Research On Key Technology Of A Down-hole Electromagnetic Transmitter Based On DSP

In the process of deep well and directional well drilling,it is very important to measure and control well trajectory.Electromagnetic Measurement While Drilling(EM-MWD)technology is an important measurement technology for non-liquid drilling,such as gas and foam,and has significant advantages in data transmission rate of underground.A down-hole electromagnetic transmitter is an important part of EM-MWD system,It is installed in a special non-magnetic drill collar,carries out real-time communication and data transmission with the directional exploration pipe,encodes and modulates the received drill string attitude information,loads it to both ends of the insulated antenna after power amplification,forms a quasi-static electric field at both ends of the insulated section,and reaches the well pad ground through the ultra-low frequency periodic excitation current led along the drill pipe and the electromagnetic field transmitted along the formation After a series of data processing,information such as well trajectory can be obtained to realize wireless transmission of downhole measurement data.Due to the particularity of working environment(high temperature,high pressure,high humidity,strong vibration,narrow space)and the uncertainty of formation parameters,in order to achieve the high accuracy transmission of measurement data in the complex underground environment,this paper makes a systematic and in-depth study on the topology and control strategy of underground electromagnetic transmitter,including the following One aspect:1.Selection of the topological structure of the main power circuit of the electromagnetic transmitter;combined with various DC-AC inverter circuit topologies,in order to ensure that the transmitter can carry out stable data transmission underground,the single-phase inverter circuit is finally selected as the main power circuit topology.2.The choice of the control strategy of the main power circuit of the electromagnetic transmitter;choose the unipolar frequency doubling modulation method on the SPWM pulse width modulation method.No change,according to various advanced control strategies,the dual PI loop control strategy of the transmitter with voltage outer loop current inner loop is finally selected.3.A down-hole electromagnetic transmitter hardware and software design;electromagnetic transmitter hardware design mainly includes DSP control circuit,power amplifier and drive circuit,RS-485 communication circuit,LC filter circuit and detection circuit,etc.The software part design includes initial design of DSP system,Double-loop control programming,SPWM subprogram design,etc.4.Simulation and experiment test;closed-loop simulation of the system through Saber and Matlab/Simulink software,using double-loop control of instantaneous output voltage outer loop and instantaneous inductor current inner loop to ensure the system can track the output voltage changes in real time,according to the formation load Changes in the output voltage reduce the total harmonic distortion(Total Harmonic Distortion,THD)of the signal.Verify the effectiveness and implement ability of the control strategy.