Battery Electric Vehicles (BEV), compared to conventional internal combustion engine (ICE) vehicles, are quite simple and easy to use. The simplest powertrain architecture consists of a high voltage battery, an electric motor with electronic power controller and a single speed gearbox. BEVs are also called pure electric vehiclesin order to distinguish them from Hybrid Electric Vehicles (HEV)which have a hybrid powertrain (internal combustion engine plus electric motor).
In a BEV, propulsion relies exclusively on the electrical energy stored in the high-voltage battery.
Battery electric vehicles are increasing their market share as they are the most viable route to a clean and efficient transportation system. Compared to ICE vehicles, the most important advantages of a BEV are the high overall efficiency, reliability and relatively low cost of the electric motor. The main disadvantage is the low energy density of the high voltage battery.
The interval of an electric vehicle is the maximum distance that can be traveled with a “full” battery. Take into account that the range is given for a particular certification test cycle (NEDC, FTP, etc.)
Based on range and top speed and acceleration performance, battery electric vehicles can be categorized as:
- local electric vehicles: small vehicles, very low autonomy (less than 25 km)
- city electric vehicles: small vehicles, low autonomy (less than 50 km)
- high performance battery electric vehicles: these are the equivalent of classic passenger vehicles, with a range of between 100 and 600 km
In this article, we are going to focus on full-performance (passenger) Battery Electric Vehicles (BEVs).
Most BEV architecture has the powertrain on the front axle and the high voltage battery in the floor, between the front and rear axle. This configuration provides plenty of volume for passenger space and trunk/trunk.
The high voltage battery, being the heaviest electrical component of the vehicle, is positioned very low, in the body floor. This gives another advantage, a very low center of gravity, which improves the overall stability of the vehicle.
High-performance BEVs, such as Tesla Model S, has two electric motors for traction, one on the front axle, the second on the rear axle. Both motors have their own power electronics controllers. This configuration provides all-wheel drive (AWD) capabilities as well as very good performance in terms of acceleration and driving dynamics (torque vectoring).
High-performance BEVs, such as Rimac Concept_A, takes performance and driving dynamics to an extreme level. The powertrain consists of 4 motors in total, one for each wheel. Each engine has its own gearbox, at the front there are single speed gearboxes while at the rear there are two speed gearboxes with carbon fiber clutches. The high-voltage battery is moved in a “T” shape, between the front and rear axles. Rimac Concept_One is the first battery electric hypercar.
The energy storage component in a pure electric vehicle is the high voltage (HV) battery. The nominal voltage is, in most cases, between 360 and 450 V. A BEV also has a low voltage battery, the usual 12 V battery, which serves as a power supply for auxiliary equipment (lighting, multimedia, etc.). ).
The battery is the key component of EVs because:
- the range of the vehicle depends almost entirely on the HV battery
- it is the heaviest electrical component
- it is the most expensive electrical component
There are different types of high voltage batteries, with chemistry being the main distinct factor. The most common HV batteries for BEV are the lithium ion batteries. These also have different “flavors”:
- metal oxides (e.g., lithium manganese oxide, LiMn2O2)
- phosphates (e.g. Lithium Iron Phosphate, LiFePO4)
In automotive applications, lithium-ion phosphate batteries are more suitable as they are safer in terms of chemical and thermal hazards.
- electronic power controller
- single speed gearbox and differential
Torque is provided by a electric machine. In passenger vehicle applications, there are mainly two types of electric motors already in use, with interest in the third:
- permanent magnet machines
- induction machines
- change reluctance machines
It is more appropriate to call them electric machines instead of motors because they can also generate electrical energy when braking the vehicle. This mechanism is called energy recovery/regeneration.
When the vehicle accelerates, the electrical machine draws electrical energy from the HV battery and produces torque. It’s the motor phase. When the vehicle brakes, the kinetic energy of the vehicle is used by the electric machine to generate electrical energy. It’s the generator phase.
The main difference between electric machines is in the way they produce the torque (permanent magnetic field of the magnets, induced magnetic field in the rotor windings or magnetically conductive path in the rotor aligned with the stator field).
- DC-DC converter
- input filter
The power electronic control module has several subsystems, each responsible for a control function. When the vehicle is charged from a household electrical network (e.g. 220 V), the rectifier converts alternating current (AC) into direct current (DC), which is fed into the high voltage battery. The DC-DC converter is responsible for lowering the high voltage (eg 400 V) to the low voltage network (12 V).
The inverter controls the speed and torque of the electric machine by converting direct current from the battery into three-phase alternating current for the electric machine. When the vehicle is in the energy recovery phase (braking), the inverter performs the reverse conversion, from three-phase AC to DC.
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