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High-Voltage Solutions Take Over HEV/EV Designs (.PDF Download)

July 2, 2018
High-Voltage Solutions Take Over HEV/EV Designs (.PDF Download)

It should come as no shock that the dated 12-V auto electrical systems are no longer viable in new vehicles, especially hybrid electrical vehicles (HEVs) and the new all-electric vehicles (EVs). The replacement systems use either 48-V batteries for HEVs or 400+-V batteries for EVs. These power-hungry systems rely on the higher voltages as well as switch-mode techniques that give them the efficiency necessary to make them practical.

Why Higher Voltage?

As an EE, it should be obvious to you why higher voltages are being adopted. Higher voltages boost efficiency. The dramatic increase in electronics designed into vehicles over the years has revealed the weaknesses of standard 12-V electrical systems. The advanced driver assistance systems (ADAS) now in most new vehicles have added multiple processors and high-current sensors and actuators, in addition to other devices. Processor power has also jumped significantly, leading to added higher I2R losses in cables, connectors, and PCB connections.

For a given amount of power, higher voltages reduce the current. That means smaller wire can be used, thereby reducing cost and weight. Increasing the 12-V supply voltage by a factor of four to 48 V results in an x16 reduction in power. Most new hybrid vehicles now include a 48-V system, and standard vehicles with internal combustion engines are moving in that direction.

As for EVs, all require high voltage to power the motor. Voltage levels of 400 to 800 V or more are needed to generate sufficient power to run the vehicle. Look for higher voltages to become the norm in vehicle electrical systems.

The challenges facing the automotive industry require innovative high-voltage electronics technology and power management throughout the signal chain. Car manufacturers and Tier-1 suppliers now have a source of advanced semiconductor solutions to support all new designs. The following reference provides more detail.

Switch-Mode Power Supplies (SMPS)

As you know, there are three basic types of SMPS: ac-dc or rectifier power supplies, dc-dc converters, and dc-ac inverters. EVs and HEVs use all three types. The ac-dc supply is used to charge the batteries. The trend is to put the charger in the vehicle; the on-board charger (OBC) converts the standard ac mains voltage into a dc suitable for battery charging. OBCs greatly simplify and cost-reduce or minimize the need for charging stations.

The dc-dc converters are used in a variety of roles for powering the processors and other electronics such as a 48- to 12-V supply.

Inverters power the ac traction motors used in EVs and HEVs. Such ac motors are used in virtually all electric vehicles because of their greater efficiency. Variable-frequency drives provide the speed control.

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