Controlled stop of an electric hydraulic fracking pump

A pumping system for hydraulic fracturing, comprising:

• a pump;
• a gearbox mechanically coupled to the pump;
• a driveline mechanically coupled to the gearbox;
• an electric motor mechanically coupled to the driveline;
• a variable frequency drive configured to provide power to the motor;
• and
• a control system configured to:
• measure angular velocity of the motor based on data from an encoder;
• and
• in response to receiving a stop command, control the variable frequency drive to stop the motor by reducing an available torque of the motor over a time period, based on the measured angular velocity.

A method of fracturing a wellbore penetrating a subterranean formation, comprising:

• pumping, by a reciprocating pump driven by an electric motor, fluid into the formation via the wellbore to form fractures in the formation, wherein the motor is coupled to the reciprocating pump by a driveline;
• and
• stopping the pumping of the fluid by:
• controlling speed of the motor in a first mode over a first time period by sending one or more speed commands to a variable frequency drive electrically coupled to the motor;
• and
• reducing the speed of the motor in a second mode, in which a torque limit is reduced over a second time period by sending one or more torque limit commands to the variable frequency drive,
• wherein the reducing of the speed of the motor in the second mode results in a torque exerted by the motor on the driveline to at least temporarily match an opposing torque on the driveline caused by fluid pressure in the reciprocating pump, and
• wherein the motor comes to rest during or after the second time period.