For UAVs close formation system with nonlinear, under-actuated and strong coupling, an improved active disturbance rejection sliding mode control algorithm is proposed. First, extended state observer is designed to estimate the uncertainties such as aerodynamic coupling and compensate them in control law. Then, in order to reduce the difficulties of parameter optimization and controlling for under-actuated system, the ADRC is combined with sliding mode control to design the compound controller. Finally, Lyapunov function is used to prove that the tracking error converges uniformly to zero. Simulation results show that the proposed method not only simplifies the design of the controller, but also has high control precision and stronger robustness. The controller can effectively transform and keep formation configuration, and has a good expandability.

Mutual coupling between the flow and pressure regulation reduces rapidity of the control system. To address this, taking water standard facility as an example, the coupling between flow and pressure regulation is analyzed. Regulating valve opening and inverter frequency are selected as the main control variable of the flow and the pressure respectively. And a quick flow and pressure control method based on back-propagation(BP) neural network and PID control is proposed. The established neural network model achieves a high predicting precision. The relative error of valve opening prediction is within ±5 % and that of inverter frequency is within ±0.6 %. The experimental results indicate that the control combining BP neural network and PID can achieve a faster flow and pressure regulation: compared with the serial PID control, the regulation time is decreased by 38.5 %~87.3 %, and compared with the parallel PID control, that is decreased by 25.4 %~83.7 %.

Time-delay is frequently encountered in many control problems． The existence of time-delay induces difficulty in stability analysis
and may thereby lead to oscillations or degraded performance in closed-loop systems． This paper investigates the stability analysis
of linear time-invariant( LTI) systems with time delay depending upon the solution of the characteristic equation． Not only the absolute
stability but also the relative stabilities the transient performances are depended on the locations of the characteristic equation roots． The
existence of time delay transforms the closed-loop characteristic equation into a transcendental equation with an infinite number of roots．
By investigating the real part and the imaginary part of the transcendental equation，the characteristic equation can be transformed into a
rotation equation with two vectors related to the system parameters． The characteristic roots on the given region boundaries can be determined
exactly and concisely． Numerical examples are provided to illustrate the proposed algorithm．