The beam pumping unit is commonly used as the main pumping equipment in various oil fields in China, which has problems such as low production, high energy consumption, and large horses pulling small cars. In recent years, with the development of power electronics technology, frequency conversion technology has been widely used in oil fields due to its advantages such as energy saving and convenient frequency adjustment. During the operation of the pumping unit, the electric motor often runs in a generating state.
In order to solve the problem of energy backflow, there are currently two main solutions for pumping units in various oil fields in China:
·Variable frequency braking unit and variable frequency feedback unit. Adding a braking unit and a braking resistor to the busbar directly consumes energy on the braking resistor, which is not only detrimental to energy conservation, but also difficult to solve the problems of heat dissipation and lifespan of the braking resistor;
·Parallel feedback units are connected to the busbar to feed back the energy generated by the motor during power generation to the grid, achieving reverse flow between the inverter and the grid. However, this does not solve the problem of low power factor and high harmonic current when energy flows from the grid to the inverter.
In response to the above situation, the four quadrant technology solution can overcome the shortcomings of the two solutions mentioned above. The four quadrant frequency conversion technology solves the problem of regenerative energy processing of pumping units when the system is unbalanced, with four quadrant operation function, while improving energy-saving efficiency, reducing harmonic pollution of the power supply, and improving power factor. The four quadrant frequency converter adopts IGBT rectification technology controlled by PWM, with bidirectional control of rectification and energy feedback. True four quadrant operation can perfectly solve the problem of energy backflow in pumping units.
Introduction to Four Quadrant Frequency Conversion Technology
1、 Principle of Four Quadrant Frequency Converter
The topology of the four quadrant frequency converter circuit, which uses three-phase pulse width modulation (PWM) rectification instead of uncontrolled rectification, is shown in Figure 1. It can convert the mechanical energy of the load into electrical energy and return it to the grid.
Four quadrant frequency converter - energy-saving solution for oilfield pumping units
Figure 1 Topology structure of four quadrant frequency converter circuit
2、 Advantages of Four Quadrant Frequency Converter
Using a high-speed and high computing power rectifier control unit DSP, six high-frequency PWM pulses are generated to control the turn-on and turn off of the IGBT on the rectifier side. The turn-on and turn off of the IGBT work together with the input reactor to produce a sine current waveform that is in phase with the input voltage. This eliminates the harmonics generated by diode rectification and analysis, and the power factor is close to 1, thereby eliminating harmonic pollution to the power grid;
The rectifier side of the four quadrant frequency conversion technology adopts IGBT power modules, which can achieve bidirectional flow of energy between the input grid and the motor. When the system is unbalanced, the potential energy generated by the imbalance can be fed back to the grid, greatly reducing the requirement for system balance;
When the motor is in the generating state, the energy generated by the motor is fed back to the DC bus through the diode on the inverter side. The rectifier side feedback control starts, reversing the DC to AC, and feeding back the energy to the grid by controlling the phase and amplitude of the inverter voltage, achieving energy-saving effects.