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Exploring a unique battery pack architecture

17 Nov 2014  | Steve Taranovich

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Many different and novel techniques for battery charging and cell balancing have gotten out lately. Designers are working feverishly to optimise cell balancing and battery safety along with improved efficiency. I have been closely watching Sendyne for a while now, ever since the SFP100 was chosen to be one of 2013's EDN Hot Products and UBM ACE Award finalist in the category of Ultimate Products in Analog ICs. This IC is a current, voltage and temperature measurement solution and can be configured for automatic compensation for resistance dependence of the shunt over temperature with a separate reference design board.

What I really like about this technique is that the method used to measure current has a high enough degree of accuracy that it can be used for Coulomb counting in State-of-Charge estimations and is still cost-effective.

Performing true active cell balancing during all stages of operation of a large battery pack extends the life of cells and maximises the energy delivered during each cycle. Many large battery packs need to be overdesigned due to uncertainties and inaccuracies in the measurement method. This creates an additional and unnecessary cost that can be eliminated with this technique. And besides, so many active balancing techniques used start out as costly to implement for most cost-sensitive applications.

The Sendyne Constant Voltage Battery Pack Architecture (CVBPA) integrates active balancing, a 93% peak efficiency DC/DC converter and charging functionality into a single circuit while providing a fixed constant-voltage output to the load. This architecture enables the implementation of smaller, more efficient, safe and cost-effective battery packs (figures 1 and 2).

Architecture for large battery packs

Figure 1: A novel architecture for large battery packs integrates active cell balancing, DC to DC conversion and pack/cell charging into the same circuit. (Image courtesy of Sendyne)

Power processing efficiency

Figure 2: Power processing efficiency experimental results (Image courtesy of Sendyne)

The active balancer in the CVBPA controls how much power it draws from each individual cell and can charge specific cells even while the rest of the battery pack is discharging. This novel system was prototyped at the Laboratory for Power Management and Integrated Switch-mode Power Supplies at the University of Toronto, under the guidance of Prof. Aleks Prodic. A US patent was issued to Sendyne on cell balancing. The company is making the technology available for licensing.

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