charging methods and respective converters and G2V/V2G Grid-to-

Vehicle/Vehicle-to-Grid circuits. The optimal approach to this problem is dividing the system in the 3 modules referred before, DC Motors, EV Batteries and G2V/V2G, then research every topic individually, comparing different topologies and solutions.

The main point of focus of this dissertation is the DC Motors as they are the most important module. There two types of DC motors, BLDC (Brush-less DC Motor) and Brushed motor, they have very different characteristics in terms of complexity, efficiency, price and weight and they also have distinct topologies and control methods.

The advantages of the Brushed motor is its lower complexity, fewer components, thus reduced price and weight/size when compared with BLDC motors, on another hand they operate on the basis of brushes which need to be replaced from time to time, while on BLDC the maintenance is practically not necessary. The advantages of the BLDC motors are low maintenance, as referred, better efficiency at higher speeds and have more optimal current waves and stable operation, but they

need complex controllers which sometimes exceeds the size of the motor and even its price. When it comes to the topologies of each motor's controller, without going too deep, there is the VSI (Voltage Source Inverter) used for BLDC which need Hall effect sensors to determine the position of the rotor and the H-Bridge circuit for the brushed motors that can control the speed directly by the DC voltage or torque based on the current.

For the EV Batteries the most common types are the Lithium-Ion and the Lead-Acid. The Lithium-Ion were developed recently and even though they are an expensive solution on acquisition they have a lot of advantages, such as high longevity, reduced environment impact, fast charging and higher energy density.

The Lead-Acid batteries, have has main advantage a low initial cost, but they have many downsides such as high cost on a long term, few life cycles, low energy density, high weight, slow charging and a big environment impact

To make the interface between the battery and the DC Bus its necessary to use a DC-DC converter, in this case the converter needs to be bidirectional so the battery can charge and discharge. The most used DC converters are the Buck-Boost and the Dual Active Bridge (DAB), and between distinct characteristics the biggest differences are the isolation provided by a transformer on the DAB topology, versus the simple but reliable Buck-Boost circuit.

On the V2G/G2V module there is two methods, the charging circuit can be, which leads to different topologies and characteristics. The Off-Board is known as fast DC charger, in which the source is DC voltage that directly charges the batteries. The On-Board method has an AC-DC inverter inside of the vehicle as its source comes from single-phase or 3-phase electrical grid. It’s possible to send back energy to the grid with benefits like better electric efficiency, and more stable energy consumption of an installation.