Downhole pumping system with variable speed pulse-width modulate

Details Downhole pumping system with variable speed pulse-width modulate Downhole pumping system with variable speed pulse-width modulate

1997-12-22

1999-06-01

Martin, David

Electricity: motive power systems

Induction motor systems

Primary circuit control

318813, A02P 528

Patent

active

059090987

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. Ongoing operation of the motor is managed by a drive routine, which generates triangular and sinusoidal signals based upon a desired chopping frequency, as well as a desired driving frequency of the motor. A sine-triangle comparison is performed upon these signals to yield three rectangular PWM signals, which are used to control the inverter.

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