Abstract : The application of beam pumping units maintains a constant number of strokes by adjusting the reference frequency inside the frequency converter. This paper analyzes the working principle of beam pumping units and designs an intelligent controller based on the torque characteristic curve of the pumping unit. Its control principle is to provide appropriate current limits when the motor is working normally. This ensures that the actual speed of the motor is less than the reference value during the motoring cycle, and that the actual speed is higher than the reference value during the generator cycle, while maintaining a constant number of strokes. A control system was designed using this controller. Practice shows that the control system operates stably and achieves good economic benefits. Keywords : VACON frequency converter, beam pumping unit, balanced load 1 Introduction Beam pumping units are commonly used in various oilfields. However, current pumping unit systems generally suffer from significant drawbacks such as low efficiency, high energy consumption, and inconvenient adjustment of stroke and stroke count. For traditional beam pumping units, Vasa Control Systems GmbH of Finland has developed dedicated software using its high-performance Vacon frequency converters. Our unit has designed a new type of intelligent electrical oilfield pumping unit multi-functional control cabinet specifically for the characteristics of traditional beam pumping units and the actual application conditions in oilfields. This control cabinet uses a Vacon programmable frequency converter as its core and employs dedicated pumping unit software developed with Vacon. Based on the mechanical structure of the beam pumping unit and the actual conditions of oilfield wells, it is a multi-functional control cabinet for beam pumping units independently developed and designed. This control cabinet is applicable to three common types of beam pumping units used in oilfields: beam-balanced, crank-balanced, and combined-balanced. In practical applications, after inputting the necessary pumping unit parameters, the controller will perform static modeling of the pumping unit. During actual operation, the controller will modify the mathematical model of the pumping unit in real time according to the actual operating conditions, achieving the goal of increasing production and saving energy. 2. Working Principle of Beam Pumping Units When a beam pumping unit is working, the load acting on the sucker head suspension point is variable. During the upstroke, the sucker head suspension point needs to lift the sucker rod string and liquid column. Under conditions where the pumping unit is not balanced, the motor has to expend a lot of energy. During the downstroke, the sucker rod string then performs work on the motor, putting the motor into generator operation. When a pumping unit is not balanced, the load during the upstroke and downstroke is extremely uneven. This severely affects the efficiency and lifespan of the four-bar linkage, gearbox, and motor, worsens the working conditions of the sucker rod, and increases its breakage rate. To eliminate these drawbacks, counterweights are typically added to the tail of the walking beam, on the crank, or both, as shown in Figure 1. During the downstroke at the suspension point, the counterweight is raised from a lower position to a higher position, increasing its potential energy. To raise the counterweight, in addition to relying on the potential energy released by the falling sucker rod string, the motor also needs to provide some energy. During the upstroke, the counterweight falls from a higher position, releasing the potential energy stored during the downstroke, helping the motor to lift the sucker rod and liquid column, reducing the energy required by the motor during the upstroke. [b][align=center]For more details, please click: Application of VACON Frequency Converters in Oilfield Pumping Units[/align][/b]