**5. Conclusions**

144 Autonomous Underwater Vehicles

(a) Surge speed response (b) Yaw keep response

(c) Depth keep response

Fig.10 shows the combined control of heave and pitch for diving in vertical plane. For this case, the velocity of surge that the vehicle is commanded to track is 1.5m/s, which is not very large so that the vertical tunnel thrusters will suffer thrust reduction to some extent but still can work to provide a portion of vertical thrust for diving. Hence when the vehicle is commanded to dive, the pitch will not experience a large change, which is reasonable design

Fig. 9. Speed control results of surge with yaw and depth keeping

consideration in the case of large inertial vehicles.

In this chapter, the design of motion control system for Autonomous Underwater Vehicles is described, which includes both position and speed control in horizontal plane and combined control of heave and pitch in vertical plane. To construct the control system, a 6 DOF general mathematical model of underwater vehicles was derived, which is powerful enough to apply it to different kinds of underwater vehicles according to its own physical properties. Based on the general mathematical model, a simulation platform was established to test motion characteristics, stability and controllability of the vehicle. To demonstrate the performance of the designed controller, simulations have been carried out on AUV-XX simulation platform and the capacitor plate model S-surface control shows a good performance.
