Study On Efficiency Improvement Of Undersea Contactless Power Transmission

In recent years, more and more underwater mechanical and electrical equipment were developed and used in undersea scientific research, resource explorations and so on. Safety and convenience are always of concern for underwater power transmission. The conventional method of linking the equipment and the power source with conductive connectors has intrinsic defects, such as the risk of seal wear, electric shock and so on. The contactless power transmission (CPT) technology is expected to resolve these problems because of its special advantages.The CPT technology has been studied for decades and widely applied in many land-based fields. The transmission efficiency is an important system performance, which is the main concern in system analysis and designation. The seawater has its electrical characteristics that may have negative impacts on the transmission efficiency. However, there is rare research and study on this matter.Based on the former research results, this thesis aims to optimize the CPT efficiency in undersea environments, through the theoretical analysis and design. In the limitation of the certain shielding structure for undersea, optimizing design method is improved. The prototype systems were designed and developed for the actual undersea environments with different application purposes. Moreover, the gap distance may have to be increased to an extent, which is beyond the ability of CPT to transfer power because shielding structure for deep-sea applications. To solve this problem, an ICPT system with a relay resonator for underwater efficiency improvement in the mid-range is presented in this thesis. Theoretical treatments and analysis of the system parameters are presented for improving the efficiency.The mutual model, magnetizing model and coupled mode theory (CMT) model of CPT were established respectively to deduce the transmission efficiency of CPT. The effect of quality factor Q, transmission frequency and load on the transmission efficiency with different compensation topologies was analyzed and discussed. CPT may suffer considerable power loss due to eddy currents in seawater when applied undersea rather than on land. The loss of power, which is harmful to transmission efficiency, was theoretical modelled and analysed. Through theoretical calculation and analysis, guidelines were presented to select the optimum frequency and parameters to maximize the efficiency for a certain electromagnetic coupler.For different undersea application purposes, prototype CPT systems including circuit and mechanical structures were designed and built. One of them was carried out a lake trial, which demonstrated that the designed system is able to transmit power contactless to actual undersea observation network equipment underwater with an efficiency of approximately85%and a5mm gap distance.The CPT system with a relay resonator (CPTR) was presented for underwater efficiency improvement in the mid-range. The dynamic model and the transmission efficiency of the presented system are introduced using CMT. The transmission efficiency performance is analyzed with respect to the different compensation topologies and loads. Theoretical treatments of system parameters such as the resonance frequency, Q-factor, the number and the positions of the relay resonators are presented for improving the efficiency. A flat spiral coil is chosen as the inductance of the relay resonator because it can be easily buried in the chamber of underwater equipment. Theoretical calculation of inductance and stray capacitance of the flat spiral coil are presented. Experiments are carried out to demonstrate that the presented CPTR system can substantially enhance the underwater transmission efficiency for mid-range distances, compared with the CPT system without the relay resonator.