Series-wound DC & regen

Hi folks,

Sorry if this has been discussed already, I was unable to find it.
I am now considering of using a series-wound DC motor on enduro motorcycle, because of it's "infinite" top speed. Of cause the problem is to implement a regen capability, because the motor does not have a permanent magnet.
I've dome some searches and found out that it is "doable" but is "very complex". I've also found some "production" controller assemblies with integrated heavy duty contactors. Well, this is not the way I'd like to go. I am electronics engineer and believe that such capability should be possible to implement in more intellectual way. I.e. transistors.
In modern systems regeneration is done with a boost converter, which is using motor's internal inductivity. So I haven't put a lot of thought into it and came up with this schematic:

In this schematic the motor represents series-wound DC motor's rotor and the inductor represents it's stator (electromagnet).
In normal operation only lower transistor is used (PWM). In regen, both transistors are PWM'ed simultaneously: both of them are opened at the same time, this means field winding is being energized and the rotor is shorted for some time and when both transistors are switched off, a self-induction of the motor spikes a current back to the battery through upper diode.

Of cause I haven't thought all of it through and there may be (and I'm sure there is) some problems with the design. For example, battery power is being used to energize the stator.


Any comments from specialists are highly appreciated. Also, please give me some links to any technical material to study.

circuit said:

I am now considering of using a series-wound DC motor on enduro motorcycle, because of it's "infinite" top speed.

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Ah...remember that you can only spin the motor up to some max RPM based on it's physical construction, otherwise it becomes a grenade as the comm bars fly off the shaft.

Of cause the problem is to implement a regen capability, because the motor does not have a permanent magnet.

Click to expand...

That actually is not the big problem. It's that if you induce a current into the armature from the field, it is also induces a current in the field which induces more current into the armature, etc. If not carefully controlled you can do some nasty things really fast.

I've dome some searches and found out that it is "doable" but is "very complex". I've also found some "production" controller assemblies with integrated heavy duty contactors. Well, this is not the way I'd like to go. I am electronics engineer and believe that such capability should be possible to implement in more intellectual way. I.e. transistors.

Click to expand...

Not sure what you mean exactly. Most controllers that have integrated contactors (like Soliton1) use them to connect or disconnect the pack from the controller, both in normal use and in an emergency.

Otherwise, they use MOSFETs in low voltage controllers, and IGBTs in higher voltage systems.

There used to be some forklift controllers, and a few production EVs, that used contactor control, but I don't know of any made nowadays that do (I'm no expert on those though).

Regarding regen on a series motor, if you haven't seen it yet, you might look up Otmar's work on it at Cafe Electric.

Regarding the controller method, remember that a series-wound motor has the field (stator) always in series with the armature (rotor), so you can't energize one without energizing the other.

There are a number of discussion threads about series regen over at DIY Electric Car forums, too, covering these points in varying amounts of detail.

You'd be better off using a Sepex (separately excited) motor if you want to do regen with it and don't want to have permanent magnets or use AC or multiphase motors.