Method for tool face angle control for rotary steerable drilling system

1 . A method for controlling a duty cycle for an AC Machine within a drilling tool, comprising:

determining an actual angular rate and an actual tool face angle of a mud flow controlling valve rotor, relative to a geostationary reference,

whereby the mud flow controlling valve rotor is actuated by the AC machine;

controlling the electrical current passing in a winding of the AC machine through a Pulse-Width-Modulation technique,

whereby the Pulse-Width-Modulation technique includes determining a regulating duty cycle for the AC machine;

calculating an angular rate error,

whereby the angular rate error represents the difference between a target-RPM angular rate command and the actual angular rate of the mud flow controlling valve rotor,

determining a duty cycle set point for the AC machine to reduce the calculated angular rate error;

calculating a first tool face error, including:

filtering a signal of the actual tool face angle through a first cut-off frequency, and calculating the difference between a tool face angle command and the actual tool face angle filtered at the first cut-off frequency;

determining a first correction to reduce the first tool face error,

whereby the first correction includes calculating a first duty cycle corrective value for the AC machine, updated at a third frequency;

calculating a second tool face error, including:

filtering the signal of the actual tool face angle through a second cut-off frequency,

wherein the second cut-off frequency is different from the first cut-off frequency, and

calculating the difference between the tool face angle command and the actual tool face angle filtered at the second cut-off frequency;

determining a second correction to reduce the second tool face error,

whereby the second correction includes calculating a second duty cycle corrective value for the AC machine, updated at a fourth frequency;

whereby the third frequency is set at a value lower than the fourth frequency;

summing the determined duty cycle set point, the calculated first duty cycle corrective value, and the calculated second duty cycle corrective value to obtain the regulating duty cycle for the AC machine.

2 . The method of claim 1 , further comprising:

determining an actual angular position of the mud flow controlling valve rotor, relative to a geostationary reference,

whereby the actual tool face angle is determined from the actual angular position of the mud flow controlling valve rotor.

3 . The method of claim 2 , whereby the mud flow controlling valve rotor is mechanically coupled to a sensor section.

4 . The method of claim 3 ,

whereby the sensor section includes one or more angular rate sensor, one or more magnetometers, and one or more accelerometers,

wherein the one or more angular rate sensor, the one or more magnetometers, and the one or more accelerometers of the sensor section provide signals in order to determine the actual angular rate and the actual angular position of the mud flow controlling valve rotor.

5 . The method of claim 2 , whereby the AC machine is mechanically coupled in rotation with a sensor section.

6 . The method of claim 5 ,

whereby the sensor section is mechanically decoupled in rotation with the mud flow controlling valve rotor,

whereby the sensor section includes one or more angular rate sensor, one or more magnetometers, and one or more accelerometers,

whereby the mud flow controlling valve rotor includes or is linked to an angular position sensor,

wherein the one or more angular rate sensor, the one or more magnetometers, the one or more accelerometers of the sensor section, combined with the angular position sensor of the mud flow controlling valve, provide signals in order to determine the actual angular rate and the actual angular position of the mud flow controlling valve rotor.

7 . The method of claim 4 , whereby the signals of the sensor section are processed through at least one digital controller.

8 . The method of claim 2 ,

whereby the regulating duty cycle for the AC machine allows driving a torque of the AC machine,

whereby the torque of the AC machine controls the actual angular rate and the actual angular position of the mud flow controlling valve rotor.

9 . The method of claim 2 , whereby determining the regulating duty cycle for the AC machine includes adjusting an amplitude and a duration of digital pulses through the Pulse-Width-Modulation technique.

10 . The method of claim 2 , further comprising:

controlling steering pads,

whereby the control of the steering pads occurs through controlling the angular position of the mud flow controlling valve rotor,

whereby controlling the steering pads includes a radial extension or retraction of the steering pads,

whereby controlling the steering pads influences a trajectory within a well for the drilling tool.

11 . The method of claim 2 further comprising:

updating the duty cycle set point for the AC machine,

whereby the update of the duty cycle set point for the AC machine includes:

detecting when the angular rate exceeds set limits over a period of time, correcting the duty cycle set point for the AC machine.

