Microsoft Word - ETASR_V13_N2_pp10432-10438 Engineering, Technology & Applied Science Research Vol. 13, No. 2, 2023, 10432-10438 10432 www.etasr.com Abdulkader: Controller Design based on Fractional Calculus for AUV Yaw Control Controller Design based on Fractional Calculus for AUV Yaw Control Rasheed Abdulkader Department of Electrical Engineering, Imam Mohammad Ibn Saud Islamic University (IMSIU), Saudi Arabia rmabdulkader@imamu.edu.sa (corresponding author) Received: 16 January 2023 | Revised: 8 February 2023 and 12 February 2023 | Accepted: 15 February 2023 ABSTRACT This research presents a fractional order integral controller strategy, which improves the steering angle for Autonomous Underwater Vehicles (AUVs). The AUV mathematical modeling is presented. A Fractional Order Proportional Integral (FOPI) control scheme is implemented to ensure the yaw angle stability of the AUV steering under system uncertainty. The FOPI controller is validated with MATLAB/Simulink and is compared to the conventional Integer Order PI (IOPI) controller to track the yaw angle of the structure. The simulation results show that the proposed FOPI controller outperforms the IOPI controller and improves the AUV system steering and the overall transient response while ensuring the system's stability with and without external disturbances such as underwater current and different loading conditions. Keywords-Autonomous Underwater Vehicle (AUV); Nelder Mean Simplex (NMS); fractional calculus; FOPI I. INTRODUCTION Water covers more than 70% of Earth's surface and the oceans holds nearly 96.5% of all the Earth’s water. The scientific area of exploration of new resources in the ocean is in rapid increase. However, investigating under sea water levels can have some limitations with manned or human operated systems, while the use of Automatous Underwater Vehicles (AUV) can provide huge benefits in terms of reducing the risk of human lives, exploring deep sea levels, underwater surveillance, and cost saving [1]. AUVs are unmanned robots that have the capability to move under the water surface typically on a pre-defined mission, with satellite networks used for communication. In the modeling and design stage, an important aspect is the mission requirements and objectives. Additional details on the process of designing underwater vehicles can be found in [2]. Underwater vehicles can be categorized into two major types, Remotely Operated Vehicles (ROVs) or manned vehicles, which need a human to function and send control instructions in order to operate. The other type is the AUV or unnamed vehicles, which can completely function independently. Currently, AUV’s are rapidly used in a wide range of applications, which include environmental monitoring, underwater surveillance, scientific research, anti- submarine warfare, oceanographic discovery, subsea structure inspection, oil and gas natural research exploration, etc. [1]. The dynamics of underwater vehicles are well-known to contain significantly nonlinear dynamics and are dependent on a variant number of the system parameters. These nonlinearities can generate system uncertainties, time-varying dynamic model and severe effect by external disturbances such as unpredicted under water current, waves and environmental disturbances [1]. Controlling the AUV system is a challenging problem, and high control accuracy is needed to keep the system safe and stable when threatened by unpredicted factors. In order to handle AUVs' uncertainty and disturbance and to enhance their tracking performance, numerous control methods have been applied to ensure the stability of AUV systems, including the LQR control [3], neural networks [4], fuzzy control [5], PI/PID control [6], and Sliding Mode Control (SMC) [7]. Research findings on non-integer controllers indicate better quality control than Integer Order (IO) controllers. Some studies showing the advantages of implementing this control technique to stabilize the steering system of AUV’s are [8-12]. In this paper, a control method is proposed that is essentially found in fractional calculus theory, a non-integer or fractional order control. At present, fractional order controller based on Nelder-Mead Simlex (NMS) algorithm has not been utilized for controlling and stabilizing the yaw angle of AUV’s. The main contribution of this research is the development of a Fractional Order Proportional Integral (FOPI) controller scheme applied to enhance the steering stability and yaw angle for AUV dynamics with disturbances being present. The performance of the AUV structure and transient response is improved by designing the coefficients of the FOPI controller using the NMS method. The proposed controller is examined and its effectiveness to maintain the system stable with uncertain conditions such as underwater currents and load variation is shown. Engineering, Technology & Applied Science Research Vol. 13, No. 2, 2023, 10432-10438 10433 www.etasr.com Abdulkader: Controller Design based on Fractional Calculus for AUV Yaw Control II. AUV MODELING A. AUV Dynamics (Coordinate System) To derive a mathematical model and the equations representing the AUV structure, analysis of the system dynamics and kinematics is demonstrated, as three subsystems are considered. Figure 1 shows the two coordinate systems describing the movement of the AUV in 6 Degrees Of Freedom (DOF). The O-xyz axis is the motion coordinates and is static to the underwater vehicle, which is denoted as the body-fixed refence system. The movement of the body-rigid system is demonstrated to the earth (E) fixed system (�, �, Ψ� [13,14]. Thus, a non-integer order PI with feedback control scheme would be implemented to the AUV structure to achieve robust yaw angle stability with/without disturbances. Table I indicates the used AUV parameter values. Fig. 1. AUV 6-DOF coordinate system. B. AUV Kinematics The physical demonstration of the AUV structure and the equation of motion follow fixed body dynamics. Consequently, it is valuable to utilize the physical system components by diminishing the number of coefficients needed to control the system. Thus, it is the main incentive for the development of the vertical description of the equations of motion, which are successful for computer processing [13]. The 6-DOF AUV equation of movement follows fixed body dynamics. �� � �� �� � , �� � � � � � is the position vector and �� � � � � � is the orientation vector of the body and earth fixed reference system. The linear and angular velocities are specified as �� � � � � � , �� � � � � � where � � �� �� � . The two essential equations to model the AUV dynamical system are obtained from Newton's laws of motion. These equations can be defined as [13]: �� � ���� � (1) ��� � ����� � ����� � ��� � ! (2) where ���� is the transformation matrix, ! is the control input matrix, � , "��� , ���� , and ��� symbolize mass, Coriolis forces, damping matrix, and the gravitational matrix respectively. By including in the AUV system non-linear equations of motion, the kinematics equation can be expressed as [13]: �� � �#� "���� � ����� � ��� � !$ (3) TABLE I. AUV PARAMETERS Parameter Name Value Unit � AUV mass 50 kg %& Cross flow drag -131 kg/m %' Cross flow drag -0.632 kg.m/rad� +$ Cross flow drag -94 kg.m� /rad +& Cross flow drag -3.2 kg ./� Additional mass -0.9 kg %$� Additional mass 1.93 kg.m /rad %&� Additional mass -36 kg +$� Additional mass -4.9 kg.m� /rad 01 Moment of inertia 3.45 kg.m� /rad �2 AUV speed 10 m/s C. AUV Model Decoupling Due to the AUV system extreme nonlinear dynamics and coupling, a reduced system model is considered and linearized for the controller design, to ensure the stability and control of the AUV steering system. The vehicle model can be reduced and decoupled to study the yaw angle steering behavior. By considering the following three states, the sway v, yaw velocity r, and the yaw rate �. The steering movement can be acquired from the rudders and fins. Also, by disregarding the gravity forces, system damping and assuming an equilibrium point, the AUV system model can be decoupled as follows: 3 4 %&� �� � �./� 4 3��5 � � %& � � %$ �, (4) 01 4 +$� �� � �%&� #./� �� � � %$� �2� �+&� � +$ � � !$ (5) where �� � � . The linear AUV system can be expressed in state-space as: �� � 6� � 7� , � � "� � �� (6) where: 6 � ⎣⎢ ⎢⎡ ;<=#;<� �>?� #=�/@A;B=#;<� 0D