The traditional suspended beam pumping unit adopts a constant speed operation with the addition of a braking unit or energy feedback scheme, which has significant drawbacks in terms of energy consumption and cost. This article introduces the application of the electronic control system with Dongli Kechuang CT100 series frequency converter as the core in oilfield pumping units, and proposes a new scheme of energy and power dual closed-loop control, which is more efficient and cost-effective.
Application of Dongli Kechuang CT100 frequency converter in suspended beam pumping unit
The traditional suspended beam pumping unit adopts a constant speed operation with the addition of a braking unit or energy feedback scheme, which has significant drawbacks in terms of energy consumption and cost. This article introduces the application of the electronic control system with Dongli Kechuang CT100 series frequency converter as the core in oilfield pumping units, and proposes a new scheme of energy and power dual closed-loop control, which is more efficient and cost-effective.
Introduction
The vast majority of oil fields in our country are low-energy and low yield oil fields, unlike foreign oil fields that have strong self injection capabilities. Most of the oil needs to be injected into the well by water injection and lifted up from the formation by pumping machines (percussion machines). In China, replacing oil with water and oil with electricity is currently the reality of oil fields, and electricity consumption accounts for a considerable proportion of the cost of oil extraction in our country. So, the oil industry attaches great importance to saving electricity, and saving electricity consumption means directly reducing the cost of oil extraction.
The energy-saving solution for the pumping unit is to use a frequency converter to modify its motor drive system. After switching to a frequency converter for the pumping unit, there are several benefits:
(1) Improving power factor: The input side power factor can be increased from the original 0.25-0.5 to above 0.9, greatly reducing the power supply current, thereby reducing the burden on the power grid and transformers, reducing line losses, and saving a lot of "capacity expansion" expenses.
(2) Improving operational efficiency: The extraction speed can be dynamically adjusted according to the actual liquid supply capacity of the oil well, which not only achieves energy-saving goals, but also increases crude oil production, greatly improving system efficiency.
(3) True 'soft start' has been achieved: it avoids excessive mechanical impact on the electric motor, gearbox, and pumping unit, greatly extending the service life of the equipment, reducing downtime, and improving production efficiency.
However, there are also several issues that need to be addressed when using a frequency converter for the motor of a pumping unit, mainly the problem of surge current and the handling of regenerative energy, which will be analyzed separately below.
Introduction to the current situation of suspended beam pumping units
Introduction to the Mechanical Mechanism of Suspended Beam Pumping Unit
The beam pumping unit is mainly composed of four parts:
(1) Beam section: donkey head, beam, crossbeam, tail beam, connecting rod, balance block (composite balance pumping unit)
(2) Bracket section: crossbeam bearing seat, work ladder, protective ring, operating platform, bracket.
(3) Reducer part: base, reducer cylinder seat, reducer, crankshaft, counterweight, brake and other components.
(4) Power distribution section: motor base, motor, distribution box, etc
Shenzhen Dongli Sci Tech Innovation Technology Co., Ltd
1. Base; 2-Bracket; 3-Suspension rope device; 4- Donkey head; 5-beam; 6-Beam bearing seat; 7-crossbeam; 8-connecting rod; 9-crank pin device; 10 crank device; 11- Reducer; 12. Brake safety device; 13- Braking device; 14- Electric motor; 15- Distribution box.
As shown in the figure, the beam pumping unit is a deformed four-bar linkage mechanism, and its overall structural characteristics are like a balance. One end is the pumping load, and the other end is the balanced heavy load. For the bracket, if the torque formed by the pumping load and the equilibrium load is equal or changes consistently, then the pumping unit can work continuously and uninterruptedly with very little power. That is to say, the energy-saving technology of the pumping unit depends on the balance. The lower the balance ratio, the greater the power required from the electric motor. Because the pumping load is constantly changing, and the balance weight cannot be completely consistent with the pumping load, it makes the energy-saving technology of beam pumping units very complex. Therefore, it can be said that the energy-saving technology of the beam pumping unit is the balancing technology.
Introduction to the Current Status of Suspended Beam Variable Frequency Transformation
From the actual situation of frequency conversion transformation, the majority of the counterweights of the pumping units are actually severely unbalanced, resulting in excessive surge current, which not only wastes a lot of electrical energy unnecessarily, but also seriously threatens the safety of the equipment. At the same time, it also poses great difficulties for using frequency converter speed control: the capacity of the frequency converter is generally selected based on the rated power of the motor, and excessive surge current can cause overload protection of the frequency converter, which cannot work normally.
In addition, in the early stage of oil well exploitation, there is a large amount of oil storage and sufficient liquid supply. To improve efficiency, power frequency operation can be used to ensure high oil production. However, in the middle and later stages, due to the decrease in oil storage capacity, it is easy to cause insufficient liquid supply. If the motor still works in the power frequency state, it will inevitably waste electrical energy and cause unnecessary losses. At this time, it is necessary to consider the actual working situation and appropriately reduce the motor speed and stroke to effectively improve the filling rate.
