48V Zonal Architecture in Advanced Electric Vehicles

The ability to scale to 48V fits with the ability of a zonal power architecture to minimize control systems and communications cables by moving to three or four zonal controllers, rather than dozens of chips scattered throughout the vehicle. It also helps reduce the development and validation costs of a new 48V wiper motor or a new 48V front lighting system by allowing designers to take the highest loads and convert them to 48V first.

Implementing a zonal architecture in the power distribution network allows selected loads to be taken and shifted to 48 V, while maintaining 12 V at the front and rear of the car and information stack. Such a hybrid power distribution system can have a 48 V core, with local conversion to 12 V if necessary. This mimics the latest board-level distributed power architectures used in embedded systems.

Voltage Conversion Strategies for Electric Vehicles

There are several approaches to address the challenges of converting high voltage (800 V or 400 V) to 48 V and then to 12 V. The standard approach uses many discrete components in a very large layout. A new approach takes miniaturized technology used in the high-power computing industry and adapts it for automotive applications to handle all of an automobile’s charge conversion needs.

One of the challenges of converting to 48V is creating the kind of power needed for the final load, whether it is a regulated load or not. Another aspect is managing the power from the regenerative braking. It is important to have a bi-directional solution so that when the regenerative braking system sends 48V back into the chain, that power can flow back into the battery.

This also applies to other advanced subsystems like active suspension and active steering systems that may have regenerative power. They can draw 48V and inject 48V back.

For example, Vicor BCM bus converters are inherently bidirectional. They can increase or decrease power without having to go through control steps, automatically switching from step-down to step-up or step-up to step-down. The converters sense which direction the current wants to go and react accordingly.

BCMs, which are high-density, high-efficiency, fixed-ratio (non-regulatory) isolated DC-DC converter modules, are available in a ChiP or VIA package. This simplifies cooling while providing PMBus control, EMI filtering, and transient protection.

They are available with inputs from 800 to 48 V, with different K-factors to suit a range of applications, including automotive. Leveraging the company’s sinusoidal amplitude converter topology, the high-voltage BCM chips are capable of achieving peak efficiencies of 98% with power densities of up to 147,000 W/l³Easily paralleled in high power networks with outputs that can be series connected to achieve higher output voltage, BCMs are inherently bidirectional and allow designers to reduce the overall capacitance required for the load.

It is therefore important to know how the system can step down or step up the voltage and switch inside the vehicle, especially when considering advanced applications such as home-to-vehicle-to-home and vehicle-to-grid-to-vehicle communications. A vehicle’s power electronics will need to continue to evolve to meet these and other emerging cross-platform capabilities.

Another example is the NBM family of fixed-ratio, non-isolated bidirectional (non-regulatory) DC-DC converters. These devices provide a complete DC-DC solution without the need for external input filters or bulk capacitors. The NBM2317 features integrated hot-swapping and inrush current limiting, with fast transient response supported by its low output impedance. The NBM family of converters is available in through-hole ChiP and surface-mount SM-ChiP packages.

Power and weight advantages in a 48 V system

Wiring harness weight is a major factor in the migration to a 48V vehicle, one of the many technical benefits of moving to 48V subsystems and motors. Higher voltage motors are more powerful, more energy efficient, and allow for smaller primary power supplies. The cost savings are significant, as a vehicle’s wiring harness can consist of hundreds of meters of cable. Thinner, lighter wiring is also easier to integrate into the vehicle and around its subsystems.

In addition to saving weight on the main electrical distribution and wiring harness, this improves thermal management because the system is more efficient, emitting fewer watts of heat. Thermal management is important in an electric vehicle to keep the batteries cool, which are very temperamental when it comes to temperature. Additionally, other electrical systems have a longer life when you manage temperatures in a way that prevents system failure and, ultimately, breakdown.

If you save a hundred watts of energy through efficiency improvements, that can be a saving of one gram per kilometer of CO₂ in an internal combustion engine, or up to 10 km of range in an electric vehicle.

Deployment of a zonal architecture in 48 V electrical networks for electric vehicles

In the case of a zonal architecture with an 800V supply, we can do a single conversion to 48V for the end-to-end network. When we get to where the loads are physically located in the vehicle, we can locally convert 48V to 12V. Without having to run cables throughout the car, you can simply have left and right front zones. You can then connect the loads to those. Then do the same thing at the rear of the vehicle with a 48V primary system and local 12V loads. This also allows for a more flexible and future-proof design as vehicles migrate to other voltages and power levels.

For example, consider a zonal architecture based on Vicor BCM, DCM and PRM devices, which are designed to operate in a network (Fig. 2). They can communicate with each other and perform current sharing so as not to overload one and not to underload the other. This makes it easier to design the electrical system, whether it is up or down, without having to do a lot of redesign work.