System and method for converterless operation of motor-driven pumps

Abstract

A converterless motor-driven pump system includes an off-grid prime mover. The off-grid prime mover has a rotational driveshaft and operates in response to a throttle control command to control a rotation speed of the rotational driveshaft. An electric power generator is driven by the off-grid prime mover to generate AC power. A variable speed induction motor is directly powered by the electric power generator. A pump that may be submersible is driven by the at least one variable speed induction motor. A system controller that may be local or remote is programmed to generate the throttle control command in response to one or more pump operating characteristics such that the off-grid prime mover, the electric power generator, and the variable speed induction motor together operate to regulate a pressure at the inlet of the electric pump.

1 . A converterless motor-driven pump system comprising:
 at least one off-grid prime mover comprising a rotational driveshaft and operating in response to a throttle control command to control a rotation speed of the rotational driveshaft;   at least one electric power generator driven directly or indirectly by the at least one off-grid prime mover to generate AC power;   at least one variable speed motor directly or indirectly powered by the at least one electric power generator;   at least one electric submersible pump driven by the at least one variable speed motor, wherein one or more operating characteristics associated with the at least one electric submersible pump are monitored by one or more corresponding sensors; and   a system controller programmed to generate the throttle control command in response to the one or more pump operating characteristics such that the at least one off-grid prime mover, the at least one electric power generator, and the at least one variable speed motor together operate to regulate a pressure at the inlet of the at least one electric submersible pump such that a desired operating point of the at least one electric submersible pump is maintained.   
     
     
         2 . The converterless motor-driven pump system according to  claim 1 , wherein the system controller is integrated with the converterless motor-driven pump system. 
     
     
         3 . The converterless motor-driven pump system according to  claim 1 , wherein the system controller communicates with an operation center remote from the converterless motor-driven pump system. 
     
     
         4 . The converterless motor-driven pump system according to  claim 1 , wherein the prime mover comprises at least one of a reciprocating engine or a turbine. 
     
     
         5 . The converterless motor-driven pump system according to  claim 1 , wherein the electric generator comprises at least one of a permanent magnet generator and a wound-field synchronous generator. 
     
     
         6 . The converterless motor-driven pump system according to  claim 5 , further comprising a generator exciter configured to provide excitation to the wound-field synchronous generator. 
     
     
         7 . The converterless motor-driven pump system according to  claim 6 , further comprising a speed sensor configured to monitor the rotation speed of the rotational driveshaft. 
     
     
         8 . The converterless motor-driven pump system according to  claim 7 , wherein the system controller is further programmed to control the excitation of the generator exciter in response to the rotation speed of the rotational driveshaft. 
     
     
         9 . The converterless motor-driven pump system according to  claim 1 , further comprising an electric submersible pump cable directly or indirectly linking the generated AC power to the variable speed motor. 
     
     
         10 . The converterless motor-driven pump system according to  claim 1 , further comprising a pressure sensor configured to monitor the inlet pressure of the at least one electric submersible pump. 
     
     
         11 . The converterless motor-driven pump system according to  claim 1 , further comprising a transformer between the at least one generator and the at least one electric submersible pump. 
     
     
         12 . The converterless motor-driven pump system according to  claim 1 , wherein the system controller is further programmed to shut down the converterless motor-driven pump system in response to one or more variable speed motor sensor signals that exceed prescribed limits or one or more electric submersible pump signals that exceed prescribed limits. 
     
     
         13 . A method of operating a converterless motor-driven pump system, the method comprising:
 controlling an AC power output of an electric power generator in response to an off-grid prime mover driveshaft speed, wherein the driveshaft speed of the off-grid prime mover is controlled via a throttle control command;   controlling a speed of a variable speed motor directly in response to the AC power output of the electric power generator;   controlling an electric submersible pump (ESP) in response to the speed of the motor, and   monitoring operating characteristics of the ESP and generating the throttle control command in response thereto such that together the off-grid prime mover, the electric power generator, and the variable speed motor operate to regulate a pressure at an inlet to the ESP and further to maintain a desired operating point for the ESP.   
     
     
         14 . The method of operating a converterless motor-driven pump system according to  claim 13 , wherein monitoring operating characteristics comprises monitoring operating characteristics via a localized controller. 
     
     
         15 . The method of operating a converterless motor-driven pump system according to  claim 13 , wherein monitoring operating characteristics comprises monitoring operating characteristics via a remote control center. 
     
     
         16 . The method of operating a converterless motor-driven pump system according to  claim 13 , wherein controlling a driveshaft speed of an off-grid prime mover comprises controlling a driveshaft speed of at least one of a reciprocating engine and a turbine engine. 
     
     
         17 . The method of operating a converterless motor-driven pump system according to  claim 13 , wherein controlling an AC power output of an electric power generator comprises controlling an AC power output of at least one of a wound-field synchronous generator and a permanent magnet generator. 
     
     
         18 . The method of operating a converterless motor-driven pump system according to  claim 17 , wherein controlling an AC power output of the wound-field synchronous generator comprises controlling an AC power output of a wound-field exciter. 
     
     
         19 . The method of operating a converterless motor-driven pump system according to  claim 18 , further comprising controlling the AC power output of the wound-field exciter in response to the driveshaft speed of the off-grid prime mover. 
     
     
         20 . The method of operating a converterless motor-driven pump system according to  claim 17 , further comprising controlling the AC power output of the permanent magnet generator in response to the driveshaft speed of the off-grid prime mover. 
     
     
         21 . The method of operating a converterless motor-driven pump system according to  claim 13 , further comprising directly or indirectly linking the generated AC power to the variable speed motor via an electrical submersible pump cable. 
     
     
         22 . The method of operating a converterless motor-driven pump system according to  claim 13 , further comprising linking the generated AC power to the variable speed motor via a transformer and an electrical submersible pump cable. 
     
     
         23 . The method of operating a converterless motor-driven pump system according to  claim 13 , wherein monitoring operating characteristics of the ESP comprises monitoring an inlet pressure to the ESP, and generating the throttle control command in response thereto such that a desired ESP operating point is maintained.