Monday, December 3, 2007

Tweaking Regen Braking

I tweaked the regen braking this morning. As I mentioned earlier, the default parameters caused an oscillation or "lurching" during regen braking. I exchanged email with the support folk at Azure Dynamics about my theory - that the default 150-volt EE2NoRegenBat caused the controller to turn regen off and on as the voltage hovered near that value. The tech people agreed that setting NoRegenBat higher would be a fine workaround. I don't want to overcharge my batteries, so I decided to go with a higher NoRegenBat but a wider ramp (set by EE2RegenRamp). This chart illustrates what I did:

EE2NoRegenBat is set to 160, instead of 150, and EE2RegenRamp is set to 34, instead of 12. This had a great effect, as the following chart shows. It plots braking as a percentage of max torque (which is 53Nm with my current 100A power max for regen):

Despite the fact that the sampling period (1 second) introduces some aliasing, you can clearly see the oscillations in the old, default parameters (the blue line). The red line shows a much smoother curve, with substantially reduced lurching. I plan on leaving regen enabled from this point on to see what it does to range.

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