Hi mani9876, I've been running Paul's 500 amp controller for nearly 2 years and 10k miles (16,000 km) in a Daewoo Matiz
Greg's 1999 Daewoo Matiz
The controller gives good performance in this size car. As far as regenerative braking, a series wound DC motor is a great traction motor but a very badly behaved generator. But most people don't need regenerative braking so I wouldn't let that stop you from doing a conversion.
I'm using a NetGain Impulse 9 motor and it is very good, only just fits into the Matiz. But another option that you should investigate is Kostov motors in Bulgaria. Being in the EU they will have a shipping cost advantage over the Netgain and also for me the dollar-sterling exchange rate is pretty rubbish at the moment which really pushes up the price of the Netgain motors over here.
You are right about the risk of a short circuit in the controller causing a potential run-away situation. But this risk is the same for any controller for this type of motor. You need to install a
Big Red Button to disconnect the pack in emergencies.
Regarding interpoles, I don't really understand them either, but the Kostov motors have them as standard. Apparently due to the interpoles you can keep the brush timing neutral, normally for voltages above 120 volts you would advance the brush timing. In order to do regenerative braking you need neutral brush timing. I only know of 2 controllers on the market that do regen on a series DC, Zapi and Kelly Controls. The Zapi are sold as off-road controllers only (ie forklifts) with a max 120 volts. I suspect the reason for this is something like a fork lift will be operating at slower speeds which means lower motor voltage (motor and pack voltage are not the same, motor voltage is determined by rpm and limited by pack voltage). In a road vehicle motor voltage is higher and this is where you get problems with regen braking and controllers going bang.