A novel concept for regenerative braking of PWM-VSI drives employing a loss-free braking resistor

In this paper a simple circuit for feeding back the braking energy from the DC voltage link of a three-phase PWM AC drive system into the mains is proposed. The operating behavior of the system which consists of a series connection of a line-commutated three-phase bridge and a turn-off power semiconductor device and in principle does not require passive components is discussed. The stationary operating behavior is analyzed by analytical calculations and by digital simulation and represented in graphical form. Furthermore, the effects on the mains caused by the system for braking operation are analyzed and compared to the conditions for motoring operation and/or to the conditions for feeding of the DC link by an uncontrolled rectifier bridge. Finally, measures for guaranteeing high system operational safety are discussed and the advantages and disadvantages of the circuit are compiled in the form of an overview.