Energy saving system and method for devices with rotating or reciprocating masses

Abstract

A system and method are provided for reducing the energy consumed by a pump jack electric motor by reducing the supply voltage to the motor when the motor would be generating energy in open loop mode. By substantially eliminating the energy generation mode, the braking action of the utility grid in limiting the acceleration of the motor and system that would otherwise occur is substantially removed. The motor and system will speed up, allowing the natural kinetic energy of the cyclic motion to perform part of the pumping action. A closed loop controller in electrical connection with the motor computes the necessary information from the observed phase angle between the voltage and current supplied to the motor. By reducing the supply voltage to the motor, the observed phase angle may be reduced to a target phase angle value. By allowing some current flow, primarily of a reactive nature, an observable feedback parameter may be used in the closed loop control system as an indication of the load condition, to which the closed loop motor controller may react, supplying power when needed, such as in the energy consumption mode. The electric motor may be effectively turned off, but without completely cutting the power to the motor. During both the energy consumption mode and the period that open loop energy generation would be occurring, the closed loop motor controller may reduce the observed phase angle to a target phase angle by reducing the supply voltage. Any further reduction in the observed phase angle below the target phase angle may be interpreted as an increase in motor load, to which the motor controller may respond by increasing the supply voltage to the motor until the target phase angle is once again reached.