Week 4 Session 5
Week 4 : Session 5
Explain the various applications of Power converters in an Electric vehicle. For Example what type of converter will you use for Horn which requires DC and less than 10V. Likewise come up with different applications.
Answer:
Power Converter is the heart of battery operated electric vehicle. Near about 70 to 80 % Power convrter are used in electric vehicle. There are various forms of energy conversion takes place in it like from electrochemical to electrical or vice versa and from electrical to mechanical and vice vesra.This energy conversion is necessary to run the vehicle. There are lots of components joined together to form a complete electric vehicle. All the compoents require different voltage level for its operation. So it is necessary to convert the high voltage into low voltage for their smooth operation. For this energy conversion, it is necessary to use the power converter.
Basically there are three types of electrical system used in electric vehicle and they are:
1) Battery & Charger
2) Powertrain : Inverter + Motor
3) Accessories : Like Airconditioner, headlight, power window, speekers, radio, horn etc.
1) Battery & Charger :
As per the architecture of electric vehicle, battery is one of the most important component in EV, because all the vehicle component take the supply from main battery. There are two types of batteries used in EV, main battery and auxilary battery. Main battery is the head of all compoent and it is having a very high voltage rating and energy storing capabilty. This main battery is charged by three methods :
1) AC Charging : AC supply is easily available at commercial as well as at home. With thr help of Adapter, we can charge the battery easily. This adapter acts as a rectifier which convert the electricity from AC to DC and get stored into the main battery. The advantage of this method is that the ac supply is easily available at home and at commercial places. Therefore, we can charge our vehicle easily. But the main disadvantage of this method is that it takes too much time (Near about 4 to 5 hours) randomly forfully charging of the battery.
2) DC Fast Charging: Like a conventional fuel vehicle, we can also charge the electric vehicle from charging station. But the supply available at charging station is in the form of DC. So we can easily charge our battery by using Connector.There are different connectors are used for different location and it depends upon the current type either AC or DC, Country,etc. The main advantage of this method is that we can charge the vehicle within few hours but less than AC charging method. Now the electric vehicle concept is growing day by day but in present situation, the charging station are available at metro cities only and not in rural areas, so it is difficult to charge the vehicle by using this method. Another disadventage of this method is that lots of charging stations want to locate at certain distance which increases the cost of implementation. They are not available at rural areas.
3) Wireless Charging: Wireless charging concept works on the principle of mutual inductance phenomenon. that means, the battery gets charged without using any type of adapter or connector. This method is implemented at commercial places like Mall, Hospitals, Cinama Halls, etc. In this method, the charging pads are located at thses locations. We have to stay out vehicle on that pad, the battery gets automatically chagred by using mutual inductance phenonmenon. This method is the advance technology therefore, its manufacturing cost is high.
The main battery is located on the chessis of the vehicle because it occupies very large space. The main battery is made up of large number of series and parallel connceted modules and each module consists of large number of celles connceted in series as well as parallel. Therefore, the weight of battery becomes bulky and hence it is located at the bottom of the vehicle.
As the main battery is the source of supply to all the electric components therefore, large amount of heat is also generated in it. Therefore, to maintain the temperature of battery is within the limit , electric vehicle uses Battery Management System( BMS). It also indicates the state of charging and discharging, whether the battery celles are damaged or not etc. Typically the voltage rating of main battery is different for different vehicles. But some of the manufacutring company uses 400 Volt for main battery or more than that.
Charger is a device which is used to charge the battery and it acts as a rectifier. It is also called as a ON-Board Charger.
2) Powertrain : Inverter + Motor :
Powertrain is a combination of energy source and drivetrain. A vehicle power train is required to produce a sufficient power to meet the demands of vehicle performance and with high efficiency. Powertrain is a devie which is used to produce a propulsion power to move the vehicle. Most of the electric vehicle uses AC motor like Three Phase Induction Motor, Brushless DC Motor,Three Phase Synchronous Motor etc. and for this type of motor, we require AC supply but we stored the energy in main battery in the form of DC, So it is necessary to convert the electricity from DC to AC. This is possible with the help of Three Phase Inverter. Inverter is a power electronic device which convertes the electricity from DC to controlled AC as per the load demand. The input of inverter takes the supply from main battery and provide a controlled AC output to the three phase motor. Now this motor converts the electrical energy into mechanical energy. The shaft of motor transfer the mechanical energy to the wheels via drivetrain. or simply transmission system. The main advantage of this powertrain is that here the motor acts as a generator also in case of deceleration. When the vehicle accelerates, it converts the energy from electrical to mechanical but when the vehicle decelerate, the motor acts as a generator and converts the stored kinetic energy in the wheel to the electrical energy and stored in battery. i.e. Battery gets charged during deceleration. There are vaious types of pulse width modulation takes place for control of output voltage of inverter like SPWM and SVPWM etc. But SVPWM is better than SPWM because this method uses more DC bus utilization instead of SPWM method.
The motors widely used in EV :
1) Brushed Permanent Magnet DC Motor.
2) Brushless DC Motor :- Two Wheeler and Three Wheeler.
3) Permanenet Magent Synchronous Motor:- Tata Nexon
4) Three Phase Induction Motor : Tesla
5) Switched Reluctance Motor :- Tesla 3 Model.
3) Accessories : Like Airconditioner, headlight, power window, speekers, radio, horn etc.
Apart from main battery, auxilary battery is also used in electric vehicle because it is used to supply low voltage to auxilary components. There are various auxilary components used in EV like, air-conditioner, Headlight, Horn, wiper, power window, speakers, radio etc. This auxalary component operate on very low voltage level i,e. it requires 10 to 20 volt voltage for its operation. It is very difficult to take the low voltage from high voltage battery. Thereofore, another battery is used in it which is called as auxilary battery, It stores the energy at very low voltage level say 48 volt. But this auxilary battery takes the supply from main battery. But it is necessary to conert the high voltage into low voltage and this is possible with the help of DC- DC converter ie, Buck Converter or Isolated Buck Conerter. With the help of this converter, we can easily convert from high voltage to low voltage level. There are different auxilary loads operate on different voltage level like some of the loads operate on 10 volt, some of the operate on 12 volt some of the loads operate on 24 volt etc. So for every voltage level, seperate DC-DC converter is either used or isolated converter is used. (LIke a autotranformer). But those the loads which require same voltage take take the supply from a single DC-DC Converter. No need to implement seperate converter for every loads. In Electric vehicle, High Voltage Bus and Low voltage bus are also used, so that we can easily extract the connection via HV and LV bus.