PMW Control Method Of Downhole Tubine Motor Torque With Feed-forward Compensation

In the rotary steerable drilling system, stabilized platform is the core of the downholeoriented tools. It plays the key role of guidance control. It is a pivotal issue that how to realizestable control of stabilized platform under the condition of downhole complex environmentand strong disturbance action and flow changing in large range.To stabilized platform control problems, dynamics rules of platform are analyzed. Byanalyzing influences of disturbance actions to the platform movement and control, anonlinear dynamics model is established, which accords with the actual situation of downholeworking environment and describes effects of nonlinear factors on performances of thecontrol system as accurately as possible. The regular pattern of rotational movement aboutthis platform is obtained under no torque and complex applied torques based on simulation ofthis model, which relates to platform structure and torque parameters. By analysises, somemeasures are done for improving stabilized platform mechanical design.Meanwhile, for improving stabilized platform control performance of flow changing inlarge range, a flow feed-forward compensation method is proposed by researching relationsbetween flow and control torque of downhloe turbine motor. However, it is not easy tomeasure flow rate, and is difficult to realize flow feed-forward compensation method.Therefore, a voltage feed-forward compensation method is put forward. Then solutions toproblems of engineering application are provided, such as turbine motor voltage accuratemeasurement, signal temperature compensation, etc. PWM control system of downholeturbine motor torque is designed. And PWM motor torque control method with voltagefeed-forward compensation is put forward, then software realization method and controlcircuit are designed. Simulation analysis of voltage feed-forward angle feedback system ofstabilized platform which uses turbine motor torque PWM control method shows that thismethod can realize platform system stabilized control during the flow changing in large range(flow changing from24l/s to72l/s) and improve additive faculty of system for flow changingin large range.