Abstract: To control the Hopf bifurcation of a Qi system， the Hopf bifurcation type was firstly determined by bifurcation stability index. Then， the state feedback controller and Washout filteraided feedback controller were designed to control the Hopf bifurcation， respectively. The effects of controller parameters on the bifurcation position and the amplitude of limit cycle were discussed based on the Normal Form method. Simultaneously， the simulations using Matlab software were carried out to illustrate the results. Simulation charts and theoretical results show that the linear gain can change the position of Hopf bifurcation and even eliminate Hopf bifurcation， while the nonlinear gain can change the bifurcation type of original system. Finally， some conclusions were obtained with a comparison between the state feedback controller and the Washout filteraided ones.The results showed that the control effect based on Washout filter is better than the effect based on nonlinear state feedback controller.

Key words: Qi system, Hopf bifurcation, bifurcation control, Washoutfilter, Normal Form method