I have been hearing about so many different and novel techniques for battery charging and cell balancing lately. Designers are working feverishly to optimize 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 maximizes 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. See Figures 1 and 2.
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.
The way these improvements are implemented are by integrating the voltage step-up and balancing functions as well as charging functions inside a single converter topology. Instead of providing the entire output voltage and power, the converter in this configuration is only assisting the battery by providing a portion of the power, instead of the full power, to be delivered to the load. That portion of power is proportional to the difference between the output and the battery pack voltages. See Figures 3 and 4.
For more detail: Unique battery pack architecture patented by Sendyne