# Basic regenerative Braking with Permanent Magnet Motor - Help me!



## major (Apr 4, 2008)

Hi Ben,

Your controller is a chopper, or buck converter. It can provide a lower voltage to the motor than the battery voltage. And it is set up for unidirectional current flow, from the battery positive to the motor. To regenerate, you need to reverse current, from motor to battery positive. This requires a higher voltage than the open circuit voltage of the battery. So, how do you get the motor to act as a generator and provide a higher voltage? Not so simple.

One way would be to switch the controller out of the circuit and connect the motor (generator) directly to the battery. This will regenerate if your motor speed is high enough. In other words, if the top vehicle speed on the level is 40 mph and you’re going at 45 or 50 mph down hill, it will regen. But at speeds lower that 40, it will motor.

To get regen at speeds less that 40, you need to put a boost converter between the motor (generator) and the battery. This will take the lower voltage from the motor (generator) and increase it to a higher voltage to the battery.

Some really smart guys might be able to reconfigure the buck converter and use it as a boost converter for regen. This is complicated and you'll blow up a few, it not many, controllers trying to get it right.

The buck converter is what I call a quarter bridge, a switch (transistor) and a diode. A regen controller can be made with a half bridge, 2 switches and 2 diodes. Then it is a buck converter for motor current and a boost converter for generator current. Maybe someone makes such a controller for PM motors. I know Sevcon makes them for SepEx motor.

Regards,

major


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