Re: (ET) Alltrax install!

[Robert Adsett <subscriptions aeolusdevelopment com>]

At 04:35 PM 2/23/06 -0800, Rob Brockway wrote:
> Don't you need 4 quadrant switching to do true regen back to the 
> battery.  I think someone in the group installed a 4q unit that does this.

Well, you need four quadrant control but since you control the direction of 
the field you have that.  Lets take the simplest case.
        Use a fixed field strength say put B+ across the field.  This now 
looks like a PM motor except you can change directions by switching the 
field connections.
        With the fixed field apply a voltage to the armature.  The speed 
will vary in proportion to the voltage you apply on the armature (after you 
have accelerated of course).
        Now consider what happens when you reduce that voltage (on the 
armature).  Lets say you reduce if from B+ to B+/2.  Now until you 
decelerate down to approx. 1/2 the speed you were before the motor is going 
faster that the voltage driving it, it is in fact now a generator and the 
current in the motor reverses.  You now have regenerative braking.  The 
current is flowing from the motor to the source and the current has changed 
direction giving you a braking torque.
        That give you two quadrants of control accel and brake in one 
direction.  When you flip the field you get two quadrants in the other 
direction and you have your full for quadrants (accel forward, decel 
forward, accel reverse and decel reverse).

 That's it, you cannot avoid the regen.

Robert


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