| Electrical submersible pump(ESP)has been widely used in the field of oil exploitation due to its high lift,large displacement and high oil extraction efficiency.The downhole information acquisition device serving for it plays a very important role in optimizing the oil extraction process,improving the oil recovery and prolonging the service life of ESP system.There is a great gap between domestic downhole information acquisition devices and foreign products in the real-time performance of parameter measurement and high temperature(HT)performance,which cannot meet the urgent need of safe and efficient production in the field of oil exploitation.The technical difficulties to be solved include: remote power supply for downhole measurement units and remote transmission method for downhole measured parameters;modeling of HT Flyback power converter and power device in downhole measurement unit;driving technology for power device in HT Flyback power converter.First of all,aiming at the problem that power supply and signal transmission based on auxiliary cables couldn't be achieved due to long distance between surface instrument and downhole measurement unit and narrow downhole space,a remote sharing cable power supply method based on the principle of equal potential was proposed.By setting up a three-phase inductor on the ground,the neutral point potential of the inductor's three-phase windings was equivalent to that of the submersible motor's three-phase windings,thus the remote power supply for downhole measurement unit with the power cable of the submersible motor was realized.Meanwhile,a remote transmission method for downhole measured signal based on current loop was proposed.Based on measured voltage signal,the power supply current which was regulated by downhole measurement unit was sampled for downhole parameters' extraction by surface instrument,and then the remote transmission of downhole measured signal was achieved.Secondly,aiming at the insufficiencies of SiC MOSFET's modeling method based on physical parameters and datasheet,such as low data density,inability to obtain parameters in saturation region of output characteristics,and difficulty in obtaining physical parameters,a modeling method for HT SiC MOSFET devices was proposed.Based on the whole output characteristic curve by a series of HT experiments,the functional relationship between temperature and parameters related to output characteristic and the temperature compensation power supplies was established by polynomial fitting method,thereby SiC MOSFET's temperature-dependent static model was established.By solving differential equations,the exponential function relations between voltage and current variables and parasitic inductance and capacitance in switching transient process were established,based on which the dynamic model of SiC MOSFET related to parasitic parameters was established.By this model,the temperature-dependent static characteristics of the device as well as the voltage oscillation phenomenon during the switching transient process of the device could be simulated,besides the switching loss of the device could be calculated with lower errors.Aiming at the problem that the zero and pole distributions of the transfer function of the Flyback converter's power stage in the downhole measurement unit were affected by temperature drift of passive components and their parasitic parameters,which led to the change of the dynamic stability of the closed-loop system,the transfer function of the power stage of the Flyback converter under the peak current control mode was analyzed and research on the influence mechanism of the temperature drift characteristics of components and their parasitic parameters on the zero and pole distribution of the transfer function was did,based on which parameters design of the compensation network of the HT Flyback converter was conducted to realize the stable dynamic characteristics of the Flyback converter in HT environment.Thirdly,aiming at the insufficiencies of active driver,GaN MOSFET bridge driver,discrete driver and resonant driver,such as hysteresis control,dv/dt crosstalk,slow switching speed and serious passive components' temperature drift,a HT driving circuit topology for SiC MOSFET based on BJT was proposed.By establishing the mathematical model of the driving circuit,the parameters passive components in the driving circuit could be obtained,and a method based on mutual compensation of components with positive and negative temperature coefficient was proposed,based on which the stable driving capability of the circuit could be achieved in wide temperature range.Aiming at the problem that in bridge topology,the SiC MOSFET's shutdown reliability and safety were affectd by dv/dt crosstalk,a HT dv/dt crosstalk suppression topology was proposed,based on which dv/dt crosstalk could be effectively suppressed by changing the driving voltage when device was turned on and off.Based on the established SiC MOSFET model,the effect of the proposed crosstalk suppression method in HT environment was verified by simulation.Finally,a 200? downhole multi-parameter measurement instrument was designed,and a comprehensive experimental analysis and verification to the research content of this paper was conducted.Whether the Flyback converter could obtain enough input power to enter the working state was dependent on the constant current characteristics of the constant current source in downhole measurement unit,and the obvious declining trend of the constant current ability of constant current source based on current regulating diode with increasing temperature was shown.Aiming at this problem,a HT constant current source circuit based on the principle of mutual compensation of the components with positive and negative temperature coefficients was proposed,by which the stability of the Flyback converter's input voltage was guaranteed.The overshoot oscillation was derived from the temperature drift of components' parameters in V/I converting circuit in the process of current loop signal transmission,thereby the accuracy of signal transmission was affected.Aiming at this problem,a model of V/I converting circuit was established,based on the model,the step response characteristics of V/I converting circuit in HT environment were studied,and then the damping ratio and undamped oscillation frequency of V/I converting circuit were designed,so that the non-overshoot response of current loop signals transmission in HT environment was realized,by which the accuracy of downhole information acquisition was ensured. |
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