Abstract: An improved downhole pumping system that employs a variable speed PWM inverter and a non-gap transformer to drive an induction motor over a range of different speeds, without saturating the transformer. The variable speed PWM inverter provides a rectangular PWM signal that may be varied according to inputs from a controller to adjust the speed of the motor. The PWM inverter is electrically connected to the transformer, and the transformer is electrically attached to the motor via cables, which may be lengthy in downhole applications. The motor may be started by ramping flux producing current to a first preset value at a low frequency, then ramping torque producing current to a second preset value. If a flux measurement indicates the motor has stalled, the second preset value is increased, and the routine is restarted. Otherwise, if no stall has occurred, the motor's speed is ramped to the desired value.

Abstract: An improved downhole pumping system that employs a variable speed PWM inverter and a non-gap transformer to drive an induction motor over a range of different speeds, without saturating the transformer. The variable speed PWM inverter provides a rectangular PWM signal that may be varied according to inputs from a controller to adjust the speed of the motor. The PWM inverter is electrically connected to the transformer, and the transformer is electrically attached to the motor via cables, which may be lengthy in downhole applications. The motor may be started by ramping flux producing current to a first preset value at a low frequency, then ramping torque producing current to a second preset value. If a flux measurement indicates the motor has stalled, the second preset value is increased, and the routine is restarted. Otherwise, if no stall has occurred, the motor's speed is ramped to the desired value.