Week-6 Challenge: EV Drivetrain
Ans 1 = Three types of power converter circuits employed in EV and HEV are :
1) AC to DC (Rectifier) 2) DC to AC (Inverter) 3) DC to DC
1) AC to DC (Rectifier) = It is an electrical device which converts AC to DC, which flows in only one direction. This process is known as rectification as it straightens the direction of current. These are most commonly used in Plug in Hybrid Electric vehicles and Plug in Electric vehicles . The battery of these vehicles needs to be charged using a direct current source. For this purpose on board chargers or AC-DC converters are employed in PHEV and PEVs.
2) DC to AC (Inverter) = An inverter is a device that converts DC power to the AC power used in an electric vehicle motor. The inverter can change the speed at which the motor rotates by adjusting the frequency of the alternating current. It can also increase or decrease the power or torque of the motor by adjusting the amplitude of the signal.
3) DC to DC converter = A DC-DC converter is an electronic device or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power conversion. DC-to-DC converters change dc power from an onboard 200-800V high voltage battery into lower dc voltages (48V or 12V) to power headlights, interior lights, wiper, window motors, fans, pumps, and many other systems within electric vehicles (EV) and hybrid electric vehicles (HEV).
Answer 2 = pdf attached for written solution
Answer 3 = V = 51.2 V, Kϕ = 0.7, Ra = 0.5, T = considered as a linearly increasing function. (For reference simulink model file (.slx) attached along with graph picture (.png file)
Answer 4 = In the blog the author Wally ripple highlights the topics related to EV technology comparing Brushless DC Motors and Induction motors .
BLDC Motor : BLDC Motor rotor includes 2 or more Permanent magnets which generates the DC Magnetic field . This magnetic field enters the stator core and interacts with the current flowing within the winding to produce a torque interaction between 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.
Advantages = Low heat generation in the rotor, cooling capacity is better as compared to induction motor
Disadvantages =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 it has 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 in the rotor 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.