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Alternative Fuels for Transportation
the motor. If the driver takes his/her foot off the accelerator, the controller
delivers zero volts to the motor. For any setting in between, the controller
“chops” the full volts thousands of times per second to create an average
voltage somewhere between 0 and full volts.
On pushing the accelerator, a cable from the accelerator connects to the
potentiometers. The potentiometer sends signals to the controller determining the amount of power to be delivered to the electric car’s motor. There
are two potentiometers in the vehicle and the motor controller reads both
potentiometers to confirm that the received signals are equal. The controller
will not operate if the received signals are unequal. A DC controller is a big
on/off switch wired to the accelerator. The operating mechanism of the DC
controller is simple and easy to understand. When the accelerator is pushed,
it would turn the switch on, and when the foot is taken off the accelerator, it
would turn it off. This mechanism of On/Off approach works well but the
task for the driver becomes difficult if he is supposed to manually control
the speed therefore the motor controller generates the pulse required to
carry on/off operation. This helps in regulating the power generated and
also the speed of the vehicle. The controller reads the setting of the accelerator from the potentiometers and regulates the power accordingly. For
example, if the accelerator is pushed halfway down the controller reads that
setting from the potentiometer and rapidly switches the power to the motor
on and off so that it is on half the time and off half the time. If the accelerator
pedal is 35% of the way down, the controller pulses the power so it is on 35%
of the time and off 65% of the time (www.howstuffworks.com).
Modern controllers adjust speed and acceleration by an electronic process
called pulse width modulation. Switching devices such as silicone-controlled
rectifiers, rapidly interrupt (turn on and turn off) the electricity flow to the
motor. High power (high speed and/or acceleration) is achieved when the
intervals (when the current is turned off) are short. Low power (low speed
and/or acceleration) occurs when the intervals are longer. The process is
shown in Figure 10.13.
The controllers on most vehicles also have a system for regenerative braking. Regenerative braking is a process by which the motor is used as a generator to recharge the batteries when the vehicle is slowing down. During
regenerative braking, some of the kinetic energy normally absorbed by the
brakes and turned into heat is converted to electricity by the motor/controller and is used to recharge the batteries. Regenerative braking not only
increases the range of an EV by 5–10%, it also decreases brake wear and
reduces maintenance costs.
In an AC controller, the controller creates three pseudo-sine waves. It does
this by taking the DC voltage from the batteries and pulsing it on and off.
In an AC controller, there is the additional need to reverse the polarity of
the voltage 60 times a second. Therefore, six sets of transistors are required
in an AC controller, while only one set in a DC controller is required. In the
Alternative Fuels for Transportation
the motor. If the driver takes his/her foot off the accelerator, the controller
delivers zero volts to the motor. For any setting in between, the controller
“chops” the full volts thousands of times per second to create an average
voltage somewhere between 0 and full volts.
On pushing the accelerator, a cable from the accelerator connects to the
potentiometers. The potentiometer sends signals to the controller determining the amount of power to be delivered to the electric car’s motor. There
are two potentiometers in the vehicle and the motor controller reads both
potentiometers to confirm that the received signals are equal. The controller
will not operate if the received signals are unequal. A DC controller is a big
on/off switch wired to the accelerator. The operating mechanism of the DC
controller is simple and easy to understand. When the accelerator is pushed,
it would turn the switch on, and when the foot is taken off the accelerator, it
would turn it off. This mechanism of On/Off approach works well but the
task for the driver becomes difficult if he is supposed to manually control
the speed therefore the motor controller generates the pulse required to
carry on/off operation. This helps in regulating the power generated and
also the speed of the vehicle. The controller reads the setting of the accelerator from the potentiometers and regulates the power accordingly. For
example, if the accelerator is pushed halfway down the controller reads that
setting from the potentiometer and rapidly switches the power to the motor
on and off so that it is on half the time and off half the time. If the accelerator
pedal is 35% of the way down, the controller pulses the power so it is on 35%
of the time and off 65% of the time (www.howstuffworks.com).
Modern controllers adjust speed and acceleration by an electronic process
called pulse width modulation. Switching devices such as silicone-controlled
rectifiers, rapidly interrupt (turn on and turn off) the electricity flow to the
motor. High power (high speed and/or acceleration) is achieved when the
intervals (when the current is turned off) are short. Low power (low speed
and/or acceleration) occurs when the intervals are longer. The process is
shown in Figure 10.13.
The controllers on most vehicles also have a system for regenerative braking. Regenerative braking is a process by which the motor is used as a generator to recharge the batteries when the vehicle is slowing down. During
regenerative braking, some of the kinetic energy normally absorbed by the
brakes and turned into heat is converted to electricity by the motor/controller and is used to recharge the batteries. Regenerative braking not only
increases the range of an EV by 5–10%, it also decreases brake wear and
reduces maintenance costs.
In an AC controller, the controller creates three pseudo-sine waves. It does
this by taking the DC voltage from the batteries and pulsing it on and off.
In an AC controller, there is the additional need to reverse the polarity of
the voltage 60 times a second. Therefore, six sets of transistors are required
in an AC controller, while only one set in a DC controller is required. In the