Week-6 Challenge: EV Drivetrain

Q-1) Which types of power converter circuits are employed in electric and hybrid electric vehicle?

What is Power Electronics ?

Power Electronics is an Combination of Electrical and Electronics power in other words It is an process and Control the flow of electric energy by supplying voltages and current in a form that is optimally suited for user loads and power electronics uses only how much power is required and in Electric Vehicles(EV) and in Hybrid Electric Vehicles(HEV) there is switching technique which is used to regulate the voltage how much it is required to start and move the vehicle and that switch is called as "Semiconductor Switch" and they are used by control signals

Electrical Vehicle Types :-

Three main types of Electrical Vehicle –

1-Battery Electrical Vehicle:–

Battery Electric Vehicles, also called BEVs and more frequently called EVs, are fully electric vehicles with rechargeable batteries and no gasoline engine. All energy to run the vehicle comes from the battery pack which is recharged from the grid.

2 -Plug in Hybrid Electric Vehicles:–

Plug-in Hybrid Electric Vehicles, or PHEVs, have both an engine and electric motor to drive the car. Like regular hybrids, they can recharge their battery through regenerative braking. They differ from regular hybrids by having a much larger battery, and being able plug into the grid to recharge.

3 -Hybrid Electric Vehicles: –

Hybrid Electric Vehicles, or HEVs, have both a gas-powered engine and an electric motor to drive the car. All energy for the battery is gained through regenerative braking, which recoups otherwise lost energy in braking to assist the gasoline engine during acceleration. In a traditional international combotion engine vehicle, this braking energy is normally lost as heat in the brake pads and rotors. Regular hybrids cannot plug into the grid to recharge and cannot charge with EVgo.

The Basically Three types of Power Converter –

1 – AC – DC Converter

2 – DC – DC Converter

3 – DC – AC Converter

1. AC -DC converter:-

In The Electric Vehicle are required various stages power conversion. The AC – DC converter are use in charging of EV battery .

The battery storge energy in DC form so its required AC in to DC conversion.

In HEV vehicle its required AC – DC converter.

2 . DC – DC Converter:–

The AC – DC converters are generate the high power. We know the vehicle are used numbers of low volt component lighting system , sensor , control system ect . so its required low level DC volt so DC – DC converters are use in Vehicles. The converter are convert voltage level in desire voltage levels also known as choppers.

3 . DC – AC Converter:–

DC to AC converter are used in convert the DC in to AC known as the inverter.

The battery power DC its converts in to AC . The AC power is supply to Motor.

The use in the HEV and Plug in HEV vehicles are mostly required.

Q-2) 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 EV steady state speed if 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:-

Vehicle Output Voltage() = Battery Voltage(V)*Duty Cycle

= 72*0.70

= 50.4 V

%% input paramater
fprintf("Input Parameter \n")

Va = input("Enter the Va battery or Aremature voltage(volt) = ") ;
Ia = input("Enter the Ia Armature current (Ampere) = ") ;
Ra = input("Enter the Ra resistance (ohm) = ") ;
Kphi = input("Enter the Kphi motor constant(volt sec) = ") ;
d = input("Enter the d duty cycle (in percentage) = ") ;

f = 400; % chopper switching frequency (Hz)

%% duty cycle (d),Vo output voltage , Va battery voltage
d1 = d/100 ;% 70 percent
Vo = Va * d1 ;

%% Tm torque for motor and O omega angular speed
syms('Tm','O')
eqn = Tm == ((Vo - (O.*Kphi)).*Kphi)./Ra ;
s1 = solve(eqn);

fprintf("\n")
fprintf("Equation of motor Tm = %s \n",s1)

%% Tv torque for vehicle
% Tv = 24.7 +(0.0051*(O.^2));
eqn1 = 24.7 +(0.0051*(O.^2));
% at steady state Tm = Tv
syms('O')
eqn2 = s1 == eqn1 ;
s2 = vpasolve(eqn2,[O]);
s2rpm =(s2(2)*60)./(2*3.14);

fprintf("\n")
fprintf(" EV steady state speed \n if duty cycle is 70 percentage = %f radian/sec %f RPM",s2(2),s2rpm)

RESULTS:-

from the above result we get speed is 38.914983 radian/sec or 371.799198 in RPM.

Q-3) Develop a mathematical model of a DC Motor for the below equation using Simulink.

ω= V/Kϕ-Ra/Kϕ^2 *T

Let us draw a model for the above equation. by considering the above data

Let,s

V=50.4V

Kϕ=0.7K

Ra=0.5Ω

and also let consider torque as a linearly increasing signal.

