Application of Renault RNB2000-U Converter on Suspended Beam Pumping Unit

Abstract: The traditional suspension beam pumping unit adopts a constant speed operation to install a braking unit or energy feedback scheme. There are great disadvantages in terms of energy consumption and cost. This article introduces the application of the electronic control system with Reynolds RNB2000-U series inverter in the oil field pumping unit, and proposes a new scheme of dual closed-loop control of energy and power, with higher efficiency and lower cost.

Keywords: RNB2000-U frequency converter Suspension beam pumping unit Double closed loop

I. INTRODUCTION The vast majority of China’s oil fields are low-energy, low-yield oilfields. Unlike foreign oilfields, which have strong self-injection capabilities, most oils rely on water injection to press oil into wells and rely on pumping units (head machines) to take oil from The ground uplifted. In China, oil-for-water and oil-for-oil are the reality of the oil field. The cost of power consumption accounts for a considerable proportion of the cost of oil extraction in China. Therefore, the oil industry attaches great importance to the conservation of electricity, and the reduction of electricity consumption directly reduces the cost of oil extraction.

Pumping unit energy-saving, the preferred solution is to use inverters to transform its motor drive system. After the pumping unit is changed to inverter, it has the following advantages:

(1) Improve the power factor: The input side power factor can be increased from the original 0.25 to 0.5 to more than 0.9, greatly reducing the supply current, thereby reducing the burden on the power grid and transformer, reducing the line loss, can save a lot of "increase Capacity" expenses.

(2) Improve the operating efficiency: According to the actual liquid supply capacity of oil wells, the extraction speed can be adjusted dynamically. On the one hand, the purpose of energy saving can be achieved. At the same time, crude oil production can also be increased, and the system efficiency is greatly improved.

(3) A true “soft start” is achieved: Excessive mechanical shock is avoided for the motor, gearbox and pumping unit, which greatly prolongs the service life of the equipment, reduces the production stoppage time, and improves the production efficiency.

However, when the frequency converter is used for the pumping unit motor, there are several problems that need to be solved, mainly the impact current problem and the treatment of the regenerative energy, which are analyzed separately below.

Second, the status of suspension beam pumping unit

2.1 Suspension beam type pumping unit mechanism introduction

The beam pumping unit is mainly composed of four major parts:

(1) Beam section: donkey head, beam, beam, tail beam, connecting rod, balance block (compound balancing pumping unit)

(2) Bracket parts: beam bearing seat, work ladder, retainer, console, bracket

(3) Reducer parts: base, reducer cylinder seat, reducer, crank, counterweight, brake, etc.

(4) Distribution section: motor base, motor, distribution box, etc.

2.2 Present status of cantilever type frequency conversion

As far as the actual frequency conversion transformation is concerned, most of the pumping unit's weight is actually seriously unbalanced, resulting in excessive inrush current. This not only wastes a lot of power, but also seriously threatens the safety of the equipment. At the same time, it also brings great difficulties to the adoption of frequency converter speed control: The capacity of the general frequency converter is selected according to the rated power of the motor. Excessive inrush current will cause the overload protection of the frequency converter and cannot work normally.

In addition, there is a large amount of oil storage in the early stage of oil recovery, large oil reserves, and sufficient liquid supply to run at a fixed frequency in order to increase efficiency. This ensures higher oil production. However, in the middle and later periods, due to the reduction of oil storage, it is easy to cause the shortage of liquid supply. If the motor is still working at the current frequency, it will certainly waste energy and cause unnecessary losses. At this time, it is necessary to consider the actual work and reduce the motor rotation speed to reduce the stroke. Effectively increase the filling rate.

Third, the introduction of traditional frequency conversion solutions

The introduction of frequency conversion technology into beam-type pumping unit control is a general trend. Frequency conversion speed regulation is stepless speed regulation, and the operating frequency of the motor is determined according to the size of the operating current of the motor, so that the stroke of the pumping unit can be conveniently adjusted according to the change of the well condition, thereby achieving energy saving and improving the power factor of the power grid. The application of the vector frequency conversion control technology can guarantee low speed and high torque output, and the rotation speed can be adjusted in a wide range smoothly. At the same time, the inverter has complete protection functions for the motor, such as short circuit, overload, overvoltage, undervoltage and stall, etc., which can effectively protect the motor and mechanical equipment to ensure that the equipment works under a safe voltage, with stable, reliable operation and improved power. Factors such as many advantages, is the ideal solution for the transformation of oil production equipment. The current mainstream solutions include the following:

Option 1: Inverter plus power braking unit

This method is relatively simple, but it is inefficient. This is mainly due to the feedback of the motor's power generation under the down-stroke condition at constant speed. When using an ordinary inverter, the input of a common inverter is diode rectification, and energy cannot flow in the opposite direction. The above-mentioned part of the energy does not flow back to the grid, and must be consumed on-site by means of a resistor. This is the reason why the energy-consumption braking unit must be used. It also directly leads to large energy consumption and low overall efficiency.

