The most complex and important system in an EV is the control system. The control system is responsible for governing the operation of the electric vehicle. The control system receives inputs from the operator, Controller feedback signals from the motor controller and motor and also feedback signals from other systems within the EV. The speed at which the control system must receive data from other systems, process the data in an algorithm and output a response to the given conditions must be accomplished in Milli seconds. This requires the control system to have a microprocessor, just like a computer, to accomplish its tasks. Though no two control systems are identical, most of the feedback signals are similar. The table below lists common components of a control system and the feedback signals that are sent to the microprocessor.
The control system must continuously monitor the feedback signals listed as mentioned in my previous post: (Electric Vehicles: Electronic Controller Mechanism). For instance, if the temperature of the windings in the motor gets too hot, the magnetic properties of that motor can be permanently altered or the windings may melt. By feeding a signal back to the microprocessor, the control system can limit the output of the motor if it senses a temperature rise. The same limiting or shutdown of any system can take place if an undesirable condition is or has occurred. Other feedback signals give information to the microprocessor to control the speed of the vehicle. The accelerator pedal functions in much the same way as conventional vehicles. As the pedal is depressed, an increasing signal voltage(not traction battery voltage) is sent to the microprocessor which instructs the motor controller to increase the amount of current in the motor windings, causing the motor to spin faster. As the signal voltage from the accelerator pedal is decreased, the motor spins slower.
In some advanced control systems, it is possible to limit the amount of current that flows to the motor, based on a switch selection. This allows the operator to adjust to a driving style that fits a particular situation. For instance, if a driver needs a certain range(in miles) from a single charge, the range selection can be set so that the microprocessor will limit the amount of output current from the motor controllers to a preset limit. If the preset limit is 100 amps, the microprocessor will not allow any current above this limit to flow to the motors. In this mode, acceleration ability is sacrificed for range. If the driver is in an area where the vehicle must climb steep grades, the range selector can be set so that the maximum current capability of the motor controller and motor can be used. The range selection feature is a valuable feature that adds to the efficiency of the motor controller. The ultimate goal of a control system is to maximize the energy stored within the traction battery and to prevent unsafe conditions from occurring within the electric vehicle.
