Is it possible to make a controlled between an electric motor and a generator to be mechanically coupled and sustainable energy system?

YES, but it can only be done long term with an electric motor that is designed to also run as a generator and if the generator will be paralleled with other generation the motor will need to be a synchronous motor.

í think it's not impossible, but the out come generated power will be very low, because energy is not created, it's transferred, so if you have a generator that gives KW, it will need mechanical power a little more than KW = HP, so motor you need should be KW to run the generator, ... which means that there is no or a little power lift to be generated and not taken by the driving motor.