Sensor commuated electric motor with sensorless angular position determination and method

1. An electric motor assembly that uses sensors for commutation and back electro-magnetic force (emf) voltage to determine an angular position, the electric motor assembly comprising:

an electric motor having a rotor and a stator that includes one or more windings;

one or more sensors on the stator and configured to determine an angular position of the rotor; and

a motor control circuitry electrically connected to the electric motor and to the one or more sensors and configured to control a commutation of the electric motor based on signals received from the one or more sensors,

a valve member attached to the rotor of the electric motor;

wherein the motor control circuitry is configured to calculate the back emf voltage from values of an overall current supplied to the electric motor, an overall voltage supplied to the electric motor and an average resistance of the one or more windings;

wherein the motor control circuitry is further configured to calculate a total angular rotation of the rotor using the back emf voltage by integrating over a period of time a product of the back emf voltage and a proportionality constant k, to produce a value of the total angular rotation of the rotor over the period of time of the one or more windings;

wherein the motor control circuitry is further configured to control the electric motor based on the back emf voltage and not based on the signals from the one or more sensors; and

wherein the motor control circuitry is further configured to track a position of a pilot valve by counting a number of phase transitions relative to the completely closed position or the completely opened position of the pilot valve, and to convert the number of phase transitions to the total angular rotation of the rotor of the electric motor; and

wherein the motor control circuitry is configured to store a pre-defined angular rotation limit corresponding to an amount of the angular rotation of the rotor of the electric motor that cause the valve member to move from a first fully open position to a second fully closed position, or vice versa.

2. The electric motor assembly of claim 1 , wherein the one or more sensors is a sensor.

3. The electric motor assembly of claim 1 , wherein the motor control circuitry is further configured to stop the electric motor from further rotating the rotor upon the total angular rotation of the rotor reaching the pre-defined angular rotation limit.

4. The electric motor assembly of claim 1 , wherein the back emf voltage is a calculated value, determined based on a formula back emf=(V−I·R)·k, where V is the overall voltage supplied to the electric motor, I is the overall current supplied to the electric motor, R is the average resistance of the one or more windings, and k is the proportionality constant.

5. The electric motor assembly of claim 1 , wherein the electric motor is a brushless direct current motor.

6. A mud pulser configured to transmit data from inside of a well to a surface of the well through pressure waves generated in a fluid column that flows inside the well, the mud pulser comprising:

a housing configured to be supported by a wall of the well;

an electric motor located in a motor cavity of the housing and having a rotor and a stator that includes one or more windings;

one or more sensors on the stator and configured to determine an angular position of the rotor;

a pilot valve connected to the electric motor and configured to move in a pilot valve chamber for closing and opening a valve orifice for generating pressure signals that propagate through the fluid column to the surface; and

a motor control circuitry electrically connected to the electric motor and the one or more sensors, and configured to control a commutation of the electric motor based on signals received from the one or more sensors;

wherein the motor control circuitry is configured to calculate a back electro-magnetic force (emf) voltage from values of an overall current supplied to the electric motor, an overall voltage supplied to the electric motor and an average resistance of the one or more windings;

wherein the motor control circuitry is further configured to calculate a total angular rotation of the rotor using the back emf voltage by integrating over a period of time a product of the back emf voltage and a proportionality constant k, to produce a value of the total angular rotation of the rotor over the period of time of the one or more windings;

wherein the motor control circuitry is further configured to control the electric motor based on the back emf voltage and not based on the signals from the one or more sensors; and

wherein the motor control circuitry is further configured to track a position of the pilot valve by counting a number of phase transitions relative to the completely closed position or the completely opened position of the pilot valve, and to convert the number of phase transitions to the total angular rotation of the rotor of the electric motor;

wherein the motor control circuitry is configured to store a pre-defined angular rotation limit corresponding to an amount of angular rotation of the rotor of the electric motor that cause the pilot valve to move from a first fully open position to a second fully closed position, or vice versa.

7. The mud pulser of claim 6 , further comprising:

a rotary-to-linear converter mechanically coupled between the electric motor and the pilot valve to enable linear reciprocation of the pilot valve when the rotor rotates,

wherein the one or more sensors is a Halt sensor.

8. The mud pulser of claim 6 , wherein the motor control circuitry is further configured to stop the electric motor from further rotating the rotor upon the total angular rotation of the rotor reaching the pre-defined angular rotation limit.

9. The mud pulser of claim 6 , wherein the back emf voltage is a calculated value, determined based on a formula back emf=(V−I·R)·k, where V is the overall voltage supplied to the electric motor, I is the overall current supplied to the electric motor, R is the average resistance of the one or more windings, and k is the proportionality constant.

10. The mud pulser of claim 6 , wherein the electric motor is a brushless direct current motor.