I'm a student and I'm working on a project that involves designing a 'DC-DC converter of an electric bicycle with regenerative braking system'. I am using MOSFET half-bridge topology as the DC motor drive (circuit is attached). Motoring operation works but regeneration doesn't. Can anybody please help me because I'm stuck with the regeneration part. Is the circuit wrong? Is there any other alternative?

 

What you need is called "two quadrant control" or "synchronous rectification" depending on the type of circuit it is used in. This uses two high side mosfet/switches. If you do a Google search on the terms it will give much information.

 

That circuit has everything you need for regen. What is the problem?

 

Question: What type of DC motor is this? shunt motor with external reactor? or is the reactor shown the series field of a compound motor?

With a shunt motor, the internal armature inductance provides sufficient reactance for the buck regulator (motoring) as well as for the boost regulator (regenerating).

Note that compound motors work poorly at regenerating--first, because without field current, there is no CEMF generated--second, if a little CEMF is generated and current starts to flow, it flows reverse through the series field, thus inverting the voltage generated by the armature--this would then be shorted via the discrete back diode as well as the MOSFET body diode.

Compound motors have a great torque /speed relationship that may be used for motoring, but in order to generate, there must at least be a combination series /shunt field arrangement--then, in addition, the series field winding must be placed within a bridge rectifier so that the series field current always flows in the same direction.

Synchronous rectification is possible with this topology, but I believe that this is above and beyond the scope of the exercise--do not attempt to go there until it basically functions.

 

You haven't explained how you're controlling the system in regenerative mode. I'd have thought that you'd need to sense the current through the lower MOSFET in order to control its duty cycle, and there doesn't seem to be any provision for that.

And is this a series-wound motor, or is it a permanent-magnet motor in series with an inductor?