BMW Developing Power Net Extension With Ultracapacitors to Support Broader Application of Improved Micro-Hybrid Functions
18 May 2008
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| The ultracapacitor-based Power Net Extension is designed to alleviate the demands placed on the 12V battery by increasing micro-hybridization and electrification. Click to enlarge. |
The BMW Group is developing an application of ultracapacitors and a DC/DC converter to extend the power of the 12V power net in its vehicles to support the increasing demands made by its Efficient Dynamics micro-hybrid functions—Brake Energy Regeneration (BER), Auto Start Stop Function (ASSF)—and Electric Power Steering (EPS). (Earlier post.)
BMW has rolled out its Efficient Dynamics package in almost all of its 1 and 3 series and MINI vehicles as part of its efforts to reduce fleet CO2. All of these Efficient Dynamics functions use an AGM (absorbent glass mat) lead-acid battery as part of the vehicle’s 12V power net.
However, BER and ASSF are causing higher battery stress and therefore increased wear on the battery. Very high dynamic steering with EPS can cause voltage drops down to 11V, especially at low temperatures.
The implementation of these functions has reached the technical limit of the 12V power net, said Frank Przywecki of BMW during a presentation at the Advanced Automotive Battery Conference 2008 (AABC) in Tampa, Florida, last week.
Increasing integration is not possible in the 12V power net. The extension of the function into larger cars with big engines is not possible in the 12V power net. Further energy storage and the increase of voltage are required.
—Frank Przywecki
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| BMW’s series configuration for the PNE. Click to enlarge. |
To address the problem, BMW is developing a Power Net Extension package using ultracapacitors in combination with the existing 12V battery. After considering both series and parallel configurations of the ultracaps and 12v battery (both using a bidirectional DC/DC converter as the connection), BMW is choosing to pursue the series connection.
Fewer ultracapacitor cells are required in the series configuration (8 vs 12), and there is lower internal resistance and power loss of the overall stack.
The strategy of the enhanced power net to support the main Efficient Dynamics functions is:
During deceleration of the car, generator power is increased to charge the ultracaps to the maximum voltage. After the deceleration, the ultracaps are discharged by the DC/DC converter into the 12 V power net. During this time, the generator output is decreased to reduce demands on the engine.
At low speed, the ultracaps are charged in anticipation of the ICE stop phase. During the automatic stop phase, the 12V power net is additionally supported with energy out of the ultracaps. The additional energy support also reduces the voltage drop which is caused by the ICE startup. After start, the ultracaps charge again.
For electric power steering, the ultracaps and battery support the peak power of the steering system together. Energy discharged out of the ultracaps is replaced continuously by the DC/DC converter, ensuring that the energy is supported from the generator and not the battery.
The DC/DC converter is connected over the CAN bus with the vehicle data network. The DC/DC converter analyzes the car and power net status. An ultracap monitor controls the voltage of every cell and stack temperature. If the condition of the stack becomes critical, its support of the power net is reduced. If asymmetrical cell voltage is monitored, the voltage limits of the overall stack are adjusted.
After shutdown, all ultracap cells are leveled again. If the thermal conditions of the stack become critical, the voltage and current limits are decreased first, then support of the Power Net Extension is prioritized to electrical power steering.
BMW plans to make ultracaps part of the Power Net Extension to support at a minimum Brake Energy Regeneration and the Automatic Start Stop Function. In luxury-class cars, Electrical Power Steering will be supported as well.
Continental is also developing ultracapacitor-based extensions to the 12V power net.
Hmmm... BMW looks like its expanding it electronic motive department. Just another indication that the transition to electrified transport is well underway. Take that GW Bush!!!
Posted by: sulleny | 18 May 2008 at 08:05 PM
BMW have gone for a broad, shallow approach to CO2 reduction. This contrasts with most companies (say Toyota) which have developed 1 or 2 full hybrid systems (Prius).
It has a lot to recommend it as it applies to the full lower end of their model range.
BMW is lucky in that they sell more expensive cars based on engineering excellence.
They appear to have frozen their attempts to produce ever faster cars (which are ever more pointless on congested roads), and replaced this with lower CO2 cars, which benefit their owners (lower fuel costs) and society with lower emissions and fuel requirements.
So well done BMW, lets see if the other premium brands can follow suit.
And perhaps, lets see how much of this can trickle down to the more cost constrained manufacturers such as Ford, Renault, GM etc.
I guess the main thing should be to make the car as efficient as possible across the board, and waste no energy in braking.
The ability to crawl electrically in heavy traffic would also be good - even if it could work up to 15 kph, you could keep the ICE off for much of the time, benefiting everyone.
Perhaps you could have a "congestion sensor" which would see the car in front and determine that the car should keep crawling at 15 kph rather than opening up the ICE to move the car 5 meters and then stop.
