High-speed on/off control for remotely operated underwater vehicles propulsion

As for the remotely operated underwater vehicle (ROV) with power between 20kW and 60kW, the weight of electric motor is too big, while the power of variable displacement motor is too high. In this paper, a virtual displacement on/off hydraulic control concept is proposed in their propulsion systems. Since the propeller is driven in switching mode, the speed fluctuation cannot be avoided. Therefore, the relation between the system parameters and speed fluctuation are analyzed by mathematical method, from which the approximate analytical Solutions of speed fluctuation and average speed are obtained. The following three parameters, switching frequency, duty cycle and moment of inertia, are of great importance. They play a key role in the speed fluctuation control. Based on these, an integrated valve-manifold is designed, which can be installed on the rear of motor to simplify the structure and to improve the response performance of the system. To reduce the speed fluctuation, a flywheel is added in the propeller shaft and a novel quasi PFM amplifier which can simultaneously regulate the frequency and the duty cycle is developed. Simulation result shows that the system has satisfactory dynamic performance and anti-interference ability. The speed fluctuation degree is only about 8.13% and the efficiency of system is 67.5%.