Vehicle Electrical System

System Components

The system simulated consists of the following component parts:

Operation of the System

The DC voltage must be kept constant so that the lights do not dim when other loads are switched on, for example: the starter motor or windscreen wiper motor. Likewise, if the A/C fan motor is running and the lights are switched on the fan motor must not slow down.

To ensure the DC voltage remains constant, even when the engine speed changes or when additional electrical loads are switched on, it is necessary to feed back the DC bus voltage and regulate the alternator generated AC voltage accordingly. The following events will help illustrate this operation:

  1. Speed variation: While the simulation is running, reduce the input DC battery voltage from 240 to say 150 V. When the simulation is over, display the DC bus voltage and the speed w of the DC motor. It is seen that the speed changes, but there is no change in the DC bus voltage.

  2. Load variation: While the simulation is running, change the value of the load resistor connected across the DC busbar. Display the DC bus voltage and current. The current changes with the load, but the voltage remains constant (as it should).

  3. To illustrate that the voltage regulator on the alternator is operating, change the constant on the second summer (the one with the two +ve signs) while the simulation is running. Display the AC and DC voltages and they will show the changes.