There is little doubt that engineers have reached the limit of the available power in the present day automobile. It does appear that the industry will be moving to a 42 V electrical system that will give engineers more electrical power and the opportunity to add more electronics. However, if one starts to add up the power requirements of some of the proposed additions, it becomes apparent that the newly found power can be quickly used up by new equipment.

An important part of the new electrical system architecture will be power management. For the power management system to be effective, it will have to be capable of coordinating information about the generation and consumption of electrical power. To accomplish this, a high level of sophisticated electronics will be required.

The power management system will have to monitor and manage precisely the state of the alternator, batteries, electrical loads, and the powertrain. Alternator management means that the system must compute the capability of the alternator at all times based on its rotational speed. Different algorithms may be required for an ISA or a belt-driven 42 V alternator. The mechanical power profile of the appropriate alternator must be determined for the desired architecture. Alternator management supplies the appropriate amount of power as requested by the power management system.

Battery management is responsible for coordinating the activity of the battery or batteries in the system. This management system will change based on whether or not a single 36 V battery will be used or if a 12 V battery will also be included. By monitoring the temperature and state of charge of the batteries, the optimal charging voltage can be determined. It can also determine the maximum charging and discharging energy.

The management system must also determine if battery power is to be used to supplement alternator power. The so-called battery management system can also be used to manage other energy storage devices such as ultra- or super-capacitors. A challenge to the battery management system will be the handling of power created during regenerative braking with systems using an ISA.

Powertrain management is an important part of the overall power management system since the two are interconnected via the alternator. Engine speed has an influence on alternator output and is therefore a limiting factor in the design of the electrical power supply. Under full implementation of the 42 V electrical system using an ISA, there will be no belt-driven accessories connected to the engine. In addition, the ISA will affect the powertrain management with its start/stop scenario.

Electrical load management handles the electrical loads that will be increasing under the 42 V system. A distinction must be made between variable, conditional variable, and non-variable electrical loads. Variable loads are ones with storage behavior or a large time constant that make the effects of power variation not immediately perceptible to the driver such as the various heating functions. A temporary lack of power would not be immediately noticed in these functions. Conditional variable electrical loads are those with small time constants such as power windows. With these types of loads, the occupants would notice a lack of power to these functions. Non-variable electrical loads are ones that are safety relevant in power off or reduced power periods and are necessary for normal vehicle operation such as electric steering.

As more mechanical systems are converted to electronic systems due to the increased amount of available power under the 42 V system, control of the electrical loads becomes more critical. Electrical load management is important to prevent power peaks during load switching and can provide an equalization of the peaks through a switching sequence.

Effective power management will go a long way to making the 42 V electrical system meet the needs of the automotive industry.