It allows a bi-directional power flow which allows for the motor to operate in all 4 quadrants (motoring and breaking). Bi-directional power flow means that when the motor is breaking and the DC link capacitor is charged up, by proper switching of the front end the breaking power is delivered to the grid. A brake chopper could be used but if breaking is going to happen often a lot of energy will be wasted.Can someone explain why and active front end (back to back inverter) improves power quality as opposed to usind simple diodes for the front end (rectifier) of the inverter?