In the last decade, from low-capacity AC drives to large-capacity AC drives, from simple open-loop systems to complex closed-loop systems, people are continually trying out applications and enjoying the great benefits that it has for human society. It is used as speed governor in AC motor which is easy to use and inconvenient to adjust speed, and it is not easy to adjust the speed of AC machine in the past either from process requirement or electrical energy saving need.

Similarly, the submersible pump as the oil field deep well pumping unit power, whether it comes from the process requirements, or the need to save electricity, the use of variable frequency speed control technology are greatly beneficial. However, due to the technical solutions used in the past is not ideal, so the application is not too wide. The company currently uses the technology program is the world's advanced technology, has a good prospect.

1 submersible pump variable frequency technology speed drive is its best transmission program

Submersible pump is a multistage centrifugal pump working underground, is one of the newer mechanical oil recovery equipment. Oil pump is a long-term continuous work in the underground 2 ~ 3km high temperature, strong corrosion of the harsh environment, due to the depth of the reservoir, so the work efficiency is higher, more widely applied in recent years. The power is not too large, generally between 55 ~ 75kW, due to deeper oil wells, in order to reduce line pressure drop, so the drag motor does not use the frequency and the general design for the 1000-volt level. The voltage is medium voltage range, not high nor low. If you reduce the voltage, the line pressure drop is too large, the motor can not work inefficiently. If the voltage is raised, the voltage drop of the line is small, but the insulation problem of the power supply line cable and the motor is prominent, the failure rate is high, the maintenance is difficult, and the reliability is decreased. Therefore, most of the current domestic oil field is 1140 volts submersible pump.

According to the survey, the main common problems are:

A, the impact of the current when starting up large, distributed inductance so that the system back pressure is too high, often resulting in system multi-part insulation damage.

B. Due to the great changes in the geological conditions of oil wells and the design allowance for the electric pumps, the oil pump pressure is too high, so the service life of the pump is shortened, and the maintenance and replacement probability are increased .

In order to solve the above problems, it is necessary to regulate the speed of the pump motor. The use of AC variable frequency speed control is the most ideal measure.

The reason is as follows:

A, the inverter has a soft-start function, during the start-up process, the motor speed with the frequency changes close to the synchronous state of speed, so the back EMF and inrush current is very small, the insulation susceptible to damage problems with a lower probability.

B, regardless of heavy load or light load, the power factor of the system is higher, especially in a small load state, reactive power greatly reduced, with significant energy-saving effect.

C, according to the current status of the oil well to regulate the oil, the well work in the best condition. Reduce the failure rate while improving work efficiency.

D, can also form a pressure, temperature closed-loop system to improve the degree of automation and to achieve the best control. The use of frequency control, the oil-rich wells, can increase production; for lean oil wells can be continuous production and reduce the number of well stops and achieve energy-saving purposes; for sand oil wells, you can reduce the number of pumps, and reversing row Sand, to extend the life of the pump; for gas wells, can increase the speed to reduce the gas-poor separation caused by the phenomenon of air lock and increase production efficiency; for waxy wells, can reduce wax, scaling and reduce the number of pipeline blockage ; For heavy oil wells, low-speed high-power operation, reduce the number of well stops and obtain considerable energy savings.

2 used in the past several frequency control scheme comparison

2.1 using common frequency converter

System diagram is as follows:

The program uses step-down, step-up transformers and power frequency under the general-purpose inverter composed of high - low - high pump motor to achieve the purpose of frequency.

The advantage is easy, the disadvantage is that the system is too bulky, especially the output side of the transformer must still be designed to work at the minimum speed, versatility is not strong or the design can not be reasonable. Due to several changes in the system, so that efficiency is reduced.
2.2 using ordinary low-voltage frequency (two-level) technology to achieve medium-voltage frequency conversion

The program uses low-voltage rectifier, and low-voltage capacitors in series, 3300V high-voltage IGBT direct inverter. The control method still adopts the traditional sine wave pulse width modulation. The advantage is that the system has a simple composition. The disadvantage is that the output voltage waveform is a high-voltage rectangular pulse, that is, an unmanageable dv / dt problem appears. This is not suitable for the long transmission line and brings about the same insulation problem to the motor, And the output current waveform is not ideal. As 3300V high-voltage IGBT applications are not yet mature and expensive, practical economic benefits are also bottlenecks.

3 the company's medium voltage inverter technical solutions

A program: 1140V medium voltage inverter

This is the use of diode clamp three-level technology, the system diagram is as follows:

The technology has been applied and promoted by foreign manufacturers since the 1980s. Toshiba, ABB, Mitsubishi, Siemens and other companies have such products, its characteristics are superior to the use of not too high in the medium voltage converter. Compared with the two levels, although the output voltage waveform is still composed of rectangular pulses, its pulse amplitude is reduced by a factor of two, which solves the problems of insulation and harmonics caused by high dv / dt. The inverter output waveform closer to the sine wave. Thoroughly solve the device commutation caused by the insulation caused by motor insulation damage, shaft voltage corrosion on the motor bearings and conducted interference, radiation interference and many other issues, reduce leakage current and motor noise. Its shortcomings have been basically overcome, the fly in the ointment is the commutation of inverter components still need to be guaranteed by the clamp diode, the system becomes a little complicated, but in the tens of kilowatts of the inverter, the lack of price does not constitute a factor. The company's 1140V inverter is the use of this technology program.

B program: 6000V and above medium voltage inverter

The company's WIN-HV series inverter is the use of this design is through the transformer isolation, the power unit series of AC - DC - AC - Direct high-voltage inverter.

Inverters use inverter technology, the output of each phase by a number of power units in series, the number of power units in series due to the output voltage varies, see the following unit configuration table:

4 Micron Technology Medium Voltage Inverter Application Brief:

The company's medium voltage inverter is under the current device conditions, due to the different grid voltage and the optimal design. The foreign medium voltage products mainly refers to the input voltage of 1140 ~ 10000V inverter. Among them, the frequency converter 1140 ~ 4160V mostly three-level mode, that Division I A program, 6000V and above the medium voltage inverter is the inverter unit in series multi-level inverter as the leading, that Division I B program.

From the perspective of technological development, the 2 kV inverter designed by our company is still optimized by the inverter unit series scheme, the main reason is that the circuit structure is simple, the mature components (1700 V IGBT) are available, the price is low, Performance / price ratio highest. The multiplexed technology (dualization) makes the output waveform sinusoidal. The harmonics on the network side are greatly reduced, and both the input and output are ideal. Therefore, we think this converter will have a broad application prospect in our country. Can be safely used in the oil field submersible pump drive.

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