Disadvantages: Low energy efficiency, and need to install braking unit and braking resistor.

Option 2: Inverter plus feedback unit control

In order to regenerate the regenerative energy and increase the efficiency, an energy feedback device can be used to feed the regenerated energy back to the grid. As a result, the system is more complex and the investment is even higher. The so-called energy feedback device is actually an active inverter. With frequency converters equipped with energy feedback units, the user can determine the pumping machine speed, speed, and liquid production volume according to the oil level and pressure of oil wells, reduce energy consumption and improve pump efficiency; reduce equipment wear, extend service life, and increase energy efficiency. Low cost, automatic operation in the state of maximum energy saving. However, due to the operating modes of the frequency converter and the feedback device, the scheme of using energy feedback has great pollution on the power end harmonics, and the quality of the power grid drops significantly.

Disadvantages: The need to install feedback devices, high cost, and pollution on the power grid.

IV. Introduction of Renault RNB2000-U Series Frequency Conversion Solutions

In view of the various drawbacks of the traditional frequency conversion reformation scheme, Shanghai Reynolds Technology Co., Ltd. adopted in-depth exploration of the process of the suspension beam pumping unit and adopted special software logic based on the control technology of the suspension beam pumping unit, adopting double closed loops of energy and power. Control, realizes the continuous smooth adjustment to the output frequency, realize elimination negative torque control, avoid the feedback of the kinetic energy of the electrical machinery, avoid the bus line voltage is too high. Therefore, the purpose of eliminating the brake unit and omitting the energy feedback device avoids the disadvantages of the conventional frequency conversion reform program.

The core control idea of ​​this solution is the constant output power control. The inverter is based on the constant PID control mode of the output power loop, and the constant output power control is achieved by adjusting the output frequency. The average output power can be effectively reduced under the premise of satisfying the rush times. Realize effective energy conservation and protect the pumping unit mechanism. In other words, the inverter does not need to set a specific operating frequency, and the actual output frequency is automatically adjusted by the PID closed loop. On the down stroke, because the load is due to a large inertia and the synchronous speed is lower than the motor speed, the motor generates power and the inverter output torque is negative. At this time, the inverter automatically increases the output frequency to eliminate the negative torque to prevent the motor from generating power. On the upstroke, the bit energy is completely converted into kinetic energy. At this time, the speed is the highest and the inertia is the largest. The motor decelerates the upstroke. When the speed is low, the inverter works in the PID adjustment mode of the constant output power, and the inverter automatically increases. Upstroke speed, complete upstroke action.

Through the entire control process, it can be seen that the motor has not been in the state of power generation, so no need to install a brake unit and RBU feedback device. At the same time, during the entire stroke, the downstroke is slow and can be immersed in more oil; the upstroke is fast and the oil leakage is reduced: the oil production is greatly increased.

Advantages: no need to install energy consumption or feedback devices, lower cost; and optimize the oil production process, the efficiency of the whole machine is greatly improved; the bus voltage of the inverter is stable, the heat loss of the whole machine is low, and the stability of the whole machine is better.

The key parameters are set as follows:

Five, Renault RNB2000-U series frequency conversion

Shanghai Renault Technology Co., Ltd. uses RNB2000-U inverter DSP control system as a platform, adopts domestic technology-leading PG-free vector control technology, and cooperates with various protection methods, and can be applied to asynchronous motors to provide excellent driving performance. Products in the air channel design, hardware configuration, software features have greatly improved customer ease of use and environmental adaptability.

Technical features:
â—† Industry-specific: Based on the software logic of the beam-type pumping unit control process, it is truly dedicated to the industry and leads the project.

â—† High-reliability selection: The key components are made of well-known brands at home and abroad, and the reliability of the components is guaranteed.

â—† Large-redundancy design: Through rigorous calculations and experimental verification, key components are designed with a large amount of margin to ensure the long-term stability of the entire machine in harsh oilfield environments.

â—† Optimized vector control: Domestic technology-leading speed-less feedback vector control, low-frequency torque, fast torque response.
â—† Software current limiting and pressure limiting function: good voltage and current limit, effectively limit the critical control parameters to reduce the risk of inverter failure.

â—†Strong environment adaptability: high over temperature point of the whole machine, independent air duct design, thick three anti-paint treatment, more suitable for long-term operation in oil field and outdoor occasions.

◆Speed ​​tracking and restarting function: It realizes no impact smooth start of the rotating motor ◆Automatic voltage adjustment function: When the grid voltage changes, it can automatically maintain the output voltage constant

â—†Comprehensive fault protection: Over current, over voltage, under voltage, over temperature, phase loss, overload and other protection functions

Sixth, concluding remarks

The traditional frequency conversion application mode of the beam pumping unit is unavoidable due to various drawbacks. Shanghai Renault Technology Co., Ltd. will inevitably lead the reform of its industry program with its original control plan. At the same time, the reliable hardware and software stability of RNB2000-U series inverters is also destined to provide customers with a cost-effective user experience.

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