nonlinear loads can be classified in to three categories. the first is voltage stiff loads such as diode rectifier with capacitive filter at DC link feeding VSI-based AC motor drive, computer's power supplies etc. these loads draw nonsinusoidal currents from grid. the second category is current stiff loads such as thyristor-converter-fed DC motor drives or CSI based AC drives or HVDC systems. the third category is a mix of these two type. neither stiff voltage nor stiff current.