Mathematical solution to vehicle energy efficiency

Researchers at the Massachusetts Institute of Technology believe they have found a solution for increasing the electrical power in cars of the future in an inexpensive way. The researchers also claim that finding could lead to an increase in a vehicles fuel economy.

‘On average we get twice as much power from the new technology,’ said David J. Perreault, a research scientist in MIT’s Laboratory for Electromagnetic and Electronic Systems. And because the technology builds on elements that already exist in a car, it can be integrated relatively easily and cheaply into existing manufacturing processes.

One of the key challenges associated with building the car of the future is increasing the amount of electrical power required for the vehicle.

Features such as heated windshields, new devices for cutting noxious emissions, and advanced suspensions will require more power than the current 14-volt automobile electrical system can currently handle.

Work on moving from 14 to 42 volts has, according to Perreault, been hindered by several subtle technical problems but Dr Perreault and Vahe Caliskan overcame such obstacles by using mathematical modelling.

‘We tried to boil it down to the simplest thing you could do to achieve the desired goal,’ said Dr. Perreault. They then built a revised alternator based on their mathematical models.

‘Essentially we replaced three of the passive elements for directing current with three active switches,’ said Dr. Perreault.

‘That gives us more ways to control the current flowing through the system.’ As a result, ‘I can use those switches to optimise current flow to get higher power.’

Dr. Perreault explained that conventional alternators are designed to optimise current flow only when a vehicles motor is idling. ‘At every other speed they’re very sub-optimal.’ The new technology optimises current flow at these other operating points resulting in higher output power and higher efficiency.

Because the new system is more efficient, ‘It also dissipates less energy as heat,’ said Dr. Perreault. ‘And that means the car burns considerably less gas to get the same amount of power.’

The increased control over current flow also solves another major problem associated with a higher-voltage system: large unexpected jumps in voltage due to changes in current.

Dr. Perreault said that in a 14-volt system, the voltage could jump to 80 volts when the system is disturbed in certain ways.

In the same situation, however, a 42-volt system could spike to 240 volts, which would mean that the car would have to be redesigned to survive the higher jolt.

The new technology solves this problem by allowing much greater control of the voltage. As a result, said Dr. Perreault, ‘our base voltage of 42 volts can be limited to about 60 volts during such an episode.’

The technology also solves another problem: jumpstarting a 42-volt vehicle with a 14-volt car. ‘People want to come out with 42-volt vehicles, but the passenger cars on the road all have 14-volt batteries,’ said Dr. Perreault. ‘If a car has a 42-volt battery, it cannot be directly jump-started from a 14-volt car. In fact, unpleasant things — like explosions — could happen.’

Any alternator, however, stores energy magnetically when it carries current. ‘Typically this actually hinders performance,’ said Dr. Perreault. ‘We’re using it here to help us.’

The energy storage ability of the alternator coupled with the increased controls of the new system would ‘allow you to take energy from a 14-volt battery and pump it up to the 42-volt battery you’re trying to charge,’ concluded Dr. Perreault.