Week-6 Challenge: EV Drivetrain

Note-This is Live EV batch 21.

Ans-1:-

• In EV/HEV's ,the power electronic converters are considerd as key elements that interface their power source to drivetrain.
• Power converter is the process and control the flow of electrical energy by providing voltage and currrent to user which are required.
• There are basically three type converter which is used in EV or Plug in hybride electric vehicle(PHEV) are as follows-

1. AC to DC converter (Rectifiers)
2. DC to DC converter (Choppers)
3. DC to AC converter (Inverters)

AC to DC converter (Rectifiers)-

AC to DC converter is mostly uses in plug in hybride vehicle or plug in electric vehicle.As PHEV/PEV,the propultion power is obtained by power source. The battery needs to be charged by a external source.As external source (grid) have alternating current while battery needs direct current.So we need a converter from AC to DC.

DC to DC converter-

• In DC to DC converter,it converts one label of DC supply of voltage to other label of DC voltage which are required to perform the specific activity.
• So by using DC to DC converter ,different type of volatege variation of device can be used and controlled easily.
• If the required voltage is more than the battery voltage then we use step up inverter or Boost inverter to obtain the required voltage.
• If the required voltage is less than battery voltage then we use step down inverter or Buck inverter to obtain the required voltage.

DC to AC converter-

As in EV/HEV,we use a three phase induction motor.The speed of motor can be controlled by varying the frequency of supply.As in EV's,there is used a battery as power source which is in DC.So it must be converted into AC to operate the motor.

So we required a DC to AC converter.

Ans-4:-

The author Wally Rippel writes this blog to explaain the difference between the two commonly used motor (DC brushless motor and Induction motor) in automobile industries.He explains about the difference between the two motors' construction,working and cost. What ever he has explained,there is not a conclusion of better and worse or which one type should be used.He has told that there is no one best engine type.We choose to according to our preference and use.

Similarly,he tolds about the motor that there is no winner.When it comes to motor selection ,both have their merit and demerit.

DC brushless motor-

According to him,the rotor includes two or more permanent magnets that generate a DC magnetic field. This magnetic field enters the stator core (a core made up of thin, stacked laminations) and interacts with currents flowing within the windings to produce a torque interaction between the rotor and stator. As the rotor rotating,the magnitude and polarity of stator currnt will countiously change or vary so that torque remains constant and we can obtain maximum efficiency.

Induction Motor-

Unlike the DC brushless rotor, the induction rotor has no magnets – just stacked steel laminations with buried peripheral conductors that form a shorted structure. Currents flowing in the stator windings produce a rotating magnetic field that enters the rotor.

Induction motor can run without inverter i.e. it can be used by connecting directly from power supply.It has ability to start under the main load applied.While in DC brushless motor can not produce starting torque when it is connected with direct power load ,it needs inverter to operate this.

As 3-phase induction motor has great utility and at the same there is alos limitation with this.Induction motor can not run with DC voltage.Shaaft speed is proportional to line frequency.Its starting torque is low as compare to DC brushless motor.

Add an inverter and it becomes possible to power an induction machine from a battery or other DC source; variable speed also becomes possible simply by adjusting the inverter frequency. Still, torque performance is low compared with DC machines.

Difference between DC Brushless motor and Induction motor-

1. DC brushless motor requires DC supply to operate while Induction motor required AC supply to operate
2. Torque is generated due to interaction of rotor and stator magnetic field in DC brushless motor while in Induction motor, Stator rotating magnetic field induc Current, which interacts with rotor magnetic field and produce current.
3. In DC brushless motor requires position sensor while in Induction motor requires speed sensor.
4. IN DC brushless motor, magnectic field strength can not be adjusted so only single torque can be obtain while in Induction motor,the magnetic field strength changes as voltage and frequency,so maximum torque can be obtain.
5. DC brushless motors are preferred in HEV while Induction motor are preferred in pure Electric vehicle.