High Energy DC-DC Conversion

An electric car still uses a 12 volt system to power all of the original 12 volt accessories: lights, horn, etc. This may also power some control circuits for the electric drive system. However, unlike a gas car, there is no alternator to keep this battery charged. One option in the early days of EVs was to use a deep cycle 12 volt battery, as heavy duty as possible, and recharge it when you charge the main battery pack.

Current practice is to integrate DC-DC converters into the power management system to step down (bulk converter) or step up (boost converter) the battery voltage to meet the needs of different devices such as traction motors, cabin electrical systems, fuel cell stacks or supercapacitors. This taps the full battery pack voltage and cuts it down to a regulated output, similar to that from an alternator. By tapping the full pack, there is no uneven discharge. Amperage required is so low that there is little effect on range. Isolation of the high and low voltage systems is maintained inside the DC/DC converter. This also eliminates the need for a separate 12 volt charging circuit for an auxiliary battery.

In future, there will be further voltage steps for supercapacitors or fuel cells; it isn’t viable to keep adding extra converters for every additional voltage. Having worked hard to reduce the cost, weight and size of battery packs and motors on hybrid vehicles, manufacturers are clearly unwilling to see those gains swallowed up by growth in the power management hardware.

Solving this problem will require the development of fundamentally new technology; The flexible converter will have to be capable of handling multiple voltages simultaneously on both the input and output sides, while achieving conversion efficiencies equal to the best single-range converters currently available.

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