The Electric Vehicle Controller is the electronics package that operates between the batteries and the motor to control the electric vehicle‘s speed and acceleration much like a carburetor does in a gasoline-powered vehicle. Controller achieves this with the help of the instructions of the gear, the throttle and the brake, to control the running state of the electric vehicle including starting operation, speed, climbing strength, etc., and also facilitating the electric vehicle to brake.Thus it is employed to regulate the torque generated by the motors of electric vehicles by means of modifying the energy flow from the power sources to the motor.
The Controller transforms the battery’s direct current into alternating current (for AC motors only) and regulates the energy flow from the battery. Unlike the carburetor, the controller will also reverse the motor rotation (so the vehicle can go in reverse), and convert the motor to a generator (so that the kinetic energy of motion can be used to recharge the battery in the form of regenerative braking when the brake is applied).
In the early electric vehicles with DC motors, a simple variable resistor type controller controlled the acceleration and speed of the vehicle. With this type of system, a large percentage of the energy from the battery was wasted as an energy loss in the resistor as during slow speeds, when full power was not needed, a high resistance was used to reduce the current to the motor. The only time that all of the available power was used was at high speeds
Modern day Controllers
Modern controllers adjust speed and acceleration by an electronic process called Pulse Width Modulation. Switching devices such as Silicon 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
Regenerative Braking by controllers
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 re-charge the batteries. Regenerative braking not only increases the range of an electric vehicle by 5 – 10%, it also decreases brake wear and reduces maintenance cost.