Application Scheme of Variable Frequency Drive System for Beam Pumping Unit

There are many problems in the practical application of the beam pumping unit driven by frequency conversion. These problems mainly focus on the processing of the energy generated by the beam pumping unit in the power generation state.

1. Adopt ordinary frequency converter plus dynamic braking unit

This method can be implemented more conveniently, but at the cost of more power consumption, which is mainly because the generated energy cannot be fed back to the grid. When the frequency converter is not used, when the motor is in the motoring state, the motor absorbs electric energy from the grid (the meter rotates forward); when the motor is in the generating state, the motor releases energy (the meter reverses), and the electric energy is directly fed back to the grid, and there is no local equipment wasted. The comprehensive performance is that the power factor of the power supply system of the pumping unit is low, which has a great impact on the quality of the power grid. But when using ordinary frequency converters, the situation has changed. The input of ordinary inverter is rectified by diode, and the energy cannot flow in the opposite direction. The above-mentioned part of electric energy does not have a path to flow back to the grid, and must be consumed locally with a resistor, which is why a dynamic braking unit must be used.

2. Inverter plus feedback unit control

In order to feed back regenerative energy and improve efficiency, energy feedback devices can be used to feed regenerative energy back to the grid. Of course, in this way, the system will be more complicated and the investment will be higher.

The so-called energy feedback device is actually an active inverter. According to the different power switching devices used, it can be divided into two types: thyristor (SCR) active inverter and insulated gate bipolar transistor (IGBT) inverter. Their common feature is that they can convert the voltage of the inverter DC circuit Feedback to the grid.

The inverter equipped with energy feedback unit is suitable for AC 50Hz, rated voltage 380V or 660V asynchronous motor and permanent magnet synchronous motor to realize soft start, soft stop and speed control operation process control. It has the advantages of small starting current, stable speed, reliable performance, and small impact on the power grid. It can realize arbitrary adjustment of up and down speed and closed-loop control operation; the user can determine the pumping unit’s stroke, speed and liquid production according to the liquid level and pressure of the oil well. Quantity, consumption reduction and energy saving, high pump efficiency; reduce wear and tear of equipment, prolong service life, high efficiency, energy saving and low cost, and realize automatic operation in the state of maximum energy saving.

3. Problems that should be paid attention to in the application of frequency conversion speed regulation

(1) The actual production conditions of oil wells should be considered in the application of frequency converters

There is a certain loss in the inverter itself. When the number of strokes remains the same, using the inverter consumes about 5% more power than not using the inverter. Therefore, if the replacement of the pulley of the low-speed motor can meet the needs of stroke adjustment, try not to use the frequency converter. Frequency converters are only used in pumping wells that frequently adjust the stroke times of pumping units and slow down of polished rods. For wells with low fluid production and less frequent pumping unit adjustments, direct selection of low-speed 12-pole, 16-pole permanent magnet synchronous motors or gear reduction motors has the best power-saving effect, and frequency converters should not be installed.

(2) Frequency inverter maintenance

Each frequency converter should be cleaned and maintained once a quarter. For maintenance, remove dust and dirt inside the inverter and in the air duct, wipe the surface of the inverter clean, and keep the panel of the inverter clean and bright; during maintenance, carefully check the inverter to see if there is any heating and discoloration inside the inverter , Whether the damping resistor is cracked, whether the electrolytic capacitor has expansion, leakage, and explosion-proof holes, etc., whether the PCB board is abnormal, and whether there is a hot and yellowed part.

(3) The design of the frequency conversion cabinet should meet the requirements of the oilfield production environment

Waterproof, dustproof and good heat dissipation are mutually contradictory, but in the harsh natural environment in the field, the frequency conversion cabinet for oil wells must meet the requirements of these indicators at the same time, which puts forward higher requirements for the design of the frequency conversion cabinet. Only by finding a balance among the three can a frequency conversion cabinet that meets the actual needs of production be designed, and can serve the production and energy-saving work of the oil production plant in a good state.