Abstract: Pumping units account for approximately 40% of the total electricity consumption in oilfields, with very low operating efficiency, averaging only 25%, low power factor, and significant energy waste. Therefore, the energy-saving potential of pumping units is enormous, and the petroleum industry is a key sector for promoting "energy-saving motor systems." This article introduces the use of variable frequency speed control technology to adapt the pumping unit's motion to the changing operating conditions of oil wells, thereby improving system efficiency and achieving the goal of energy saving and increased production. I. Overview Pumping units are currently the main equipment in oil production, numbering over 100,000. The total installed capacity of electric motors is 35 million KW, with annual power consumption exceeding tens of billions of kWh. Pumping units account for approximately 40% of the total electricity consumption in oilfields, with very low operating efficiency, averaging only 25%, low power factor, and significant energy waste. Therefore, the energy-saving potential of pumping units is enormous, and the petroleum industry is a key sector for promoting "energy-saving motor systems." II. Several benefits of frequency conversion retrofitting of oil pumping units: 1. Significantly improves the power factor (from 0.25 to 0.5, increasing to over 0.9). Reduces the supply current, thereby reducing the load on the power grid and transformer. 2. Dynamically adjusts the extraction speed, saving energy while increasing crude oil production. 3. Achieves true "soft start" for the motor and gearbox of the oil pumping unit, avoiding excessive mechanical shock and extending equipment lifespan. III. Oil Pumping Unit Load Analysis 1. The most widely used type in China is the beam-type vertical well pumping unit, which consists of three parts: 1) Surface section: composed of a motor, reducer, and four-bar linkage; 2) Downhole section: the oil pump (suction valve, pump barrel, plunger, and discharge valve), which is suspended at the lower end of the casing; 3) Sucker rod string: the intermediate part connecting the surface pumping unit and the downhole pump. [align=center][IMG=Application and Measures of EDS2880 Series Frequency Converters in Oil Pumping Units]/uploadpic/THESIS/2008/1/2008012410244764273I.jpg[/IMG] Oil Pumping Unit Operating Scene[/align] 2. The motor load of the oil pumping unit changes periodically. At the start-up, the load is very large, requiring a large starting torque. During normal operation, the load rate is very low, generally around 20%, and at its highest, the load rate is only 30%. The motor load curve has two peaks, which are the "dead points" of the oil pumping unit's upstroke and downstroke. Under unbalanced conditions, the load of the upstroke and downstroke is extremely unbalanced. During the upstroke, the sucker rod and liquid column need to be lifted, requiring the motor to expend a lot of energy. During the downstroke, the sucker rod does work on the motor, putting the motor in a generating state. Usually, a balance weight is added to the crank of the oil pumping unit to eliminate the load imbalance between the upstroke and downstroke. A well-adjusted counterweight results in a shorter power generation period and less energy generated. Since the pumping load changes constantly, the counterweight cannot perfectly match the load. Most pumping units suffer from severe counterweight imbalance, leading to excessive inrush currents—up to five times the operating current, or even three times the rated current. Adjusting the counterweight can reduce the inrush current to 1.5 times the normal operating current. The pumping unit's load characteristics are: constant speed operation, but variable torque and power due to the counterweight, resulting in two power generation states within one cycle; large starting torque and high inertia. Common problems with pumping units used in domestic oilfields include: long operating times, oversized components, low efficiency, high energy consumption, inconvenient stroke and stroke rate adjustment, and occasional dry pumping. IV. Challenges in Retrofitting Traditional Pumping Units with Variable Frequency Drives Many attempts have been made in China to retrofit pumping units with variable frequency drives for energy saving, but none have been very successful. The main problems are: 1) Pumping units generate electricity twice during a single working cycle. Especially when the counterweight is unbalanced, the resulting "pump rise voltage" is very high. Increasing the DC-side electrolytic capacitor of the variable frequency drive and decreasing the braking resistor value cannot completely solve the problem, and the "pump rise voltage" also changes with the oil layer. 2) Pumping units require a large starting torque. If the variable frequency drive parameters are not set properly, it can easily cause overcurrent or prevent starting. 3) Previous variable frequency energy-saving retrofit designs rarely considered changes in oil level and concentration in the oil well. The effect on increasing production is not good. V. Solutions To address the problems existing in the current retrofitting of pumping units with variable frequency drives, our company proposes the following solutions: 1) Adopt variable frequency speed control technology to match the motor speed with the pumping unit load. In early-stage wells, due to the large oil volume from the initial extraction, the frequency converter is run at 65Hz, increasing the motor speed by 30%, resulting in a 20% increase in oil recovery rate and a 1.2-fold increase in efficiency compared to the power frequency. In mid-to-late-stage wells, as oil volume decreases, the speed and stroke are reduced, typically operating at a frequency between 35 and 40Hz, decreasing the motor speed by 30%. This achieves energy savings of up to 25% and improves the power factor. 2) Dynamically adjusting the pumping unit's stroke frequency: As wells are extracted from shallower to deeper areas, the oil volume gradually decreases, leading to insufficient pump filling and reduced pump efficiency. When the well's supply capacity is less than the pump's displacement, pump cavitation and liquid hammer occur. Reducing the frequency decreases the motor speed, increasing filling, saving energy, and increasing crude oil production. 3) Dynamically adjusting the pumping unit's up-and-down stroke speed: Appropriately reducing the down-stroke speed increases pump filling, while appropriately increasing the up-stroke speed reduces leakage during lifting, allowing the pumping unit to operate at its optimal state and effectively increasing crude oil production per unit time. 4) High starting torque, low load during operation, and high inrush current: To fundamentally solve this problem, increase the number of pole pairs of the motor or increase the speed ratio of the gearbox to increase the output torque. The frequency converter should operate at 80-90Hz. This also helps reduce energy consumption during power generation and reduce "pump voltage rise". 5) Regenerative energy handling: Increase the capacity of the DC-side filter capacitor of the frequency converter; reduce the braking resistance value to improve the power consumption capacity of the braking system, or directly use regenerative braking to reduce energy loss; increase the frequency during power generation. 6) Prevent dry pumping and increase production: Dynamically adjust the stroke frequency and up and down stroke speed of the pumping unit. Set a standard value for the motor's output power, monitor the motor's output power in real time, control the motor speed; if it exceeds the standard value, accelerate; otherwise, decelerate to achieve closed-loop control. VI. Actual Measured Data of the Pumping Unit The Daqing Oilfield 82-X110 pumping unit is a beam pumping unit with a motor power of 22KW and 8 magnetic poles. Energy-saving retrofitting of the frequency converter was carried out using an intelligent high-efficiency pumping unit energy-saving device manufactured by Shenzhen Yineng Electric Technology Co., Ltd. During the pumping unit's upward stroke operation, the frequency converter output frequency was set to 50Hz, and during the downward stroke operation, it was set to 30Hz. Pumping unit operating parameters at power frequency: Current variation over one cycle: 20.1A～30.7A; Average power consumption over 4 hours: 4.7 kWh/hour. Pumping unit energy-saving operating parameters: Current variation over one cycle: 4.9A～18.7A; Average power consumption over 4 hours: 3.9 kWh/hour . VII. Conclusion Due to the wide variety of oil well types and operating conditions, downhole oil and water seepage rates change constantly. The load variation of the pumping unit is irregular. Therefore, variable frequency speed control technology is adopted to adapt the pumping unit's motion pattern to the changing operating conditions of the oil well, thereby improving system efficiency and achieving the goal of energy saving and increased production.