Analysis Of The Influence Of Load Torque On The Rotary Valve Speed And The Speed Closed-Loop Control Research

The measurement while drilling(MWD)technology is used for real-time measuring and uploading downhole information during drilling.The measurement while drilling system usually adopts the continuous pressure wave of drilling fluid to carry out the remote transmission of the downhole data to the ground.The key component of the system is the rotary valve.The speed control of the rotary valve is related to the generation and quality of drilling fluid pressure signal,which is a key problem to be solved urgently in the field of MWD.In this paper,the polynomial calculation model of rotary valve load torque was established by combining theoretical calculation and CFD simulation analysis basing on the force analysis of rotary valve structure and rotor.In order to accurately describe the variation law of rotary valve load torque with the rotation angle.The calculation model of load moment is divided into two parts by the process of opening and closing the rotary valve.According to the specific angle or time to calculate the model quickly switch.According to the balance equation of motor speed,the mathematical model of rotary valve speed is established.And linearization correction is carried out for the speed open-loop control system by the nonlinear compensation method which achieve linearization of the speed equation.Based on the linearization of the rotary valve speed open-loop control system,the PID closed-loop control system of the rotary valve speed was established.By selecting PID parameters reasonably,the ability of fast tracking control pulse and anti-interference ability of rotating valve speed can be improved.In the theoretical research,the Laplace transform of the speed equation and the transfer function analysis method of the speed are used to construct the complex frequency domain expression of the speed and the interference amount.The time domain response of the speed is obtained by inverse Laplace transform.The influence of the quick switch of the rotary valve load torque calculation model on the speed control is studied which is compared with the result of Simulink simulation analysis.The theoretical study shows that the quick switching of the load moment calculation model of the rotary valve not only produces certain interference itself,but also has a great influence on other interference quantities.The interference caused by the rotational speed time constant,flow measurement error and the calculation model deviation of rotary valve load moment is strengthened.So the influence on rotary valve speed control increases.The theoretical analysis results are verified by simulation analysis.In addition,in order to realize the experimental simulation of rotating valve speed control effect,the braking torque of magnetic powder brake is used to simulate the load torque of rotating valve.The dynamic response speed of braking torque is improved by using incremental compensation method of excitation voltage of magnetic powder brake.A rotating valve speed control simulation experiment device was established to measure and verify the speed control effect of drilling fluid pressure PSK modulation process at low speed.The research of this paper is helpful to the development and control of high speed rotary valve.