Design and implementation of a dual PWM frequency converter used in beam pumping unit for energy saving

Improving energy efficiency is very important in solving the problem of energy crisis and environmental problems. Beam pumping units consume significant amount of electricity because they are widely used but usually have relative low efficiency especially of the induction motor in petroleum exploitation. This paper first analyzes the beam pumping unit´s motion law in petroleum exploitation, and derives the up slowly and down fast (USDF) operation principle of the suspension point to improve its efficiency. For the practical application, a dual PWM frequency converter for a beam pumping unit with a 45kW induction motor is developed and field tested. The unit is capable of starting the motor softly, operating at near unity power factor, providing near sinusoid current and emitting low THD in grid side, making power flows in dual direction; and capable of adjusting frequency smoothly in the range of 5Hz to 75Hz in motor side. Thorough consideration on the protections schemes and special designs in framework make it working reliably in atrocious environment. Field operations results show significant energy savings of the proposed design.