Electric Vehicles Key Parts
An electric vehicle uses a battery to store electrical energy that is ready to use. A battery pack is made up of a number of cells that are grouped into modules. Once the battery has sufficient energy stored, the vehicle is ready to use.
Battery technology has improved hugely in recent years. The three types main batteries is being used today are leadacid; nickel-metal hydride; and lithium-based batteries. Except leadacid battery the nickel-metal hydride and lithium-based batteries have the greatest potential. Current EV batteries are lithium based. These have a very low rate of discharge. This means an EV should not lose charge if it isn’t driven for a few days, or even weeks. Lithium batteries are used in most EVs and hybrids today
The lead-acid battery uses lead oxide and spongy lead electrodes with sulfuric acid as an electrolyte. Generally, they consist of several cells put in series to form a battery, such as an automobile battery. The group of cells is generally in a polypropylene container. The advantages of the lead-acid battery are commercial availability, recyclability and low cost. The disadvantages are that they are heavy and the amount of energy stored per kilogram is less than other types of batteries.
Nickel-metal hydride operates by moving hydrogen ions between a nickel-metal hydride cathode and a nickel hydroxide anode. During discharge, hydrogen moves from cathode to anode. During charging, ions move in the opposite direction.
There are two types of lithium batteries, the lithium ion and the lithium polymer. A lithium ion type works by dissolving lithium ions, and transporting them between the anode and cathode. The battery has an anode made of lithium cobalt dioxide and a cathode from a non-graphitizing carbon. During operation, lithium ions move through a liquid electrolyte that contains a thin, microporous membrane. The lithium polymer uses lithium as an electrochemically active material and the electrolyte is a polymer or polymer-like material that conducts lithium ions.
Electric vehicles are more efficient than internal combustion engines for several reasons.
1. The electric motor is directly connected to the wheels, so it consumes no energy while the car is at rest or coasting.
2. A regenerative braking system can return as much as half an electric vehicle’s kinetic energy to the storage cells.
3. The motor converts more than 90% of the energy in its storage cells to motive force, whereas internal combustion drives use less than 25% of the energy in a gallon (3.75 L) of gasoline.
Various types of Electric Motors used in Electric Vehicles
DC Series Motor
Brushless DC Motor
Permanent Magnet Synchronous Motor (PMSM)
Three Phase AC Induction Motors
Switched Reluctance Motors (SRM)
1. DC Series Motor
High starting torque capability of the DC Series motor makes it a suitable option for traction application. It was the most widely used motor for traction application in the early 1900s. The advantages of this motor are easy speed control and it can also withstand a sudden increase in load. All these characteristics make it an ideal traction motor. The main drawback of DC series motor is high maintenance due to brushes and commutators. These motors are used in Indian railways. This motor comes under the category of DC brushed motors
2. Brushless DC Motors
It is similar to DC motors with Permanent Magnets. It is called brushless because it does not have the commutator and brush arrangement. The commutation is done electronically in this motor because of this BLDC motors are maintenance free. BLDC motors have traction characteristics like high starting torque, high efficiency around 95-98%, etc. BLDC motors are suitable for high power density design approach. The BLDC motors are the most preferred motors for the electric vehicle application due to its traction characteristics.
In this type, the rotor of the motor is present outside and the stator is present inside. It is also called as Hub motors because the wheel is directly connected to the exterior rotor. This type of motors does not require external gear system. In a few cases, the motor itself has inbuilt planetary gears. This motor makes the overall vehicle less bulky as it does not require any gear system. It also eliminates the space required for mounting the motor. There is a restriction on the motor dimensions which limits the power output in the in-runner configuration. This motor is widely preferred by electric cycle manufacturers and two-wheeler manufacturers
ii. In-runner type BLDC Motor:
In this type, the rotor of the motor is present inside and the stator is outside like conventional motors. These motor require an external transmission system to transfer the power to the wheels, because of this the out-runner configuration is little bulky when compared to the in-runner configuration. Many three- wheeler manufacturers like Goenka Electric Motors, Speego Vehicles, Kinetic Green, Volta Automotive use BLDC motors. Low and medium performance scooter manufacturers also use BLDC motors for propulsion.
It is due to these reasons it is widely preferred motor for electric vehicle application. The main drawback is the high cost due to permanent magnets. Overloading the motor beyond a certain limit reduces the life of permanent magnets due to thermal conditions.
3. Permanent Magnet Synchronous Motor (PMSM)
This motor is also similar to BLDC motor which has permanent magnets on the rotor. Similar to BLDC motors these motors also have traction characteristics like high power density and high efficiency. The difference is that PMSM has sinusoidal back EMF whereas BLDC has trapezoidal back EMF. Permanent Magnet Synchronous motors are available for higher power ratings. PMSM is the best choice for high performance applications like cars, buses. Despite the high cost, PMSM is providing stiff competition to induction motors due to increased efficiency than the latter. PMSM is also costlier than BLDC motors. Most of the automotive manufacturers use PMSM motors for their hybrid and electric vehicles. For example, Toyota Prius, Chevrolet Bolt EV, Ford Focus Electric, zero motorcycles S/SR, Nissan Leaf, Hinda Accord, BMW i3, etc use PMSM motor for propulsion.
