How to control braking circuit of the three phase voltage source inverter?
As the user Andy already told you, regeneration means that you dump the energy back into the mains. This is rather dynamic braking with braking resistor. There is no need of PI controller or something other complex algorithm, rather an on/off controller with hysteresis. It turns the transistor on at certain DC link threshold value and then it turns off, when the DC link voltage drops to a certain value.