1 Introduction
In order to mine “three high†heavy oils containing colloidal asphalt, wax and high freezing point, oil fields are usually mined by means of steam absorption, chemical viscosity reduction and hot water jet. These methods have disadvantages such as high investment and inconvenient management. . At present, in the exploitation of heavy oil, Jiangsu Oilfield uses steel hollow sucker rod induction heating technology in combination with its own characteristics. The technology has the following requirements: simple equipment required, convenient downhole operation and maintenance; adjustable input power; easy to realize automatic control; uniform heating along the process, no local overheating; high thermal efficiency (heating in the center of the tubing); Extend the operation cycle; improve production efficiency; no pollution to the environment; safe use, convenient management; less one-time investment, faster capital recovery [1].
According to the current domestic power supply mode, the hollow sucker rod induction heating system uses a power frequency induction heating method. In order to balance the three-phase power, the power frequency heating power supply superimposes one phase of the power frequency three-phase alternating current through the phase shift phase of the reactor and the capacitor to the other two phases, and then directly becomes suitable for various heating requirements through the transformer. Connect the heating conductor after single-phase power frequency AC. Therefore, the power frequency heating power supply is costly, bulky, cumbersome, and inefficient.
The oil medium frequency induction heating power supply adopts IGBT as the inverter switching device, and the volume is reduced by 40% and the weight is reduced by 50% compared with the common power frequency heating power source.
2 IF induction heating power supply
See Figure 1 for the circuit structure of the IF induction heating power supply. The three-phase rectifier rectifies the power frequency three-phase alternating current into direct current. After filtering, the full-bridge inverter converts into a single-phase intermediate frequency alternating current whose frequency and duty ratio are continuously adjustable within a certain range, and then outputs the output to the isolation transformer. Heat the load. The full-bridge inverter adopts pulse width modulation (PWM) zero-voltage switching circuit, which has the advantages of low switching loss and small electromagnetic interference [2]. The control circuit uses the SG3524 integrated block to adjust the 9-pin voltage to ensure the dead time of the output signal. The pulse width of the output signal is modulated by a petroleum temperature detector. The temperature of the oil is controlled at 45 to 70 ° C. Excessive temperature can easily change the chemical properties of petroleum. Too low a temperature will reduce the fluidity of the oil.
3 IGBT gate drive circuit
3.1 Selection of IGBT gate drive module
IGBT gate drive modules EXB841 and M57962L can be used to drive IGBT modules within 1200V series 400A, with overcurrent detection and protection. The output waveform of these two drive modules under short-circuit protection is shown in Figure 2. The EXB841 internally generates a 5V negative bias and is not adjustable; the M57962L externally uses a Zener diode to generate a 9V negative bias, and the gate reliability is higher than EXB841. In addition, the protection action time of the M57962L (from overcurrent to gate voltage dropped to 0V) is 6.3μs (see Figure 2a); the protection action time of the EXB841 is 16μs and the gate voltage cannot be reduced to less than 2v (see figure). 2b), the risk of causing IGBT fuses is greater than that of the M57962L. Therefore, M57962L should be used.
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