Week-6 Challenge: EV Drivetrain

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

Power Electronics:

Power electronics is the application of solid state converters to the control and conversion of electric power.

The first high power electronic devices were mercury arc valves. In modern systems, the conversion is performed with semiconductor switching devices such as diodes, thyristors, and power transisitors such as the power MOSFET and IGBT. In contrast to electronic systems concerned with transmission and processing of signals and data, in power electronics substantial amounts of electrical energy are processed. An AC/DC converter (rectifier) is the most typical power electronics device found in many consumer electronic devices, e.g. television sets, personal computers, battery chargers, etc. The power range is typically from tens of watts to several hundred watts. In industry a common application is the variable speed drives that is used to control an induction motor. The power range of VSDs start from a few hundred watts and end at tens of megawatts.

The power conversion systems can be classified according to the type of the input and output power

• AC to DC (rectifier)
• DC to AC (inverter)
• DC to DC
• AC to AC
• AC to DC converter (rectifier):
• Half way rectification
• 
• A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction.

• Full wave rectification

• DC to AC converter(inverter):
• 
• A power inverter, or inverter, is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC).The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source.A power inverter can be entirely electronic or maybe a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use moving parts in the conversion process.Power inverters are primarily used in electrical power applications where high currents and voltages are present; circuits that perform the same function for electronic signals, which usually have very low currents and voltages, are called oscillators.
• DC to DC converter(Chopper):
• 
• 1) Step down Chopper :
• 
• Step down chopper as Buck converted is used to reduce the i/p voltage level at the output side. Circuit diagram of a step down chopper is shown in the adjacent figure.
• 
• 2) Step up Chopper or Boost Converter
• 
• Step up chopper or boost converter is used to increase the input voltage level of its output side. Its circuit diagram and waveforms are shown below in figure.
• 
• 
• AC to AC converter:
• 
• ANS.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%?ϕ">
  .T

• Given data:

  Rated Armature voltage = 72V

  Rated armature current = 400A.

  
• 

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

ω">ω�= V/Kϕ">ϕ� -Ra/Kϕ">ϕ�^2 .T

matlab program speed-torque char.

clear all

close all

clc

% given data

V = 72; % rated armature voltage

I = 400; % rated armature current

R = 0.5; % armature resistance

K_phi = 0.7; % constant factor

f = 400; % chopper switching frequency

omega = linspace(0,100,50);

% Speed-Torque characterstics equation

T_v = 24.7 + 0.0051*omega.^2;

V = 72*0.7;

T_m = 70.56 - 0.98*omega;

omega = (V/K_phi)-((R*T_m)/K_phi);

% plotting the result

plot(omega,T_v)

hold on

plot(omega,T_m)

axis([30 80 0 80])

xlabel('Speed(rad/s)')

ylabel('Torque(N-m)')

results are ploting speed - torque char.

ANS.4:- Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

A brushless DC electric motor (BLDC motor or BL motor), also known as an electronically commutated motor (ECM or EC motor) and synchronous DC motors, are synchronous motors powered by direct current (DC) electricity via an inverter or switching power supply which produces electricity in the form of alternating current (AC) to drive each phase of the motor via a closed-loop controller. The controller provides pulses of current to the motor windings that control the speed and torque of the motor. This control system replaces the commutator (brushes) used in many conventional electric motors.

The construction of a brushless motor system is typically similar to a permanent magnet synchronous motor (PMSM), but can also be a switched reluctance motor, or an induction (asynchronous) motor. They may also use neodymium magnets and be outrunners (the stator is surrounded by the rotor), in runners (the rotor is surrounded by the stator), or axial (the rotor and stator are flat and parallel).

The advantages of a brushless motor over brushed motors are high power-to-weight ratio, high speed, electronic control, and low maintenance. Brushless motors find applications in such places as computer peripherals (disk drives, printers), hand-held power tools, and vehicles ranging from model aircraft to automobiles. In modern washing machines, brushless DC motors have allowed replacement of rubber belts and gearboxes with a much simpler and more reliable direct-drive design.

An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction motor can therefore be made without electrical connections to the rotor. An induction motor's rotor can be either wound type or squirrel-cage type.

Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable, and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service, induction motors are increasingly being used with variable-frequency drives (VFD) in variable-speed service. VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable-torque centrifugal fan, pump, and compressor load applications. Squirrel cage induction motors are very widely used in both fixed-speed and variable-frequency drive applications.

Conclusion:

It has been concluded that 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.