Development Of Continuous Wave Signal Generator Based On Oscillating Shear Valve

It is very important to get the real-time uplinking downhole data in the MWD and LWDsystem. For quite a long time the data transfer rate has been restricting the development ofMWD and LWD technology, and the development of high-speed data transmission system isimminent. At present, the mud pulse transmission is the most widely used downhole datatransmission method in the LWD measurement system, and the drilling fluid continuous waveis the fastest transmission method. The continuous wave signal generator based on the rotaryvalve or shear valve is widely applied to the MWD logging system.This thesis introduce the working principle of continuous wave signal generator based onthe shear valve and its mechanism for generating pulses. The overall structure of the systemand a few more critical parts are also analyzed. A mathematical model of rectangular valveport and the circular valve port is established according to the thin-walled holes throttlingprinciple and the certain structural parameters of the valve port are given. Based on abovedesign, the influence of shape of the valve port and the number of the blades, the rotormoving mode, the axial clearance of stator and rotor on the pressure wave signal arecomprehensively analyzed. Then the modulation and the signal transmission characteristics ofthe continuous wave signal generator are analyzed according to the bi-directional oscillatingcharacteristics of the shear valve rotor. In the end, the modeling and simulating of controlsystem for motor which is used in the continuous wave signal generator is implemented.The continuous wave signal generator based on shear valve employed a rectangularvalve port and the transmission mode of planetary gear. The motor of drive system employeda permanent-magnet synchronous motor. It is proved that a1mm axial gap of the stator androtor is conducive to the transmission of the signal. When the rotor operation mode is similarto a square wave, the pressure wave curve would be a sine wave. The modulation is flexible, stable and efficient, and the modulation mode is capable of ASK, PSK, FSK, ASK plus PSK,ASK plus FSK,etc. The signal transmission characteristic is strongly impacted by the welldepth, carrier frequency and drilling fluid parameters. The speed of motor is adjustable andthe response is rapid because the motor control system is based on the vector control ofSVPWM.