Study On Optimization Of Structural Parameters Of Downhole Generator In Directional Rotary Steering System

Point-the-bit rotary steerable drillingsystems are one of the most advanced steering drilling tools in the world,but there are no point-the-bit rotary steerable drilling systems available for production in China so far.And the development of large downhole generators is one of the technical difficulties.The difficulties of downhole generators include: how to minimize the loss of generators and how to stabilize the output voltage of downhole generators under the conditions of maximum output power at high temperature and limited space.In this paper,the design and optimization of underground high-power generators are studied in depth.Firstly,according to the installation position and working environment of downhole generators in point-the-bit rotary steerable drilling systems,this paper presents the selection method of the topology and internal structure of downhole generators in directional rotary steering system.Considering the calculation methods of copper loss and iron loss under different frequency and magnetic induction intensity,the accuracy of loss calculation of permanent magnet synchronous generator is further improved,which provides a theoretical basis for further research in this paper.Secondly,the variable flux linkage method is proposed to solve the problem that the output voltage of downhole generator varies greatly with the change of drilling fluid discharge volume.The Parker equation of permanent magnet synchronous generator is established,so as to calculate the length of stator and rotor that need to be coupled under different rotational speeds.The correctness of the method is verified by Ansoft finite element analysis software,which lays a theoretical foundation for the development of downhole self-stabilized generator.In order to maximize the output power and minimize the loss of downhole generators,Taguchi experimental analysis method is used to optimize the structural parameters of generators,and the method is verified for the rapid realization of the structural optimization for single objective.Furthermore,in order to achieve the optimal combination of maximum output power and minimum loss of downhole generators,this paper combines the fuzzy control method with Taguchi experimental analysis method to optimize the downhole permanent magnet synchronous generator prototype with rated output power of 3 kw,and finds the optimal combination of generator structural parameters under multi-objective conditions,which can not only meet the demand of downhole power system,but is practical to get relative low losses.Finally,the optimization effect of downhole generators is verified by laboratory high temperature test and load experiment.The downhole generators can work smoothly in a long time under 150 celsius degree,and the permanent magnet has no demagnetization,no reduction of insulation and less than 10% of output voltage adjustment.Through the test of slurry loop in Beijing Petroleum Machinery Works,the directional rotary steering system can be driven to realize the steering operation in clear water loop,and each index meets the power supply demand of the system.