Week-6 Challenge: EV Drivetrain
1.Power converters:
Power converters are semiconductor switches used for high switching operation to control the flow of power.
In EV power converters are a key device used to control the power flow.Three major power converters are used in EV,
1.DC-DC converters or choppers.
2.DC-AC converters or inverters.
3.AC-DC converters or rectifiers.
AC-DC converters or rectifiers:
The rectifiers are used for charging operation of the EV the supply fed from the grid is a ac supply which has to be converted into a dc before storing in a battery.It is widely found in plug in type electric vechicle.
DC-DC converters or choppers:
The choppers can be used in a electric vechicle in order to increase or decrease level of voltage level received from the battery.The DC-DC link wiil depend on the characteristics of EV like speed torque and acceleration.It is also used to control a dc motor connected in the EV.
DC-AC converter or inverters:
The inverters are used to control any ac application in the EV.The dc power delivered by the battery is converted into ac power by the inverter.The main application of inverter in EV is control of AC motors like induction motor connected in EV.
2.Steady state speed:
The given parameters are,
Battery voltage(V)=72V
duty cycle(d)=0.7
Armature resistance(Ra)=0.5
Motor constant(K`phi`)=0.7
Rated current=400A
Rated voltage=72V
Vechicle speed-torque characteristic,`Tv=24.7+(0.0051)omega^2`
Tv=Vechicle torque(Nm)
`omega`=Steady state speed of vechicle(rad/s)
Motor voltage (Vm)=Battery voltage*duty cycle
=72*0.7
Vm =50.4V
Motor torque equation is given by,
`Tv=(VmKphi-omega(Kphi)^2)/(Ra)`
Substituting the known values,
Tv=((50.4*0.7)-(0.7*0.7*`omega`))/0.5
On simplification we get,
Tv=70.56-0.98`omega`
We already have,Tv=24.7+(0.0051)`omega^2`
On solving these two equations we get,
`omega`=38.854rad/s and `omega`=-230.952rad/s
We can take the positive value,
The steady state speed of the vechicle is 38.85 rad/s.
4.Induction motor vs Brushless DC motor:
The key takeaways from the author Wally Ripple,Tesla.
- The author at first disccussed the dominance of engine in the world of transportation.There are lot of engine available and yet there is no clear conclusion about which is a better engine.
- Like the engines,the author also dicuss about induction motor and brushless dc motor over its contractiction.
- He also explains the working of Induction motor and brushless motor.He also pointed the differances between the two motor,like the stator of the two motor remains the same but the rotor varies.The rotor in brushless dc motor is of a permanent magnet whereas that of induction motor is a laminated sheet of coil .
- He also spot some advantage and disadvantage of these two motor.
- The induction motor has advantage like it has no magnets and it has capacity to start even with load and the disadvantage includes the need for a ac supply,the torque and speed are low when compared to the dc motor.
- The brushless dc motor has advantage like less rotor heat is generated,the efficiency of the drive remains somewhat greater than the induction motor.The disadvantage includes the larger size,magnetic loss due to the permanent magnent,expensive and it is difficult to handle.
- Finally the autor concluded that he cannot choose the better drive between the brushless dc motor and induction motor byt he is clear in the fact that brushless dc motor will rule the field in hybrid and plug in hybrid electric vechicle whereas the induction motor will rule the field in pure electric vechicle.