Research On Control Allocation Of Ducted Fan UAV Based On Active Disturbance Rejection Control

The ducted fan UAV is a kind of aircraft with redundant control surfaces.One of the problems to be solved in the design of its control system is how to allocate the control law to the redundant control surfaces,that is,the control allocation problem.In the control allocation of the ducted fan UAV,the control law will be used as the desired moment.The control allocation algorithm solves a set of control surface commands according to the desired moment,so that the moment generated by all the control surfaces is equal to the desired moment as much as possible.For a type of ducted fan drones studied in this paper—single fan ducted UAV and twin ducted UAV,the control allocation problem is usually solved by using the pseudo-inverse method.However,the pseudo-inverse method cannot return to admissible control for all the moments in the attainable moment set,making the redundanted control surface sacrifices some control ability.In the design of the control system of aircraft with redundant control surfaces,the control allocator is closely related to the controller,and the control allocator is the next link of the controller.This paper designs an active disturbance rejection controler for attitude control of a type of ducted fan UAV,and on this basis,focuses on the control allocation of two types of ducted UAV:For the single fan ducted UAV,in order to not only return to admissible control for all the moments in the attainable moment Set,but also to further optimize the unattainable moment,This paper proposes a priority control allocation method to solving this problem.This method first decomposes the desired moments into a sequence of prioritized partitions,and then solves the constrainted optimization problem to obtain admissible control.Compared with the pseudo-inverse method,the proposed method can return admissible controls for a larger range of desired moments,and when the desired moments is unattainable,it can prevent the system into coupling due to actuator saturation.The proposed method is applied to the control allocation of ducted fan UAV.Simulation and experiments verify the effectiveness of the method.For the Twin ducted fan UAV,the difference in rotation speed of the left and right ducted fans is introduced as a new control surface to provide additional rolling torque for the rolling channel.Because the aerodynamic control vanes and fan are driven by actuators with differ-ent bandwidth(digital servos and brushless DC motor),and the actuator dynamics cannot be ig-nored.dynamic control allocation is used to solve the Control distribution issues.First,based on the weighted least squares method,the rate of the executor instruction is punished in the penalty function.Secondly,for the actuator whose transfer function can be approximated as the first-order inertial link,the post-compensation method is used to compensate the actuator com-mand attenuation.The simulation results show that the dynamic control distribution method with actuator dynamic compensation can distribute the expected torque of different frequencies to actuators with different bandwidths for execution,and can reduce the adverse effects caused by the actuator dynamics.