Tham khảo tài liệu 'advances in flight control systems part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Hierarchical Control Design of a UAV Helicopter 247 s col s . ped Fig. 6. Simulation of the inner-loop of Subsystem 1. Outer-loop controller In the outer-loop of Subsystem 1 we use a P-controller Kp1 Fig. 7 . We can redraw this system as shown in Fig. 8 in which Gjn1 ịC1 SI A1 B1F1 1 B1G1. It can be shown that Gjn1 is a 2x2 multi-variable system. Unfortunately in general designing a P-controller for an MIMO system is difficult. However if we consider KP1 in diagonal form as Kp1 kp1 I2x2 we can apply the generalized Nyquist theorem Postlethwaite MacFarlane 1979 to design kp1 such that it stabilizes the system as described in the following part. Fig. 7. Control structure of Subsystem 1. Fig. 8. Redrawing the control structure of Subsystem 1. Stability analysis The characteristic loci of Gjn1 are shown in Fig. 9 where the dash-dot lines correspond to the infinite values. In Subsystem 1 Fig. 8 the inner-loop has already been stabilized using an Hx 248 Advances in Flight Control Systems controller. Therefore due to the presence of the integral term Gin1 has two poles at the origin and the remaining poles are in the LHP plane. Hence Gjn1 has no pole in the Nyquist contour. It follows from the form of the characteristic loci of Gjn1 in Fig. 9 that kp1 Ễ 0 TO will keep the entire system stable. However in practice we are subjected to the selection of small values of kp1 to avoid saturation of the actuators. kpi is a typical value. Fig. 9. Characteristic loci of Gin1. Tuning the controller With the above outer-loop controller the stability of the whole system has been achieved however the controller in the form of Kp1 kp1 X I2X2 with only one control parameter is not an appropriate choice. We need to have more degrees of freedom to tune the controller and achieve better performance. By considering the proportional feedback gain Kp1 diag Kp11 Kp12 as a diagonal matrix we have more degrees of freedom and can control each of the output channels in a .