Posted by: mahonj | 18 May 2008 at 11:47 PM
mahonj:
That "congestion sensor" could be the driver ;-)
I like your idea. Hundreds (thousands or millions) of engines idling to be ready to move 5 meters is wasting a massive amount of fuel.
I sometimes shut off my engine and only move every second time the line of stuck cars move one more ahead. But beware, it can lead to irrational reactions from the drivers behind you!
Posted by: Thomas | 19 May 2008 at 01:33 AM
Lame! Why don't they just bite the bullet and move to the 42 volt standard.
Posted by: DS | 19 May 2008 at 02:49 AM
You would think that at least the secondary power grid would be at 42V (cf 30 V).
It also explains why they introduced the new technology on the cheaper models, which is backwards to normal.
Posted by: DavidJ | 19 May 2008 at 04:29 AM
This is the kind of refinement in how energy is used that needs to occur. Unfortunately it is a yawner of an application aimed more at battery durability (read that as improved customer satisfaction and reduced warranty costs) than actual energy efficiency.
But, still, aimed in the right dir- ....Zzzzzz.....
Posted by: NCyder | 19 May 2008 at 12:29 PM
@sulleny,
GW Bush's mid-range Energy program is and was to transition to electric cars. It appears that is going to be a smashing success, in a few years. Have you forgotten that he created the US ABC to take the Li-Ion battery from lab curiosity to practical device? Li-Ion is the threshold battery technology required to make PHEV hybrids realistic.
Meanwhile he planned for ways to power the coming fleets of electrified cars, with realistic renewables, re-invigorated and next generation Nuclear, and cleaner Coal, like IGCC, while maintaininfg our progress toward clean air and water.
He even supported things like Bio-fuels and hydrogen as possible alternatives in the race.
Long Range, he re-initiated the ITER Fusion program, cajoling the rest of the World to proceed with it. Its another triumph of US diplomacy that you've never heard about, from the MSM.
His only failure was in the short term; he never got the, ahem, "gentlemen" in the Congress to drill for Oil in the US, to provide supplies until the electrified fleets arrived in the 2010-2020 timeframe. Instead we have supply shortages, and $4.00 gasoline.
Thank your local Watermelon for that. What are their proposals?
Walking is GOOD for you proles. Downsize your expectations; and downsize your lifestyles, according to the Gorebull.
"Power plants?" "We don't need no stinkin' power plants." say the noveau animist religious chanters of GAIA. Don't forget to subsidize the legal leaches.
We need to bleed the oil companies, the auto makers, and the electric utilities; it will make you happy (or at least distracted,) to see others converted to Devils, (aka kulaks, Jews, counter-revolutionaries, capitalists, businessmen, Church-goers, honkies, etc.) punished and as miserable as yourself.
Confiscate their money. Make sure that they have no money left to build anything either. Besides they need to pay off their campaign contributions to the legal leaches who corrupt the noble profession of Law.
A sound program, apparently to you.
Plus it clears the roads for their Government Furnished Equipment limousines with their GFE paid for fuel, that can whisk them about, with no traffic.
Posted by: stas peterson | 19 May 2008 at 06:34 PM
relax buddy!!
Posted by: | 20 May 2008 at 10:54 AM
Amen, stas. One only has to read this forum to know that the DOE has pumped hundreds of millions of dollars into alternative energy research during the Bush administration. So, please, lets give credit where credit is due.
Posted by: shigley | 21 May 2008 at 03:26 AM
Hmmm... Then Hugo Chavez was talkin' smack at the UN?
Posted by: sulleny | 21 May 2008 at 10:11 AM
Some combination of the EFPOWER lead acid battery for several distributed bipolar batteries might be easier to implement. Atraverda is working on bipolar as well and Firefly technology might be used as well...hg..
Posted by: Henry Gibson | 24 May 2008 at 08:58 PM
42V is not a solution. The primary advantage of 12 V is that there are only 6 battery cells, where as 42v would have at least 21, for more 3 to 4 times the battery management complexity.
Posted by: | 23 June 2008 at 02:20 AM
Last one was by me.
Posted by: Michael McMillan | 23 June 2008 at 02:20 AM
By mating an ultra-capicitor stack with a 12V lead acid battery they can achieve most of the advantages of each, leaving the primary disdvantage of total energy storage to be taken care of by the engine.
A lead acid battery in this use has at least 5 times the life while having 1/15th the cost of any lithium cell except the A123 cells which have a slow rate of charge,
The capacitor bank effectively acts as a buffer to reduce the ripple to the battery, and dampen the hard discharges and hard charges which would otherwise be transmitted to the battery.
The main reason to slow the charge and discharge rate is to keep the battery from getting too hot. Hot batteries degrade faster. The capacitor bank also gives the effect of having a much larger battery connected, without increasing the cost of maintenance.
Posted by: | 23 June 2008 at 02:28 AM
again by me, this time checking the box to remember info.
Posted by: Michael McMillan | 23 June 2008 at 02:29 AM