POWER DISTRIBUTION

A high frequency distribution system can help with the power demands of modern vehicles

The increasingly complex and power hungry demands being placed on the electrical systems in modern cars are forcing manufacturers to look at new technologies to overcome the limitations of the 12V dc supply. Various alternatives have been proposed such as higher voltages, dual or multi-voltage systems. While some aspects were improved, other problems were created.

For its part, Tunewell Technology has developed FlexiGrid, a high frequency power distribution system comprising a power supply, flat flexible cable structure and novel control transformers.

Providing the basic distribution at a higher voltage than normal, at 84V bi-phase, the current carrying requirements are dropped considerably, allowing a reduction in cable size and therefore cost and weight. The use of a flat flexible cable minimises EMC problems and allows easy installation into vehicle body interiors. In critical areas, the cable can be provided with further shielding, and the performance can be better than that of co-axial cable.

One of the key aspects of the system is the use of transformers to provide both optimum power delivery to each electrical device, as well as power switching. Small enough to be built into a connector, these transformers, called Flexitips, can also provide isolation from the main supply.

Each local area, or set of applications, is regulated from a node which provides a constant current loop. Redundancy can be provided by using two or more loops from a single regulator node. Power to each node is supplied by a constant voltage bus while signals from a multiplex control system such as Canbus are decoded and distributed to each Flexitip transformer.

The topology provides not only the optimum power for each application, something a dc system can only provide with the addition of costly dc-dc converters, but also facilitates multiplex control without resorting to relays or expensive electronic switches. The combination of single stage filtering and protection with the dc-ac inverter eliminates the need to protect individual devices against these problems, providing cost savings. The voltage and current regulation inherent within the system also reduces the input voltage range requirement. The need for fusing is also eliminated, as fault detection and current limiting provide inherent safety.

Perhaps the most significant aspect to the new technology is its production method. The use of a flat non-branching cable allows the wiring harness to be manufactured automatically, just-in-time for installation onto the car. The self adhesive nature of the harness cuts installation time and reduces the possibilities of errors.

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