Parasitic inductance in power delivery cables may cause unwanted effects in the devices they are powering, such as switching power supply ringing, noise injection into the power line, and power line voltage drooping. The inductance of a wire increases with its length. This is a concern for Midnight Sun because power delivery in the car requires some fairly long cables. Some simple simulations are shown below to illustrate this effect:
Consider this circuit, where the 5uH inductor represents the parasitic inductance of a 3m long, 24AWG wire. At steady state, when the switch is closed, 120mA are expected to flow through R1. However, because of the inductance, the change in current is not instantaneous. For a period of time right after the switch is closed, the current slowly ramps up to 120mA.
The red curve represents the voltage at the top right node (at R1). Note that the voltage on the power line slowly ramps to its final value at steady state. With real devices, this effect may be compounded with yet more parasitics and cause further noise injection into the power line. This effect is the result of the wire/power supply inductance.
The solution to this is to add bulk capacitors, which serve as a large "tank" of power located closer to the load (i.e. after the long 3m wire).
