Among the control methods which have loop transfer recovery ability, such as the LQG/LTR approach, the design of target feedback loop (TFL) is one important step of the procedure for control system design because the performance of the control system designed is limited by its TFL. However in the LQG/LTR approach, the performance in crossing frequency region of TFL designed by Kalman filter or LQ regulator is undesirable, and this results in poor dynamic performance of the control system. In this paper zero placement (ZP) technique is utilized to design TFL for minimum phase plant. The TFL designed by ZP has two advantages over TFL designed by Kalman filter: (1) It has desirable performance in crossing frequency region; (2) Its transfer function approaches to a diagonal matrix at most under the meaning of least square. Obviously if the TFL is recovered well, then the control system has two corresponding features: good dynamic performance and good decoupling performance. Also the ZP/LTR control for a turbofan engine is studied, and simulation results show that the ZP/LTR control system has superior performance to the LQG/LTR control system.

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