Hi,

Many of us look forward to supercapacitors becoming a buffer for our hybrid battery packs but the design issues are a little tricky. This design note, aimed at "Power Ride-Through" gives a clue to the types of problems that have to be solved:

Supercapacitors Can Replace a Backup Battery

The issues are:

• traditional lead-acid - a voltage managed device
• NiMH/LiON - a current managed device
• supercapacitors - a charge managed device, extreme voltage

Supercapacitor energy storage is not trivial and requires active electronics. But it does offer some very nice attributes. When I say "active electronics," all power has to pass through power electronics. This is not a 'connect and forget' technology.

Bob Wilson

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Thanks for the post -- good read. We are starting to use these now in aviation for ride-through of critical systems like avionics during buss switching and reversionary power switching.

The cell balancing problem is particularly difficult for application in a hybrid. If resistance techniques are used, the efficiency goes way down. The available semiconductor technolgies have limited ability to buffer current, an important consideration in the extremes of demand and charge typical of a hybrid environment.

In addition, any cell balancing circuit must provide for cell differences in the device related to forward flow vs. reverse flow characteristics. Many ultracaps exhibit significant differences in this area while the "ideal" device for a hybrid would be a totally balanced one with uniform charge/discharge curves (one inverted, of course).

The other challenge is plain old capacity. We need higher voltage devices and much greater current/cycle capacity to avoid excessively large arrays that are too complex.

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