Week-6 Challenge: EV Drivetrain
AIM : 1.To discuss about different power converters in EV
2.To calculate EV steady state speed if duty cycle is 70%
3.To explain induction motor and DC brushless motor.
SOLUTION :
1.
* The usage of electrical system in vehicle has made the system look compact and increased efficiency.
*Power Electronic Circuits have replaced many hydraulic,pneumatic and mechanical system in vehicles.
*The two major PEC are DC-DC converter and DC-AC inverter.
*Power converters control the flow of electrical energy by supplying voltage and current in a form suited for user load as the electrical components in a vehicle system vary in voltage requirements.
*DC-DC converter : They are classified into two types , unidirectional and bidirectional converters.
*Unidirectional converters are less powered and they provide necessary power to units like sensors and switches.
*Bidirectional converters are used in driving electric motos and also used to charge the battery while using regenerative breaks. Usually output and input voltages are varied according to the output load. In such cases step up and step down converters are used where input voltage<output voltage and input voltage>output voltage respectively.
*DC-AC converter : Here DC power supply is converted into AC supply. An inverter plays a role in adjusting speed,power and torque by adjusting amplitude of input signal. They are also used in recharging battery during regenerating breaking system.
2. To find steady state speed , torque speed equation of dc motor is equated with
-(1)
T=((v*k)-(w*k*k))/R; -(2)
* As the duty cycle is 70%, it is multiplied with 72V battery pack.
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
*By sub, the parameters in equation 2 we get,
T=((72*(70/1000)*0.7)-(w*0.7^200))/0.5
*now we get, 70.56-w0.98=T -(3)
* equating 3 with 1 we get,
0.005w^2+0.98w-45.86=0 -(4)
resolving the above equation in quadratic formula we get two values for speed , w=38.9 & -281.9 rad/s
3.
*In the given link the author discusses about DC brushless motor and induction motor and how they differ.
* Both system follows electromagnetic induction.
* In DC motor , permanent magnets are present where as the induction motor , there isnt any permanent magnets. Torque in induction motor is produced due to the magnetic field develops in the stator as current flows in stator. There isnt any electrical connections with the rotor in induction motor.
* In DC the current flows in armature windings which in turn causes rotation of rotor. Another Major difference between these two is the rotor.
* DC motor is connected to an inverter and it plays a major role as it controls speed and power by adjusting amplitude of signal. Inverter is not need in induction motor.
* The induction motor working is little complex compared to DC brushless motor. But settting up permanent magnets is costlier. So induction motor is little cost efficient than DC. The efficiency of both system is almost same but peak point efficiency of DC is little higher than induction motor.