The virtual vehicle: making power management easier

Due to the increase in vehicle comfort and safety features, there is a significant demand for more reliable electrical systems. An increasing number of vehicle electrical components require a greater amount of electrical power, which has to be ensured at all times. In order to effectively meet this challenge and enable early validation of the power network quality, vehicle manufacturers are now relying on simulation-based development methodologies.

In a modern automobile it is increasingly critical to balance sometimes competing power usage requirements, as well as regulate overall energy consumption. After turning off the combustion engine for instance, there must remain a sufficient amount of energy in the vehicle battery for the starter motor to re-start the engine.

Even when the engine is not running, some electricity is still being consumed, and a sufficient power supply must be ensured for this "sleep" mode, as well as for the active operation of the electrical network. The power supply must also be structured to avoid critical voltage drop-downs and compensate for voltage-drops as quickly as possible in active mode.

Today modern electrical networks leverage power management systems, which control the network and are responsible for electrical energy distribution. The intention is to make sure that power bottlenecks are addressed in an appropriate manner, which includes monitoring the on-board battery.

Simulation of power management strategies provides the best possible development tool for power network validation. The figure below illustrates a typical vehicle power network simulation.

A typical vehicle power network simulation Click on image to enlarge.

Simulation enables virtual test drives, "drive cycles," as well as the accurate prediction of the electrical network's behaviour. Simulation considers the following input data:

Utilizing the input data, simulation provides information on the characteristics of all voltages and currents within the network for evaluation. The behaviour of the battery state of charge (SOC) for example is available right after simulation has been completed. This information allows seeing whether there is a sufficient amount of energy available in the vehicle battery to restart the combustion engine.

Information on the generator's utilization is also available as part of the simulation results. As a result one can immediately determine if the generator size is sufficient, or whether the power management system has to apply additional strategies such as increasing the idle-running speed. By considering the algorithm, the power management's quality and impact can be evaluated in a clear and straightforward manner.