Week-6 Challenge: EV Drivetrain

1.  Which types of power converter circuits are employed in electric and hybrid electric vehicle?

Electric and hybrid electric vehicles (EVs and HEVs) use various types of power converters to efficiently convert between AC (alternating current) and DC (direct current) voltages as well as to regulate DC voltages. Here's a breakdown of each of these converter types:

1. AC to DC Converters (Rectifiers): AC to DC converters, also known as rectifiers, are used to convert the AC power from external sources, such as charging stations or the grid, into DC power suitable for charging the vehicle's battery. These converters are typically used in plug-in electric vehicles (PEVs) and EVs. They ensure efficient and controlled charging of the traction battery.
2. DC to AC Converters (Inverters): DC to AC converters, often referred to as inverters, play a crucial role in electric vehicles. They convert the DC power from the vehicle's traction battery into AC power to drive the electric motor. Inverters are responsible for controlling the speed and torque of the motor, making them a key component in electric and hybrid powertrains.
3. DC to DC Converters: DC to DC converters are used to step up or step down the voltage levels within the vehicle's electrical system. They convert the high-voltage DC power from the traction battery into the lower voltage required for various auxiliary systems, such as lights, fans, and onboard electronics. Conversely, they can step up voltage when needed for specific components.
4. AC to AC Converters (Frequency Converters): AC to AC converters, also known as frequency converters, are less common in EVs but can be found in some advanced systems. These converters are used to change the frequency of the AC power while maintaining its voltage level. This can be useful in applications where different frequency AC power is required for specific components or subsystems.

These converters are essential for the efficient operation of electric and hybrid vehicles, enabling power management, motor control, and voltage regulation. The specific design and configuration of these converters can vary between vehicle models and manufacturers, depending on the electrical architecture and requirements of the vehicle's components.

02)

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

 So, the vehicle voltage is 50.4 V

Now, Equation for Vehicle torque is :

Tv</math>">Tv��= Vv</math>">Vv��.KϕRa</math>">KϕRa����-(Kϕ)2Ra</math>">(Kϕ)2Ra(��)2��.w</math>">w� ................ (1)

Where,

Tv</math>">Tv��= Vehicle Torque (N-m)

Vv</math>">Vv��= Vehicle Voltage (Volts)

w</math>">w�= Steady State speed of Vehicle (rps)

K</math>">K�ϕ</math>">ϕ�= Motor Constant

Ra</math>">Ra�� = Armature Resistance

Substituting all the values in equation 1, we get

Tv</math>">Tv��= 50.4×0.70.5-(0.7)20.5×w</math>">50.4×0.70.5−(0.7)20.5×w50.4×0.70.5-(0.7)20.5×�

Tv</math>">Tv��=  70.56-0.98w2</math>">70.56−0.98w270.56-0.98�2 .................(2)

Now, the vehicle speed torque characteristics is given as,

Tv=24.7-0.0051w2</math>">Tv=24.7−0.0051w2��=24.7-0.0051�2  .....................(3) 

At Steady State,

Eq (2) = Eq (3)  ...................(4)

24.7-0.0051w2=70.56-0.98w2</math>">24.7−0.0051w2=70.56−0.98w224.7-0.0051�2=70.56-0.98�2

0.0051w2+0.98w-45.85=0</math>">0.0051w2+0.98w−45.85=00.0051�2+0.98�-45.85=0  ..................(5)

To solve the above eq we have to apply the QUADRATIC EQUATION formula,

x=-b±b2-4ac2a</math>">x=−b±√b2−4ac2a�=-�±�2-4��2�

x=-0.98±0.982-4(0.0051)(-45.85)2⋅(0.0051)</math>">x=−0.98±√0.982−4(0.0051)(−45.85)2⋅(0.0051)�=-0.98±0.982-4(0.0051)(-45.85)2⋅(0.0051)

w=</math>">w=�=38.92 rad/sec

So, The steady-state speed of the vehicle is 38.92 rad/sec.

03)

Results:

04)

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.  

 Inference:-

 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