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Design and Development of a Depth Controller for an Autonomous Underwater Vehicle with Variable Buoyancy Engine using Coefficient Diagram Method

Although the 'Coefficient Diagram Method (CDM)' can generate a stable controller which is robust and give the desired performance, the optimality and cost function are not yet under consideration. Herein, we design and develop an optimal controller for the depth control of an 'Autonomous Underwater Vehicle (AUV)' by analyzing a 'Linear Quadratic Regulator (LQR)' based controller using the CDM. The coefficient diagrams of conventional LQR controller and CDM controller are analyzed and the parameters to design an optimal LQR controller are identified. This controller is implemented for the depth control of an AUV with a 'Variable Buoyancy Engine (VBE)' and is found to have better performance as compared to the LQR and CDM. The objective here is to reduce the control efforts needed for depth control. Finally, we report the detailed theoretical analysis and simulation results.