The quadrotor unmanned aerial vehicles (UAV) are rich system with attractive and challenging properties such as nonlinearities and underactuated dynamics, which motivates researchers to design advanced and robust control algorithms. In this paper, we contribute to a further improved design of quadrotor UAV. The quadrotor dynamics and kinematics equations are briefly presented. Then, an improved integral sliding mode controller (ISMC) has been proposed and applied within an inner loop to stabilize and track the quadrotor attitude at the desired values. The aim is to enhance the performance of the ISMC controller by eliminating the chattering problem, meanwhile maintaining the trajectory tracking in a robust fashion. In our design, the switching function (sign(s)), causing the chattering, is replaced by the approximated functions (tan h, error, saturation, quasi-sliding mode method) in the ISMC control law. PD controller is applied as an outer loop controller to enable the quadrotor to track the desired position. The performance of the proposed ISMC controller is studied with regard to the chattering attenuation and trajectory tracking robustness and tested by simulation MATLAB/SIMULINK. Finally, a comparison with the switching function (sign(s)) is performed to alleviate the superior performance of the proposed design.

四旋翼无人机（UAV）是一个具有诱人且具有挑战性的特性（例如非线性和欠驱动动力学）的丰富系统，这促使研究人员设计出先进而强大的控制算法。在本文中，我们为进一步改进四旋翼无人机的设计做出了贡献。简要介绍了四旋翼动力学和运动学方程。然后，提出了一种改进的整体滑模控制器（ISMC），并将其应用于内环中，以将四旋翼姿态稳定并跟踪到所需值。目的是通过消除抖动问题来提高ISMC控制器的性能，同时以可靠的方式保持轨迹跟踪。在我们的设计中，引起颤动的开关函数（符号）被近似函数（tanh，误差，饱和度，准滑模方法）。PD控制器用作外环控制器，以使四旋翼飞机能够跟踪所需位置。针对颤振衰减和轨迹跟踪的鲁棒性研究了所提出的ISMC控制器的性能，并通过仿真MATLAB / SIMULINK对其进行了测试。最后，与开关功能（一个或多个）进行比较以减轻所提出设计的优越性能。