Week-6 Challenge: EV Drivetrain
1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?
Answer:
Difference between electric vehicle and hybrid electric vehicle:
| Specifications | Hybrid Cars | Electric Cars |
| Power/Fuel Source | Electricity and Fossil Fuel (Petrol and Diesel) | Electricity Through Battery Pack (DC) |
| Engine | Internal Combustion Engine (ICE) and Electric Motor(s) |
Electric Motor(s) |
| Fuel Efficiency | Combination of ICE and Battery Range | Depends on Battery Range |
| Emission Levels | Higher Compared to Electric Cars | Lower Compared to ICE and Hybrid Cars |
| Price Range | Similar to Conventional ICE Cars | High |
| Charging | Not Needed | Needed |
Power Converter:
Types of Power converter:
There are four main types of power converter circuits , which are used in electric and hybrid electric vehicles...There are ,,
AC to DC Converter:
- AC to DC Converters are one of the most important in power electronics because there are lot of real applications are based on this conversions..
- The AC current DC current conversion process is known as Rectification. The Rectifier convert AC supply into the DC supply at loaad end connection..
- Normally Transformers are used to adjust the AC source to get step down transformer to reduce the volatge level to have better operation range for DC supply.Noramlly AC to DC converter converts low voltage values..
- In most of the countries , the electrical power generation and transmission are purely based on alternating current .DIfferent types of eleectrical power stations use alternators to generate electricity.
- Most of the electrical appliance which use DC current for their operation such as Television,computers,mobiles etc..
- In the case of EVs and HEVs the battery pack which operates with a DC power supply is charged at home or at a charging station both of which are supplied power inAC form from the electric grid ,, so the charges for these vehicles are an example of the AC to DC power converter..
DC to AC converter:
- A power inverter is a power electronic device or circuitry that changes direct current to alternating current .The input voltage ,output voltage and frequency ,and overall power handling depend on the design of the specific device .The inverter does not produce any power , the power is provided by the DC source ..
- A power inverters can be entirely electronic or may be a combination of mechanical effects and electronic circuitry.Static inverters do not use moving parts in the conversion process
- An inverter is a device that converts DC power to the AC power uesd in an electric vehicle motor .The inverter can change the speed at which the motor rotates by adjusting the frequency of the alternating current ..
DC to DC converter :
- In electric engineering , a DC to DC converter is a category of power converters and it is an eletric circuit which converts a source of direct current from one voltage level to another , by storing the input energy temporarily and then releasing that energy to the output at a different voltage ..
-
DC/DC converters can be designed to transfer power in only one direction, from the input to the output. However, almost all DC/DC converter topologies can be made bi-directional. A bi-directional converter can move power in either direction, which is useful in applications requiring regenerative braking.
1. Non-isolated converters:
The non-isolated converters type is generally used where the voltage needs to be stepped up or down by a relatively small ratio (less than 4:1). And when there is no problem with the output and input having no dielectric isolation. There are five main types of converter in this non-isolated group, usually called the buck, boost, buck-boost, Cuk and charge-pump converters. The buck converter is used for voltage step-down, while the boost converter is used for voltage step-up. The buck-boost and Cuk converters can be used for either step-down or step-up. The charge-pump converter is used for either voltage step-up or voltage inversion, but only in relatively low power applications.
2. Isolated converters:
Usually, in this type of converters a high frequency transformer is used. In the applications where the output needs to be completely isolated from the input, an isolated converter is necessary. There are many types of converters in this group such as Half-Bridge, Full-Bridge, Fly-back, Forward and Push-Pull DC/DC converters . All of these converters can be used as bi-directional converters and the ratio of stepping down or stepping up the voltage is high.
AC to AC converter:
- Ac to Ac converters is used for converting the AC waveforms with one particular frequency and magnitude to AC waveform with another frequency at another magnituide .This conversion is mainly required in case of speed controlling of machines ,for low frequency and variable voltage magnitude applications as well.
- We know that there are different types of loads that work with different types of power supplies like single phase ,three phase supply ,and the supplies can be differentiated based on the voltage and frequency range also..
- We require a paricular voltage and particular frequency for operating some special devices or machines ..for speed control of induction motors ,, AC to AC converters is used majorly for obtaining a desired AC power supply from the actual power supply ,we need some converters called AC to AC converters
---------------------------------xxxxxxxxxxxxxxxxxxxxxxxx----------------------
An Electric Vehicle's powertrain with 72V battery pack in shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 'd2'.
The other parameters of the electric vehicle is given below,
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω, KΦ= 0.7 Volt second
Chopper Switching frequency= 400 Hz
The vehicle speed-torque characteristics are given by the below equation
What is the EV steady-state speed if the duty cycle is 70%?
Given:-
The following input parameters are given:-
Battery Pack voltage(V) = 72 V
Rated armature current = 400 A
Armature Resistance(Ra) = 0.5
Motor Constant (K) = 0.7
Chopper Switching frequency = 400 Hz
Duty Cycle = 70%
Solution:-
----------------xxxxxxxxxxxxxxxxx----------------------
3rd
Develop a mathematical model of a DC Motor for the below equation using Simulink.
simulink model
output graph
-----------------------xxxxxxxxxxxxxxxxxxxxxxxxxxx
4. Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective
Answer:
This blog is about the walley reppel about the brushless DC and induction motor..
What or who is walley?
Walley is proponent of electric vehicle , he was engineer at Aeroenvironment .He also worked in jet propulsion laboratory on electric vehicle battery research ,among other projects proponent means someone who is in favor of something..
He said the lead acid battery is replaced by lithium and brush DC motor with brushless DC motor or induction motor,Next he talk a closer look of the brushless DC motor and induction motor there technologies ..
He said that induction motor not require inverter and the motor has ability to start under the load ..with the fixed utility power dc brushless motor produces no starting torque it needs inverter ..
then heading is brushless or induction ...here comparision between DC brushless and induction motor
| DC Brushless | Indution Motor |
| Require an absolute position sensor | Require an absolute position sensor |
| less rotor heat is genereted ,rotor cooling is easier and peak point efficiency higher operate at unity power factor | Power factor is about 85%,peak point efficiency higher compare to DC brushless |
| average efficiency is low | Average efficiency is high |
| Permanent magnets are expensive | No magnet there is advantage in cost |
| They are easy to control | The control laws are more complex and difficult to understand , so difficulties to control |
And finally here both are best as per the requirement ...