Self-compensating oscillatory pump control

In an oscillatory pumping system of the type having a pumping member reciprocably slidable within a well bore, a counterbalance member connected to said pump member for at least partially counterbalancing the weight of the pump member to affect an oscillatory action, means for reciprocating said pumping member in upward and downward stroke directions comprising a pump cycle wherein the pump member is moved cyclically in an upward direction to a top stroke position and in a downward direction to a bottom stroke position, and a reversible electric motor for operating said reciprocating means, the improvement in combination therewith comprising control system means for applying power to and removing power from the motor at optimally determined points during the pumping cycle so as to minimize motor peak load current requirements including:

• sensing means for establishing at one or more points during the pumping cycle and for a plurality of cycles, values representative of pump member movement;
• means for continually calculating from said established values a first reference position in said pump cycle including means for applying power to the motor when the pump member reaches said first position and is moving in the upward direction at a point following pump member reversal at the bottom of its stroke so as to smoothly accelerate the motor to synchronous speed and to continue pump member movement in the upward direction;
• first means for removing power from the motor before the pumping member reaches the top of its stroke so that the pump member reverses direction and begins moving in the downward direction;
• means for continually calculating from said established values, a second reference position in said pump cycle including means for applying power to the motor when the pumping member reaches said second position and is moving in a downward direction at a point following pump member reversal at the top of its stroke so as to smoothly accelerate the motor to synchronous speed and to continue pump member movement in the downward direction;
• and
• second means for removing power from the motor before the pumping member reaches the bottom of its stroke so that the pump member reverses direction and begins moving in the upward direction, said first and second calculated reference positions being chosen so as to minimize the motor peak load current when power is applied to the motor.