The Downhole Turbine Torque Motor Voltage Feedforward Control

Rotary steering drilling is a new drilling technology that can control the direction of drilling by using an automatic control device, which is named as steering tool, near the bit. In a fully rotary steering drilling system, downhole inertial navigation control device, which is named as sevro platform, is the key device in direction control. It is a key problem how to realize stable control of stablilized platform in the drilling fluid flow under the condition of wide range and strong disturbance.To stabilize platform control problems for the structure and the effect of turbine motor torque. By analyzing the relationship between motor electromagnetic torque, the control signal, rotating speed of platform, the drilling fluid flow rate, establishing and perfecting the nonlinear dynamic model of the machine.A feed-forward compensation method of drilling fluid flow rate is proposed based on an analysis of the relationship between the drilling fluid flow rate and the control torque of turbine motor in the platform. After that, some disadvantages of this compensation method are pointed out. Then, another compensation method, which compensates the control signal according to the voltage of turbine motor is proposed. This control can be realized by adapting digital form or digital-analog mixing form. The system structure of digital-analog form has been built, which employed a voltage feed-forward circuit of the downhole turbine motor and an angle position feedback program of the stabilized platform. The feed-forward circuit has been designed and its PCB has been debugged. Tests of this PCB demonstrate that the signal arithmetic precision of this PCB can meet requirements of the platform’s angle control as well as downhole working conditions of temperature performance. Hydraulic driving tests’ results show that the controlling performance of digital-analog form has been preceded over the other in this platform. It is the first time that the platform can be controlled vibrational stably for a long time in four quadrants.The research works on reversal pattern of rotary steering drilling tool has theoretical significance and practical application value.