Control and optimization of the generator electromagnetic torque of rotary steering drilling tools

Steering function of all-rotary steering drilling tools is achieved through adjusting electromagnetic torque of the downhole turbine generator. Through the control circuit model in a pulse-width-modulation (PWM) chop mode, the mathematical expression of electromagnetic torque of rotary steering drilling tools was deduced. A relationship between electromagnetic torque and control factors was established by means of numerical calculation and verified by bench test. The internal cause of ripple torque from a generator and its calculation were discussed in terms of magnetic energy storage and an active power factor calibration was introduced into the chopper control circuit. An optimized chopper control circuit was designed, which can improve power factors and circuit stability. The test result shows that the optimized chopper control circuit can eliminate harmonic ripple torque and enhance the stability of circuit while increasing the adjustment range of electromagnetic torque.