Study On Active Front-end Rectifier Of Rotary Steerable System

With the advance of the rotary steerable technology,the functions of rotary steerable tools are becoming more powerful.The measurement of downhole geological parameters,guidance and control of electronic compartments,and data communication is becoming more and more complex.This poses a greater challenge for voltage stable output and power factor of downhole power supply systems.The use of passive diode rectifiers in the rotary steerable system leads to the following problems:(1)large voltage fluctuations at the AC end due to changes in mud displacement and high dynamic events;(2)the wide range of changes in the DC bus voltage increased the complexity of downstream device selection and circuit design;(3)the electromagnetic interference generated by harmonic generation affects the normal operation of the guidance and control electronic compartment;(4)low power factor leads to additional losses and shortens the service life of the tool.To solve these problems,this thesis proposed the use of an active front-end rectifier to replace the passive diode rectifier,which can achieve harmonic suppression of input current,improve power factor and stable control of bus voltage.This article analyzed the generation and rectification technology of the rotary steerable system,electronic device selection,power management,system composition,and actual working conditions,and designed an active rectification system for the rotary steerable tool.Firstly,theoretical analysis was conducted on the downhole turbine generator and the active front-end rectifier.Secondly,to ensure the accuracy of the input AC source of the active frontend rectifier,a Simulink model of the downhole turbine generator was established based on the measurement and calculation of the actual parameters of the downhole turbine generator,and the output of the simulation model and the actual prototype was compared through performance testing.Thirdly,focusing on the actual working requirements of the rotary steerable system,the design parameters of the active front-end rectifier were proposed.Meanwhile,a simulation model of the active front-end rectifier for the rotary steerable system was designed in Simulink,and the static and dynamic performance of the simulation model was tested and analyzed.Finally,the active front-end rectifier system was designed,a laboratory test platform was built,and the performance of the active front-end rectifier was tested and verified.The results show that under both static and dynamic test conditions,the control system of the active front-end rectifier starts quickly,and the DC bus voltage is stably controlled and reaches the expected voltage value of400 V.When the system is in steady-state operation,it has good robustness,no steady-state error in the DC bus voltage,the low harmonic content of the generator-side current and sinusoidal waveform,total harmonic distortion coefficient THD<5%,and the system operates in a high power factor state with a power factor PF>90%,and all parameters meet the design requirements.This study has completed the research on the active front-end rectifier of the rotary steerable system,achieved application innovation of active rectification technology,and is expected to achieve closed-loop active management of DC bus voltage under changes in mud displacement and high dynamic events,harmonic suppression of generator-side current,and improvement of power factor.It is of great significance to improve the utilization efficiency of the rotary steerable system for power generation,simplify the circuit design and device selection of the guidance control electronic compartment,and improve the control precision of the guidance motor.It makes the entire rotary steerable system more efficient,compact,and coordinated.