12 . A method for controlling a tool face angle of a drilling tool, comprising:

determining an actual angular rate and an actual angular position of a mud flow controlling valve rotor, relative to a geostationary reference,

whereby the tool face angle is determined from the actual angular position of the mud flow controlling valve rotor,

whereby the mud flow controlling valve rotor is actuated by an AC machine,

whereby the AC machine includes a winding adapted to pass an electrical current;

controlling the electrical current in the winding of the AC machine through a Pulse-Width-Modulation technique,

whereby the Pulse-Width-Modulation technique includes determining a regulating duty cycle for the AC machine;

calculating an angular rate error,

whereby the angular rate error represents the difference between a zero-RPM angular rate command and the actual angular rate of the mud flow controlling valve rotor;

determining a duty cycle set point for the AC machine to eliminate the calculated angular rate error;

calculating a first tool face error,

whereby the first tool face error represents the difference between a tool face angle command and the actual tool face angle, filtered at a first frequency;

calculating a second tool face error,

whereby the second tool face error represents the difference between the tool face angle command and the actual tool face angle, filtered at a second frequency, wherein the second frequency is different from the first frequency;

determining a first correction to reduce the first calculated tool face error,

whereby the first correction includes calculating a first duty cycle corrective value, updated at a third frequency;

determining a second correction to reduce the second calculated tool face error,

whereby the second correction includes calculating a second duty cycle corrective value, updated at a fourth frequency,

whereby the third frequency is set at a value lower than the fourth frequency;

summing the determined duty cycle set point with the calculated first and second duty cycle corrective values, to determine the regulating duty cycle for the AC machine.

13 . A method for controlling a tool face angle of a drilling tool, comprising:

determining an actual angular rate and an actual angular position of a mud flow controlling valve rotor, relative to a geostationary reference,

whereby the tool face angle is determined from the actual angular position of the mud flow controlling valve rotor,

whereby the mud flow controlling valve rotor is actuated by an AC machine,

whereby the AC machine includes a winding adapted to pass an electrical current;

controlling the electrical current in the winding of the AC machine through a Pulse-Width-Modulation technique,

whereby the Pulse-Width-Modulation technique includes determining a regulating duty cycle for the AC machine;

calculating an angular rate error,

whereby the angular rate error represents the difference between a zero-RPM angular rate command and the actual angular rate of the mud flow controlling valve rotor;

determining a duty cycle set point for the AC machine to eliminate the calculated angular rate error;

calculating a first tool face error,

whereby the first tool face error represents the difference between a tool face angle command and the actual tool face angle, filtered at a first frequency;

calculating a second tool face error,

whereby the second tool face error represents the difference between the tool face angle command and the actual tool face angle, filtered at a second frequency;

determining a first correction to reduce the first calculated tool face error,

whereby the first correction includes calculating a first duty cycle corrective value, updated at a third frequency;

determining a second correction to reduce the second calculated tool face error,

whereby the second correction includes calculating a second duty cycle corrective value, updated at a fourth frequency,

whereby the third frequency is set at the value of the fourth frequency divided by a value comprised between 2 and 200;

summing the determined duty cycle set point with the calculated first and second duty cycle corrective values, to determine the regulating duty cycle for the AC machine.

14 . The method of claim 13 , whereby the mud flow controlling valve rotor is mechanically coupled to a sensor section.

15 . The method of claim 14 ,

whereby the sensor section includes one or more angular rate sensor, one or more magnetometers, and one or more accelerometers,

wherein the one or more angular rate sensor, the one or more magnetometers, and the one or more accelerometers of the sensor section provide signals in order to determine the actual angular rate and the actual angular position of the mud flow controlling valve rotor.

16 . The method of claim 13 , whereby the AC machine is mechanically coupled in rotation with a sensor section.

17 . The method of claim 16 ,

whereby the sensor section is mechanically decoupled in rotation with the mud flow controlling valve rotor,

whereby the sensor section includes one or more angular rate sensor, one or more magnetometers, and one or more accelerometers;

whereby the mud flow controlling valve rotor includes or is linked to an angular position sensor,

wherein the one or more angular rate sensor, the one or more magnetometers, the one or more accelerometers of the sensor section, combined with the angular position sensor of the mud flow controlling valve rotor, provide signals in order to determine the actual angular rate and the actual angular position of the mud flow controlling valve rotor.

18 . The method of claim 16 ,

whereby the regulating duty cycle for the AC machine allows driving a torque of the AC machine,

whereby the torque of the AC machine controls the actual angular rate and the actual angular position of the mud flow controlling valve rotor.

19 . The method of claim 16 , further comprising:

controlling steering pads,

whereby the control of the steering pads occurs through controlling the angular position of the mud flow controlling valve rotor,

whereby controlling the steering pads includes a radial extension or retraction of the steering pads,

whereby controlling the steering pads influences a trajectory within a well for the drilling tool.