4. Three Phase AC Induction Motors
The induction motors do not have a high starting toque like DC series motors under fixed voltage and fixed frequency operation. But this characteristic can be altered by using various control techniques like FOC or v/f methods. By using these control methods, the maximum torque is made available at the starting of the motor which is suitable for traction application. Squirrel cage induction motors have a long life due to less maintenance. Induction motors can be designed up to an efficiency of 92-95%. The drawback of an induction motor is that it requires complex inverter circuit and control of the motor is difficult.
In permanent magnet motors, the magnets contribute to the flux density B. Therefore, adjusting the value of B in induction motors is easy when compared to permanent magnet motors. It is because in Induction motors the value of B can be adjusted by varying the voltage and frequency (V/f) based on torque requirements. This helps in reducing the losses which in turn improves the efficiency.
Tesla Model S is the best example to prove the high performance capability of induction motors compared to its counterparts. By opting for induction motors, Tesla might have wanted to eliminate the dependency on permanent magnets. Even Mahindra Reva e2o uses a three phase induction motor for its propulsion. Major automotive manufacturers like TATA motors have planned to use Induction motors in their cars and buses. The two-wheeler manufacturer TVS motors will be launching an electric scooter which uses induction motor for its propulsion. Induction motors are the preferred choice for performance oriented electric vehicles due to its cheap cost. The other advantage is that it can withstand rugged environmental conditions. Due to these advantages, the Indian railways has started replacing its DC motors with AC induction motors
|5. Switched Reluctance Motors (SRM)|
Switched Reluctance Motors is a category of variable reluctance motor with double saliency. Switched Reluctance motors are simple in construction and robust. The rotor of the SRM is a piece of laminated steel with no windings or permanent magnets on it. This makes the inertia of the rotor less which helps in high acceleration. The robust nature of SRM makes it suitable for the high speed application. SRM also offers high power density which are some required characteristics of Electric Vehicles. Since the heat generated is mostly confined to the stator, it is easier to cool the motor. The biggest drawback of the SRM is the complexity in control and increase in the switching circuit. It also has some noise issues. Once SRM enters the commercial market, it can replace the PMSM and Induction motors in the future.
The controller is like the brain of a vehicle, managing all of its parameters. It controls the rate of charge using information from the battery. It also translates pressure on the accelerator pedal to adjust speed in the motor inverter.
Device managing electricity flow from batteries to motor(s), from “on-off” function to vehicle throttle control.
The controller gets all the inputs form the user like the amount of throttle (acceleration), breaks pressure, driving mode etc and controls the speed of the motor accordingly. If motors are considered to the muscle of a car, controller is its brain. A controller is often a generic term and it might include other circuits like a DC-DC converter, Speed controller, Inverter etc. The DC-DC converter is used to power all the peripherals of the car like the infotainment system, Headlights and other low level electronic devices.
Apart from this the controller also takes care of regenerative braking. It is the process of converting kinetic energy into electric energy. That is when the EV runs down a slope the motor are rotating freely due to the kinetic energy, at this situation the motors can be made to act as a generator so that the power thus obtained can be used to charge the batteries. Most modern day EV’s have this but its performance and functionality is still debatable.
Another important component in an EV which requires advancement is the Chargers. An average E-Car takes a minimum of 5 hours to get charge that combined with its very low mileage becomes a disaster. An average American drives more than 50km per day, in this scenario an EV which gives a rage of 90km for full charge has to get charged almost every day. This makes the charges a most used component.
It gets plugged into the AC mains and converts the AC to DC to charge the batteries. But there are more to add to it. Charging is a process in which the batteries and charger should coexist you cannot push current inside a battery if the battery is not ready to accept it. There are many types of chargers; the most common types are discussed below.
|Level 1 Charger: These are the most basic chargers and it is probably the one that you get along with your car. They take a long time to charge the batteries since they operate in 120V AC, They convert this 120V AC to DC and use it to charge the batteries. The current rating of the charger will also be low somewhere near 8-10 A, this means you will be sending less current and thus taking a long time to charge your batteries overnight. On the positive side, this method improves the life cycle of the battery since our charging current is less.|
Level 2 Charger: These are a bit faster that Level 1 charger, it depends on the manufacturer to provide you with Level 1 or Level 2 charger. Level 2 chargers operate on higher voltages like 240V or above and also have high current rating near 40A to 50A. This makes the car to get charged faster.