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Aim 1. To find types of power converter circuits are employed in electric and hybrid electric vehicle. 2. To EV steady state speed if duty cycle is 70%. Given: m=1000bkg, Cd =0.2, A=2 m2, C0=0.009, C1=1, ρ=1.1614…
abhijeet dhillon
updated on 30 Apr 2020
Aim
1. To find types of power converter circuits are employed in electric and hybrid electric vehicle.
2. To EV steady state speed if duty cycle is 70%.
Given:
m=1000bkg, Cd =0.2, A=2 m2, C0=0.009, C1=1,
ρ=1.1614 kg/m3
Radius of the wheel= 11 inches
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω, La= 8 mH, KΦ= 0.7 V-s
Chopper Switching frequency= 400 Hz
The vehicle charaacteristics are given by the equation
TTR=24.7+0.0051w2
3. To explain Induction Versus DC brushless motors by Wally Rippel.
Solution:
1.Types of power converter circuits are employed in electric and hybrid electric vehicle.
Within every electric vehicle is a battery that outputs a certain voltage.
Given that this voltage might not be appropriate for the various devices being driven, we need to install another device along the signal path.
This device is known as a DC/DC converter, and without it, the modern electric car wouldn’t be possible
While DC/DC converters can be based on a number of different designs, the underlying function remains the same. We might be talking about a step-up converter, which turns a low-voltage input into a high-voltage output, or a step-down converter, which does the opposite.
The batteries of an electric vehicle typically output several hundred volts of DC. The electric components inside the vehicle, however, vary in their voltage requirements, with most running on a much lower voltage. This includes the radio, dashboard readouts, air conditioning, and in-built computers and displays.
In electric vehicles which use a DC motor, actually running the motor can use up to three times the voltage provided by the battery. With the help of the right converter, we can bridge this gap without having to resort to a larger, prohibitively-heavy battery.
The following types of converters are used in electric vehicles :
1.Providing low voltage (12V or 14V) for low voltage loads
2.Boosting the voltage level of the battery such that it matches the level of theDC bus voltage for driving the AC motor inverter if the traction motor is ACmotor.
3.Motor propulsion if the traction motor is a DC motor
1.Providing low voltage (12V or 14V) for low voltage loads
2. EV steady state speed if duty cycle is 70%
The torque speed relation is given by:
T = V*Km/Ra - Km*phi^2/Ra*w
Where
T = torque
Km = constant
Ra = armature resistance
Now voltage of motor is given by : duty cycle * battery voltage
There motor volatge = 0.7*72
= 50.4 volts
Therefore substiting the values we get :
T = 50.4*0.7/0.5 - 0.7^2/0.5*w
Also we know that TTR=24.7+0.0051w2
Putting the value in the above equation we get :
24.7+0.0051w2 = 50.4*0.7/0.5 - 0.7^2/0.5*w
This is a quadratic equation as below
0.0051*w^2 + .00098*2 -46.56 = 0
Solving this equation we get :
w= 38.82 or w =-230 rad/s
Therefore the ev steady state speed is 38.82 rad/s
3.Induction Versus DC brushless motors
Authors perspective : The author tells us that there are various kinds of engines and each engine is suitable for a specific requirement and in the same there are different kinds of motors required for different purposes .
The difference between the induction motor and the brushless motor is that the induction motor does not have any permanent magnet and it has laminations of wires wrapped around it . The induced voltage in the rotor is directly proportional to the speed difference of the electrical frequency and rotor frequency .
An induction motor does not require an inverter and can be directly connected to the power supply and can be started under load condition compared to an bldc motor .Drawbacks of the dc motor is that it need only ac supply and have low torque producing capability compared to dc motors . Adding an inverter with a feedback loop removes these drawbacks .
DC OR INDUCTION MOTOR :
BLDC motors have less heating andhigher efficiency ,better cooling and higher torque .
In an ideal brushless drive, the strength of the magnetic field produced by the permanent magnets would be adjustable. When maximum torque is required, especially at low speeds, the magnetic field strength (B) should be maximum – so that inverter and motor currents are maintained at their lowest possible values. This minimizes the I² R (current² resistance) losses and thereby optimizes efficiency. Likewise, when torque levels are low, the B field should be reduced such that eddy and hysteris losses due to B are also reduced. Ideally, B should be adjusted such that the sum of the eddy, hysteresis, and I² losses is minimized. Unfortunately, there is no easy way of changing B with permanent magnets.
In contrast, induction machines have no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency). This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized. Thus, the induction machine when operated with a smart inverter has an advantage over a DC brushless machine – magnetic and conduction losses can be traded such that efficiency is optimized. This advantage becomes increasingly important as performance is increased. With DC brushless, as machine size grows, the magnetic losses increase proportionately and part load efficiency drops. With induction, as machine size grows, losses do not necessarily grow. Thus, induction drives may be the favored approach where high-performance is desired; peak efficiency will be a little less than with DC brushless, but average efficiency may actually be better.
Conclusion:
DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets, and that induction drives will likely maintain dominance for the high-performance pure electrics. The question is what will happen as hybrids become more electrically intensive and as their performance levels increase? The fact that so much of the hardware is common for both drives could mean that we will see induction and DC brushless live and work side by side during the coming golden era of hybrid and electric vehicles.
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