Part 1 of this article discussed the origins of automotive electrical system overloads and the problems posed by load transients.
The automotive accessory electrical transient overload situation portrayed in Part 1 of this discussion can be further explained by way of simulation. For this illustration, let's say the electric power steering (EPS) function is exercised on the vehicle while both engine management and some climate control electrical functions are in continuous operation. The EPS is assumed to demand 90A from the automotive electrical supply wiring (PowerNet) for a duration of 300 ms. This may represent a hard lane change maneuver for example or some parking lot maneuver at low speed.
In the first case shown below, the EPS is activated when the PowerNet is relatively heavily loaded, but without any supporting ultracapacitor electrical distributed module. The connected loads represent engine management at 27A, climate control at 55A, and a remote electronic control unit (ECU) at 15A. This remote ECU could be an audio module for example and is intentionally shown with local electrolytic capacitor for filtering and smoothing.
This PowerNet circuit has steering (EPS) active but without an ultracapacitor distributed module.
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In the figure above, the vehicle charging system is represented by an alternator and lead acid battery. The battery in this case is a relatively detailed Simplorer electrochemical model from the Ansoft automotive toolbox. The PowerNet is highly simplified into four branch circuits modeled as wire gauge resistances and includes the engine controls, cabin climate control, a local ECU, and the EPS (at far right). The PowerNet distribution point is noted as PDB or power distribution box.
The figure below illustrates the PowerNet transients for the above circuit when the EPS is active. Note the initial battery charging current from the alternator as the network stabilizes.
The PowerNet transients shown occur when the EPS is activated.
The plots shown in the figure above, left to right and top to bottom are: Alternator output current, battery current, battery voltage, EPS current, and voltage at the local ECU terminal. Note that the battery is demanding 20A of continuous charge current prior to the EPS transient. In this simulation the battery state of charge was assumed to be low and requiring charging. The key point is the high variability of the ECU terminal voltage: 13.8V to 13.2V, to 12.2V, and back to 13.2V. This is a very disruptive transient and one that is well beyond the capability of the large electrolytic filter capacitor to smooth.
Many such transients occur on the vehicle PowerNet so that the vehicle electrical environment becomes highly corrupted with such noise, subjecting the ECUs to wide power line surges and sags.
This PowerNet circuit has electrical power steering active and includes an ultracapacitor distributed module (upper right).
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The figure above is the same PowerNet circuit shown previously but with the addition of an ultracapacitor distributed module placed right at the EPS load point. This ultracap module is a standard automotive design product that provides battery-like stiffening and smoothing of the PowerNet in the vicinity of heavy electrical loads. All else equal, the presence of the distributed module can readily be observed in the smoothing action on the PowerNet and ECU voltages.
The ultracapacitor distributed module smoothes the PowerNet electrical transients when the EPS is activated.
As can be seen in the above figure, the PowerNet responses show a much more benign behavior with the distributed module. Note that the scales are changed and variations much lower than in the previous plots without the ultracapacitor module. The important point is that the EPS current is unchanged so its function is maintained. The salient feature of ultracapacitor distributed modules is that the terminal voltage at another branch circuit of the PowerNet feeding the local ECU sees a significantly reduced power line disturbance (lower right trace).
The benefits of distributed modules, or localized energy caches, provided by carbon ultracapacitor technology are very effective in PowerNet stabilization and help smooth and stiffen the power line at even remote branch circuits in the automobile.