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 oil recovery efficiency, fixed frequency operation can be adopted 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 operates at the current 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 charging rate.
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:
Option 1: Variable frequency drive 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.
Option 2: Variable frequency drive 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.
Through in-depth exploration of the suspended beam pumping unit process, a dedicated software logic based on the suspended beam pumping unit control process is adopted, and a dual closed-loop control of energy and power is used 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 idea of this scheme is constant output power control. The frequency converter is based on a PID control mode with a constant output power loop. By adjusting the output frequency, constant output power 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 speed is highest and the inertia is maximum. The motor decelerates to perform the upstroke action. When the speed is low, the frequency converter works in the PID regulation mode with constant output power. At this time, the frequency converter 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, lower cost; And optimized the oil extraction process, greatly improving the overall efficiency of the machine; The bus voltage of the frequency converter is stable, the overall heat consumption is low, and the overall stability is better. 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 long-term stability of the entire machine in harsh oilfield 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