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Sendyne awarded second patent for active cell balancing technology for large battery arrays

5 October 2012

Sendyne, a developer of semiconductor components and advanced circuits for the management of battery systems used for grid storage and EVs, was awarded a new patent for its active balancing technology. Patent number 8,269,455 was issued by the US Patent Office for a Charge Balancing System with high efficiency and the ability to provide continuous and bi-directional charge transfers among cells in a large battery array.

Currently most battery packs employ what is called “passive balancing” to equalize cell charge. Passive balancing works by dissipating the energy of cells with greater charge to harmonize them with cells of lesser charge. The excess energy is dissipated as heat.

This process works only during the charge cycle; no balancing occurs during discharge and idle. In addition to wasting energy, Sendyne says, this method slows down the charging process. During battery operation “stronger” cells end up underutilized— their effective energy capacity left untapped. Finally, this method cannot correct imbalances that occur during a normal battery cycle nor account for power output differences among cells.

Sendyne’s active cell balancing method does not have these limitations. Balancing can be performed at any point in time, with or without the presence of a charger, with very small power losses. Utilizing this method, “weak” cells can be protected from overstressing, thus extending their life expectancy and subsequently the life expectancy for the whole pack. More of the total energy storage capacity of all cells is utilized, regardless of variations in capacity from one cell to the next. This reduces the need for pack overdesign.

Proper cell balancing not only increases available capacity for each discharge cycle, but also extends the lifetime of a large-scale battery pack. Effective balancing technology thus has a direct impact on the cost of battery storage.

—John Milios, Sendyne’s CEO

This is the second patent issued to Sendyne for its novel charge management technologies. This patent strengthens Sendyne’s IP portfolio, which includes 5 issued patents and numerous patent applications for technologies and semiconductor circuits aimed at reducing the cost and increasing the performance of energy storage systems.

In February, Sendyne and the University of Toronto entered into a research agreement to develop systems and electronics with the goal of accelerating the adoption of large scale battery storage for Electric Vehicles (EV) and utility-scale battery packs. (Earlier post.)

That research project is intended significantly to improve the cost and performance of such systems.

Sendyne is providing its patented technology as well as access to intellectual property, development tools and scientific expertise. The University of Toronto has developed significant technology on power supplies and power management systems which will be utilized for this project.

Leading the project team is Professor Aleksandar Prodic, from the Electrical and Computer Engineering (ECE) Department of the University of Toronto and the founder of the Laboratory for Power Management and Integrated SMPS, where the development will take place. Dr. Prodic, a recipient of several IEEE awards and distinctions, is an expert in power system design.

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This is patentable?  I had roughly this idea some time ago, and dismissed it as "something that is obvious to anyone schooled in the art"... and I've never worked in battery management.

@E-P: I once worked for an inventor who spent much of his time filing patents, which, after some back and forth with the patent office, were always granted. Getting a patent is 'easy' if you know what you're doing, regardless of the merit or originality of the idea. Having the means to defend your patent is another thing altogether...

This is so obvious that one can wonder why it was not done 20 years ago? Seems to be an easy way to extend battery pack life while maintaining higher performance.

Coupled with improved battery temperature management system it could improve reliability, durability and over all performance of current and future battery packs.

The difficult in such a system has always been been complexity, cost and efficiency of implementing such a system. I haven't read the patent fully to see if they have designed a novel way way of doing so - though I see they are touting high efficiency.

It has probably been easier to simply oversize the pack slightly to account for uneven capacity/power loss in a pack than to wire up each cell individually to shunt large amount of energy between cells to maintain balance.

Performing top-balancing of each cell is cheap and simple. It does waste some energy, but as long as you don't have any cells with significantly more internal resistance than the rest, the pack generally stays balanced fairly well on it's own with minimal balancing each day.

DaveR, I don't have the TIFF plugin to view the schematics in the patent, but the text description sounds a lot like a switching power supply.  All a cell has to do is shift energy to adjacent cells, and the full energy capacity of the battery can be used (and the risk of over-charged and over-discharged cells is slashed).

Active cell-balancing technology is based on switch-mode power supply (SMPS) circuit design. Energy is basically "pumped" north of a given cell by a simple inductor-based V-boost circuit.
The basic technology allows cell balancing at any time including discharging. There are distinct advantages but there are also cost and noise impacts to consider in the BMS design tradeoff. TI has patents as well and a variety of products that incorporate the technology (under the name of PowerPump) for smaller multi-cell batteries and EV battery stacks.
http://www.ti.com/lit/an/slyt322/slyt322.pdf
http://www.ti.com/lit/ds/symlink/bq77pl900.pdf
http://www.ti.com/lit/ug/sluu481/sluu481.pdf
These products include the bq77PL900, bq78PL114 and 116.
TI is apparently having some tech problems with the 114 and 116 chips which don’t seem to be limited only to lower-voltage LiFePO4 cells.
I’ll be on the phone with a TI FAE next week to learn more.

http://www.freepatentsonline.com/8269455.pdf

I suppose you cannot just stear each cell via 2 diodes to the input of a single switching PS which then takes current from the highest voltage cell and puts the output across the entire stack.

Cell temperature differences would be ignored, for one thing.

And we're dealing with some heavy currents, even for trimming, I suppose.

It is an old idea rendered necessary for lithium based battery packs, and rendered possible with high power semiconductors and switched mode regulators. Since every computer made this year and many years in the past use less than one volt power supplies to the processor and the memory, it is well known how to generate low voltage efficiently. Generating high voltages from low can also be done efficiently to operate lights as CFLs and others from 12 volt supplies.

This or another system uses the full battery voltage to keep individual cells charged and not being reversed charged during battery use. Reverse charging of cells often destroys them besides lowering the total battery voltage sometime by a double voltage loss

The ZEBRA cells and the new similar DURATHON cells have very little internal cell current leakage and are not harmed by heat so there is limited chance that the cells are not balanced and no chance that they will cause a fire.

Much of the cell problems would be reduced if flywheels or ultracapacitors were used at all times to deliver or receive the heavy currents. And there always should be a range extender generator available for electric vehicles. ..HG..

The makers of small solar garden lamps avoid the problem of cell imbalance entirely by having only one nickel cadmium cell and using switched mode semiconductors to convert the voltages for the solar cell to battery voltages and the battery or cell voltage to operate high voltage LEDs.

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