The nonlinear phenomena of active power filter (APF) with structural instability are analyzed in this paper. The nonlinear structural stability problems

caused by the instability of the gate drive voltage of IGBT and the transmission process of the instant pulse current produced from the process of IGBT on-off

are investigated. The conclusion is that the restraint of structural instability can be changed into interdiction of the spreading path of the instant pulse current. By researching anti-interference capability of forward and flyback convertors in simulation and experiments

it is certainly concluded that the flyback switching convertor can be used in the auxiliary switching power supply of APF to restrain the nonlinearity phenomena of APF effectively.