I'm an undergraduate student and I'm member of university's team, which deals with the development of an electric vehicle. One of our projects, is the implementation of a complete regenerative braking system. We have almost achieved that but there is a problem with our charging system. To be more specific let me tell you some basics about our system:
1) during decelaration of the vehicle, the 3-phase electric motor functions as generator and transforms kinetic into electric energy,
2) the ac of the motor (generator) passes through an ac/dc inverter that produces a dc output voltage with range 0 to 34 Volts,
3) that dc passes through a dc/dc converter (buck converter) which produces a fixed output of 15 Volts,
4) that dc/dc converter (buck converter) is used to charge a supercapacitor bank (156 Farads) with rated voltage 15 Volts.
You can see a graphical depiction of the topology in the following image. The green arrow shows the direction of the dc current that flows from the motor to supercapacitors via the ac/dc inverter and the dc/dc converter during charging process.
During laboratory tests, we increase gradualy the rpms of the motor (by using another motor) and then the charging system smoothly starts to charge the supercapacitor bank.
Unfortunately when we took our vehicle for a ride to test the regenerative braking system on a real deccelaration, the dc/dc converter (see the orange box in attached pdf) burned.
The difference, in relation to laboratory tests, is that during the real deccelaration, the vehicle is moving with a high speed and suddenly the charging switch (see attached pdf) turns on for the charging process. We think that at those moments (while the charging switch is turning on), instantly some dc current spikes are produced with result the disaster of the dc/dc converter.
We think that a solution to that could be the placement of a coil either at the input of dc/dc converter or at the output, so as to eliminate the spikes. Is our thought right or something else happens?