Week-6 Challenge: EV Drivetrain

1) The various applications of power converter in an Electric vehicle and Hybrid electric vehicle is as follows:

• Used in charging system
• Used to deliver power to auxilary loads operating at different voltages
• Battery to charger station compatibility
• HV battery and LV battery link
• Using low voltage battery with high voltage motor system
• Used in cell combinations for energy storage solution

The type of converter used for Horn which requires DC voltage less than 10 V is DC-DC Buck converter because of the step down voltage requirement.

The DC-AC converter usually called as inverter can control both magnitude and frequency of the output voltage. This is widely used in the control of motor in EV and HEV. 

Similarly the AC-DC converter commonly known as rectifier is widely used in battery charging of EV and HEV.

2)

3) A mathematical model of a DC Motor for the below equation using Simulink is as follows:

The equation of speed-torque characteristic equation is 

 ω</math>">ω =   V/Kϕ</math>">ϕ -Ra/Kϕ</math>">ϕ^2 .T

Let us consider,

V = 50 Volts, Kϕ</math>">Kϕ= 0.7, Ra</math>">Ra= 0.5Ω</math>">0.5Ω

0.5Ω</math>">The simulink model is a develop by using the constant block for the parameters in the equation

0.5Ω</math>">and the product and sum block to obtain the desrided output.

0.5Ω</math>">The ramp block is considered for the linear output of the torque.

0.5Ω</math>">The developed simulink model is as follows:

0.5Ω</math>">

0.5Ω</math>">The result of the simulink model is as follows:

0.5Ω</math>">

4) 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.