| During the drilling process,the downhole data communication method plays a vital role in the quality of the drilling engineering.Real-time downhole data can enable the surface staff to discover hidden dangers in the drilling process in time.Downhole data communication methods are divided into wired communication and wireless communication.Wired communication requires the use of physical media such as cables and optical fibers.As a result,the lower pressure gauge data cannot be obtained during the shut-in period,which has been eliminated.Wireless communication has the advantages of simple and fast construction and real-time data transmission,and is widely used at home and abroad.The wireless communication method based on electromagnetic field coupling is to form an electromagnetic field through coil coupling.The electromagnetic wave signal needs to pass through a complex channel composed of wellbore,tubing,bottom hole fluid,formation,etc.,to reach the ground.The requirement for penetration ability is extremely strong,so electromagnetic wave The signal frequency is very low,generally 1?20Hz.Since the impedance of the channel is only milliohm,how to drive the milliohm load is an important research content of downhole extremely low frequency communication.At this stage,the research on the milliohm-level load driving technology of downhole extremely low frequency communication is mainly based on the patented technologies of foreign companies such as Schlumberger,Geoservices,and Expro.These companies generally use the method of impedance transformation to use coils to perform the milliohm-level load.Drive,because the signal frequency is extremely low,the coil is too large and the efficiency is very low.Based on the research of LLC resonant converter,this paper proposes an improved digital power amplifier that can directly drive extremely low frequency milliohm-level loads without using coils to drive milliohm-level loads.The drive efficiency is significantly improved.The milliohm-level load drive technology of underground extremely low frequency communication provides a new solution.The main work is as follows:1.An improved digital power amplifier is designed,including: resonant conversion circuit,sampling circuit,and digital control circuit.The resonant conversion circuit is the conversion and output part of the circuit.The sampling circuit samples the output and feeds it back,and the digital control circuit controls the switch tube.This design uses two pairs of full-wave rectifier circuits to switch on and off,which enables the load to output a very low frequency square wave signal with a current of 10 A and a frequency of 10 Hz under a milliohm impedance.2.For the designed digital power amplifier,the steady-state fundamental wave analysis method is used to set and calculate the parameter values of the circuit.On the basis of the PI adjustment to set the output current value of the milliohm load,the double dead Zone control,allowing two sets of full-wave rectifier circuits to switch and generate an extremely low frequency signal.At the same time,synchronous rectification technology is used to make any group of full-wave rectifier circuits work in resonance when they work alone,which greatly reduces circuit losses.3.The improved power amplifier is simulated and designed.The simulation results show that when the load is 70m?,a square wave signal with a current of 10 A and a frequency of 10 Hz can be obtained on the load.Analyzing the voltage across the switching tube,the current flowing through the switching tube,and the drive signal shows that the converter is in resonance when it is working,the switching tube is in a soft switching state,and the switching loss is small. |
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