Introduction to Traditional Frequency Conversion Solutions
The introduction of frequency conversion technology into the control of beam pumping units is the trend. Variable frequency speed regulation belongs to stepless speed regulation, which determines the working frequency of the motor based on the magnitude of its working current. This allows for convenient adjustment of the stroke of the pumping unit according to changes in well conditions, achieving energy conservation and improving the power factor of the power grid. The application of vector frequency conversion control technology can ensure low-speed and high torque output, and the speed can be smoothly and widely adjusted. At the same time, the frequency converter has complete motor protection functions, such as short circuit, overload, overvoltage, undervoltage, and stall, which can effectively protect the motor and mechanical equipment, ensure that the equipment works at a safe voltage, and have many advantages such as smooth and reliable operation, improved power factor, etc. It is an ideal solution for the transformation of oil production equipment. The current mainstream solutions are as follows:
Inverter with energy consumption braking unit
This method is relatively simple, but its operational efficiency is low. This is mainly due to the feedback of energy generated by the motor during the downstroke state during constant speed operation. When using a regular frequency converter, the input is diode rectified, and energy cannot flow in the opposite direction. The above part of the electrical energy does not have a path to flow back to the grid and must be consumed locally using resistors. This is why energy consuming braking units must be used, which directly leads to high energy consumption and low overall efficiency.
Disadvantages: Low energy efficiency and the need to install braking units and braking resistors.
Inverter with feedback unit control
In order to feedback the regenerated energy and improve efficiency, an energy feedback device can be used to feed back the regenerated energy to the power grid. In this way, the system becomes more complex and the investment is higher. The so-called energy feedback device is actually an active inverter. By installing a frequency converter with an energy feedback unit, users can determine the flushing, speed, and liquid production of the pumping unit based on the liquid level and pressure of the oil well, reducing energy consumption and improving pump efficiency; Reduce equipment wear and tear, extend service life, achieve high efficiency, energy saving, and low cost, and realize automated operation under maximum energy-saving conditions. However, due to the working mode of the frequency converter and feedback device, the use of energy feedback scheme causes significant harmonic pollution at the power supply end, resulting in a significant decrease in the quality of the power grid.
Disadvantages: It requires the installation of feedback devices, which is costly and causes significant pollution to the power grid.
Introduction to Dongli Sci Tech CT100 Series Frequency Conversion Solution
In view of the various drawbacks of traditional frequency conversion transformation schemes, Shenzhen Dongli Sci Tech Innovation Technology Co., Ltd. has conducted in-depth research on the suspended beam pumping unit process, adopted a dedicated software logic based on the suspended beam pumping unit control process, and adopted dual closed-loop control of energy and power to achieve continuous and smooth adjustment of output frequency, eliminate negative torque control, and avoid feedback of motor kinetic energy and high bus voltage. Furthermore, the goal of eliminating the braking unit and energy feedback device is achieved, avoiding the various drawbacks of traditional frequency conversion transformation schemes.
The core control concept of this scheme is constant output control. The frequency converter is based on a PID control mode with a constant output loop. By adjusting the output frequency, constant output control can be achieved, which can effectively reduce the average output power, achieve effective energy saving, and protect the pumping unit mechanism while meeting the impulse requirements. That is to say, the frequency converter does not need to set a specific operating frequency, and the actual output frequency is automatically adjusted through PID closed-loop. During the downstroke, due to the large inertia of the load, when the synchronous speed is lower than the motor speed, the motor generates electricity, and the output torque of the frequency converter is negative. At this time, the frequency converter automatically increases the output frequency to eliminate the negative torque and avoid the motor being in a generating state. During the upstroke, the potential energy is completely converted into kinetic energy. At this time, the maximum speed and inertia occur, and the motor decelerates to perform the upstroke action. When the speed is low, the frequency converter works in constant output PID regulation mode, and automatically increases the upstroke speed to complete the upstroke action. Through the entire control process, it is known that the motor has not been in a generating state, so there is no need to install a braking unit and RBU feedback device. Meanwhile, during the entire stroke process, the downstroke is slow and more oil can be immersed; Fast upstroke, reducing oil leakage: greatly increasing oil production.
Advantages: No need to install energy consumption or feedback devices, and optimized oil extraction process, greatly improving overall efficiency.
Introduction to Dongli Sci Tech CT100 Series Frequency Conversion
The CT100 frequency converter of Shenzhen Dongli Kechuang Technology Co., Ltd. is based on a DSP control system and adopts domestically leading PG free vector control technology, combined with multiple protection methods, which can be applied to asynchronous motors and provide excellent driving performance. The product has greatly improved customer usability and environmental adaptability in terms of air duct design, hardware configuration, and software functionality.
Technical Features
Industry specific: Based on the software logic of the beam pumping unit control process, it truly achieves industry specific and leading solutions.
High reliability selection: Key components are all from well-known domestic and foreign brands, ensuring reliable and reliable stability of the components.
◆ Large redundancy design: Through rigorous calculation and experimental verification, key components are designed with large margins to ensure the integrity of the entire machine in oil fields
Long term stability in adverse environments.
Optimized vector control: domestically leading speed feedback free vector control with high low-frequency torque and fast torque response.
◆ Software current and voltage limiting function: Good voltage and current limiting, effectively limiting key control parameters to reduce the risk of inverter failure.
Strong environmental adaptability: With a high overall overheating point, independent air duct design, and thickened three proof paint treatment, it is more suitable for long-term operation in outdoor oil fields.
◆ Speed tracking restart function: achieve smooth start of rotating motors without impact
◆ Automatic voltage adjustment function: When the grid voltage changes, it can automatically maintain a constant output voltage
Comprehensive fault protection: overcurrent, overvoltage, undervoltage, overtemperature, phase loss, overload and other protection functions
Conclusion
Due to various drawbacks of the traditional frequency conversion application mode of the beam pumping unit, continuous improvement of the frequency conversion transformation control scheme is inevitable. Shenzhen Dongli Sci Tech Innovation Technology Co., Ltd. will lead the industry's transformation with its innovative control solutions. At the same time, the reliable software and hardware stability of the CT100 series frequency converter also ensures that it will provide customers with a highly cost-effective user experience.