Monday, September 28, 2020

The Beginner's Guide of Electric Vehicle Technology

Electric vehicles (EV) are gaining much more importance and interest now a days. India rank's at 14th position of 20 most polluted regions in the world. The main reason for this is the excessive usage and dependence on petrol and diesel engines, also we keep importing petrol and diesel which is the prime reason for the depletion of our currency globally. In order to overcome this situation our movement towards EV (Electric vehicle) can be our best remedy.

EV is 4 times more energy efficient than petrol and diesel engines. Also it consists of less moving parts which will cause less problem during its maintenance and improve its performance and efficiency.

ICE efficiency 22% to 23%
EV efficiency 90%

Electric Vehicle

An EV (electric vehicle) is also known to as a PEV (plug-in electric vehicle). An EV is an Vehicle with a electric motor and a battery that is rechargeable by plugging it to an source of electricity. Batteries in EV act as a storage for  electricity which then provides either a part or all the power needed to run the vehicle and various mechanisms and systems.

There are two basic types of EV and they are as follows

  • PHEV
  • BEV

PHEV (Plug-In Hybrid Electric Vehicle)

These vehicles are powered by both ways i.e

  • Gasoline engine.
  • Electric motor.

The battery which stores the power to run the vehicle can be charged using the vehicle’s gasoline engine and breaking system or by plugging the vehicle into any source of electricity. Some types of PHEVs are also known as Extended Range Electric Vehicles (EREV) named for the extended driving range the primary functional gasoline engine provides to it.

Block diagram of plug-in hybrid electric vehicle

BEV (Battery Electric Vehicle)

These vehicles are somewhat different form the PHEV as they are powered entirely by an electric motor and battery and do not require the gasoline engine. All of the electricity which is required to recharge the battery comes from the utility grid or the secondary regeneration braking system. BEVs as compared to PHEV have typically a larger battery pack and greater electric driving range than PHEV.

Constructional diagram of battery electric vehicle

Driving Range

Typically the all-electric drive range for a PHEV is 15 to 40 miles, after which the gasoline engine mechanism will engage, which in case will lead to the extension of the driving range to an additional 300 miles or even more.

PHEV can also be filled up by using the gas tank and can be driven as far as needed, similar to that of a traditional car.

The thumb rule is that the vehicle batteries provide approximately 4 miles of all-electric driving range for each “usable” kW-hr of the energy stored in it.

The driving range for the BEV can be up to 90-100 miles. Two-thirds of all drivers travel 30 miles or even less a day, so for those drivers it is easy to recharge their EV at home overnight.

Various types of Electric Motors in EV's

  • DC Series Motor

  • Brushless DC Motor

  • Permanent Magnet Synchronous Motor (PMSM)

Three Phase AC Induction Motors

  1. DC Series Motor

    High starting torque is the main feature of the DC Series motor which makes it the best available option for traction application. In the 1900s this motor was the most used motor for traction purpose. The advantage of DC series motor are

    1. Easy and adjustable speed control

    2. The motor can also withstand a sudden increase in load.

    All these points make it an ideal electric motor.

    The main drawback of DC series motor is high maintenance and repair problems caused by its brushes and commutators. These motors are mainly used in Indian railways.

    Constructional diagram of DC series motor
  2. Brushless DC Motors

    It is somewhat similar to the DC motors which are having Permanent Magnets. This motor is called brushless because it does not have the commutator and brush mechanism in it. The commutation is done electronically and due to this reason the BLDC motors are maintenance free.

    BLDC motors have characteristics like high torque, high efficiency around 95-97%, etc.

    The BLDC motors are the most preferred motors for the electric vehicle application mainly due to its superior traction characteristics.

    Brushless DC motor
  3. Permanent Magnet Synchronous Motor (PMSM)

    This motor is also somewhat similar to that of the BLDC motor which consists of permanent magnets situated on its rotor. Similar to BLDC motors these motors also comprises of the superior traction characteristics like high power density and high efficiency.

    The difference is that PMSM has sinusoidal EMF whereas the BLDC motor has trapezoidal EMF. PMSM are available for higher power ratings.

    Permanent magnet synchronous motor
  4. Three Phase AC Induction Motors

    The 3 phase induction motors do not have a high starting toque under fixed voltage and frequency conditions.
    But this property can be easily altered by using suitable control techniques like FOC or v/f. By using these control techniques, the maximum torque gets available at the starting of the motor which is suitable for traction purpose.
    An example to this is the squirrel cage induction motors which have long life due to their less maintenance.

    Three phase induction motor

Energy storage and transportation

As we know that much of the electric vehicles charging occurs at night and during the weekends, when electricity value and the price are relatively lower, and while passenger vehicles are not needed much or used, some electric vehicles will need to charge during the day and also even during the peak demand periods when the grid is already providing the maximum amount of power needed.

If the EV charging occurs in parts of the grid that doesn't  have sufficient capacity or you can say “head-room” to accommodate the extra power needs, then there are 2 basic choices as follows.

  • The utility can increase the amount of generation, transmission, and distribution (GT&D) infrastructure to add the needed capacity.

  • Secondly is to install distributed energy resources (DERs)which includes the distributed generation and storage. To achieve the desired effect, the DER capacity must be installed downstream from that of the congestion points to serve the added on-peak demand locally as well as at a large level.

EVs can also act as an electricity resource themselves, however. When they are plugged in, the batteries in these electric vehicles could provide many of the grid services that the stationary energy storage systems can provide and can also can be actively managed to reduce the impacts that their charging can have on the electric grid – an increasingly important capability as more and more number of EVs are plugged into the grid.

Energy storage and transportation block diagram

Automotive Battery Management System

Automotive Battery Management Systems also known as BMS must be able to meet the important features such as voltage, temperature and current monitoring, battery state of charge (SoC) and also most importantly the cell balancing of lithium-ion (Li-ion) batteries.

Apart from this the main functions of a Battery Management System for electric vehicles areas follows:

  • Battery protection is the most important task which includes providing a barrier type protection to battery so that the outside operations do not alter its function in any manner.

  • Battery monitoring is done by estimating the battery pack state of charge (SoC) and the state of health (SoH) of the battery during its charging and discharging process.

  • Battery optimization is mainly done due to cell balancing process which improves the battery life and it's capacity, thus optimizing the all-driving range for the plug-in (PHEV) and battery electric vehicles (BEV).

BMS block diagram