Model:-

[w=V/(Kϕ)-(Ra)/( Kϕ^2)*T]

Result:-

Q-4) Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

Wally Ripple:-

is a long-time proponent of electric vehicles. Prior to joining Tesla Motors, he was an engineer at AeroVironment, where he helped develop the EV1 for General Motors and was featured in the documentary movie, Who Killed the Electric Car? Wally has also worked for the Jet Propulsion Laboratory on electric vehicle battery research, among other projects. In 1968, as a Caltech undergraduate student, he built an electric car (a converted 1958 Volkswagen microbus) and won the Great Transcontinental Electric Car Race against MIT.

In the beginning, the author describes the dominance of Internal Combustion Engines(ICE) in the world of automobile industry. He explains that all engines were similar and it was up to the user to select according to their requirement. Next, the author highlights topics related to EV technology especially related to DC Brushless Motor and Induction Motor.

According to him, DC Brush Motors is replaced by either DC Brushless Motor or Induction Motor. Also, the Lead Acid Battery is replaced by lithium-ion batteries for EVs.He also quoted that there will be the future of both the technology (DC Brushless Motor and Induction Motor) depends upon their demands and uses.

DC Brushless Motor:-

With brushless machines, the rotor includes two or more permanent magnets that generate a DC magnetic field (as seen from the vantage point of the rotor). In turn, 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 rotates, it is necessary that the magnitude and polarity of the stator currents be continuously varied – and in just the right way - such that the torque remains constant and the conversion of electrical to mechanical energy is optimally efficient. The device that provides this current control is called an inverter. Without it, brushless motors are useless motors.

The author also said that a brushless DC motor produces no starting torque when directly connected to fixed frequency utility power. They really need the aid of an inverter whose “phase” is maintained in step with the angular position of the rotor.

Advantage:-

The advantage of DC Brushless Motor is that there is low heat generation in the rotor and its cooling capacity is better as compared to Induction Motor. Also, peak point efficiency is generally higher for this drive. The DC brushless drive can also operate at unity power factor, whereas the best power factor for the induction drive is about 85%. This means that the peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive.

Disadvantage:-

As Machine size grows, the magnetic losses increase proportionately and part load efficiency drops. Permanent magnets are expensive and difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them.

Induction Motor:-

The technology behind the induction motor is that it basically uses a 3-phase induction motor which was invented by Nikola Tesla sometime before 1889. 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. In an Induction motor current interacts with the Magnetic field generated by the stator to produce a force which is required for rotor torque.

When a 3-phase induction motor is connected to utility type 3-phase power, torque is produced at the outset. The fact that induction motors are directly compatible with conventional utility power is the main reason for their success.

Advantage:-

The induction motor does not have any magnets and in this the B field is adjustable. The motor has the ability to start under load and there is no need of an inverter. In an induction motor B field is proportionate to V/f (Voltage to frequency). This technology is used to reduce the magnetic losses and conduction losses, due to which efficiency will remain at maximum peak. This all leads to increasing the performance, induction motor is very useful and efficient for high performance.

Disadvantage:-

An induction motor cannot operate from DC Voltage it always requires an AC voltage supply. In an induction motor, the Shaft speed is proportionate to line frequency. Hence, when used with utility power they are constant speed machines. When operated from utility power, they have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC-type machines.

Diffrence B/W BRUSHLESS DC MOTOR and INDUCTION MOTOR:-

Both DC brushless and induction drives use motors having similar stators. Both drives use 3-phase modulating inverters. The only differences are the rotors and the inverter controls. And with digital controllers, the only control differences are with control code. (DC brushless drives require an absolute position sensor, while induction drives require only a speed sensor; these differences are relatively small.)

One of the main differences is that much less rotor heat is generated with the DC brushless drive. Rotor cooling is easier and peak point efficiency is generally higher for this drive. The DC brushless drive can also operate at unity power factor, whereas the best power factor for the induction drive is about 85 percent. This means that the peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive.

The Authour have Conculeded:-

In the end, the author couldn't choose which drive is better than the other but makes it clear that DC Brushless motor drives will likely continue to dominate in the Hybrid and upcoming Plug-in hybrid markets and induction motor drives will likely maintain dominance for the high-performance pure electric.

Conclusion:-

• Types of power converters used in electric and hybrid electric vehicles explained.
• EV stead speed at 70%duty cycle is 38.92 rad/sec
• Explained in brief what was author's perspective to Induction VS DC brushless motor.