International Rectifier showcasing advanced energy management system to extend battery life in EVs
20 October 2011
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| IR’s Evaira EMS provides the battery pack designer the ability to make trade-offs between battery pack service life, cycle times, and usable capacity without necessarily incurring cost penalties.Source: IR. Click to enlarge. |
Power management technology company International Rectifier is showcasing an advanced energy management system, Evaira, designed to extend battery life in electric vehicles at SEMA 2011 in Las Vegas, 1-4 November 2011.
The performance of a multi-cell battery pack is limited by the differences between the weakest and strongest cells in the pack. IR’s Evaira advanced energy management system (EMS) ensures all cells age uniformly by balancing the state of charge (SOC) of all of the cells within a battery system, resulting in an extension of battery life and significantly improving battery performance, according to IR.
Evaira EMS monitors the characteristics of each individual cell while the battery is in operation (discharge mode) and dynamically adjusts its relative loading to match its capacity using a process called Rapid-Bypass. Advanced algorithms are employed, performing SOC calculations based on voltage levels, discharge rates, coulomb counting, and pack SOH (state-of-health), which are compensated for temperature passed through Kalman filters.
This capability gives the battery pack designer control to make trade-offs between pack capacity, service life, discharge time, and cost parameters.
Designed to maximize convenience for the system integrator, Evaira EMS’s telematic features support remote statistics, including real-time pack voltage, current, ambient temperature, SOC, SOH, amps expended, and operating time through its integrated external interfaces. The unit has isolated digital I/O expansion lines available for custom applications. These can be used to drive indicators, turn on or off chargers, remote fans, etc.
Communications interfaces are also robust, being tolerant to EMI generated in high-current and high-voltage applications.
The battery management system targets electric vehicle applications for the automotive, commercial and military segments.
It's a lot of effort and money to recover small amounts of energy. In installing it to you car your adding a lot of complexity and some components that could fail.
Here's an important question:
If I don't install this system, but simply add more batteries to match the extra capacity the system gives will I have spent more or less?
Posted by: Dilbert Dilbertby | 20 October 2011 at 08:21 AM
Better battery management couple with much improved future batteries will push batteries expected useful life from 10 to 20 years by next decade or so.
BEVs with 1000+ Km range will become common place in about 10 years with smaller lighter battery pack. On-board genset (ICE or FC) may not be required for the average car. Long range heavy buses-trucks-locomotives-ships may be the exceptions.
Electric vehicles are here to stay and prosper. Resistance is futile.
Posted by: HarveyD | 20 October 2011 at 08:28 AM
Posted by: Engineer-Poet | 20 October 2011 at 06:23 PM
Very interesting but can you imagine doing this for the 192 cells used in a Leaf?.. Perhaps its a low cost integrated circuit that can be manufactured into each cell, and then be controlled wirelessly.
That graph is useless, it would have been nice if they had presented a nice graph with real numbers from a real example.
"If I don't install this system, but simply add more batteries to match the extra capacity the system gives will I have spent more or less?"
That depends on how cheap and rugged cells get. Actively controlling the load on each cell sounds expensive.
Posted by: Herm | 20 October 2011 at 09:27 PM
@Dilbert,
Until a robust chemistry is discovered, that withstands deep cycles without noticeable degradation, this is a key system in all batteries.
It prolongs the life of the battery and reduces risk of a bad cell degrading more rapidly because it is depleted more than the other cells. Or, if you don't want that, you can opt for the 'chain is as strong as the weakest link' approach, limiting the depletion of the battery to a safe level for the weakest cell. In essence, this means that the worst cell in a battery determines its capacity.
Now, the situation is that car manufacturers are obliged by law to guarantee their products for a minimum time and distance. They do not want a lot of owners claiming guarantee because of a few bad cells in their battery. The guarantee will probably set a minimum usable capacity. IIRC Renault guarantees 75% usable capacity after 5 years. And another thing not to forget is the damage to their reputation if a lot of batteries do not fulfill the owner's expectations.
Lastly, this is just a bunch of electronics with a microcontroller. Once it is developed, it will be quickly commoditized and become very cheap.
Posted by: Arne | 21 October 2011 at 06:12 AM
We need better batteries.
Meaning more kWh per $.
System complexity drives cost UPWARDS.
"Evaira EMS monitors the characteristics of each individual cell while the battery is in operation (discharge mode)"
Posted by: ToppaTom | 22 October 2011 at 04:29 AM
Evem with better batteries, capacity and self-discharge will never be perfectly matched in a string of cells. This leads to cells being over-discharged or even reverse-charged when the pack is called to supply maximum energy, with catastrophic results.
The BMS equalizes charge and reports incipient problems before damage is done. It's something like the oxygen sensor in an ICE car; you can run an engine without it, but you're running blind.
Posted by: Engineer-Poet | 22 October 2011 at 07:00 AM
TT...why not get the best of both worlds with better managed improved batteries? Even the best has to be protected.
Posted by: HarveyD | 22 October 2011 at 10:08 AM
Because monitoring some 1000 cells sounds doable but expensive and unreliable.
I assume they are searching for some low cost mechanism that can be part of each cell - a little like they do for christmass tree lights.
Posted by: ToppaTom | 22 October 2011 at 02:40 PM
Better cells will actually need less management, not more. Closely matched cells need very little active management at all, the closer they get in capacity and resistance the less needs to be done. I think this is a lot of hype trying to sell product. If it adds any sort of significant costs above existing BMS's it won't sell.
Posted by: JRP3 | 22 October 2011 at 02:46 PM
The question is whether it's cheaper to pay for ultra-precise cell manufacturing or a relatively simple mass-produced BMS module. So far the money is on BMS modules.
Posted by: Engineer-Poet | 23 October 2011 at 02:10 PM
You have to hand it to them for going to such heroics so as to squeeze out the last drop of juice from a lousy battery technology to begin with.
What's really needed something as robust as the original Edison nickel iron battery with much higher energy density of course.
Posted by: Mannstein | 24 October 2011 at 12:54 PM
And until you have that... Li-ion+BMS is the cheapest way to go.
Posted by: Engineer-Poet | 24 October 2011 at 07:21 PM
Umm yes - I can see a mass produced BMS system that has 1000 wires to 1000 cells to monitor them and can balance the state of charge of each of them.
I am not sure I see a relatively simple, low cost mass-produced BMS system.
Posted by: ToppaTom | 26 October 2011 at 11:24 PM
The BMS board fits on top of a cell and connects to adjacent cells. It has an isolated communications bus to talk to the central system monitor. These things need computing power on the order of a keyless remote transmitter and can be built very, very cheaply.
Posted by: Engineer-Poet | 27 October 2011 at 09:56 AM